I have a hill in my backyard, several years ago, the adjoining property was built on by Habitat for Humanity. Since that time I have had two ongoing issues, #1. Extreme erosion on my property.
#2. The people living in the home have cut down my trees, each years they poison all of the plantlife, and kill it.
I am disabled, and can not often go up on the hill to see how much more damage they do on any regular basis, and by the time I do see what they have done, it was too late, or I didn't know that I should have called the police. (I have a seizure disorder, along with a few other health issues).
My question is: Do I have any legal recourse? Can I sue them? I want to save what is left of my property before it all washes away and/or is totally cut down and destroyed.

Yes, They admitted to one of the trees, and there are the remains of others on their property. They are impossible to talk to, but yes, at one time I tried. No the property lines are not "clearly" marked, but they put up a fence about three years ago, (to keep ME off their property) (long story), and their fence may also be partially on my property in certain areas. I have repeatedly put up No Tresspassing signs, they somehow rip themselves off where I hang them and fall to the ground. (the neighbors do it).

The question is whether you can prove they are the ones doing the damage. Have you tried talking to them? Are your property lines clearly marked and do you have No Trespassing signs up?

first who built the home has no real bearing on it, Habitat for Humanity is a great group and would not build anything that did not have proper zoning and permits. They help 1000's of people each year become homeowners and do a lot of great work.

So you eneded up having someone move in that does not seem to know properly lines and the such. You can sue them for the value of the trees to your property, you can call the police and see if they will charge them with destruction of property and trespassing.

You can also build a fense, put up no tresspassing signs and the such.