Litter decomposition in fynbos vegetation, South Africa

The Western Cape of South Africa is characterized by the hyperdiverse vegetation of the Fynbos biome. Typical fynbos vegetation is a fire-adapted sclerophyllous Mediterranean-type ecosystem on poor, sandy or stony soils. It is characterized by plants with low nutrient content producing slowly decomposing litter. Fire is recognized as a major factor for carbon and nutrient cycling in this vegetation type. However, knowledge of biological decomposition processes in this biome is limited. We used litter-bags to measure mass loss and changes in chemical composition in litter from three species representing characteristic taxa in fynbos, a Protea exima hybrid, Erica multumbellifera, and Restio multiflorus, during approximately 180 days. In addition, we used a standard litter of a species with high nutrient content, Galenia africana, and a mixture of Protea and Erica. We compare our results with a previous study from renosterveld including the geophyte Watsonia borbonica, which occurs in both vegetation types and occurs commonly in the study area. We found that decomposition rate among the true fynbos plant species P. exima, E. multumbellifera, R. multiflorus and W. borbonica varied almost eight-fold. Litter decomposition was strongly correlated to litter stoichiometry, i.e. C/N and C/P-ratios. Most litters accumulated one or several nutrients during the study period. The mixture of litters decomposed faster than expected from the results of each litter separately. Our study indicates that biological decomposition may be more important for carbon and nutrient cycling in fynbos than previously thought. These results are in accordance with recent studies showing large variation in plant litter quality within vegetation types and biomes. Such large variation in litter quality and decomposition rate suggests that some generalisations about ecosystem processes in the fynbos may need reevaluation.