Effects of invasive alien acacias on nutrient cycling in the coastal lowlands of the Cape fynbos

Nutrients and decomposition of leaf litter of Acacia saligna was compared with that of the indigenous sclerophyllous shrub Leucospermum parile in sand-plain lowland fynbos with acid soils low in P during the early stages of alien invasion. The same was done for A. cyclops and Pterocelastrus tricuspidatus in strandveld with alkaline soils high in P. The Acacia spp. had twice the leaf N concentrations of the indigenous species; P concentrations were highest in the strandveld species. The Acacia spp. tended to produce more litter, with 3 times the N content of that of the indigenous species. Decomposition turnover times were longer in the fynbos species than those of the strandveld. Nitrogen was immobilized in the leaf litter of the indigenous species; N contents of the acacias varied little. Phosphorus was immobilized in the fynbos species compared with a release of c50% from P. tricuspidatus after 2 yr. Soil N concentrations and litter-layer N contents were elevated under acacia canopies. -from Author