Wolves in the backyard

In a Youtube video that has been viewed more than 25 million times,  George Monbiot explains with masterful clarity How Wolves Change Rivers. The short film tells the story of Yellowstone National Park, where wolves were reintroduced in 1995 after an absence of 70 years. Heralded as a successful example of “trophic rewilding” (Svenning et al 2015) – whereby missing “trophic levels” in the food pyramid are re-installed to exert top-down control- the returning wolves are credited with controlling numbers and behaviour of herbivores (elk), thereby allowing vegetation to return. This then has multiple cascading benefits throughout the  eco-system, providing food and habitat for many other species including bears and beavers, and ultimately stabilizing river systems and raising the water table. With stunning photography, the film paints an irresistible picture of holistic ecological restoration through a whole landscape, successfully brought about by the return of one of the most iconic and charismatic carnivores.

How realistic is it? Certainly, there is evidence for many of the beneficial effects of trophic rewilding claimed in the video, including restoration of willow and aspen along riparian zones, and an increase in beaver and bison (Ripple and Beschta 2004), but it is not clear just how uniform these effects are. A 2010 study found that aspen was not recovering in many areas by that time after wolf reintroduction (Kauffman et al 2010). Another study suggested that willow communities did not readily return with the wolves either, since hydrological conditions had changed so much in the intervening 70 years since the wolves were banished (Marshall 2013). In other words, removing a trophic level and then replacing it decades later is unlikely to create a symmetrical effect- too much else will have changed in the meantime.

Moreover, such behaviorally mediated trophic cascades (BMTCs) are highly complex and can have unintended consequences far beyond the immediate aim of reducing foraging. Mesopredator release in the form of dramatic increase in the new top-dog, coyotes, was observed when the wolves left, but when they returned and preyed on the coyotes, this resulted in an increase in longhorn and rodent populations, with consequent impacts on vegetation…(Berger et al 2008). It is a tangled web we weave. She swallowed a spider to catch a fly…

Emma Marris has a nice summary of the literature, concluding that while the powerful image of the role of charismatic carnivores play trophic cascades may be beneficial in resurrecting interest in the conservation movement, the potential downside is unrealistic expectations and possibly the sidelining of complex realities in favour of a good story (Marris 2014).

The appeal of Monbiot’s lyrical storytelling in the video perhaps comes from the strong influence on ecology and environmentalism since their early days of the myth of the “balance of nature” and simplistic interpretations of how the “web of life” works. Our ecological thinking is still strongly influenced by quasi-religious myths about pristine nature and the Fall from Eden caused by humans and their meddling technology (Botkin 2012).

Since Monbiot’s influential book Feral (Monbiot 2013), the prospect of wolf reintroduction to Britain has come to the fore in discussions of rewilding. Wolves have been absent here for over 300 years, so there is perhaps even more reason to be skeptical that predictable, beneficial effects can be expected by their reintroduction to these islands. However, simulations have found that wolf reintroductions to the Scottish Highlands could help control red deer, and public opinion has been found to be fairly supportive in some surveys. Even farmers have not always been as negative as might be expected (Nilsen 2007).

The big question is of course livestock-wolf conflicts. Wolves have been making a dramatic comeback across most of Europe in recent years, largely as a result of stringent EU conservation policy giving them protected status: hunting is illegal unless special dispensation is granted under license. But they may be becoming a serious and widespread problem for farmers: a long article in the Economist this week gives estimates a wolf population of between 12- and 20,000 are eating anything from 20-80,000 domestic animals each year. In many countries, farmers get compensation for animals killed, although apparently the bodies are often hard to find making this difficult; perhaps partly because of this, and the challenge of getting farmers to accept sharing the landscape with carnivores, the policy seems to be moving towards a flat rate subsidy given to farmers who live in wolf country.

Conservationists argue that farmers can adapt to live with carnivores amicably. This was born out by a presentation I saw at the Future of Wild Europe conference in Leeds last week about perceptions of wolves in Saxony, NE Germany. Surprisingly, there had been no recent reports of livestock-wolf conflicts at all. That is not to say that there have not been problems in the past, but subsidies for preventative measures such as guard dogs and electric fencing appear to have helped broker a truce at least in that region for now. A bigger conflict seems to be with hunters, who find in the wolf unwelcome competition for their game. I couldn’t help but wonder if the real tension, and reason perhaps for the apparent compliance of farmers there, is pressure from the other half of the community who are benefiting from the boom in wolf tourism in the region.

Elsewhere, things are not so quiet. Reports from the Southern French Alps, where wolves have found their own way back (presumably) in recent years, show the extent of the impact on shepherds: individual kills are the least of it, with wolf presence severely stressing the flock causing weight loss, and the continual risk of attack from protected animals leading to a sense of helplessness in shepherds, some of whom have felt compelled to give up altogether. Other side-effects include modification of the landscape and a loss of a sense of “wildness” through proliferation of protective fencing, and the large, non-native Pyrrenean guard dogs that have been brought into the area have themselves been reported to have attacked hikers, making the area feel even less safe and possibly impacting tourism (Buller 2008).

Against the backdrop of the strong return of wolves across Europe, it is perhaps surprising to read recent reports that Norway is about to cull most of its wolves. It only has 68 animals, and licenses will be granted to shoot 47 of them. Paradoxically, controlled experiments lethal control measures may not be the best way forward though:

Although it seems obvious that killing a carnivore
about to take a lamb should ensure the latter’s
short- term survival, most lethal methods are applied
indirectly in wholly different situations. Lethal intervention
is usually implemented after carnivores are observed
near livestock or days after a predation event has
occurred, sometimes far from where the attack occurred

(Treves et al 2016).

Given the potential opposition and difficulties carnivore reintroduction is likely to pose to existing landowners, why do people feel so strongly about bringing back the wolf to these islands?

In my own research over the summer in North Wales and the Scottish borders, apart from controlling foraging, I was given reasons such as: wolves have a right to be here for their own sake. We [humans] take up too much space, it is time to give some back for other species. The sense of wilderness, fear and danger is important- it is something we have lost in our modern, coddled and insulated lives. Walking in a landscape with wolves would make us feel more alive.

None of the rewilding advocates I interviewed seriously felt there was a prospect in the near-term of wolf reintroductions however, much as they would like to see it, not in their lifetimes. There is too much controversy and opposition. They would however like to see education programs to help persuade people that we could live happily alongside wolves. They would not necessarily impose that much on everyday life- people can typically live their entire lives in wolf country without ever actually seeing one.

It is also said that were it not for the geographical accident of being an island, wolves would already have re-colonized Britain, just as they have spread through the continent. To counter that, we could say that, being an island is also a natural state, and maybe we don’t need wolves to be everywhere. There are also islands that never had wolves- should we bring them there aswell? As keeping down the deer population- while we might not currently be doing such a brilliant job of it, why should humans not play the role of top predator- is that not, in fact, what we are?

There is also the minor issue that, as mentioned in the Economist article, wolves do sometimes kill people. Statistically, not very many compared to most other forms of death, but perhaps not something that should be lightly dismissed. We have lived without carnivores in our landscapes for  over 300 years, much longer than they were absent for in Yellowstone, and maybe we would find it harder to adapt.

I do wonder – and worry – though, about the “fear” factor- is that really what people want? I also share a thrill at the thought of big scary wild animals in the landscape, but for me, hearing people say they would actively seek a bit more danger evokes images of Grizzly Man– the logical, terminal conclusion of the wish to “go back to nature”. Anecdotally, research on the West Coast of Scotland has observed that community members often feel nervous about large carnivore reintroduction even in areas where they are not planned. That his was in an area earmarked for some level of “rewilding”, but not where there was any proposals for wolf reintroductions,  suggests how the “rewilding” debate has been so strongly framed as something involving animals with big teeth.

Wolves carry a lot of mythological baggage with them, invoking both unreasonable fear of the darkness of the forest- or perhaps the even darker, animalistic side of our own nature- and also unrealistic expectations of a return to some kind of pristine wilderness. In reality, as wild creatures, they are adapting readily to anthropogenic landscapes and hybridising with dogs and other animals,  challenging our conceptions of what constitutes “wild” (Buller 2008).

If the strongest argument for wolf reintroduction is that, how can we expect other countries to protect wildlife if we cannot do the same here, the counter might be that big animals pose a huge challenge to farmers elsewhere also ,and  how much biodiversity value would they really bring to Britain anyway?

Fractious debates between conservationists and farmers are likely to continue, but in Britain at least, there would seem to be a huge amount of other restoration work to be done in any case before there need be serious consideration of bringing back the wolf.


