allelopathy

The chemical inhibition of the growth, seed germination etc. of one plant species by another. Allelochemicals are secondary metabolites which are released by root exudation, the decomposition of litter and leaching. They are often said to represent competition between species but plants of the same species may also be adversely affected (see replant disease).

This definition is abridged from A – Z of tree terms: A companion to British arboriculture.
Read the preface. Order the book.