Hmmm.... reducing the size of the texture has also reduced the overall 'treeishness' of it. I'm not quite sure why that is, but its still pretty horrible.

What you need are some good quality top view tree brushes and a bit of patience to stamp them around in various very slightly different shades of green (remembering to leave small gaps between them all), followed by a drop shadow on the new tree layer to create a broken canopy.

Here's a screen shot of what I mean.

Forest demo.jpg

When you are making a landscape its best to start from the ground up, so you start with the dirt, add the grass, then the bushes, and finally the trees. In this crude example I skipped the dirt and the bushes and started with a decent grass texture 'Just add Bison' (one of the textures in my texture album here) and a tree brush of my own making. At this kind of scale, however, a decent sponge brush would work just as well.