Berger, K.M., Gese, E.M. and Berger, J. 2008 Indirect Effects and Traditional Trophic Cascades: A Test Involving Wolves, Coyotes and Pronghorn Biological Sciences Faculty Publications. Paper 78

Botkin, D.B. 2012 The Moon in the Nautilus Shell: Discordant Harmonies Reconsidered OUP USA

Buller, H. 2008 Safe from the wolf: biosecurity, biodiversity, and competing philosophies of nature Environment and Planning A 2008, volume 40, pages 1583- 1597

Kauffman, J.M., Brodie, J.F. and Jules, E. S. Are wolves saving Yellowstone’s aspen? A landscape-level test of a behaviorally mediated trophic cascade Ecology, 91(9), 2010, pp. 2742–2755

Marshall, K.N., Hobbs, N.T., Cooper, D.J .2013 Stream hydrology limits recovery of riparian ecosystems after wolf reintroduction Royal Society Publishing 2013

Marris, E. 2014  Rethinking predators: Legend of the wolf Nature Nature 507, 158–160 (13 March 2014)

Monbiot, G. 2013 Feral: Rewilding the Land, Sea and Human Life Allen Lane

Nilsen et al 2007 Wolf reintroduction to Scotland: public attitudes and consequences for red deer management Proc. R. Soc. B (2007) 274, 995–1002

Ripple, W. J. & Beschta, R. L. 2004 Wolves, elk, willows, and trophic cascades in the upper Gallatin Range of Southwestern Montana, USA Forest Ecol. Management 200, 161–181

Svenning et al. 2015 Science for a wilder Anthropocene – synthesis and directions for rewilding research. Proc. Natl. Acad. Sci. USA

Treves, A., Krofel, M. and McManus, J. 2016 Predator control should not be a shot in the dark Front Ecol Environ 2016; 14(7): 380–388, doi:10.1002/fee.1312

Tree Pathology in a Changing World

Critical Essay: Silviculture in a changing world–a case study:

Impacts of tree pathology on silviculture in the UK and Ireland

  1. Introduction

Epidemics of tree diseases such as Dutch Elm Disease (DED) in the UK (Lamb 1979) and Chestnut blight in the US may represent the most profound and sudden cases of irreversible environmental change in recent times (Potter et al 2011). Since 2012 the public’s awareness has been drawn to the threat to one of Britain’s principle landscape trees, the ash tree, from Chalara fraxinea (Rackham 2012).

Trees in the landscape provide valuable ecosystem services including erosion control and greater infiltration rates for floodwater, which are lost or impaired due to disease or mortality (Broadmeadow and Nisbet 2010). Disease can also have significant economic impacts for forestry and timber production. Beyond economic issues, loss of trees on such a scale carries great cultural implications. This essay will consider the need for silviculture to adapt to new challenges from current and novel diseases. Continue reading “Tree Pathology in a Changing World”

Bialowiezça: the Myth of the Primeval Forest

Over the past few weeks there have a been a series of reports raising concerns about the felling of old-growth trees in the ancient Bialowiezça forest in eastern Poland. A recent piece in the Guardian begins

Europe’s last primeval forest is facing what campaigners call its last stand as loggers prepare to start clear-cutting trees, following the dismissal of dozens of scientists and conservation experts opposed to the plan.

and goes onto blame Poland’s “far right” government for cashing in from logging operations, and ruthlessly purging the state council for nature conservancy of environmentalists,  replacing them with officials connected to the forestry industry. Greenpeace are considering direct action, and the WWF and others have lodged a complaint with the European commission over the proposed “illegal” logging, and various petitions have been run to oppose the governments’ intervention.

P1010762Photos: Bialowiezça forest, Graham Strouts 2013

Bialowiezça forest covers approximately 143,000ha split between Poland and Belarus, the larger part of some 80,000 ha in Belarus.  About 10,000ha -1/6th- of the Polish side falls under the stricter regulation of National Park status, originally designated in 1932.

Ostensibly, the logging is an attempt to slow the spread of the latest bark beetle outbreak, affecting more than a million trees in Bialowiezça. In some respects the conflict can be seen as being between differing management approaches, but on deeper examination cuts to the heart of similar conflicts surrounding environmentalism where Nature is placed above the needs of people.

While the foresters prefer an active approach of sanitation felling, removing whole sections of affected trees to prevent further spread of infection, conservation organisations- and many ecologists- prefer an adaptive strategy of  letting nature take its course, more in keeping with the designation of the Puszcza as one of Europe’s last primeval, untouched wildernesses. The foresters are accused of being concerned only for profit, while the environmentalists are slated for having no concern for the needs of the local community- which has traditionally foraged firewood, fungi and more from the forest- and placing a reified version of “pristine Nature” above the needs of ordinary people.

There is certainly good reason to consider adaptive approaches. Bark beetle outbreaks can be so devastating over such a wide area that anything other than hoping for natural adaptation may be unfeasible.  Genetic resistance will show up in the few surviving trees, and the forest will take on a more clumpy patchwork and diverse structure, leaving it less open to future attacks (Six, 2014). In the medium term however, the transformation of the landscape with over 90% of mature trees dead is likely to be devastating.


Despite Bialowiezça being widely valued as “primeval” forest, nearly all of it has been managed to some extent for centuries, and since the mid-19th century, with the exception of the inner core of the National Park, much of it has in fact been logged on a number of occasions: by the Germans in World War 1, the Polish administration in the years after the war; by the British Century corporation in the late 1920s, the State forestry service and then the Soviets in the early years of WW 2 (Szujecki). Ironically perhaps, it was the Germans in WW2 who made the first serious move for stricter conservation controls, putting an end to the logging and driving thousands of Bellarussian farmers out of their forest villagers in order to keep the forest for their own hunting-  in keeping with the more esoteric and ecological strand of thinking that ran through Nazism and which valued the purity of Nature over the needs of people  (Biehl and Staudenmaier 1995)- and which has left a legacy of misanthropy running through the darker side of the conservation movement today.

Most of the forest- 84% – is outside of the national park and not subject to its strict hands-off regulations- and it is here that the proposed felling will take place. Although the new felling does represent a tripling of the existing quota, this is still less than historic amounts, and will not be in previously unmanaged protected inner core,  representing perhaps just 1-2% of the total forest area.

Polish foresters argue that the current beetle attack is not only far larger than previous ones- perhaps exacerbated by climate change leading to greater water stress on the trees- but that it is also attacking younger trees which would usually be expected to be more resilient, and is spreading to other species including pines and larch. Moreover, the current outbreak is a result of stricter conservation policies that were introduced to much of the greater forest area in 2012, prohibiting the more frequent, smaller judicious sanitation felling that was part of a general beetle control program up until then. As a result, the infestation has spread to a much greater area, threatening the whole forest.

This has parallels with fire management in Yellowstone National Park. In the early days of the park, fires were suppressed, leading to a build-up of litter on the forest floor. Eventually a much greater conflagration would occur with devastating results (Bengtsson et al 2003). Since then, practice has changed to allow non-man-made fires to run their course. In this way, small, periodic disturbances can lead to greater forest resilience.

The Myth of the Primeval Forest


Such disputes over management practices in the Puszcza are by no means new, but in fact seem to recur as periodically as the beetle outbreaks. Franklin (2002) argues that Bialowiezça has suffered for the cause of “crisis environmentalism” whereby policies are promoted under the guise of emergency legislation. The ancient, so-called “primeval” and supposedly pristine forest- an untouchable jewel of natural perfection – is portrayed as being under threat of imminent destruction by greedy foresters, when in fact the forest has always been used by the local communities for meeting their immediate needs and gaining livelihoods (Marris 2013). This practice can be traced to a sensationalised newspaper article of 1992 (Franklin 2002) claiming the forest was dying, leading to demonstrations by Greenpeace and US Deep Ecology groups demanding higher protection status for the forest. Today’s social media outcry, with petitions and threats of direct action, reads very much like a re-run of these earlier events.


As with other ex-Soviet nations (Schwartz 2005), these conservation conflicts in Eastern Poland have also been tied up with a search for national identity and a shifting of attention away from other areas of environmental concern- such as industrial pollution- to appease the sensibilities of Western conservation interests and ideologies. It has been in the Polish States interest to play up the “pristine” image of Bialowiezça, at least when the national park was first established, so much so that carefully crafted propaganda films were made editing out any sign of human influence.

Eventually, moves towards significant enlargement of the protected area met up with local opposition concerned at the removal of their forest rights by outside environmental organisations. A protest in March 2000 by a consortium of foresters, local councilors and Bellorussian groups put and end, for the time being, to the myth of the pristine forest with no people.

Where does the truth now lie? Possibly as is often the case somewhere in the middle: in the past, over-zealous conservation movements, muscling in from outside with lack of consultation with local communities and without fully understanding the politics of the region, created a backlash which may now be being exploited by some interests eager to exploit disaffection with outside interference in order to make a quick buck. It is hard to know more without being much closer to the ground there. The Bialowiezça forest does have unique biodiversity value, but leaving it entirely to nature with no management at all will not guarantee the best outcome for biodiversity; at the same time, local concerns about loss of employment and access to forest resources need to be considered if successful conservation is to be achieved (Blicharska and Angelstam, 2010).

The dispute over management practices will no doubt continue, perhaps for as long as the forest stays standing- and there is no reason it will disappear for many centuries yet, whatever happens. While it could be argued that leaving the trees to the fate of the bark beetle is the best course of action, that would be likely to change the  nature of the forest for a very long time. In place of the giant hundred-year-old spruce trees there would likely emerge instead extensive patches of willow and alder. The dark, mysterious atmosphere and sense of timelessness that a visit to the forest currently evokes may be lost, and while the forest will still be there, its image as one of the last refuges of pristine wilderness be tarnished for good.P1010774

For Martin


Biehl, J. and Staudenmaier, P. 1995 Eco-fascism: Lessons from the German Experience
AK Press

Bengtsson et al 2003 Reserves, Resilience and Dynamic Landscapes Ambio Vol. 32 No. 6, Sept. 2003

Blicharska, M. and Angelstam, P. 2010 Conservation at risk: conflict analysis in the
Białowieża Forest, a European biodiversity hotspot International Journal of Biodiversity Science, Ecosystem Services & Management, 6: 1, 68 — 74

Franklin, S. 2002 Bia•owiezça Forest, Poland: representation, myth, and the politics of dispossession Environment and Planning A 2002, volume 34, pages 1459 ^ 1485

Marris, E. 2013 The Rambunctious Garden: Saving Nature in a Post-Wild World
Bloomsbury USA

Schwartz, K.Z.S. 2005 “Masters in Our Native Place”: The politics of Latvian national parks on the road from Communism to “Europe” Political Geography 25 (2006) 42e71

Six, D.L., Biber, E., Long, E. 2014 Management for Mountain Pine Beetle Outbreak Suppression: Does Relevant Science Support Current Policy? Forests 2014, 5, 103-133; doi:10.3390/f5010103

Szujecki, A. The Bialowieza Primeval Forest- Conflicts over its Conservation and Managment
Białystok Regional Directorate of the State Forests NFH


What would Eat a Badger? Rewilding at the Hay Festival

I took a trip last week to the Hay Festival with my supervisor Dr. Sophie Wynne-Jones of Bangor University, and trustee of the Cambrian Wildwood group,  who was participating in a panel debate on rewwilding, along with Minette Batters,  deputy president of the NFU, and Julia Aglionby, Executive Director of the Foundation for Common land.


