We share equally in the valleys, hills, rivers and seas. Phantom Treeplanters have no formal organisation, no joining fee, and only the Earth holds its membership list throughout time. To belong, simply plant a tree without expectation of material gain, help care for existing ones, or hold in your heart what they mean. With due sensitivity, plant trees on any land and in any place where they have a chance of surviving. Do not be put off by feeling you always have to get permission.
Nature sows without asking.
You are part of nature. Reconstituting the world is a duty and a right which extends beyond legal concepts of land ownership. You can buy suitable native species from nurseries. But better still, root a length of willow in a bottle or collect and sow seed from original local sources. Maybe you do not need to live so fast that only instant results satisfy.