We recently bought our first home in Berkeley, CA, which came with what is to us a fairly enormous yard (about 55'x65'). The fences are edged with trees that do a wonderful job of creating a feeling of seclusion and blocking a tall, neighboring apartment building. I believe the trees to be a combination of very tall mock oranges, ash trees + a million or so suckers, a lovely apple tree, a large magnolia, and what I think is some kind of willow - plus the neighbors have two redwoods. The south-facing yard is also a weird combination of completely overgrown and bare dirt. The bare bits had me concerned, so this weekend I decided to collect some soil for testing so I know what I'm dealing with (my concerns aren't as much about pollutants as about nutrient deficiencies).

Well, I think I figured out the problem: the soil is so completely bound up with roots that I couldn't get more than about 1/2" into the dirt without a pick axe. I can only assume that the trees connected to these roots are taking all moisture and nutrients from the soil, which explains the sickly ferns and azaleas, and bare dirt. The one shrub that looks pretty healthy is a camellia, though it's yet to bloom at all (I've been in the house since February).

As you might imagine, this is a little bit concerning! I have plans to put in a small native lawn ringed with beds of shrubs and flowers, but I'm now questioning whether that's going to be possible. I've done some reading on-line, and the consensus seems to be that building up beds over roots is at best a temporary solution (the roots simply move into the new soil) and at worst a risk to the trees. I've learned similar things about cutting the roots.

So, my question is: what on earth can I do about this? I'm not going to be able to dig in any soil amendments without either breaking my back or using heavy machinery, and I have serious concerns about damaging the largest trees (I'm not so worried about the ashes, which appear to be sending suckers up all over the place). Should I dig anyway or look for plants that can compete with tree roots? Or should I consider taking down some trees? Any and all suggestions most welcome!