Allelopathy is where a species of plant contaminates the ground with some secondary metabolite produced within it in order to poison another species of plant which may decide to try and grow nearby and shade it. The chemical compound(s) the allelopathic plant produces to pollute the soil may only be repulsive to one species of plant, or maybe to several species. The toxins may have ne effect of other species, they may be naturally immune (it is not toxic to them) or have, by repeated exposure to the compound, evolved immumity. The allelochemical may be released into the soil from the roots of the allelopathic plant, or it may just be present in the leaves or in the flowers and only contaminates the soil when these fall. Some allelochemicals may just inhibit the germination of seeds of some competitive species, or it may be toxic to the already growing competitor. In some trees the allelochemical is produced in the bark. The allelochemicals may or may not remain long in the soil afterwards; some may decompose into relatively harmless chemicals, some may be water soluble and eventually wash away, some may be consumed or absorbed by other organisms or roots in the soil.

The whole topic of allelopathy has only recently (in the 1980's(?) been confirmed to occur in some species by chemical analysis and experimentation. For unless you can identify the compound(s) responsible, you stand little chance of proving that it was the chemical(s) produced by the allegedly allelopathic plant which prevented or inhibited the growth of another plant. This requires experimentation to prove conclusively, otherwise it is just guesswork. Airborne volatile chemicals produced by one plant to deter another does not count as allelopathy (???) [it may count as something else, though].

Species of plants either known or suspected to produce allelopathic compounds: Laurel (Prunus laurocerasus) Bearberry (Arctostaphylos uva-ursi) Rhododendron () Elderberry () Forsythia () Goldenrod (Solidago ) Fern () [some ferns] Perennial Rye () Tall Fescue () Garlic Mustard () Black Walnut () [susceptible species include Pine & Birch trees, Solanaceae, Azalea] Maple () Pine () Eucalyptus () () () ()



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