Edge Effects

Now, there's a strange term – edge effects – you say, but it is an important part of any forest or grassland. Perhaps you all have noticed, along major roads, that the vegetation is taller right next to the road than it is, say, ten feet from the road. Roads are usually "crowned" slightly to encourage water runoff for driving safety. The runoff supplies the edges of the road with additional water, as compared with the earth ten feet away. Thus there is more robust growth nearest the roads.

Grasses along the Lime Ridge Trail

Forests also have edge effects, especially older forests. The trees that are sheltered well within a forest are not subjected to the buffeting by winds and can use their energy to grow tall. They also need to grow tall to reach sunlight, so a mature forest usually is almost all the same height. The trees on the forest edge are the ones that are shorter and much of this is due to the constant buffeting by winds as they stand alone. One forest research group grew two stands of trees to find out about the effect of wind. One group was sheltered and these trees grew tall. The other group was subjected to an artificial wind several times a day and was shorter than their siblings only a few hundred feet away.

Each summer, grasses along foot trails grow taller than in the fields a few feet away. Again, this is due to water runoff; because these foot trails are compacted by foot traffic they do not absorb moisture well. Therefore, water runs off to the edges and we have more robust growth due to the additional water.

Jerry Fritzke
June 2003