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We analysed nearly 31 years (1991–2022) of tree population dynamics in 108 permanent plots each 0.04 ha of the Lilyvlei Nature Reserve, a section of the Knysna Forest in South Africa which has not historically been disturbed by harvesting. The Knysna Forest is the only large piece of forest in South Africa and is marginal for tall forest, having low mean annual rainfall of only about 1000 mm and occurs on nutrient poor soils. In contrast to many studies of other forests globally, we found almost no change in overall biomass. Even at the scale of our small plots and on 10–30 year time scales, there has been little change. The forest has very low recruitment and mortality rates and thus low growth rates. Climatic changes too were minimal over this 30‐year period. The proportion of stems that died per size class was concentrated in the larger size‐classes per species, even for shorter species. This suggests that senescence rather than external disturbances determines the low mortality and thus the low dynamism and the high biomass (approx. 600 Mg ha−1AGB or 41 m2 ha−1 basal area) of the forest. Mortality of some species exceeded conspecific recruitment, a trend accompanied by non‐significant declines in biomass. However, these trends are not significant. In conclusion, neither composition nor biomass has changed significantly in these forests over a period of 30 years. This suggests that not all Southern Hemisphere forests are in a state of decline. [ABSTRACT FROM AUTHOR]

Background and Aims Mediterranean ecosystems have a high vascular plant species richness (SR) relative to their surface area. This SR, representing the balance between speciation and extinction, has been attributed to multiple mechanisms that result in both high rates of speciation and/or low rates of extinction. An abiding question is, however, what is special about Mediterranean ecosystems that enables this high SR? Apart from the long-term climatic stability of the region, SR has also been related to resource availability, the many individuals hypothesis, resource spatial heterogeneity, temporal heterogeneity and biotic feedbacks. Methods Spatial patterns of species richness were related to climatic, edaphic and biotic variables and to spatial variability within the Greater Cape Floristic Region (GCFR) of South Africa. Boosted regression tree models were used to explore the strength of relationships between SR and environmental predictors related to each hypothesized mechanism. Key Results Water availability (i.e. precipitation) was a stronger predictor of SR than potential evapotranspiration or temperature. Scarcity of nutrients was also related to SR. There was no indication that SR was related to the density of individuals and only temporal heterogeneity induced by fire was related to SR. Spatial heterogeneities of climatic, edaphic and biotic variables were strongly associated with SR. Biotic interactions remain difficult to assess, although we have some evidence for a putative role in regulating SR. Conclusions While the lack of ecosystem-resetting disturbances (e.g. glaciation) is undoubtedly a key requirement for high species accumulation, predictably, no one explanation holds the key to understanding SR. In the GCFR high SR is the product of a combination of adequate water, nutrient scarcity, spatial and temporal heterogeneity, and possibly biotic feedbacks. [ABSTRACT FROM AUTHOR]

Background and Aims In many systems, postfire vegetation recovery is characterized 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 to 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 Fynbos communities display a clear decline in species richness with time since fire, whereas 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 that are nutritionally costly. In contrast, families that 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 species adapted to more fertile soil. This mechanism has the potential to operate in any resource-constrained system in which episodic disturbance affects resource availability. [ABSTRACT FROM AUTHOR]

Aim: The variability in regional species richness is determined by the balance between speciation, extinction, and migration, but the underlying causes of high species richness in some regions (e.g. tropics, Mediterranean ecosystems) are challenging to explain. Species richness variability may be amplified by biotic feedbacks that promote species richness in some areas, while decreasing elsewhere. Following the example of species abundance, we speculated that species richness per area in arbitrary geographic units (e.g. quarter‐degree squares) follows a hollow‐shaped curve with the ranks of species richness to yield a species richness rank (SRR) curve. The hollowness of such an SRR curve may indicate biotic feedbacks. Location: South Africa, South West Australia, and global. Materials and Methods: We used vascular plant (VP) and bird data from distinct geographic regions and global syntheses of VP, bird, mammal, and amphibian species richness. These data were subdivided into geographic grids and the deviation from normality of the species richness quantified using skewness and kurtosis and the values ranked to yield SRR curves. Results: These SRR curves all had a consistent hollow shape (corresponding skewness 1.08–3.4, kurtosis 0.23–18.40) distinct from a normal distribution arising if species were allocated randomly to geographic units. The SRR curves indicate that relatively species‐rich regions are rare, while species‐poor areas are common. Main Conclusions: Neutral processes, abiotic determinants, environmental heterogeneity, historical factors (e.g. climate stability), and biotic feedbacks all likely play a role in contributing to the shapes of the curves. Although these curves for diverse taxa and regions integrate these multiple drivers of species richness, they indicate an acceleration of species richness as a function of species richness as a result of speciation and/or immigration, limited by increasing extinction likelihood. Biotic feedbacks provide a parsimonious explanation for the shapes of the SRR curves across taxa and regions. [ABSTRACT FROM AUTHOR]