The idea of alternate stable states (ASS) has been used to explain the juxtaposition of distinct vegetation types within the same climate regime. ASS may explain the co‐existence of relatively inflammable closed‐canopy Afrotemperate forest patches (‘Forest’) within fire‐prone open‐canopy Fynbos in the Cape Floristic Region (CFR) on sandstone‐derived soils. We evaluated the hypothesis that although fire and local topography and hydrology likely determined the paleogeographic boundaries of Forest, present‐day boundaries are additionally imposed by emergent edaphic properties and disturbance histories. We studied vegetation and edaphic properties of Forest‐Transition‐Fynbos vegetation at two sites within the CFR on sandstone‐derived soils and tracked historical change using aerial photography. Whereas Forest and Fynbos have changed little in extent or density since 1945, transition vegetation increased into areas formerly occupied by Fynbos. Forest soils were ubiquitously more nutrient‐rich than Fynbos soils, with transition soils being intermediate. These edaphic differences are not due to geological differences, but instead appear to have emerged as a consequence of different nutrient cycling within the different ecosystems. Soil nutrients are now so different that a switch from Fynbos to Forest is unlikely, in the short term (i.e. decades). Floristically and nutritionally, transitional vegetation is more similar to Fynbos than Forest and may be less resilient to changes in exogenous drivers (e.g. fire). Our findings are consistent with the idea that geologically Forest and Fynbos are largely fire‐derived long‐term ASS, with the stability of each state reinforced by marked soil nutrient differences. In contrast, the intermediate transitional vegetation that might switch states is unlikely to be stable.

Summary Phenotypic plasticity facilitates species persistence across resource gradients but may be limited in low‐resource environments requiring resource conservation. We investigated the tradeoff between trait plasticity and resource conservatism across a biome boundary characterized by high turnover in nutrient and light availability, and whether this contributes to the maintenance of alternative stable states. Differences in plasticity were determined by comparing species’ leaf and foliar nutritional trait responses to light, represented by leaf area index (LAI), and soil nutrient availability across forest–shrubland boundaries in South Africa. Although forest had higher LAI and soil nutrient availability than shrubland, forest species experienced greater resource variation. With increasing LAI and nutrient availability, forest species increased their leaf size, specific leaf area and leaf area/stem length, and decreased their foliar [N] and [K]. Although these responses are indicative of plasticity, shrubland species appeared to lack plasticity as evidenced by limited trait variation with environmental heterogeneity. Inhabiting diverse light environments imposed by forests probably selects for plasticity, whereas light‐saturated, fire‐prone, nutrient‐poor environments that select for conservative leaf traits and below‐ground investments compromise plasticity in shrubland species. This pattern suggests a tradeoff between trait plasticity and resource conservatism, which may support the stability of alternative vegetation states.

No abstract

Non-forest ecosystems, dominated by shrubs, grasses and herbaceous plants, provide ecosystem services including carbon sequestration and forage for grazing, and are highly sensitive to climatic changes. Yet these ecosystems are

Abundance of Fabaceae declines in representation through post-fire-succession in fynbos vegetation of the Cape Floristic Region (CFR). This reduction in legume occurrence coincides with a known decline in post-fire soil P availability. It was hypothesized that the disappearance of legume species during post-fire succession is due to an inability to acquire P effectively from sparingly soluble sources. P-acquisition strategies and response to P supply were compared between legume (Aspalathus, Cyclopia, Indigofera, Podalyria) and non-legume (Elegia, Leucadendron, Protea) genera when supplied with 1 or 10 mg P kg −1 dry sand. Each genus consisted of a seeder (non-persistent) and resprouter (persistent) species. Non-legumes showed a greater investment in below-ground biomass, more root clusters, with higher concentrations of carboxylates exuded by cluster roots and carboxylates that were better suited to the mobilization of sparingly soluble P compared to legumes. The growth response to increased P supply was 53% higher in legumes than in non-legumes. The lack of a growth response to an elevated P supply in the non-legumes was attributed to N-limitation. Legume resprouters had a higher investment in cluster-root biomass and a lower capacity to down-regulate P-uptake than the seeders. Therefore the inability to acquire sufficient P from low concentration and sparingly soluble soil Psources may contribute to the lack of indigenous legume persistence in fynbos vegetation of the CFR.