Left to Right: Julia Aglionby, Sophie Wynne-Jones, Minette Batters, Rob Yorke

Chaired by independent rural commentator Rob Yorke, about 100 people turned up to listen and ask questions. In his introduction, Rob showed he has an in-depth understanding of the topic, and began by proposing two variants of rewilding- passive, as in taking a step back and letting nature run its course, and active, including such things as herbivore and carnivore re-introductions, and asked the panelists how important they felt it is to have an agreed definition. Sophie felt it was not so important and the greater issue currently was to build bridges and make connections with all stakeholders; Julia felt that however it was defined, rewilding would need management in some shape or form: farming is a long-term activity and land cannot just be abandoned. One problem already occurring in some areas is the rapid spread of bracken, a result of reduced sheep grazing and milder winters. Minette later argued this is bad for climate change since the build-up and subsequent rotting of such vegetation releases a lot of methane. Is this what we mean- or wish for- when we say “rewilding” ?

Rob suggested that we might conceive of scales or degrees of rewilding- with something akin to Yosemite in its early days- when all the native peoples were forcibly removed in order to make room for “wild nature”- at one end of the spectrum, and something much more managed perhaps at the other, though it was not made clear what this might be, though Juila did make the comment that “wilderness is in the eye of the beholder”.

Rob briskly moved the discussion on, asking whether rewilding had been used at times more as a weapon against existing land use and users than as a tool- at this point, a farmer in the audience piped up to assert that as farmers “we love our farm and we love the countryside”. Rob again pointed out that the fault line in these discussions is often drawn between those for whom the “wild place” is seen for leisure and those for whom it is their place of work and source of livelihood.

Should production landscapes be focussed in the fertile lowlands, thus allowing the uplands to be for culture, heritage and nature? It was here that clear differences between the panelists emerged: Minette was adamant that it would be disastrous to take stock off the uplands. Farmers are the custodians of the land and we must not allow their skills to be lost by such drastic changes in land use. There is a danger that all this talk of rewilding will alienate farmers and put them off from improving biodiversity on their own farms. James Rebanks’ 2015 book The Shepherd’s Life was referenced, perhaps to provide balance with the bad press brought upon sheep farmers by Monbiot’s laying the blame on them for what he sees as the current “sheepwrecked” state of Britain’s uplands.

It was when the discussion moved onto animal reintroductions that positions became even more entrenched: I was somewhat taken aback by the stridency with which Minette dismissed the idea of carnivore reintroductions: lynx are a danger to man and our animals, she argued, and there is a very good reason they were got rid of. It would be disastrous to bring them back. She had to back-track a bit and extol the virtues of the fine animal that is a lynx when challenged by a member of the audience who asked if, then, it was a generally good policy to deliberately cause the extinctions of animals we don’t like, but I felt she then contradicted her own position by saying, “look what has happened with the badger- their numbers are out of control because they have no predator.”

Isn’t this one of the main arguments for rewilding, I asked? Badgers are not top predators in the same way a lynx would be, and are generally classed as mesopredators, generalists and omnivores which prey on smaller animals like hedgehogs- and are blamed for drastic impacts on the numbers of the latter and other small animals.

Badgers are the center of a long-standing controversy over culling and TB which I have not really looked into and shall not get into here- but this has nothing to do with the issues of threats to sheep and people by the lynx. However, Minette’s response to me was, “What would eat a badger?” which did give me pause for thought and became something of a joke between myself and Sophie on the way home. Further research later that night suggests that  badgers do not in fact have many natural predators, being well-adapted for their own defense, and probably would not be the first choice of a lynx looking for its lunch, although badger cubs might be taken by various predators including lynx and eagle. Mesopredator release – the rapid increase in numbers of mesopredators as a result of the elimination of higher carnivores- is a real thing (Prugh et al 2009), but it is unclear that there are good documented examples of this happening with badgers, apart from a controlled experiment in Texas when Cayotes were removed. In this case however “the increase in mesopredators did not lead to the decreased rodent numbers that classic trophic cascade theory would predict”  I don’t know why, or if, then, badger populations have increased relative to historical levels.

Much more worrying was Minette’s concern about the danger of lynx to humans or stock: Lynx are a shy animal and pose no real threat to humans, and any increase in sheep take would barely register against the several hundred attacks by domestic dogs each year. These arguments against carnivore re-introductions are common and understandable, and should not be dismissed, but seem to me to be the weakest, and such fears should not be fueled by representatives of the NFU . Far more serious are the concerns raised by Rob about our own duty of care to such animals, which may not survive in any case, or be vulnerable to being hit by traffic.

Another application of rewilding is flood mitigation, through riparian plantings (trees can increase infiltration rates) and re-meandering of rivers as we saw at Pickering on the Study Tour. Minette was also completely opposed to this, arguing that the most fertile land is generally the flood-plains and should be kept for farming; the water should not be “slowed” but sped up through the towns to be got rid of as soon as possible. If only it were so simple…

Sophie was keen to focus on practical examples such as the Pontbren in mid-Wales, which is cited as a a successful case of using trees to help in flood mitigation- however she cautioned against extrapolation from relatively little data and experience which might lead to over-stating the case for what trees in the landscape can achieve, and also made the important point that this was a farmer-lead project not originally connected with flood mitigation at all, but originally driven by using trees and hedgerows to shelter livestock.

An hour was far too short and the conversations continued over drinks afterwards, when I had some interesting discussions with countryside blogger Ben Eagle who also has a nice write-up of the event.  Ben had also pointed to the recent policy briefing by Paul Jepson which disentangles some of these debates and shows the way forward for a possible policy framework for rewilding.

A local farmer who was present, a neighbour of Rob’s in the surrounding Black Mountains,  also emphasised the crucial importance to farmers of maintaining their role of food producers. Why? Going back to Rob’s question earlier, could not the less fertile upland areas be rewilded, and food produced where more intensive methods can be implemented? Earlier Minette had explained to me that lambs do not stay long in the upland areas, being soon sold to lowland farmers, and sheep farming is highly integrated across the landscape; I am not sure if this really makes the case though. The conversation turned to policy- would farmers not simply do what they are paid to do? Would they not be just as happy to be paid for conservation as to produce food? For me it was something of a revelatory moment when the table went quiet as it seemed all parties present agreed on one thing at least: noone was really sure what the current farming payments are actually supposed to be for.

I have a lot to learn about farming and farming policy in the UK, as well as about rewilding in its various ramifications, but the diverse opinions I heard at Hay have provided plenty of fodder for this week at least. I shall  post more findings and insights as I continue my research through the summer.


Prugh, L.R. et al 2009 The Rise of the Mesopredator BioScience 59: 779–791

Feedback on the Forest Garden

My last post dealt with the permaculture edible forest garden, and it received some commentary on a couple of Facebook groups and permaculture forums. A lot of the responses were, predictably, from permaculture advocates who took umbrage at my having deigned to critique their philosophy at all, but there was one very valid criticism concerning yields: while I had compared weights of different crops per acre, a more useful approach would be to compare calorific yield. Doing this for the crops I listed gives a result looking something like this:

Crop                         tonnes/ha                 Cal/100g              m cal/ha

potatoes                           40                                  70                        27

wheat                                 8                                  333                        26.6

hazelnuts                       3.5-4                             646                       25.8

Sweet chestnuts             4.75                             200                        9.5

Corn (US)                          10.5                               360                       37.8

apples                                  44                                50                           22

As you can see, hazelnuts do perform extremely well on this score, having a very high calorific value, but as explained in the article, in a forest garden, the trees would be at wider spacing and the yield per hectare would be lower as a result.

As was pointed out to me by one commentator, apples score very high, comparable to wheat and potatoes and coming in behind only US corn (maize). Can apples substitute for those foods as a staple crop? For a food to be classified a staple it requires not just calories but high levels of macronutrients including proteins and oils; so I do not think we would thrive on a diet of mainly apples, although the person who pointed this out to me was adamant that we could and indeed should, precisely because they are a tree crop. An original argument for sure, and not one I have heard before in any of the forest gardening literature. Once again, though, the yields cited are from conventional apple orchards, not forest gardens.

Most of the other critiques were based on misunderstanding the article (aka not reading it properly!). The whole issue of yields was questioned- why am I comparing yields from tree crop monocultures- we know that forest gardens produce far more than they would, even though there is no data! This is of course the whole point: unless anyone has any better ideas, the use of tree crops as a proxy makes perfect sense, as they will almost certainly be producing the staple crops with the highest yields (and the most calories)- but they will not be achieving such yields in forest gardens, and indeed one of the best known forest gardeners, Martin Crawford, grows his nuts in a separate orchard, with nothing but mown grass beneath the trees.

