Allelopathy

Allelopathy is a biological phenomenon by which an organism produces one or more biochemicals that influence the growth, survival, and reproduction of other organisms. These biochemicals are known as allelochemicals and can have beneficial (positive allelopathy) or detrimental (negative allelopathy) effects on the target organisms.

Allelopathy is characteristic of certain plants, algae, bacteria, coral, and fungi.  Allelopathic interactions are an important factor in determining species distribution and abundance within plant communities, and are also thought to be important in the success of many invasive plants.

List of allelopathic plants

Shrubs

Adenostoma fasciculatum ( chamise )

Allaiaria petiolate ( garlic mustard )

Artemisia californica ( California sagebrush )

Asparatus officinalis ( asparagus )

Bassia scoparia ( burning bush )

Centaurea maculosa ( spotted knapweed )

Chromolaena odorata ( Siam weed )

Cyperus rotundus ( nut grass )

Encelia farinose ( brittlebush )

Forsythia spp

Helianthus annuus ( sunflower )

Lantana camara ( bunga tahi ayam )

Rhododendron spp

Salvia leucophylla ( purple sage )

Sambucus spp ( elderberry )

Solidago spp ( goldenrod )

Trees

Ailanthus altissima ( tree of heaven )

Arctostaphylos uva-ursi ( Manzanita )

Casaurina equistifolia ( rhu pantai )

Delonix regia ( red flame )

Eucalyptus spp

Juglans nigra ( black walnut )

Pinus spp ( pines )

Prunus laurocersus ( cherry laurel )

Crops

Avena spp ( oats )

Coffea Arabica ( coffee )

Hordeum vulgare ( barley )

Nicotina tabacum ( tabacco )

Oryza sativa ( rice )

Secale cereal ( rye )

Triticum aestivum ( wheat )

In the wilder area, oaks have little growing underneath..this was a eerie, foggy morning.

Casuarina equisetifolia litter completely suppresses germination of understory plants as shown here despite the relative openness of the canopy and ample rainfall (120 cmyr) at the location

 Eucalyptus have rather suppressed other vegetation spp. through allelopathic affect

Manzanita ‘circle’ can be easily seen and means “Don’t plant here!”

Casuarina equisetifolia - Rhu Pantai

Synonym : Casuarina litorea

Common names : Casuarina, Australian pine, beach she-oak, beef wood-tree, whistling pine

Etymology

Casuarina is from the Malay word ‘kasuari’, an allusion to the twigs of cassowary bird.

equisetifolia is derived from the Latin ‘equinus’, pertaining to horses, and ‘folium’, a leaf, in reference to the fine, drooping twigs, which are reminiscent of coarse horse hair.

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Natural Habitat & Origin

Sandy coasts of subtropical & tropical ( between 12-31.5°s and 18-22°N ) - Australasia, SE.Asia, islands of the western Pacific Ocean, possible Madagascar.

Classification

Magnoliophyta Magnoliopsida Fagales Casuarinaceae

Description

Evergreen tree with capable to grow up to 20 meters in height.

Crown shape initially conical but tends to flatten with age.

Trunk straight, cylindrical, usually branchless for up to 10m, up to 100cm in diameter. Bark reddish brown colour, rough, brittle, peeling.

Branchlets are deciduous, dropping, needlelike, terete but with prominent angular ribs, 23 – 38 cm x 0.5 – 1 mm, greyish-green.

Flowers unisexual, perianth absent. Monoecious. Pollination by wind.

Male flowers in terminal, simple, elongated spike, 7-40mm long, in whorls, single stamen.

Female inflorescence on a short lateral branchlet, cylindrical, cone-shaped or globose.

Infructescence woody, conelike.

Fruit grey or yellow-grown winged nut (samara).

Seed solitary.

Propagation & Cultivation

Propagation by seeds; cutting from branclests, treated with IBA/IAA/NAA; air-layering is practice, but too costly for large scale operation.

Inoculation with pure strains of Frakia prior to transplanting to field.

Planting density of 2,500stem/ha. Harvested at 10^th – 15^th years.

May plant up to 8,000-10,000 stems/ha for firewood. Harvested at 4^th – 5^th years. Yield 10 – 20 MT/ha/year.

Economic Importance

Firewood : Calorific value 500kcal/kg. Highly regarded wood, ignites readily even when green. Regarded “the best firewood in the world”.

Charcoal : Calorific value 7000kcal/kg .

Paper : Wood to produce paper pulp using neutral sulphate and semi-chemical process.

Timber : Heavy hardwood. Density 900-100kg/m³. Used as house post, rafters, electtic poles, tool handles, oars, wagon wheels, etc.

Folk medicine : Root extrcts are used for treating dysentry, diarrhea, stomach ache. Twigs are used for treating swelling. Powdered bark is used for treating pimples.

Erosion control : planted along coastlines, estuaries, riverbanks, waterways.

Horticulture : Landscape, bongsai.

Weed : Reported to be an invasive weed in Hawaii, the Bahamas, Florida, Nauru.

Others : Tannin, boat making, wind breaker, living fences, nitrogen-fixing.