They can't walk or run anywhere. Plants have a different way of getting their own space. They use allelopathy. Allelopathy is a chemical process that a plant uses to keep other plants from growing too close to it. Some plants that use allelopathy are black walnut trees, sunflowers, wormwoods, sagebrushes, and trees of heaven.
Some pine trees are allelopathic.
When its needles fall onto the ground, they begin to decompose . The soil absorbs acid from the decomposing needles. This acid in the soil keeps unwanted plants from growing near the pine tree.