PLease some mindstorming to this piece land! what to plant

http://essbaresheidelberg.wordpress.com/beete/

I need some mindstorming some ideas fomr elders.
Whats your thought on this land? We re a small group of people trying to make the city and free public spaces in edible gardens.

What would be good to plant and how to deal with the tree?

Its a small space, is vertical gardening an option? Will you be able to designate a small area to compost local scraps? Would a practical medicinal garden interest you? Will underground pipes prevent you from planting larger fruiting trees? Personally, not against the tree but in some years it will dedicate a much larger section of the small plot to its own needs.