Conservation biology and the repair of our damaged and degraded ecosystems
I had an opportunity to try a fresh approach to explaining rewilding during a talk a few weeks ago. The meeting on an introduction to the law, science and practice of rewilding was put on jointly by the Institute of Environmental Management and Assessment, the United Kingdom Environmental Law Association, and by Enviro UK Consultants (1). When Prof. Colin Reid of Dundee University dropped out beforehand from giving a talk on the legal issues, my colleagues in the IUCN Rewilding Task Force stepped in, with Adam Eagle of Clifford Chance covering (by video) the legal context for rewilding in the UK, whilst Prof. Ian Convery and Sally Hawkins talked about the Lifescape Project of the Centre for National Parks & Protected Areas, University of Cumbria, as well as about the Task Force. It was my job with Steve Carver of the Wildland Research Institute to do the rewilding bit, Steve on its definition and the rewilding continuum, myself on the ecological concepts, along with its application, and with Steve finishing by showing a bit of wildland mapping. I kicked off my section with some basic ecology on food chains, food webs and pyramid of numbers (2) how unrestrained herbivory results in ecological meltdown, explaining what a trophic cascade and a trophic pyramid are, and how our trophic ecology is so diminished in our agricultural systems (see from slide 21 in (3)).
Frequent fox droppings showing who had been keeping the small mammals in check
In describing how to restore trophic occupancy, I expanded on the example of Bwlch Corog in the Cambrian Mountains that I had written about a couple of months ago. It was an exercise in the article on what can be achieved that has any ecological credibility, given the inherited constraints on large carnivore reinstatement. In the article, I had described how I looked at the records on the National Biodiversity Network (NBN) Atlas for the species in and around this 140ha area of degraded moorland in the Cambrian Mountains, finding little on site, but many species that could migrate in from a short distance (4). Amongst the birds were buzzard, carrion crow, raven, grey heron, sparrowhawk, kestrel, green woodpecker and tawny owl, whereas common shrew, water vole, field vole, as well as weasel, badger and fox were among the mammals. I had equated the upland conditions of Bwlch Corog to that of two other uplands locations - South House Moor and Carrifran - that were also landscape traps like Bwlch Corog that would have struggled to recapture tree species, but where the removal of livestock grazing and the planting of trees had led to an abundant autogenic return of small mammal and bird species. I was at Carrifran again last week, and could see all the holes in the ungrazed sward that indicated the presence of small mammals, as well as frequent fox droppings showing who had been keeping the small mammals in check. The same could happen at Bwlch Corog, once its natural vegetation was on a trajectory of restoration, and so I suggested that the rough capacity for harbouring in-migrating species should be calculated, based on their home ranges, and a potential trophic pyramid could be constructed for the location. The site specific trophic pyramid would have predictive quality against which monitoring habitat and species return can be judged, and barriers to progress evaluated.
I followed this same logic in the talk, but went further than the article by constructing an eight-level trophic pyramid for Bwlch Corog after a more thorough check of the NBN Atlas species data (see slide 26 in (3)). I put a large question mark at the apex of the pyramid, representing our lack of large carnivores, how we beat ourselves up in promoting and opposing their return (4,5) and how their absence creates a trophic imbalance (6,7). As I noted in the article, this imbalance is a question of niche reciprocity in trophic interaction – if there is not equality of species size in these niches, then trophic interaction at that level of the emptied food web will not take place, and the potential for ecological damage and disruption within the trophic pyramid is too great (4). This gave me a question for the audience, as I asked if they could see any inherent ecological problems with the potential in-migrating species. There had been no issue when I first trawled through the species for the article, but the more thorough search threw up fallow deer that I had overlooked. At least one person spotted the potential of a trophic imbalance if fallow deer did migrate into Bwlch Corog, there being no possibility for a predator of a size capable of having a controlling effect on the herbivory of the deer. It reinforced my point about monitoring species return for their potential to disrupt the progress of ecological restoration.