Not everyone on the permaculture forum took the same defensive line- one commentator asked “So who ever said it was a good idea to grow vegetables under trees anyway?” implying my whole article was a straw man, apparently missing that I had carefully quoted directly from the principle authors in Britain and America who  advocate this kind of system. Again, the question of yields is important since these authors- Jacke, Whitefield, Hart, and the UK Permaculture Magazine, really do position forest gardening- including growing vegetables under the trees in a multi-storey system- as a sustainable and viable alternative to modern industrial agriculture.

Another recent permaculture author who makes similar claims- not specifically for forest gardens but for general systems based on perennial woody agriculture- is Mark Shepard. There is an interesting review of his book here, coming to similar conclusions to myself, and further commentary here on the issues of perennials vs. annual crops.

Another commentator seemed indignant that I was not only critiquing Hart’s invocation of a new “Age of Gaia” but also, apparently, that I completely discredit ecology aswell. They did not say exactly where I do this, but I guess it might be in the section on systems and complexity, where I cite to Gleason’s 1926 paper The Individualistic Concept of the Plant Association. Far from  dismissing ecology as a science, I am here quoting one of the most fascinating chapters in the history of this young science, the famous Clements-Gleason debate. The earlier view- originally from Tansley who coined the word “ecosystem”- saw nature as best represented on the community level, with more or less fixed boundaries around ecosystems and communities of plants and animals who had co-evolved over long periods of time. This was promoted by Clements and became the dominant paradigm, but later gave way to  Gleason’s view of nature more as a continuum, in constant flux, with no fixed boundaries around communities.

I suggested by the response above, the permaculture community has not moved on with the new paradigm. It is certainly this old conception of nature being in a state of balance on which the whole philosophy of permaculture rests- which is precisely why forest gardens, based as they are on the adage of “copy nature”, are still considered so important. Hart explicitly takes this further almost into the realms of religion with his Gaia quote, but so do many others in the permaculture community-  as indeed I did once myself. Even Clements probably never saw natural systems in this way. Forest gardens are however largely entirely novel systems, resembling nature only in structure and function and relying on previously untried assemblies, mixing wild, “native”, exotic and domesticated species together, so it is questionable to what degree they could be said to be “mimicing nature” in any case.

The Clements-Gleason debate is still ongoing, and demands an essay in its own right- perhaps I shall return to it as some point.

Finally, some conspiracy theories were spun around my essay, with comments along the lines that my real intention was to make a hatchet job on permaculture in an attempt to justify modern industrial farming. I have no hidden intentions, but simply wanted to explore the origins of the forest gardening idea and consider theoretical reasons why it is unlikely to meet the claims being made for it from within the permaculture community. Certainly, if it really held the promise being made for it, everyone would be doing it, but as I point out at the outset, despite some 30 years of promotion, the concept has failed in any way to capture the interest of more than a handful of farmers. The undeniable fact that there are costs and externalities for industrial agriculture does not mean that forest gardens- or even agroforestry- are necessarily a viable alternative solution.

More interestingly from a sociological point of view is the question as to why they are still so popular (within the permaculture fraternity) as an idea, with so much being claimed for them, when for the most part what are actually planted as forest gardens here are little more than orchards with a few herbs and soft fruit bushes, with even the most enthusiastic advocates getting most of their produce from more conventional annual vegetable beds. It is relatively easy to create wildlife gardens, or low-intensity food gardens that are also great habitat, and require few inputs, but for the time being at least it seems that the low-input high-output garden remains an appealing but unattainable dream.




Permaculture and the Edible Forest Garden: a Critical Analysis

I’ve been interested in the edible forest garden idea for over twenty years and have planted and designed several myself in Ireland in that time, and visited several others. But they have never lived up to my expectations and were largely unproductive, despite sourcing as many perennial vegetables and other interesting edible plants as I could. Here I review the claims made for them and what evidence there is to support the idea- and conclude that, as Permaculture founder Bill Mollison said in the first place, in temperate regions you are far better growing your fruit trees and vegetables separately.

Temperate permaculture– is this a passing fad, an idealist’s hobby or is there a case for wider promotion of the practice?

  • Introduction- Design By Nature: Permaculture and the Forest Garden Concept

 “Permaculture” – derived from permanent agriculture – is a concept of sustainable land use and design coined and developed by Bill Mollison and David Holmgren in 1974. Mollison defined the concept as:

The conscious design and maintenance of agriculturally productive ecosystems which have the diversity, stability, and resilience of natural ecosystems

 (Mollison 1988).

 Since then, permaculture has grown into a worldwide movement of activists and designers applying permaculture principles to the whole of society (Holmgren 2002). Permaculture is more an approach or philosophy than any specific technology, but where it has come under academic scrutiny, many of the kinds of practices frequently advocated have been found lacking in supporting evidence (Chalker-Scott 2010).

In this essay we shall focus on one of the best-known expressions of permaculture design, the edible forest garden or food forest for temperate regions, which are designed with the intention of mimicking the structure and functions of natural woodlands. Successful integration of trees with agriculture for multiple environmental and crop protection functions, nitrogen fixation and fodder is well established in traditional systems in many parts of Europe (Rigueiro-Rodriguez et al 2009), and is gaining renewed interest today as an essential part of agricultural sustainability. It is worth examining why, then, while forest gardens continue to be popular amongst the permaculture fraternity and the sustainable food movement, they have attracted little academic research, and very little uptake by farmers, orchardists or market gardeners. As we shall see, evidence to support the claims that forest gardens achieve both low inputs and high yields is lacking, and there are good theoretical reasons why the concept is unlikely to succeed in temperate zones.

  1. Definitions, Origins and extent of current practice

 Edible forest gardensalso known as forest gardens, woodland gardens, food forests or analog forests have been defined as “a perennial polyculture of multi-purpose plants” (Jacke 2005) and are comparable to the multistory agroforestry systems common across the tropics known as homegardens (Kumar and Nairn 2006). Robert de J. Hart is generally credited with being the first to bring the concept to Europe in the 1980s when he started the UK’s first forest garden in Shropshire (Hart 1996). He cites as his influences Smith (1950), Yeoman (1971) and Sholto Douglas (1985), and his work in turn went on to influence Patrick Whitefield (1996) and Martin Crawford (2014) in the UK and Jacke and Toensmeier (2005) in the US.

Based on the definitions used by the authors cited above, for this essay we will define edible forest gardens as:

Gardens which are primarily or entirely perennial polycultures, containing at least three identifiable vertical layers of food-bearing plants including trees, shrubs and perennial herbaceous understory.

 This definition differentiates them from both annual vegetable gardens as well as other well-established agroforestry systems such as broad-scale silvoarable systems, which generally include only one or two annual crops in between rows of trees (Rigueiro-Rodriguez et al 2009).

Crawford (2014) estimates there are some 800 hectares of forest gardens in the UK and lists approximately 160 forest gardens in his Forest Garden Network, including 9 in Ireland, 30 in Europe and a handful in the US. They range in size from small gardens of as little as 50 square meters to smallholdings of up to about 5 hectares, with the smallest area for a “fully functional” forest garden estimated at around 1000 square meters.

Perhaps ironically given their continued popularity in permaculture, Mollison did not himself advocate perennial edible forest gardens for temperate regions. He was well aware that temperate gardening was characterized by annual or biennial seed crops and tubers and by the need to store root vegetables over the winter, and that tree crops are more likely to be for fruit than for staples (Mollison 1988). The academic literature also indicates that temperate gardens have traditionally tended to be based on annual vegetables, often arranged in relatively formal beds and generally requiring full sunshine (Ninez 1987; Vogl and Vogl-Lukasser 2003).


Despite this, Jacke and Toensmeier (2005) cite the ancient practice of coppicing of woodlots for firewood and poles as an example of traditional forest garden practice. However, coppice woodlands are not primarily food gardens, and generally only involve one or two layers, the coppiced hazel and sometimes a standard timber crop. In the UK, orchard trees were commonly grown with an intercrop of soft fruit—blackcurrants or gooseberries—prior to 1955; less commonly some (mainly annual) vegetable crops were included, and there are examples of intercropping between trees with annual vegetables (Kumar and Nairn 2006). One of the few examples that do meet the definition of a three-layered system included asparagus as a perennial vegetable (Newman 1986, citing Fekete 1958), but apart from these cases it seems unlikely there was any widespread traditional practice of genuine three-story perennial edible homegardens in Europe or the US.

In a recent effort to correct the dearth of research on edible forest gardens, the UK Permaculture Association began a 10-year forest garden trial in 2009, publishing a baseline survey of 117 forest gardens in the Europe and the US in 2013 (Remiarz 2013, 2014). The oldest sites were started in the 1980s, with the majority starting since 2000. Nearly half reported that “food self-reliance” was their main objective, with the majority saying this has been largely achieved, though what proportion of each gardener’s food requirements was met is not quantified. In fact, the species lists suggest that in reality the crops grown in most of these forest gardens differ little from the fruit and green vegetables typically grown in traditional home gardens from the 1950s (Ninez 1987).

This apparent mismatch between aspirations and practice requires some explanation: why are forest gardens still believed in and promoted—at least within the permaculture fraternity—if the practice falls so far short of expectations? To answer this we now consider the philosophy of copying nature underpinning the forest garden concept.

  1. Philosophy: Return to the Garden?

 Along with other more recent influential permaculture writers (Crawford 2005, Jacke 2010), Hart (1996) saw planting forest gardens as not only a practical way of growing food but also about ushering in new ways of living and seeing the world:

My mini-forest is the culmination of many years’ study and practice of the system that has come to be known as Agroforestry or Permaculture, and which many people, including myself, believe has a major role to play in the evolution of an ‘alternative’, holistic world order. A Green World. The World of Gaia.

