Well I would agree with a lot of te posts that your trees may not be the only problem. Permaculture is about working to your strengths, what are the positive things about having a patch of dry land? I can think of a lot as I come from waterlogged area where no amount of trees can drain the soil! If you need more land for growing I would look for an area that isn't dry and hack up the trees from that area instead. I mean if your gonna need to take down trees why take them from a bad area of soil where tey are thriving? Maybe a tree is te only thing that can go deep enough to bring up moisture. Your also never draining anything really, just converting it. So the tree is converting moisture into leaves and that's a valuable product. I think mostly trees drain below surface, except for some shallow rooted trees so if the area is super dry it either gets no rain, drains too readily, ie there might be a pocket of sandy soil that allows water in bit doesn't let it stay, or it is on top of perhaps a boulder so it's roots are taking surface moisture. If that were te case then taking them up would leave you with better moisture but you probably won't know till you dig down. Where you can go around something rather than through it go around it. And where you have a situation work to it's strengths. Honestly here it's so wet, so so wet, and I would even cry for how wet it is, but that's the reality. And you either work with what is, or against it. And often the fight is long hard and brutal and you don't win anything, and sometimes just changing your plans to fit the environment is less of a struggle and more of a creative parameter. Blue berries. They grow great in bogs. So I grow berries. And you find the thing tht works. What works on dry soil? Picnics. Buildings, smoke houses. Fire pits. So many things that are wonderful about a dry patch and if you get rid of it you'll find some need for it and be at a loss of how to recreate such a lucky coincidence! Swap ya a few yards of bog for somewhere dry to change my wellies?? Any time!!!