Dalton Kane and the Greens

When humankind first settled Molorthia Six a hundred years ago, they thought it was uninhabited. It turns out that the treelike Greens were just holding very still—and that they have teeth.
These days, humans live in the Molorthian desert, far from the bloodthirsty forests. Life seems to be going rather miserably for widowed Sheriff Dalton Kane, so it's no real surprise when unexplained forest fires send refugee Greens fleeing toward town.
When a violent Green attack leaves several citizens dead, Dalton and his new deputy, an ex-conman named Chumley Fanshaw, make the treacherous journey north to see what they can do to stop the fires that keep sending the Greens in their direction. They soon find themselves fighting not only for their lives, but for the lives of every human on Molorthia Six.