– Robert Hart (1996)


The belief underpinning permaculture that “nature knows best” and agricultural systems are best shaped in the image of the natural world stems from the “organismal metaphor” proposed in the early 20th Century (Clements 1916), seeing ecosystems as behaving like a “super-organism,” and on Odum’s cybernetics, seeing ecosystems as analogous to machines (Odum 1981, cf. Holmgren 2001). Conservationists such as John Muir then popularized these ideas of an ideal state of “natural balance” for both nature and man (Marris 2011), but while still a dominant idea in both popular culture and much environmental policy (Botkin 2012), most ecologists today see natural systems as being characterized by continual change and adaptation rather than any ideal state of stability, and some suggest that the ecosystem concept itself may have outlived its usefulness (O’Neill 2001).

Permaculture and other alternative approaches to farming are rooted in the post-1960s counter-culture’s beliefs about the need to prepare for an inevitable collapse of industrial society and a consequent return to subsistence farming (Gold and Hanover 1987). Botkin (2012) traces this idea of a “Fall” and “Return to Eden” back to the roots of Judeo-Christianity, a powerful metaphor that also helped shape early ecology and environmentalism. Perhaps these deeply held cultural beliefs help explain the ongoing interest in close-to-nature approaches to farming such as forest gardens, which are seen as a way of restoring a presumed ideal state of natural balance that humans have disrupted by clearing the forests and tilling the land.

  1. Design Principles: Diversity, Complexity and Balance

There is a common-sense appeal to the permaculture concept of mimicking nature. Unlike a conventional annual vegetable garden with its ongoing needs of digging, weeding and applications of fertilisers, forest gardens are intended to be self-maintaining, with minimum inputs or labour, and to function with the diversity, complexity and the perceived “balance” of a natural woodland while conveying the following advantages (Hart, 1996; Jacke 2005; Crawford 2010):

  • the trees make use of vertical space which in principle would allow more food to be grown in the same area;
  • perennial plants don’t require annual tilling of the soil and planting of new seeds;
  • the diversity of polycultures should reduce problems with species-specific pathogens;
  • mulches and nitrogen fixing plants, common to other agroforestry practices obviate or reduce the need for fertilizer applications;
  • diverse systems are more resilient due to greater complexity;
  • forest gardens have multiple functions and yields including therapeutic and environmental benefits.

Taking each in turn we can establish theoretical explanations for why these principles in themselves are insufficient to make forest gardens viable as alternative food production systems.

Vertical space

 Yields from tree crops are limited by a trade-off between yield produced and the energy used by the tree itself in maintaining its woody structure. In addition, while yields increase over time as the trees grow larger, they will also produce more shade and roots (which will extend at least as far as the leaves), both of which are likely to reduce the yield of understory plants via competition for light, water, and nutrients. Crawford recommends up to 50% wider spacing than in conventional orchards to allow enough light through to the lower layers, and so most of the advantages of the vertical space are lost. We will compare figures for yields of tree crops and arable crops below.

 Annuals vs Perennials

 Perennials have the advantage of not requiring annual cultivation and planting, and often emerge earlier in the spring than their annual counterparts, but have the disadvantage of being static and not easily changed in response to changing conditions. By contrast, annual crops can reach optimal yields within just one or two seasons, and an annual system is much more flexible in that a different variety or crop can easily be switched to in the event of disease, climate change or even nutrient depletion. Annual grains were the first plants to be domesticated for the very reason that, in setting seed each year, they have lent themselves to dramatic improvements for yield and other traits through plant breeding (Kingsbury 2009).

Monocultures vs polycultures: Diversity and Intercropping

 Diversity is one of the “principles of permaculture” (Holmgren 2002) providing the notional underpinning for forest gardens, yet this diversity may compromise yields. The competition between species has already been noted. Also, polycultures lend themselves less to mechanization of cultivation and harvest, and nuts that fall from trees are likely to be lost in any groundcover vegetation. However, some researchers have pointed to the work already done on intercropping—traditionally practiced around the world—as a basis for promoting more complex polycultures such as forest gardens (Gowland 1996; Watson 1998). Resource partitioning (soil and light), the ability of combinations of crops to access more soil nutrients than monocrops, and modification of the microclimate, have been shown to increase yields compared to the individual crops grown alone. (Vandermeer 1989, Innis 1996).

While intercropping has also been shown to increase yields in relatively simple silvoarable systems such as vegetables between fruit trees (Newman 1986), Vandemeer also found cases where yields were lower if inappropriate crops were chosen. Whitefield (2013) was also aware of this, pointing out that the largest gain from intercropping is gained from the first crop addition and is likely to decline with the addition of each subsequent crop. In a review, Denison (2012) found that achieving optimum spacing in intercropped systems was difficult, and that while intercropping increased yields compared to the average of the two crops, they were often still less than the best crop grown as a monocrop. Thus, for many farmers the pragmatic choice was to grow the single best yielding crop alone.

The apparent lack of variety in the crops we eat is also cited as a reason to prefer forest gardens over conventional agriculture, but there are good reasons why only some crops have been adopted apart from ease of improvement breeding mentioned above. Being readily storable and transportable, corn, rice and wheat alone account for nearly half of humankind’s calorific intake. Another reason is pollination- a crop suitable for agriculture requires reliable methods of pollination to produce good yields, and so these grains tend to be either self-fertile, pollinated by many different insects, or wind pollinated, in contrast to many other plants that have co-evolved with specialist pollinators (Warren 2015).

Efficiency: inputs and outputs

Along with Jacke, Crawford (2014) argues that it is the efficiency of the system that acts of a measure of sustainability, not the total yield. He claims that modern agriculture often achieves an energy return of 5:1, and sometimes less than 1, with more energy going into the system than coming out, while forest gardens can achieve as much as 40:1. Even if this were true in terms of absolute physical energy- it is not explained how these figures are arrived at- fertilizer accounts for only about 2% of global energy consumption and farming without it would be far more labour-intensive and require up to four times the land to grow the same amount of food (Smil 2011). Thus, while low-input systems may be less dependent on fossil fuels overall, this advantage is vastly outweighed by the land-sparing benefits of continued increases in production from modern agriculture.

Systems, resilience and complexity

 Permaculture advocates the importance of the number of connections between elements in a design, arguing that such diversity of interactions leads to greater resilience: if one synergistic relationship breaks down, plenty of others are there to pick up the slack and prevent system failure. Natural systems are presumed to be in a natural “balance” which can easily be disrupted, with a change to one part unbalancing the whole system

Yet according to Denison (2012), an evolutionary perspective applied to agriculture reveals that natural systems have evolved more by chance than by any design (Gleason 1926) and that the defining unit in terms of function, adaptability and resilience is the individual species and not the system as a whole. Plant assemblies in nature may be as malleable as in a designed garden, readily incorporating newcomers in the form of aliens, invasive or naturalized plants and often continuing to function well even after the loss of many native species (Wilkinson 2004).

Multiple functions- habitat and therapy

Other kinds of “yields”, such as the aesthetic and therapeutic value of gardening and working close to nature, are often cited as highly valued reasons for promoting forest gardens (Hart 1996; Jacke 2005). There is no question that these are important aspects of gardening, but may be served as well if not better in other ways. Urban gardens, though not primarily for food, already provide habitat for a wealth of biodiversity (Goddard et al 2010). Equally, there is good evidence that gardening and gardens have great therapeutic value (Haith 2015) but again, there is no reason to suppose edible forest gardens will significantly add value to this.

  1. Yields- Land Sharing or Land Sparing?


 Despite absence of data, claims for high yields produced in such temperate permaculture systems can be extravagant (Sustainability Centre 2015). Hart (1996) for example states that “the forest garden is the most productive of all forms of land use”, supporting some of the most densely populated countries on earth. This might be plausible in tropical climates, at least in terms of total biomass production if not food yields, but the limitations of light and the relatively narrow range of productive tree crops available in temperate zones make this an unlikely scenario for the UK.

Comparative yields of staple crops

In the UK, most food produced in forest gardens is fruit or leafy green vegetables. Yet for forest gardens to prove their worth in production terms, they need to compete with other staple crops with high value of protein and carbohydrates. The main option for tree crops here is nuts.

Cobnuts (hazelnuts) can achieve yields of 3.5-4 tonnes/hectare 8-10 years after planting (CALU 2006), walnuts potentially 1tonne/hectare and sweet chestnuts up to 4.75 t/ha (Crawford and Newman 2006). This is still a long way from typical UK yields for barley and oats of 5-6 t/ha or wheat over 8 t/ha (DEFRA 2014). Potatoes can yield over 40 t/ha  (FAOSTAT 2013) -assuming 80% water content, this would equate to 8 t/ha in dry weight.  These best-case values for nut trees in the UK are not found in forest gardens with a complex understory, but generally in monocultures. Additionally, nut yields in the UK vary from year to year and are vulnerable to poor weather during pollination or early wind-fall (Crossland 2013) and hence are unlikely to grow much beyond their current niche market.

Discussion of yields is important because the driving rationale of the forest garden is that modern agriculture is unsustainable, laying the blame at the feet of monocultural systems based on annual grains and pulses. However, despite often well-founded fears of soil erosion and nutrient depletion, global yields of these crops continue to increase through improved varieties and technology (Ausubel et al 2012; Grau et al 2013). Indeed, total land used for agriculture may have already peaked (Our World in Data 2015) as a result of ongoing improvements in efficiency, and substantial area of land has been “spared” for nature as a result (Stevenson et al 2010). This dramatic and sustained increase in agricultural productivity over the past century has resulted in only 2% of the population in the U.S. being required to farm (AFBF 2015). In these respects then, modern farming is arguably more resilient because of its continual innovation and adaptability.

