If you let trees seed into a wild flower meadow, then it stops being a wild flower meadow. The same goes for heathland.
The trees that grow in boglands are very good at sucking large amounts of water out of the ground. Before you know it, the bog has dried out and filled with leaf litter.
There are several types of habitat in the UK that declined massively over the 20th century, with growing towns and mechanised farming. If we're not constantly managing things, trees will soon wipe out what's left.
This is an interesting point over where do we define ‘nature/natural’. Man has affected the landscape for thousands of years. Large areas have been changed (sometimes better, sometimes worse) by the grazing of livestock. Do we stop eating meat so that mountain pastures that are not suitable for crops return to whatever their ‘natural’ state is? Will they be wild flower meadows, forests, scrubland?
Man has also made much more recent land use changes with the biofuel industries, wood pellets, ethanol etc. What natural point should we return these to?
the countryside that folk admire from their car windows is not really very “natural” - lots of brambles and tangled woods is probably closer to the default state, onto which we have added animals, hedgerows roads and so forth, but also allowed other species to thrive in many cases.
The correct question, and I have no answer, is how to work with and direct nature in a way that is not self destructive. That may well involve more trees, but they do need to be the right sort and in the right places, if not they are just as unwelcome as big weeds.
