Recently I was walking round Ferry Wood with a Swiss ecologist who works at the University of Ulster. He pointed out areas to the north of the wood which exclusively consist of birch: birch of an even age.
He explained that an ecologist back in the 1940’s or thereabouts had put forward the theory (since proved) that such woods were cyclical. It goes like this:
A good seed year on grassland with adjacent birch trees plus lack of browsing animals results in the growth of an even-age birchwood. Masses of saplings appear to begin with, but as the trees mature they thin themselves out. Then the wood becomes senescent: trees start to rot and fall over and eventually the wood disappears so that it becomes grassland again. Then, as long as the grazing is still light, the cycle begins once more.
I found this fascinating, as had thought of thinning the birch and planting oaks, but Pierre thought this a bad idea. “It’s good to have a diversity of woodland types, so don’t interfere, let it stay a birch wood.”
I’m going to follow his advice.
bioregioning 
I have come to the same conclusion, having recently bought a small house in the middle of a birchwood.