 6. Conclusions

 The three—or more—layered perennial edible food forest we have examined here is an attempt to improve agriculture and food production by mimicking nature. What works well in the tropics however does not seem to work well in cooler climes. While interest and research into sourcing promising novel crops and new cultivars from around the world continues, most temperate forest gardens seem little different from the fruit gardens and orchards commonly found in Britain prior to the 1950s.

Temperate forest gardens do offer great potential for further research on plant interactions within multi-strata perennial systems, and there is great scope for improvements in cultivars of many tree crops. A warming climate may offer a greater range of possibilities for novel crops to be grown in the UK, as is being tried, for example, by Otter Farm in Devon where they are now growing olives and almonds, but it is as yet unclear whether multi-tiered systems will provide any significant advantage.

Despite the lack of promise forest gardens show in becoming a viable alternative to industrial farming, the ongoing interest in permaculture philosophy together with public concern about sustainability will ensure that they continue to be experimented with by enthusiasts. The myth of the need to return to a “balance with nature” remains a powerful influence in many areas of public policy well beyond the permaculture movement and will continue to shape ideas about food, farming and conservation for a long time to come.


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Forestry Study Tour

Last week was the study tour for some 40 Bangor MSc Forestry students who traveled by coach to the Lake District, the Scottish borders and North Yorkshire to see a range of sites demonstrating Continuous Cover Forestry (CCF), rewilding and flood mitigation. The theme for the week (and subsequent essays we will have to write): the Resilient Landscape. Here is a brief review of the week with some photos and descriptions of the sites. Apologies for any mistakes or ommissions, this is largely a quick write-up of notes taken during the visits.

Day 1 Wythop Forest Continuous Cover Forestry, Lake District.

Gareth Browning of FC England was our host for the day, and explained the management of 156 ha of mixed forests under CCF.
CCF has been practiced in much of the forest here since 1980, with douglas fir as the main species, and there are some impressive specimens (for the UK!!) of up to 52m tall. These areas are now under transition to broadleaf as they fall under the Plantation on Ancient Woodland Site designation (PAWS).


The markets for the Douglas fir are mainly in Germany where it is used in port infrastructure; some also goes for ships masts. The Workington paper mill 

has provided a new market for wood chip, used to power the mill, making thinnings and better forest management more viable. Douglas fir is worth 2-3 times that of Sitka spruce as timber.

There are 16 separate forests in the area, ranging in size from 9ha to 1000ha. The lack of connectivity is a mixed blessing: for example, about 120 roe deer are culled every year, and the separation between the forest areas makes this much easier since roe tend to cover a large area; red deer would be more problematic since they would rarely break cover.
A significant constraint is the proximity of the A66: safety regulations require a minimum of two tree lengths in distance between any public road and tree felling; since CCF requires large seed trees to be grown, this distance becomes quite large. When felling within this limit takes place the road needs to be closed for some weeks- an expensive proposition.
CCF is fairly new here, just 30 years, compared to 300 years in Switzerland for example. In the last 10-20 years, the forests have begun to regenerate themselves.
Douglas fir needs a certain degree of warmth and sun for the seeds to germinate- it will not regenerate on north-facing slopes and requires underplanting here. Other species being introduced now include western red cedar, silver fir and Montgomery pine.
Large Douglas fir  frame tree surrounded by thicket of regeneration which will subsequently be thinned
One advantage of CCF is that it produces more wind-firm trees (although on other sites we learned that CCF for spruce is not practical for windy sites- any thinning leads to more windthrow, for spruce at least). Larger trees can develop good buttresses for stability. A more diverse structure is the aim. About 50 frame trees are retained per hectare, which works for shade tolerant species such as Douglas; more than that and it becomes hard to maintain a diverse structure with gaps that can regenerate.
Some plantation forest has now been designated ancient woodland, influencing future management plans and species choice. Increased species diversity is favoured for resilience to future pests and diseases and climate change. One species mix is beech, planted under conifers. As with other sites we visited, most larch here has succumbed to Phytophthora ramorum and has been felled.
Gareth argued that forests will be increasingly valued for other reasons, recreational and flood mitigation perhaps, and should be at least as deserving as subsidies as farming.
We drove round to nearby Dodd wood where the recreational value was obvious. Osprey viewing stations bring in £1-2million to the area annually. The birds need a diverse structure, with the precise species being unimportant. Some of the frame trees will be left to continue to grow with no plans of harvesting- visitors to the park appreciate this since “Big trees make us feel very small.” They have a Wow factor.
There was some discussion of the difficulties of extraction for very big trees close to the road or on steep slopes. In some cases helicopters might be considered. But the extraction process, although disruptive to the soil, creates a seed bed leading to more regeneration. Even opportunities for windthrow can help this and the end result is a “self-healing” forest. Ultimately however, small areas of CCF are not enough.
Stunning view from the hostel in the morning
Day 2- visit to the Eddlestone water project with Hugh Chalmers of the Tweed Forum. This is for flood mitigation involving engineering meanders into the river, planting trees, bank stabilization, log flow restrictors. To access the land used in this project, some £2.3million has been paid to farmers in the area either in compensation of land purchase. Hugh pointed out that it is not just the trees, which can help reduce flooding through increased water infiltration, but also the vegetation growing beneath them. Fish benefit from up to 50% shading of the water by trees. The project also benefits from carbon credits for carbon sequestration, though some of the land is peat bog and might be better left unplanted. Hugh made the wry comment “there is nothing logical in land management- people love peat for growing trees in [as a potting medium]!” The possible role of beavers was mentioned (not in this area at present) but that their beneficial effects could be replicated partly by growing willow on the riparian zone and regularly coppicing it- beavers apparently only use fairly small material (like willow coppice) for their dams, while constructing log flow restrictions would use bigger material which could cause a problem if large logs moved downstream rapidly in a flood. Impressive to see something of how this kind of project can happen in practice. As we have also seen on the course in North Wales, the key issue is successfully working with many stakeholders, especially the farmers with land along the river. As High said, it is good to get farmers working together and thinking in terms of the whole catchment.

Glen Tress Trial Area

This Forestry Commission forest is half way through a 120-year transition process from single-aged stand Sitka spruce to CCF with diverse age structure and mixed species.

From the FC website:

When the Trial Area was established in 1952 most of the plantations were 20-30 years old.  The 117 ha area was divided into six Blocks and the plan was to transform the area over a 60 year period by felling and regenerating groups totalling two hectares in each Block every six years.
Various different mixes are being trialed in different plots, with the prevailing philosophy of “anything but Sitka”. The problem is, as we were to find in other sites also, is that Sitka regenerates so vigorously that it is a major headache trying to establish anything else. On poor land, it even regenerating under itself is problematic as it tends to come up so thickly it gets checked and fails to thin itself, simply not growing. In some cases the most efficient thing is to simply mulch the entire seedling crop and plant into the bed of mulch.
Glentress is also the preeminent site in Scotland for mountain biking. Some of our group opted for a mountain bike session rather than the forest tour, but I decided to see the forest this time. There was considerable discussion about the challenge of combining hosting  quarter-of-a-million mountain bike visitors with the practice of felling large trees. A minority of bikers seems unwilling to always heed the No Entry signs when felling is taking place, and there have on occasion even been conflicts.  Ospreys and other protected species are also a challenge for the timber industry, but recreation here is an increasingly significant income generator.
As a forest, Glentress seems to play the role of laboratory, trying different species mixes for CCF, but the constant incursion of Sitka makes it difficult to really achieve what they want to do. In the meantime, it is a great example of how forests are being  asked increasingly to fulfill diverse functions for society well beyond simple timber production.

Day 3 Carrifran Wildwood

The Wildwood project was started in 1993, a grass-roots community project to restore “native” woodlands  in the Southern uplands, as a demonstration of the kind of vegetation that was once found over most of southern Scotland. The 650ha site at Carrifran was purchased on Milenium Day, 01-01-2000. Regeneration would have been far too slow because of lack of seed source – in fact, as with Glentress, the main regeneration would be Sitka from neighbouring plantations, which requires constant weeding-out anyway! Over a half million trees have been planted since then, 75,000 by volunteers, and all the trees were grown by seed collected by volunteers and contracted to nurseries to grow on.
The choice of species was made after a site classification based on assessing what woodland type was likely to have been there in Neolithic times, which mainly upland birch-oak mix.
Our host for the day Philip Ashmole, one of the projects’ founders and author, with his wife Myrtle, of The Carrifran Wildwood Story (2009).IMG_4117
Philip explained that there was a deliberate decision made not to incorporate more southerly species that might subsequently move northwards in a warming climate; the range of elevations available at Carrfiran allow for a certain amount of migration for differing climates here anyway. But no attempt at building in either climate or disease resilience is being made through species choice- it is all about demonstrating what the lowlands of Scotland might have been like 6000 years ago before intensive farming, forest clearing and sheep grazing. The patchy plantings is also deliberate- there would always have been herbivores such as deer which would have prevented complete canopy closure, their numbers held in check by wolves and lynx which would have kept the herbivores moving.
A major expense has been a deer fence- “the best fence in Britain” paid for with lottery funding, which is hoped to last 10-20 years with maintenance. A group of mountain goats that had been living here were captured (bar three that could not be caught and were shot) and moved to the Windsor Forest park, ironically to aid in a peat conservation project by grazing regenerating trees and shrubs! This caused some conflict in the early days as the goats removal was fiercely opposed by another local group- a good example of conflicts than can arise between differing conservation goals.
80% of funding comes from private investors, there is also income from carbon credits, and the project has over 1000 subscribers.
Juniper in the foreground.
Little formal research is being undertaken at Carrfiran, deliberately so since research markers etc would interfere with the projects aim- to give visitors an experience of wilderness. However, despite being favourable to wolves and lynx in principle Philip disliked the word “rewilding” since it “has a lot of baggage associated with it”- though we did not hear what he was referring to.

