George Monbiot/ The Guardian:

What’s missing from this picture? I mean the picture of rural Britain many of us hold in our heads, whether it be a thatched and mullioned idyll, or the bare hills fetishised by naive nature writers? Well, quite a lot. Trees in the uplands; soft boundaries between habitats (ecotones) that are crucial for thriving food webs; dead wood, of which there’s a dearth in this country; scrub (a vital but derided habitat); undrained wetlands; and wild, healthy rivers. But there’s something else, something whose absence is less visible but just as important. Wolves.
Not just wolves, but any large or middling terrestrial predators. We talk here of wolves and lynx as “top” predators. But our native top predators, until modern humans finished them off, were lions, hyenas, bears and scimitar cats. Wolves and lynx would better be described as mesopredators. The wolf that didn’t howl helps solve the mystery of how this country, for all its love of nature, remains one of the most ecologically barren places on Earth.
A few years ago, and centuries after the last definite record in Britain (an animal killed in Sutherland in 1621), we started talking about wolves again. We also flirted with the idea of reintroducing lynx. Then we forgot again. While rewilding has spread further and faster in the past 10 years than I could have dreamed, it follows a certain pattern, described by ecologists as “non-trophic”.
Trophic rewilding means bringing back important missing species, to restore ecological processes and create self-regulating systems. Instead, most of our rewilded places, while now much richer in nature, remain closely managed by people. People assume the role of wild predators, limiting the number of herbivores and moving them around. That’s fine as far as it goes. But we’re not very good at it.
Until the early 20th century, deer were absent from much of Britain. The roe deer was extinct in England, the red deer confined to isolated pockets, and non-native fallow deer to deer parks and grand estates. A century later, Britain has six species of deer, four of them exotic: red, roe, fallow, Reeves’ muntjac, Chinese water deer and Japanese sika. Up to a point, the expansion of the deer population was a great success. Beyond that point, it’s a tremendous failure. Deer have done so well (except in Wales) that they now present a major problem.
There are no reliable estimates of deer numbers in Britain, but there’s no doubt they’ve grown massively and continue to rise.
There are several reasons: more affordable food (until recently), which meant less poaching; new woodlands and plantations; warmer winters; and autumn sowing, which ensures there are crop plants for deer to eat all year round. But above all, their numbers grow because there are no effective means of controlling them.
The result is success of the kind you wouldn’t expect in nature: one study estimates the survival rate of muntjac born in the UK at 60-70% and of roe deer at an astonishing 83%.