Tuesday, 26 November 2013

False opposites in rewilding

A criticism of the rewilding debate at the moment is the artificial certainty that some have about what wild nature must have been like.  This is simply unknowable.  There is evidence but this can be interpreted in different ways and can give rise to apparently different models.  This is one criticism of George Monbiot’s book, and articles he has since published; he has a clear and unshakable view of the wild in Britain – dense woodland - a certainty that cannot be maintained.

The nature of a past wild state is only part any argument for a proposal for rewilding today; nevertheless, it may be helpful to go over some apparently conflicting ideas of “wilderness”. 

Ideas for pre-human wilderness apparently fall into two camps: the “closed canopy” model and the “open savannah” model.

The closed canopy model is probably what most people think of as “natural”.  Leave an area alone and it goes through the process of succession to climatic climax - bare land becomes colonised by small plants which give way to bigger plants, then scrub, then small trees, then big trees and eventually the trees form a closed canopy.  This is the “climax” vegetation which is supposed to be of a particular type for a given climatic zone – hence “climatic climax”.  It is said that once formed this climax stays basically intact with only small and temporary open patches within it.

At the other end of the spectrum is the open forest or savannah model.  The closed canopy model forgets the effect of most natural processes, especially the effect of large herbivores.  The savannah model, it is said, imagines a completely open landscape, dominated by grazed habitat, with occasional groves of trees.  A cycle is envisaged whereby you start with, say a grassland, trees become established in patches of spiny shrubs or when grazing happens to be low and then this patch develops into a grove of trees.  Large herbivores then shelter in these groves, eating regeneration so trees are not replaced so the canopy opens and grassland reforms.

Both models are probably just extremes; the reality of original wilderness probably included both concepts and a great spectrum of diversity in between.  But look at the two models a little closer and perhaps the models are not too far apart.

Once a range of natural processes are introduced into the picture, proponents of the closed canopy model generally accept that openings must have been present in the wildwood, not just small scale and transient but maybe including some that are long term and even quite large.  People talk of about 80% cover in trees, and even the wooded area would have been more diverse than we could imagine.

The “groves” in the open savannah model, however, (according to its major proponent) could well have been extremely large – say 700 hectares in size, and maybe would have joined up.  The model envisages up to 70% of the wildwood might have been in closed canopy groves.

80% trees in the closed canopy model against 70% trees in the open savannah model.  Not quite the divergence you might have imagined!

So, was the original wildwood mostly forest with occasional opening or largely savannah with joined up groves of trees – and does it matter?

In my view – no it doesn’t matter!  The point is that the original wildwood was probably far more diverse than we can imagine.  It would have included all the precursor habitats to the semi-natural habitats we know today, and probably a great deal more besides.  It only matters if people use a quasi-wilderness argument to push for the destruction of habitats that for some reason they don’t like!  We don’t know what the wildwood was like, we don’t know how it relates to current habitats and we don’t know how relevant it is to modern day nature conservation.  With all that uncertainly it seems a good bet to conserve the best of the range of ecological variation we have today.

This, however is also not an argument against rewilding.  But rewilding should be about putting the natural processes in place and heading towards an unknown end point – rather than recreating some supposition of the wild (and destroying things that don’t fit your idea).

1 comment:

Scores Birder said...

I agree with much of what you say here, Tony, and particularly the point that we don't really know what European temperate landscapes driven largely by natural processes looks like in the past and might look like in the future. It's pretty obvious that open habitat species cannot have maintained viable populations across very large dense forest systems - metapopulations of sun-lovers in restricted open patches widely spaced and relatively isolated surely would not have been viable? I've yet to see any landscape models to test how extensive and interconnected the open portions of a landscape might need to be to sustain open habitat biodiversity. I'm also doubtful that herds of grazers and intermediate feeders (like Equids, European water buffalo, aurochs and bison) could maintain themselves and segregate feeding niches under a closed canopy forest. Of course, the best way to work this stuff out would be natural experiments at a sufficiently large scale to allow seasonal movements and grazing / browsing facilitation among the herbivore (including surrogates for extinct species), and see what happens, ideally starting with a mixed closed-open area.
I'll be talking about this stuff on my blog too.....