The woodland to your right is relatively young - less than one hundred years old - and was formerly an extension of the heath of St Pauls Cray Common.
This is why there are many young birch trees here. These are short-lived early colonisers which die as slower growing trees become established.
They are often killed by a bracket fungus called birch polypore.
In autumn look on the woodland floor for the fruiting bodies of fly agaric. Do not eat this; it is poisonous!
The fine threads of the fungus (hyphae) form a cap around the root tips of birch, across which sugars pass from the tree to the fungus and water and phosphates pass from the fungus to the tree, enabling both to survive.
This is known as a mycorrhizal relationship.