Aye, this is the true deep work of Bryce. You will grow used to plop-rendering soon enough... One way to do it is to use a paint program, like Photoshop. Copy into the clipboard your greyscale heightmap, then open it in Photoshop, and make white dots right where you want each set of trees. Start small. Try it with five or six tree-spots. Duplicate the original terrain in Bryce and then load in the white-dotted image map from Photoshop. Clip the levels, until you just get a terrain of your white tree-placing dots. Select the inverse, lock, box, and hide everything, then place some Bryce trees on your five or six dots. Seems complex, but this technique only works in 2 dimensions. After you place the trees on the tree-spots, unlock and unbox and unhide everything else, and delete or lock-and-hide the treespot terrain, and all you have left is to make sure the trees land properly. Usualy, you want to push them a bit below the terrain surface, due to Tree Lab roots. Good luck, and please show us what you come up with!