Bwlch Corog was an exercise for me in the art of the achievable within the palette of species available through in-migration, and given an expectation of what might happen from the experiences of South House Moor and Carrifran. It was satisfying in applying some joined up thinking to a real location, but it was the simplest of approaches when set against the extensive literature available on ecological restoration for ecosystem repair in both terrestrial and riparian systems. Some of this literature focusses on identifying reference information, often historical, to determine the restoration potential of sites, define restoration goals, and evaluate the success of restoration efforts (8-17) while others have a strong emphasis on restoring trophic structure, identifying the number of ecological interactions that can be restored in a focal area by species in-migration or reinstatement (15-23). All good stuff, but from amongst these, there must be some unifying thread that takes us nearer to rewilding having a solid, ecological sense rather than it just be a whimsical panchreston, as was foretold it may become (24).
Focal species planning for ecological restoration
There is a concept in conservation biology of relative community importance and interaction strength of a species within a natural community that marks it out as being a keystone species, a species whose impact on its community or ecosystem is large, and disproportionately large relative to its abundance (25,26). Keystone species are often selected from the total species pool in a landscape to be among a set of focal species, their requirements for survival being a good indicator for the overall attributes of an ecosystem, its composition, quantity and configuration of habitat patches, and thus provide an umbrella of security for other species (27,28). I delved into focal species a few years ago when I noted that natural processes are missing in our wider landscapes because the components that bring life to them – the focal species – are also missing (29,30). I gave evidence that there were positive ecological relationships associated in particular with large carnivores and, since trophic function is a key element of ecology, then we must prepare ourselves for its reinstatement by understanding the requirement for the return of those focal species around which ecological restoration could take place. In a subsequent article, I identified the wildcat – our only remaining native feline carnivore, but whose future is parlous -as a species whose protection gets us into the territory of thinking about the ecological requirements of a focal species, the types of vegetation cover it relies on, and what and where its prey is found, all good lessons if we are to reinstate those larger focal species like the lynx and the wolf. It seemed to me, given the habitat selection of the wildcat, that the third dimension in our landscape vegetation is the last refuge of the wild.
While I found that the focal species approach is a useful way to explore the ecology of our natural processes and its complexities in a nature-led land, my choice of only one species could risk giving too much emphasis to that species. Reed Noss, recently retired Professor at the University of Florida, was in at the beginning of conservation biology, along with Michael Soule (see later) and he recommends in his checklist for Wildland Network Designs (WDN) that a set of 3 – 10 focal species is probably best in most regions (31). It is in the multitude of linked WDNs that the Wildlands Project (now Network) in America developed its action plan for the continental conservation of N. America through mega-linkages – wildways - that sweep up and across the continent (32). Many articles in Wild Earth, the magazine allied to the Wildlands Project, featured heavily over the decade of the 1990s in the development of the concept of rewilding, the strong roots it has in conservation biology, and how rewilding is a key aspect of ecological restoration in the WDNs. This is illustrated by the Sky Islands Wildlands Network (SIWN) a part of the Western Wildway, the mega-linkage that runs between Mexico and Alaska (33). The aim of SIWN is to establish extensive linkages between large natural areas from Tucson in south-eastern Arizona to southwestern New Mexico next to the border with Mexico (34) to ensure the continuation of migrations and other movements vital for the survival of healthy populations of wild species (35). Articles in a special edition of Wild Earth in 2000 described the different elements that were used to produce the WNDs for the SIWN Conservation Plan based on rewilding and focal species planning, and which was a conceptual design for long-term efforts to restore and maintain the region’s native wildlife and ecological processes. It’s worth noting that the Sky Islands are so-called because of the characteristics of mountain ranges along this linkage being isolated from each other by intervening valleys of grassland or desert, the mountains thus forming islands of habitat that have elements of insular or island biogeography (36). More importantly, these islands rise at the meeting point of temperate North American species and warm subtropical species, straddling two major floristic provinces (the Neotropic and Holarctic) and two faunal realms (the Neotropic and Nearctic) and are at the point of convergence of three climatic zones: tropical, subtropical, and temperate (35).
