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Effect of Invasive Australian Acacias on the Regeneration, Growth and Nutrient Chemistry of South African Lowland Fynbos
C. F. Musil
Journal of Applied Ecology
Vol. 30, No. 2 (1993), pp. 361-372
Published by: British Ecological Society
Stable URL: http://www.jstor.org/stable/2404637
Page Count: 12
You can always find the topics here!Topics: Habitats, Plant architecture, Seedlings, Fynbos, Plants, Vegetation, Taxa, Plant growth, Lowlands, Botany
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1. Regeneration, mortality, local extinction, growth and foliar elemental concentrations of indigenous (ericoid, restioid, proteoid) and alien (acacia) plant forms and concentrations of soil elements were compared in stands of the invasive Australian Acacia saligna and in surrounding sand plain lowland fynbos vegetation after an autumn fire. 2. All indigenous forms regenerated less successfully in acacia-infested than in natural habitats. Seedling:parent ratios of proteoids were 32%, restioids 42% and ericoids 65% of those in natural vegetation. Seedling mortalities of all plant forms were not different in the two habitats. 3. Simulated probabilities of extinction, based on the measured spatial variation in seedling:parent ratios of different forms in acacia stands and in natural vegetation, showed that the risk of local extinction after fire was three to four times greater for ericoids, five times greater for proteoids and seven times greater for restioids in acacia-infested than in natural habitats. Within a 10-m2 acacia stand area, the probability of extinction of proteoids was high (99.7%) and moderate (56-57%) for ericoid and restioid forms. 4. Soil N, Ca, Mg, K, Mn and B concentrations were higher and soil Fe concentrations lower in acacia-infested than in natural habitats; but the only significant concentration increases recorded for all plant forms were in the N and K of seedling leaves in acacia stands. 5. Seedling shoot and root dry masses of all forms, except restioids which had the lowest foliar elemental concentrations, were unaffected by the higher soil nutrient concentrations beneath acacias. Increased shoot:root ratios observed among indigenous forms in acacia-infested habitats reflected responses to shading by burnt acacia parental remnants rather than soil mineral enrichment. Acacia shoot:root ratios were unaffected by the different environmental conditions in acacia stands. 6. It is concluded that the mineral enrichment of lowland fynbos soils by acacias has no detrimental effect on post-fire seedling growth and survival of indigenous taxa. The depletion of indigenous taxa, particularly obligate reseeding forms, beneath acacia stands results mainly from their poor seed regeneration success and associated increased risk of local extinction from stochastic causes in this habitat after fire.
Journal of Applied Ecology © 1993 British Ecological Society