Downy Birch is a tree tolerant of damp places and has established itself when there was more light due to coppicing.
There are examples of Grey Poplar originally planted for cropping. They live for around 100 years and our starting to fall over. The deeply textured bark can provide shelter for small creatures such as bats.
Honey fungus helps the process of decay by spreading like a black web. The fruiting part of the fungus was found on a rotting tree.