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. Follow this link Overview about Allelopathy. Various plant species have evolved competitive advantages which enable them to grow under specialized environments such as alkaline or acidic conditions, low light and low redox mud. Plants grow at vastly differing rates and fast growing plants easily out compete slow growing neighbors for light.