The book Trees and How to Grow Them is a brilliant (though not a field) guide to our native and common trees. I bought it as a gift from Gus to his dad when Gus was just a month old. Finally this autumn, it has come down from the shelf and been put to use. It gives plenty of instruction on collecting and preparing different seeds for planting; as well as planting trees out where they will be only beneficial and not a nuisance.
So far we have collected wild plum and cherry stones, hazelnuts, horse chestnut, bird cherry and rowan. There will be more as we find them locally over the next few weeks. I would like some more edibles, such as sweet chestnuts and apples. After a few sessions looking for seeds and edible treats, we here can highly recommend an afternoon spent in the friendly company of your local trees. They filter out the noise of the city, they welcome inquisitive children (and adults), they sometimes offer up a little food or a place to shelter and watch the world go by; and they lift your spirits after a few hours of walking amongst them. Which is why in a city of 200,000 people, there should be more than 30,000 trees.
In a year or two, with a little TLC, we will hopefully have some strong saplings, ready to be planted out around the city. In a world where I consume so much, including many, many trees, many habitats and many foraged fruits, I know that I have actually put something (small) back with my own two hands. Which is a start.