The high diversity of flora and fauna amongst the Sky Islands is unsurprising, given these intersections, and thus there were a good many species to choose from in their Focal Species Planning, having first classified them into different categories based on their functional traits (37,38). The categories included Umbrella species that cover large, ecologically diverse areas, protection of their habitat providing habitat and resources to many other species; Keystone or ecologically pivotal species that enrich ecosystem function, their effect being disproportionate to their numerical abundance; Habitat Quality Indicator species that require natural habitat of high ecological integrity and so provide an early warning as they are sensitive to ecological changes; Wilderness Quality Indicator species that are sensitive or vulnerable to human disturbance and thus require remote, least modified habitat; and Prey species for predators. Amongst the latter were bison, deer and pronghorn, along with beaver and prairie dog (39). The bison, deer and pronghorn were also classified as Umbrella species, and beaver were classified as a Keystone as well as Habitat Quality Indicator species. Most of the carnivores were regarded as Umbrella species. However, it was only Mexican wolf, Mountain lion and otter that were regarded as Keystone species, but all the feline and canine carnivores were Wilderness Quality Indicator species, as were the Mexican spotted owl, Northern Goshawk and Thick-billed parrot.
There is a further subdivision of Umbrella
species possible based on functional traits that could have been carried out,
and which would have characterised a range of different spatial and
compositional attributes. Thus a process-limited species is sensitive to an
ecological process such as fire, flood, or grazing; dispersal-limited species
that are restricted in their ability to move between patches of habitat;
resource- limited species such as nectar feeding birds, cavity-nesting birds,
require relatively uncommon or patchy resources, their availability
determining carrying capacity; and an area-limited species where habitat
patches are just too small to support them (27). You can see from this and the
categories above how you can start to build robust priorities for protection
and restoration. The authors chose to use the simple category of Umbrella
species, selecting those and Habitat Quality Indicator species as the focal
species for the WNDs on the basis that protection of sufficient habitat for
the identified focal species would ensure full ecosystem representation of the
region's native habitats. In some of the areas, rewilding the landscape
required reintroduction of extirpated species as well as ecological
restoration. That it was seen as a rewilding was because the Wildlands Project
had formally resolved around the time of that special edition of Wild Earth
that "the long-term goal of reserve design (for The Wildlands Project) is
rewilding" (39). Usefully, the main SIWN article gave a straight forward
definition of rewilding that implied a restoration of trophic occupancy, but a
more encompassing definition had been given in the same issue in a broad
article that looked at the potential of the conservation planning of the
Wildlands Project to restore balance in the face of continuing losses of wild
nature in N. America – the simple definition is in the last sentence (40):
Species interaction and its consequences
You will probably have seen beaver being
described as ecosystem engineers (41) a term coined to describe the
role that species play in the creation, modification and maintenance of
habitat and which, as is the case for beaver, can also be indicative of a
Keystone species ((42) and see above). I have used the term system
directing species in relation to the effect large carnivores have on
herbivory (43) the term describing a species that, if removed, would have
dramatic effects on the system because of the number of other species that are
substantially affected by their presence or absence (44). From an ecological
perspective, the protection of these system directing species is more
important than those that do not fill such an important role (45). The more I
think about rewilding, and how it has now turned into that panchreston where
it “can explain almost anything” and thus means everything and nothing
- it is meaningless (46) the more I realise it has become detached from its origins in
conservation biology. As example, I found myself falling asleep before I got
to the end of a recent redefinition of rewilding, put forward as providing
clarity on the basis that it was not reliant on the concept of wilderness; it
encapsulated all forms of rewilding discussed so far; and that it allowed for
transitions into and through self- sustaining novel ecosystems (47):
I don’t get any visceral thrill in reading that
mostly utilitarian redefinition, but I do from “allow natural ecological
and evolutionary processes to reassert themselves” (see above). In
reality, the self-absorbed anthropocentrism of setting nature on a preferred
trajectory to provide ecosystem services is particularly distasteful.
