Ann Bot. 2023 Dec 27:mcad199. doi: 10.1093/aob/mcad199. Online ahead of print.
ABSTRACT
BACKGROUND AND AIMS: In many systems, postfire vegetation recovery is characterised by temporal changes in plant species composition and richness. We attribute this to changes in resource availability with time since fire, with the magnitude of species turnover determined by the degree of resource limitation. Here we test the hypothesis that postfire species turnover in South African fynbos heathland is powered by fire-modulated changes in nutrient availability, with the magnitude of turnover in nutrient-constrained fynbos being greater than in fertile renosterveld shrubland. We also test the hypothesis that floristic overlaps between fynbos and renosterveld are attributable nutritional augmentation of fynbos soils immediately after fire.
METHODS: We use vegetation survey data from two sites on the Cape Peninsula to compare changes in species richness and composition with time since fire.
KEY RESULTS: Whereas fynbos communities display a clear decline in species richness with time since fire, no such decline is apparent in renosterveld. In fynbos, declining species richness is associated with declines in the richness of plant families having high foliar concentrations of nitrogen, phosphorus, and potassium, and possessing attributes which are nutritionally costly. By contrast, families which dominate late-succession fynbos possess adaptations for the acquisition and retention of sparse nutrients. At the family level, recently burnt fynbos is compositionally more similar to renosterveld than is mature fynbos.
CONCLUSIONS: Our data suggest that nutritionally driven species turnover contributes significantly to fynbos community richness. We propose that the extremely low baseline fertility of fynbos soils serves to lengthen the nutritional resource axis along which species can differentiate and coexist, thereby providing the opportunity for low-nutrient extremophiles to coexist spatially with more fertile adapted species. This mechanism has the potential to operate in any resource-constrained system in which episodic disturbance affects resource availability.
PMID:38150535 | DOI:10.1093/aob/mcad199
