Superiority in competition for light : A crucial attribute defining the impact of the invasive alien tree Schinus molle (Anacardiaceae) in South African savanna

Iponga, D M
Milton, S J
Richardson, D M
Journal of Arid Environments
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Invasion of ecosystems by woody alien plant species is a widespread phenomenon. Interspecific competition has often been suggested as a mechanism for replacement of one species by another, but this is rarely tested. We investigated the potential of an invasive alien tree to transform vegetation by quantifying the relative abilities of the alien tree Schinus molle and dominant native trees Acacia tortilis and Rhus lancea to compete for light when growing in association within a South African semi-arid savanna. Due to dispersal of its fruits by birds, seedlings of S. molle establish under tree canopies. Using canopy symmetry as an index of ability to compete for light, we found that the alien S. molle consistently out-competes the dominant native tree species. The results also show that pod production of A. tortilis was higher when it grew alone compared to when it grew with S. molle or R. lancea. The percentage of dead branches was higher on A. tortilis trees growing in association with the S. molle. The outcome is that the alien tree will gradually increase in abundance, changing woodland structure and ecosystem processes. Our findings provide evidence for the role of competition in the process of alien plant invasions. We suggest that S. molle, previously considered a benign naturalized species in South Africa, should be declared a noxious weed in some parts of that country.
Name of Journal: 
Journal of Arid Environments
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Journal Issue/Article
Grassland Society of Southern Africa

The Grassland Society of Southern Africa (GSSA) is involved and concerned with the science and practice of range and pasture management. This broad field involves primarily the use and conservation of natural resources. It encompasses applied fields such as livestock production, wildlife management, nature conservation, water catchment management and range and mine-dump rehabilitation. The disciplines include, amongst others, ecology, botany zoology, range and pasture science, animal science, soil science and genetics. This collection includes journal articles from the African Journal of Range and Forage Science as well as related articles and reports from throughout the Southern African region.