I'm reading Wilding by Isabella Tree that contests this view of the past flora in the British Isles. The impact of megafauna on the development of woodland is seemingly not accounted for in the accepted view of the historic landscape.

While it's true that if you leave a patch of land to its own devices currently, it gradually becomes scrub, then dense woodland, it turns out if there are deer and other large herbivores about they do quite a good job at reducing tree cover and turning the landscape into a variety of other ecosystems.