ECOLOGY

Soil enhancers & inhibitors

The Acacia component of a community plays a useful and beneficial service to other members of the plant community. Their rapid re-establishment and fast growth following fire or other disturbances provides food for herbivores. They in turn redistribute nutrients to the soil. The litter fall from short lived acacias produces an early source of readily available nutrients which are released during decomposition of the detritus. Along with other legumes and casuarinas the symbiosis of Acacia roots with the nitrogen-fixing bacteria Rhizobium augments the soil nitrogen content. This important plant nutrient then becomes available for the other plants of the community. As some acacias flower more than once during the year, and some flower when few other plants are flowering, such as during late summer and through the winter, they become an important food resource for aminals.

Competition between species may be reduced by phytotoxic secretations from roots or leaf litter. Little investigation of such secretations from Acacia species has been undertaken. The Western Australian species, Acacia saligna, appears (Jones, Roux & Warren 1963) to be one such species which inhibits the growth of its competitors, and this may be a causal factor in its spread and weediness in the eastern states.

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