Moreover, I am not yet prepared to surrender to the mongrelisation of our wild
nature in “novel” ecosystems full of non-native species that put our
own species communities at risk. Why would you also wish to divorce rewilding
from wilderness, when wilderness is the best classroom for learning about
ecological restoration, the natural processes of a wilderness, as I have
written, being dependent on the presence and abundance of organisms with
particular functional traits (43):
If you look back, you will see that species interaction and its consequences crop up frequently in this exploration of ecological restoration, as it should also do in rewilding. Michael Soulè, Professor Emeritus at the University of California, Santa Cruz and a colleague in the IUCN Rewilding Task Force (48) was also in at the beginning of conservation biology, seeing it as a need to preserve biological diversity by linking the theory of ecology with conservation policy and practice (49). It was with his colleague Reed Noss that the scientific basis of rewilding was developed (50). Michael went on with others to argue that a primary mission of conservation should be to identify and restore species that interact strongly with others. Thus conservation plans should call for recovery or repatriation of “highly interactive species” at “ecologically effective densities” because the often rarity or absence of those species “leaves a functional void that can trigger linked changes leading to degraded or simplified ecosystems” (51). The authors noted that a relatively high frequency of such interactive species were amongst endangered mammals, and to illustrate the functional void in their absence, two strongly interactive species were given as examples: the relationship between the disappearance of sea otters and the degradation of marine kelp forests by overgrazing from sea urchins; and what was called the "National Park Syndrome" where ungulate-caused landscape simplification was occurring through overgrazing of vegetation by deer in the absence of wolves. In a remarkable proposal, Michael and his co-authors wanted protection of ecological interactions embodied in laws and policies that applied to the conservation of biodiversity, such as the U.S. Endangered Species Act, as there was no evidence of its inclusion. They sought to have two goals enshrined in conservation plans and objectives, the first of which was about geographic representation of interactions that called for an extensive geographic persistence of highly interactive species within the historic range of those species. The second was about ecological effectiveness within ecosystems so that conservation plans should contain a requirement for ecologically effective population densities; these are densities that maintain critical interactions and help ensure against ecosystem degradation. They called the point at which highly interactive species fell below the densities needed to regulate their ecosystem the “breakpoint density”, distinguishing this from minimum viable populations that only stave off extinction, but which do nothing to prevent or repair ecological degradation. In the case of the National Park Syndrome, they saw that operational targets or thresholds for ecosystem recovery should be established, the qualitative objectives of which would be the restoration of canopy recruitment of trees and forest understory diversity where plant reproduction had been arrested by excessive herbivore browsing - in Yellowstone National Park, it was by reinstating the wolf, whereas the Rocky Mountain National Park ducked the issue of reinstating wolves by going for fencing exclusion of deer (38).
In a follow-on paper, Michael and others gave greater detail and examples on what was meant by strongly interactive species, laying out some guidelines for assessing interactivity based on the impacts of the absence or decrease in abundance of the species, as well as how to estimate ecologically effective densities for a sample of species so that they could be maintained above thresholds for ecological effectiveness (52) There was the assertion again of the importance of strongly interacting species in recovery planning, and natural-resource and environmental laws. To the authors, it was a matter of embracing new scientific knowledge in conservation as soon as it became available, and this included the ecological knowledge about the significance of species interactions. Thus they encouraged conservation biologists and natural resource managers to apply new biological knowledge in their work. Such a doctrine of “best conservation practices based on the best science” was tantamount to an ethical obligation to them.
Just a habitat indicator for the scrub that can develop anywhere without cows
I can’t help noticing that it has been the
strongly interactive species that have been extirpated from our landscapes,
based on their inconvenience to human use of lands and rivers, such as all of
our large mammalian carnivores, the wolf, lynx and bear, as well as the beaver
until recently, plus the avian predators that have been reinstated in recent
times, such as the goshawk and sea eagle. What remains of the smaller
carnivores like the wildcat, fox, pine marten, stoat, weasel, polecat and
badger, and otter until recently, as well as avian predators such as hen
harrier, peregrine falcon, red kite, golden eagle and common buzzard, continue
to be persecuted. It is the ever-downward spiral of destruction our native
trophic pyramid from using predator control in land management and then nature
conservation (53,54). We don’t view wild nature in terms of its intrinsic
interaction in natural ecosystems, only on the basis that it can be tolerated
within our cultural landscapes. Without the need for any deep analysis, this
would suggest that the tolerated species must be the least interactive, and
