From working heavily in conservation, exotics removal and habitat restoration, I can say that it becomes somewhat conflicting to do what is the right thing to do. The most important thing I've learned is that more is not always better. A grassland is an important habitat to protect, as a specific group of animals typically lives in such an area, overgrowth can be damaging to different habitats, especially in areas where there *should* be annual fires which would naturally control these areas, but due to human encroachment, do not.
And a tree where it doesn't belong can certainly be more hurtful than helpful. Melaleuka, for example, was introduced to Florida in an effort to "dry up" the everglades. While the tree is perfectly at home in Australia, it completely took over Florida, growing so thick that no animals could utilize the area where it was growing, and out-competing native habitats, like the now-extinct habitat Pond Apple Swamp, a habitat vital to the survival of the endangered snail-kite. Just because we think something is more beautiful, or appears to be "better", does not always make it so. I don't know the specifics of the area, but it is true that different species of wildlife depend just as heavily on grasslands as they do forests. Removing trees in a habitat that is historically grassland, is preserving a grassland habitat.
This is a hard, but important thing to remember.
We must live, we must, true to our childhood dreams, or they are worthless, and our youth is insincere.