Dan Bailey: What would a natural upland habitat have looked like in Britain before humans started having the dominant influence?

George Monbiot: This is a particularly interesting question, because we have two completely different baselines in Britain. The more recent one is the situation that prevailed after the ice retreated, and a temperate climate returned. I’m talking about parts of the Boreal and Atlantic stages, roughly between 9000 and 5000 years ago. It seems that during this period, Britain was more or less covered by closed canopy rainforest from top to toe. I’m using the term rainforest precisely: to denote forests that are wet enough to support epiphytes, plants that grow on other plants. Wherever you see polypody, the many-footed fern, growing along the branches of a tree, it's a reminder that you are looking at a rainforest fragment.

Hardly any land in this country would have been treeless at this time. With the exception of the summits of the Cairngorms, Ben Nevis and one or two other mountains, there is nowhere here that is too high for them to grow. Our bare and rocky hills are an artefact of deforestation, heavy grazing and the subsequent loss of soil.

But even that state arguably reflected the dominant influence of humans. To see what the land would have been like without them, you would have to go back to the previous interglacial period, the Eemian. At this time, the climate was almost identical to ours, but for some reason the people driven out by the previous ice age appear not to have returned to this country. At this stage, there was plenty of forest, but it seems that it was not continuous. The closed canopy rainforest was punctuated by more open forest, as well as wood pasture and savannah. Why? Because humans had not wiped out the dominant species. During the Eemian, Britain had a fairly similar collection of wildlife to the one we know today. You know: foxes, badgers, hedgehogs, deer, robins, jackdaws, elephants, rhinos, hippos, scimitar cats, hyenas and lions.

Ah yes, not the same in all respects. Like everywhere else on earth, we had a megafauna, and this shaped the ecosystem. The large herbivores were driven out of Britain by the ice, then driven to extinction in southern Europe about 30,000 years ago when modern humans arrived.