Allelopathy is a chemical process that occurs in plants. It is a natural self defense mechanism that prevents other plants or trees from growing too close. Some pine trees are allelopathic, allowing them to grow without fighting for space.
Pine trees use allelopathy when they shed their pine needles. When these needles fall to the ground, they prevent other plants and trees from growing underneath, stopping them from robbing space and nutrients from the pine tree.
These pine needles all contain an acid that leaches into the ground as the needles begin to decompose. These acids do not hurt the pine tree or its roots but act as a deterrent to other plants looking to move into the area.
Scientists study allelopathy in pine trees and other plants such as sunflowers and black walnut trees and use the results to develop natural herbicides and pesticides. Some scientists consider allelopathy an ecological conversation between pine trees and other plant life.