Does planting lots of trees in a treeless area generally make the soil more acidic or more alkaline? I've read that it does one or the other (and the change in the water table, resulting from the trees has to do with it).
I'd like to know where you read that - the only thing I can think of is if you plant a lot of coniferous trees such as pine - the needle drop from those will increase pH of soil and any water courses nearby.
You may be confusing agricultural crops with trees - persistently farmed land may finish up with an altered pH which then needs correcting. So far as I am aware, planting a lot of trees in an area which previously had none doesn't make a difference to soil pH (other than coniferous varieties) - however the pH of the soil may be of some significance to the variety of tree/s you wish to grow.