Follow this link Some Introductory information about Allelopathy. Sometimes we all need to be alone. Plants and trees need to have their own space, too. 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 .