One of the few original trees, a rowan, is visible on the bank behind Philip, now protected from grazers it has several seedlings growing around it.

Perhaps the main issue regarding resilience is that the project relies heavily on a small group of dedicated volunteers, but these are predominantly males over 60. A local hillwalking group regularly walk the entire fenceline to inspect it for faults.

A beautiful place and an inspiring project, well worth a visit.

Day 3: Eskdalemuir

For a complete contrast, our next stop was plantation forestry sites at Eskdalemuir characterized by single-age stands, hard edges and clear-fells. The forestry covers some 20,000 ha of mainly Sitka spruce established in the 1970s and 80s, grown on a 40-year rotation- much of it now ready for or just after felling and re-planting. The forestry is managed by a number of different forest management companies, and we were met by two forest investment fund mangers who discussed the project with us.

This site was the subject of a recent CONFOR report comparing incomes and carbon storage from forestry with upland sheep farming on similar areas, finding that while forestry only receives about 1/6th the subsidies of agriculture, before subsidies it can generate up to 3x the income, as well as being a net carbon store as opposed to an emitter of CO2 in the case of sheep farming.

Much of the discussion was about improving public relations regarding the impact of forestry of this nature. For the second rotation, regulations now stipulate greater age-structure diversity, softer edges with native species on the boundaries, much smaller areas of clear-fell. However, Sitka seems here to stay- in terms of productivity and profitability in difficult environments, it ticks all the boxes while few other species show any real promise. They certainly would not grow so fast-although given some of the limitations of timber quality resulting from the fast growth of Sitka this might not be a bad thing. However, for now the economics of upland forestry manged purely for profit seem to dictate no real increase in species diversification is likely- although worth in excess of  £100million, as only a small fraction of the investors’ total portfolio, the risks of catastrophic disease outbreak in Sitka seem to be something that will just be absorbed should the situation arise.

We were told that there has been next to no new conifer afforestation in the past few years, and that this is due to bureaucratic filibustering. Delays spawn further delays and the necessary permissions are just never signed off on. Broadleaf is ok, but while fracking licences for example are guaranteed to be granted within 16 weeks, applications for new conifer plantations have been sitting for several years without progress. This shows perhaps just how far public opinion has swung against conifer plantations, despite their profitability in recent years, which will have serious consequences for British forestry in the future which will meet a supply crunch by 2030 unless new afforestation occurs. In the meantime, with returns on investment forestry still very strong, our fund managers were looking to Ireland for new opportunities (though conifers are certainly not popular there either!).

Day 4 Galloway Forest Park


IMG_4152 Above- larch stand due for sanitation fellingIMG_4155

Examining the Forest Management Plans in the Clatterinshaws visitors’ centre.

Dumfries and Galloway is the biggest FC district in Scotland  covering 115000 ha with 20% of production at 700,000 cu m. The district generates £80m from timber and recieves £20m from the Scottish government for visitors centres and other recreational facilities.

The species make up consists of:

78% spruce

10% pine

8% broadleaf- this is expected to increase to help meet the national target of  20%

4% larch- all of which is scheduled for sanitation felling on account of Phytopthera ramorum which has been present since 2010. Some of the larch shows signs of healthy branches, and cuttings are being taken for grafting onto rootstocks in the hope of finding resistance- but “noone really expects to find any.”

Great spruce bark beetle has been present since the 1980s but so far can be controlled with one of the few successful biocontrol methods.

Afforestation at Clatteringshaws was begun in the 1940s, with most of these now felled and active felling underway for most of the 1970s plantations also. The area is now being managed to meet a range of production, environmental and landscape demands. New plantings include intimate species mixes to maximise soil benefits, such as shelterwood systems of beech, Silver fir and sycamore. A dozen conifer species and a dozen broadleaf species are in the plans. Rotation lengths for conifers are being extended. 60% of the plantation area is bog and in some cases on deep peat de-forestation is occurring, with the peatlands being restored after felling.

Public opinion was discussed: do the public understand forestry> A resounding “No!” was the answer given. Every two years, the FC commission a public opinion survey which makes for depressing reading (according to one of our lecturers) – forests are generally held in very negative regard, often associated with crime and vandalism. There is serious arson problems in forests closer to the big cities. On the other hand, around Clatteringshaws, while larch is generally preferred aesthetically for its more diverse herbaceous layers and understory, after an initial outcry when sanitation felling takes place (were it not for Phytopthera, most of the larch would be held onto for as long as possible), often the felling of the older blocks has opened up the views and improved opportunities for mountain biking and other activities, and generally been quite well received.

For further information on Scottish FC managment and planning see here.

Day 5 Slowing the Flow, Pickering

Last stop- another flood mitigation project, this time on a much larger landscape scale. The project was initiated after Pickering suffered severe flooding in 2007. The aim is to prevent chronic flooding up to a 1 in 25-year event. Slowing the Flow is a partnership project lead by Forest Research and with DEFRA as the main funder. The project is believed to have saved the town from the worst of the flooding in 2010.

Over a catchment of 66 square kms, there are 50 ha of woodland planted, 140 mini dams and a large bund protecting the railway. There are also mini-bunds and stockades made from spruce, and 170 large woody debris dams.

Although the media has focussed mainly on the soft landscaping measures of tree-planting etc, the engineered bund (see photos) is by far the most significant contribution. The key in flood mitigation is to reduce the peak- “slowing the flow”.

In terms of forestry, planning for species diversification is designed to meet climate scenarios for 2080, when 30% of the public estate is expected to become unsuitable for current species due to higher temperatures. 20% diversification is planned, including shag-bark hickory as a possible alternative to ash, grand fir, Macedonian pine and oriental spruce.

Beavers were discussed as being considered for introduction, with the proviso that they will simply be shot if they get out of hand: they will almost certainly undermine the railway through burrowing. There is roe deer and some red and muntjac, and our FC host, who advocated much more extensive re-planting of the moors which have suffered “centuries of abuse from grazing” commented “lynx would help.”


A great trip all considered, very informative and lots to think about. Now all there is to do is write the assignment… Many thanks to our lecturers Mark, James and Tim for organising everything and all the hosts who patiently answered all our questions.

I leave you with some atmospheric photos from where we stayed Thursday night, the beach at the funky and wonderful Boggle Hole hostel just below Whitby, the heart of Dracula country…





Into the New Wild

Book review: The New Wild: Why invasive species will be nature’s salvation by Fred Pearce

Icon Books 2015 new-wild

In 1910  New Zealand’s great botanist Leonard Cockayne described the dramatic change in  plant communities which had occurred since the first visit of Captain Cook to the country in 1769 (1). Some 560 new species from Europe, Africa and elsewhere had by become established by then, with half of them common throughout the country from the coasts to the highest mountains:

At first thought, the idea of 560 different sorts of plants- some of them the most aggressive weeds in Europe- having not only been loosed to do their will, but also having established a secure footing, would lead to the conclusion that, if not the flora of New Zealand, at any rate the primitive vegetation was doomed. No conclusion could be more incorrect. Were it not that man has changed, and is changing, the face of nature by means of his farming operations, his grazing animals, his fires, his drains, and his intensive exploitation of rain forest and flax swamp, the host of foreign plant invaders would be powerless- the indigenous plants, attuned to the special life conditions f their native land, would laugh these aliens to scorn. Why, even now, when the introduced plants have man as their potent ally, 66 percent of the species are rare or local, 40 percent being so rare as to be negligible, while merely 34 percent can be classed as extremely common, common, or fairly common, these being taken together. But these percentages do not emphasise the real state of affairs, for many of the commoner plants are confined to sides of toads, neglected building sites, and rubbish heaps- in short, to “waste ground” as it is called- and there are many other species restricted to cultivated land. In fact, probably only about 100 species are established on land where the vegetation would be exposed to modification only by grazing, fire, and other causes due to the indirect action of man.

The warfare, indeed, between the plant inhabitants of primitive New Zealand and the alien invaders is waged almost entirely under conditions where man takes a powerful hand, for, except for certain rock, stony debris, and water-plant formations, no primitive plant community has been desecrated by a single foreign invader. This is a very different version of the story from that even yet current in biological literature, where it is affirmed ad nauseum that the New Zealand vegetation is powerless when it comes into competition with the European plants, which by natural selection have become the very elite of the weed world.

Cockayne’s observations made over a hundred years ago are almost identical to those made forcefully in Fred Pearce’s provocative new book which takes to task invasion biology– the view that non-native species are generally “invasive”, constituting one of the greatest threats to biodiversity and ecosystem health, and need to be controlled and where possible eradicated completely- almost at any cost.

The European Commission on the Environment describe Alien Invasive Species (AILs) as “a major threat to native plants and animals in Europe, causing damage worth billions of euros to the European economy every year.” Bird Life International call for a far more extensive policy than that currently proposed, listing over 200 invasive species as of “high priority for urgent risk assessment” in addition to the 37 that are currently listed for control; while the WWF quote the World Conservation Union as saying

the impacts of alien invasive species are immense, insidious, and usually irreversible. They may be as damaging to native species and ecosystems on a global scale as the loss and degradation of habitats.

Hundreds of extinctions have been caused by invasive alien species. The ecological cost is the irretrievable loss of native species and ecosystems.

