If you are looking for something to do tomorrow afternoon you could go on this guided walk about trees at Hyde Park, 'Walking with giants'. You'll get to hear about tree folklore. The walk lasts an hour and a half. All the details are on the royal parks website, which by the way is a really good. Oh and the best bit is it's free, just call up and book.
And whilst you're getting in the nature mood take a look at british-trees. Its got great links to identification sheets (which you can print out ) and a native tree guide. Enjoy.