yet they undoubtedly represent a large part of the species that are a priority
for conservation in Britain – as an example, you won’t see any avian predators
on the UK Biodiversity Action Plan priority bird species list (55). You will,
however, see European Turtle Dove (Streptopelia turtur). As I noted last time,
this migratory bird has assumed enormous significance through being
claimed as a primary and unexpected outcome of the rewilding at the Knepp
Estate in Sussex (56). This success of the process-led approach
driven by cows at Knepp can be seen splashed in every media account,
including in the recent much fawned-over, fey account from Isabella Tree as
first lady of the Estate, extracted from her forthcoming book (57). I
wrote last time that turtle doves turning up at Knepp would not be a real
boost to its trophic ecology, looking at its diet, and noted that
closed-canopy scrub was among one of its main nesting habitats, the scrub
having developed at Knepp before livestock were introduced (56). That the
livestock thus had nothing to do with the arrival of the turtle doves is
confirmed by a study of species changes in bird assemblages on abandoned land
in Galicia in NW Spain where traditional agricultural and livestock activities
had ceased. During the period 2000-2010, a gradient of change from bare ground
and open shrubland to closed shrubland and woodland in the absence of
livestock grazing led to a significant increase in 13 shrubland and forest
bird species, including species of conservation concern such as turtle dove,
Dartford warbler and Western Bonelli’s warbler, the authors concluding (58):
Turtle doves are not a strongly interactive focal species in rewilding - just a habitat indicator for the scrub that can develop anywhere without cows. I echo Michael Soulè’s admonition at the absence of consideration of ecological interactions in our legislation, policies and conservation priorities, let alone in any plans of mainstream conservation. Why are we not discriminating in the strength of ecological interactions and working out ecologically effective population densities for strongly interactive species? It’s an exceedingly poor defence just to say that those strongly interactive species are no longer around, or that we don’t have the space to bring them back. We have, as Michael says, an obligation to apply the lessons that conservation biology gives us, even if that means starting out by developing the ecological knowledge about the significance of interactions of the species that we do have in our highly diminished wild nature. It will bring science and understanding to our ecology, as it also does to our understanding of what rewilding really means, and how it can be applied to repair our damaged ecosystems, rather than this panchreston of nonsense on rewilding so beloved of the media. If we get that, we will also get the need for our wild nature not always to have to co-exist alongside our land use – a compromise that always works to the detriment of wild nature – and that wild nature needs places of its own, big enough to be home to ecologically effective populations of strongly interactive species.
Real National Parks
I always delight in visionaries unbeknown to me,
the latest I found being Brunsdon Yapp, zoologist and senior lecturer at
Birmingham University, who is the first person I have come across that also
castigated the Addison Committee report from 1931, as well as being an
advocate of the real national parks that are needed to be a home for those
ecologically effective populations of strongly interactive species (4,54).
Yapp was appointed to the National Parks Commission in 1953, he says by
accident, and found that he was the only member with any knowledge of biology
(59). The latter gave him a unique opportunity to evaluate the development of
the concept of National Parks in Britain, and the eventual realisation of the
first in 1951. He later wrote a viewpoint on Real National Parks in 1984 where
he also saw how the Addison Committee report set the pattern for what would
eventually emerge, in particular citing that it had “dismissed any natural
history interest in National Parks with a few lines and a contemptuous
reference to bird sanctuaries”. He noted that the preservation of nature,
one of the two purposes of National Parks, had “been neglected, partly
through ignorance and partly through a misguided attempt to maintain
‘established farming use’”. His solution to turn this around was that
“it would be necessary for the individual park authorities and the central
authority, which I should hope would be a restored National Parks Commission,
to set out to acquire over a period of years all the important parts of the
Parks”. (The National Parks Commission became the Countryside Commission
in 1968, and which itself went in 1999.) He was particularly scathing of the
National Trust who he judged that “having shown itself incapable of
properly looking after its land in the National Parks, should have it
expropriated and given to a new National Parks Commission to own”. This
public ownership in National Parks could have dated from the Addison Committee
report if it had got it right this first time National Parks were looked at
(54). The gap of 50 years before someone like Yapp would see the need for it
is depressing, but at least he got it right that it would allow removal of
human exploitation, his prescription being – “To a great extent they should
be left to themselves. This would mean the removal of sheep, which at the
least prevent tall grasses and herbs from flowering and trees from
regenerating”. While Yapp may not have made the link at the time, his
proposal was firmly rooted in those contemporaneously early years of
conservation biology and, had he lived longer, he may have come to see his
vision as an opportunity to reinstate the large carnivores (59):
Mark Fisher 25 April 2018
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