Definition: Allelopathy

Chemical territoriality. "Even in Spring the Manzanita has no weeds or grass under it, not even filaree." - Sierra Foothill Garden. Click image for link.

“The word allelopathy derives from two separate words.  They are allelon which means “of each other”, and pathos which means “to suffer”.  Allelopathy refers to the chemical inhibition of one species by another.  The “inhibitory” chemical is released into the environment where it affects the development and growth of neighboring plants.

Allelopathic chemicals can be present in any part of the plant.  They can be found in leaves, flowers, roots, fruits, or stems.  They can also be found in the surrounding soil.  Target species are affected by these toxins in many different ways.  The toxic chemicals may inhibit shoot/root growth, they may inhibit nutrient uptake, or they may attack a naturally occurring symbiotic relationship thereby destroying the plant’s usable source of a nutrient.

… Allelopathy is a form of chemical competition.  The allelopathic plant is competing through “interference” chemicals.  Competition, by definition, takes one of two forms–exploitation or interference.

Competition is used by both plants and animals to assure a place in nature.  Plants will compete for sunlight, water and nutrients and, like animals, for territory.  Competition, like parasitism, disease, and predation, influences distribution and amount of organisms in an ecosystem.  The interactions of ecosystems define an environment.

When organisms compete with one another, they create the potential for resource limitations and possible extinctions.  Allelopathic plants prevent other plants from using the available resources and thus influence the evolution and distribution of other species.  One might say that allelopathic plants control the environments in which they live.”      Cornell University

Table 1. Some allelopathic plants, the chemicals they produce, and the plants they affect.

Allelopathic Species Type of Chemical Affected Species
Trees:
Sugar Maple Phenolics Yellow Birch, White Spruce
Hackberry Coumarins Herbs, grasses
Eucalyptus Phenolics Shrubs, herbs, grasses
Black Walnut Juglone (Quinone) Pines (Austrian, Scots, red, white), Apple, Birch, Black Alder, Hackberry, Basswood, Azalea, et al.
Juniper Phenolics Grasses
Sycamore (Planetree) Coumarins Yellow Birch, herbs, grasses
Black Cherry Cyanogenic glycosides Red Maple, Red Pine
Oaks Coumarins, Herbs, grasses
Other phenolics
Sassafras Terpenoids Elm, Silver Maple, Boxelder
Balsam Poplar Green Alder
Southern Red Oak Sweetgum
Shrubs:
Laurel — Kalmia angustifolia Phenolics Black Spruce
Manzanita Coumarins, Herbs, grasses
Other phenolics
Bearberry Phenolics Pine, Spruce
Sumac Phenolics, terpenoids Douglas fir
Rhododendron Phenolics Douglas fir
Elderberry Phenolics Douglas fir
Forsythia intermedia Kentucky Bluegrass
Other:
Goldenrod, Aster Phenolics, terpenoids Sugar Maple, Bl. Cherry, Tulip Poplar, Red Pine
New York Fern Phenolics Black Cherry
Bracken Fern Phenolics Douglas fir
Shorthusk Grass Phenolics Black Cherry
Clubmoss Phenolics Black Cherry
Reindeer Lichen Phenolics Jack Pine, White Spruce
Tall Fescue Phenolics Sweetgum, Black Walnut, White Ash
Red Fescue, Kentucky Bluegrass Azalea, Barberry, Forsythia, Flowering Dogwood, Yew
Colonial Bentgrass Azalea, Barberry, Yew, Forsythia
Perennial Rye Apple, Forsythia, Flowering Dogwood
Foxtail, Smooth Brome Populus spp.

List from Sustainable Urban Landscape Information Series (SULIS)

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