Blow 'em out!! Ahem. Failing that youll need strong arms, a strong back and some good digging and hacking tools. Good luck!
My next door neighbour had two acres of thorn trees to remove, he owned a four tonne digger and struggled, he then hired an eight tonne digger to remove them. the roots are still there and he has now bought an eight tonne digger for the Winter campaign. The roots that keep the tree upright take a lot of moving and if only an odd one or two stumps then cutting up is the only way to remove them.
Its not too difficult......... Excavate Time Team style, chop off ends of main roots, lever up stump. hey presto. Patience and planning over brawn and nature. 3 to go................. The chain saw helped a bit Howard