Trophic rewilding sites: how big is big enough?

Rewilding sites in southern England are all or rather modest scale. Most are a few tens of hundreds of hectares. They’re a brilliant start. But if you zoom out a bit they’re still tiny habitat fragments relative to the scale needed for a fully naturally functioning place to emerge.

What exactly do I mean by ‘modest scale’, ‘tiny’, ‘scale needed’ and, erm, ‘naturally functioning’?!

Rewilding science, especially temperate rewilding science, is a vibrant and very young discipline. So I don’t know what I mean! I can’t do a literature review to get a definitive answer to ‘how big should our rewilding areas be’.

One way of looking at this question might be to look at the most area demanding species we might include within a rewilding area. White-tailed Eagles are pretty ‘area demanding’ - those from my patch on the Isle of Wight have ventured across the UK, up to Scotland, across to Cornwall, east into the near continent. They’re area demanding. But they don’t ‘need’ rewilding areas to thrive.

Are there species that are both area demanding and restricted to wilder landscapes? A few. No necessarily restricted by their ecology: take the Aurochs. If they weren’t globally extinct we’d be doing all we can to sustain and build up their populations in Europe including the UK. But they’re elastic as far as habitat requirements go. I’m pretty sure that, like Wolves, Aurochs would do very well out of farmland if not persecuted. They would come into very direct conflict with cattle. farmers (and motorists). So Aurochs would be both area demanding and confined to wilder landscapes, if they weren’t extinct. European Bison is an extant example, similar to Aurochs. Although I’m sure Bison would thrive across European farmland, grazing on all that cropland and improved grassland, it can’t because cattle farmers would struggle seeing Bison eating grass meant for their cattle. And there’s disease transmission (from the intensive cattle out to the Bison).

I’m rambling. Let’s get to the point. Aurochs, although extinct, is a reasonable model species for working out how big a trophic rewilding area might ultimately need to be.

By way of thought experiment, one might liberate a small founder population of Aurochs into a landscape. Multiple herds would form as the population slowly increases. Each herd would range across the landscape, sometimes meeting, usually segregated. There’d be dispersal between herds.

How big an area would one need for a viable, persistent group of Aurochs herds for develop, with enough space for natural resource tracking, through days, months and across seasons? Not a few hundreds of hectares, not a low few thousands of hectares. Probably not 50,000 hectares. 100,000 hectares big enough?

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