From Homestar Runner Wiki
The foliage consists mainly of multiple instances of one or two Spooky Tree designs in various sizes, orientations, and colors. (Similar trees are found in the Punkin Patch, which may be the Old-Timey version of the Spooky Forest.) In the daylight, the forest is much less spooky, and the trees come to life during the day, as seen in Happy Hallow-day. Strangely, there are much fewer trees during the day, and pumpkins appear during the day as well. One possible explanation for the lack of trees is that they are the spherical trees in the background, which fits in with the fact that the trees are alive during the day and dead at night.