Yes it is an early start here after a non-existent winter. 

5 tons is what we hope for and some people are talking of 6...but bugs and fungi usually take their share despite of all the spraying and I am really happy with 4.5!

The trees are growing wild in the fence of the adjacent gardens...they often are full of fruit in july, they are edible but most somewhat sour. Good for jam, less for eating fresh. My guess is that that they originally were saplings from  the rootstock of a cultivated plum tree, as prunus cerasifera is used as rootstock for grafted plum trees, and is not often cultivated as a fruit tree itself.