Now select your Texture layer again, and click the Layer Styles button, which is circled in yellow in the following screenshot. From the drop-down box, choose Bevel and Emboss...
Now you can play with the settings to get just the texture you want. You'll want to set the Highlight color to a light green and the Shadow color to a very dark green. The Contrast value you chose when applying the Grain filter will strongly influence what settings work well here. A lower contrast grain will probably look better with an Inner Bevel style, while the higher contrast that I used works best with an Outer Bevel.
Here's what my texture looks like at this point, filling the entire document:
Go ahead and flatten the image at this point and rename the resulting layer "Forest." Then click the "Add Vector Mask" button.
Click once on the white rectangle that appeared in the Layers window and use the Paint Bucket to fill the mask with black. Your forest will vanish, leaving an apparently blank document.
Switch to the Channels window (Window > Channels if the tab is not visible next to the Layers window tab), and click on the Forest Mask channel. Now, using a large white brush, paint on the mask. Everywhere you paint white, the forest texture will reappear. Painting black will hide it again.
You can use the technique of your choice to roughen up the edges. I like the Spatter filter. Filter > Brush Strokes > Spatter. Remember that you want to roughen the edges of the mask channel, not the texture layer itself.