Quite satisfied! I’m almost sure I won’t be able to achieve PSSM texture shadows with hundreds/thousands of trees on a single scene. I decided to add here some ground shadow using vertex normals CPU computation. Result is a GPU free shadow on the whole map. I still have some issues precalculating the exact position of future trees, and shadows are nothing but blured spots… but it should fit quite enough for distant shadows, and for low-end GPU cards.