Pearce, winner the UK’s environment journalist of the year in 2001 and author of other books on climate change, population and sustainability, comprehensively rejects these assessments. Exactly as  Cockayne  describes above, “invasives” are more accurately thought of as opportunists which generally only move into ecosystems that have already been severely degraded by other human activities, and are able to thrive on our pollution where nothing else can. For example, the infamous Zebra mussels that spread through Lake Erie at such a rate in the 1980s were moving into an ecological desert so atrophied that everything else had already died- and apparently did a fairly good job of cleaning it up. In time, the previously endangered lake sturgeon, bass and migrating ducks moved back  to feed on the mussels.

This is a typical pattern with so-called “alien invasions” which are generally the consequence rather than cause of previous disturbance. Another infamous “invasive exotic”, Kudzu, from Japan- which became known as “the vine that ate the South” because of its rapacious spread through the southern US- had previously been widely planted as an ornamental, and for animal fodder and erosion control. It only got out of hand as a result of other land-use changes:

The vine hasn’t changed. It is still revered in Japan. What has changed in America is the land and people’s expectations of the land. Kudzu’s foliage is no longer needed to feed grazing farm animals, which now live in feedlots. The pastures are abandoned. No longer kept in check by grazing, kudzu now grows where it is not wanted, spreading unchecked almost anywhere south of the Mason–Dixon line. It is the enemy. The pastures are being turned into woodland, where kudzu is a problem.

The reality is that out of tens of thousands of introduced species- including most of our food plants and garden ornamentals- only a tiny minority ever become problematic or a threat to “native” vegetation in this way. Often, for all the trouble they cause, they also can do a lot of good; the costs they are claimed to incur are often wildly exaggerated based on simplistic extrapolations (2), and these could well be exceeded in some cases by the costs of control, which mainly are doomed to failure anyway. Nor is it true that they are generally likely to cause extinctions- Pearce concludes that this is based more of the assumption that  “exotics are bad” than supported by rigorous evidence. While there have certainly been cases of loss of biodiversity on remote islands, where local species have little options to extend their range, there are plenty of counter examples where introduced species have increased biodiversity. The problem is that “invaders” are simply not valued in the same way that “natives” are:

In fact we seem to have gone a long way from any interest in biodiversity. The interest is entirely to do with protecting natives and avoiding change.

…alien species don’t count and are not counted. They do not exist as part of nature. They have no place. They are un-nature, if not anti-nature. They should be gone. Under this definition, biodiversity in the 21st century can only go down. Extinction could cut the number of species, but introductions could never increase it. Thus the inconvenient fact that alien species actually increase real biodiversity in many places is simply defined away. Big Brother in Nineteen Eighty-four would be proud. Franz Kafka would be proud. Joseph Heller would have added an ecological chapter to Catch-22, if he had known. It sounded more like an ideology than good science.

A lot of the problem has to do with conflating “invasive” with “exotic/non-native”, but just as most “exotic” novel species are not invasive, so there are also “native invasives”. Bracken fern Pteridium aquilinum,  brambles Rubus fruticosus, and gorse Ulex europaeus,  all “native” to the UK but invasive as vigorous weeds or early colonisers of disturbed ground if they come across the right conditions.

More than that, and fundamentally to the whole debate, the line between what is considered “native” and “non-native” is not just blurry but scientifically meaningless. “Everything is visiting. Nothing is native” observes Pearce. What specific combination of plants have ended up living together in different areas at any given time is largely a function of chance. Some species made it across to Britain when there was a land bridge, some got stuck across the water when the sea levels rose again. In trying to maintain “native” vegetation we are necessarily picking a particular period in time from which to judge what can stay and what must go.

Rhododendron ponticum, a major target of conservation control in Britain because of its ability to prevent regeneration of woodland, had been “native” here before the last ice-age. Does this discount it on the basis that plant communities here have since evolved without it? The difficulty is that many other species are in the same category, but are not persecuted as invasive in the same way. Ken Thompson, author of another recent book on the same topic (2) points out that Fritillaria meleagris is generally considered a full-blooded British native, but was first recorded in the wild here only in 1736; while R. ponticum  first introduced to Britain in 1753, is still an “invasive exotic.” To further complicate matters, it is really a hybrid of three other Rhododendron species, which has evolved uniquely in the UK and is not found anywhere else! What, then, can it mean to call it anything but a native? Rhododendron  probably only became so widely spread anyway as a direct result of being extensively sown throughout British woodlands to provide cover for game.

(Conversely, Thompson gives the example of the quintessentially “English” oak  which,  having spent more than 99% of the last 2million years in Iberia, might more properly called Spanish.)

While there are specific cases of co-evolution between two species, they tend to be more exceptions than rules, and it is relatively rare for any group of species to be entirely dependent on their specific co-evolutionary companions- it turns out that ecosystems can usually function perfectly well, and often with increased diversity, with a mixture of old friends alongside new neighbours.  Pearce points out that Darwin did not see co-evolution as a principle driver of evolution, and quotes ecologist and invasion biology critic Mark Davis who states ‘nativeness is not a sign of evolutionary fitness’. Darwin was clear that the individual species is the primary unit of natural selection, not the “ecosystem”- a nebulous and controversial concept in itself. Much of the ideology surrounding the desire to keep nature in an idealized state of pristine “natural balance”, frozen at an arbitrary period of time (generally pre-Columbus) has less to do with Darwin than, as Daniel Botkin has argued, with the much older Judeo-Christian belief in the Great Chain of Being and guilt over the Fall from Eden (4).

Nature is always changing, and is proving in many respects far more resilient and adaptive than it is often portrayed. While most conservation efforts focus on extermination of plants that happen to make it onto the “invasive species” lists,  entire new ecosystems, and often highly diverse regenerating secondary forests are emerging all around us.  Perversely, such habitats are not deemed worthy of conservationists’ efforts to protect them- despite increasing evidence that even most so-called “pristine” habitats were subject to significant anthropogenic change in pre-history (5). Pearce sees this as a blinkered and narrow view and a sad lost opportunity. It is this “New Wild” that he feels we should now turn our attention to, since in the rapidly changing world of the Anthropocene,  there is very little, if any, “pristine” wild left. With more ecologists like Davis speaking out from this perspective of a “new ecology”(6), science has already moved on to a large degree from earlier conceptions of ecosystem balance. Now it is time for public understanding of this science, and conservation policy, to catch up.

Pearce has written an engaging book that should be a valuable contribution to this often confusing debate. If he falls short in any area, it is perhaps the cursory passing over of the threat posed by novel pathogens, which are increasing due to global trade of plant material with potentially devastating consequences to trees and shrubs (7).  In general though he is careful not to fall into the trap of claiming there is no issue at all with introducing new species which might be at the very least weedy or have unintended consequences. Some newcomers can cause serious problems, more for humans than for “nature” though,and noone wants rampant weeds in their gardens. Plants should be investigated on a case-by-case basis, not assumed to be inherently bad or noxious on the basis of the largely spurious notion of nativeness: the vast majority are benign. This raises another issue, as pointed out by Thompson: the public’s goodwill, without which even the most favourable eradication or control efforts cannot in any case succeed. The public do not intuitively divide plants into native or non-native, but assess them on their characteristics of usefulness or aesthetics, which is exactly why plants are frequently assumed to have been native for a long time when, like the fritillary they are relative recent arrivals, and vice-a-versa. It is not just environmental issues at stake here, but the public’s trust in the integrity of science.

More than just a critique of conservation, Pearce also presents a damning indictment of science. With honorable exceptions, few scientists have spoken up against the tendency of NGOs and policy makers to rely heavily on just one or two studies which have either been misrepresented or have little real evidence to back them up, and costly and often damaging alien eradication programs have been allowed to continue unnecessarily, often for decades. As is clear from Cockayne’s book written at the beginning of the last century, there was never any very solid science behind invasion biology, and it is time for this to be more widely understood and debated in the public realm.


  1. Cockayne, L.  1910 New Zealand Plants and their Story
  2. see Pimentel, D. et al 2000 Agriculture, Ecosystems and Environment 84 (2001) 1–20
    Economic and environmental threats of alien plant,
    animal, and microbe invasions Agriculture, Ecosystems and Environment 84 (2001) 1–20.  Pearce claims the widely cited figure of $1.4 trillion being the annual coast to the global economy from invasive species is an extrapolation to the entire world from just six major economies, and the biggest three causes of these costs coming from rats, weeds and plant pathogens in agriculture; among other problems Pearce points out,  no accounting is allowed for possible benefits to the economy from aliens (such as cleaning water pollution in the Lake Erie by the Zebra mussel mentioned above).
  3. Thompson, K. Where do Camels Belong?
  4. Botkin, D. The Moon in the Nautilus Shell
  5. Bowman, David MJS, et al. “The human dimension of fire regimes on Earth.” Journal of biogeography 38.12 (2011): 2223-2236.
  6. see for example Brown, J. and Sax, D. An Essay on Some Topics Concerning Invasive Species Austral Ecology (2004) 29 , 530–536:

    The rare, restricted species are disappearing and the common widespread species are becoming even more abundant and widely dispersed. This hasbeen referred to as the homogenization or cosmopolitanization of the world’s biota (Brown 1995; McKinney & Lockwood 1999).Is this decrease in global biodiversity a bad thing? Is the net increase in local species richness due to invasions a good thing? Is high species richness desirable? We do not believe that these are scientific questions.Science can elucidate the causes and consequences of these changes in biodiversity, but ultimately deciding what is good or bad is a moral and social issue. Few people would question whether the dozens of exotic flower and vegetable species in their gardens are desirable. The value judgements may change, however, if some of those same species were to become naturalized and spread into wild areas or to become serious weeds in agricultural fields.

  7. Rackham, O. 2014 The Ash Tree Little Toller Books, Dorset