I had been thinking of buying saplings to plant. There were various reasons for not doing this. I live in an apartment and have no place to store them. It's a hassle to get permission to plant trees. Transplanted trees have a lower survival rate. Plus, I want to plant a lot and do not have much of a budget or manpower. All I'm investing is a couple of weekends and a few bags of composted manure.
I know that chestnuts grow well from seed because I used to live next to a chestnut tree and squirrels were constantly burying them in my flower beds. Some species of chestnut do not do well in clay soil and this is a clay-based area. I will seek out sandy soil but chestnuts may just not be the best choice. On the other hand, global warming is changing the dynamics of tree survival.
Wild apples seem to grow everywhere and again, my squirrel experience assures me that you can plant an apple and get a tree.
Sumac is supposed to be slow to germinate so I won't worry if I don't see plants next year. I don't know what to expect from the wild rose seeds: my rose bushes never reseeded themselves. Also, roses may require better soil than I will be able to find.
The key to guerilla community gardening is to plant hardy, drought-resistant varieties that can survive in the place you plant them. It's easy enough to get the information you need on the internet; or just choose something that is already growing wild on its own.