Competition by interference occurs when an individual directly prevents the physical establishment of another individual in a portion of a habitat. Established plants can preempt the invasion and colonization of other individuals by way of dense root mats, peat and litter accumulation, and mechanical abrasion. Amensalism Amensalism is an interaction where one species suffers and the other interacting species experiences no effect. One particular form of amensalism is allelopathy which occurs with plants. Allelopathy involves the production and release of chemical substances by one species that inhibit the growth of another.
Allelopathic substances range from acids to bases to simple organic compounds.
Secondary substances are chemicals produced by plants that seen to have no direct use in metabolism . This substance is known to inhibit the growth of trees, shrubs, grasses, and herbs found growing near Black Walnut trees. Often these chemicals accumulate in the soil during the dry season reducing the germination and growth of grasses and herbs in an area up to 1 to 2 meters from the secreting plants. Mutualism Mutualism is the name given to associations between pairs of species that bring mutual benefit. In most ecology or biogeography textbooks mutualisms are generally underemphasized or ignored.