SummaryContrasting fire regimes maintain patch mosaics of savanna, thicket and forest biomes in many African subtropical landscapes. Species dominating each biome are thus expected to display distinct fire-related traits, commonly thought to be bark related. Recent Australian savanna research suggests that bud position, not bark protection alone, determines fire resilience via resprouting.We tested first how bud position influences resprouting ability in 17 tree species. We then compared the effect of both bark-related protection and bud position on the distribution of 63 tree species in 253 transects in all three biomes.Tree species with buds positioned deep under bark had a higher proportion of post-fire aboveground shoot resprouting. Species with low bud protection occurred in fire-prone biomes only if they could root-sucker. The effect of bud protection was supported by a good relationship between species bud protection and distribution across a gradient of fire frequency.Bud protection and high bark production are required to survive frequent fires in savanna. Forests are fire refugia hosting species with little or no bud protection and thin bark. Rootsuckering species occur in the three biomes, suggesting that fire is not the only factor filtering this functional type.

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AimDoes complex topography facilitate the establishment and persistence of fire‐sensitive (forest) vegetation in a fire‐prone landscape? We test the prediction that fire‐sensitive vegetation will establish and persist in areas where the fire return interval is lower due to a topographic hindrance on fire spread.LocationHluhluwe–iMfolozi Park, KwaZulu Natal, South Africa.TaxonTerrestrial Plants.MethodsUsing aerial photographs from six time periods between 1937 and 2013, we mapped vegetation changes in Hluhluwe–iMfolozi Park (HiP). Using a generalized additive model (GAM), we built a habitat suitability index (HSI) map for forest vegetation based on topographic variables related to fire behaviour and the vegetation distribution maps from each time period. We investigated transitions between vegetation types between time periods based on the HSI map, as well as the effects of neighbourhood vegetation on transition probabilities.ResultsForest cover has increased overall from 1937 to 2013, however, this has not been a linear increase with a peak in extent in the early 1990s. The HSI, using topographic predictors associated with fire behaviour, correlates with areas of expansion and contraction of forest vegetation. The patterns of expansion and contraction are, however, more nuanced, with the in situ vegetation neighbourhood playing a large role.Main ConclusionsForest distributions in HiP have not remained static over time and have expanded into areas that were once savannas. This is a dynamic system where both forest and savanna boundaries can change considerably. Fire refugia are important for the long‐term persistence of forests in fire‐prone landscapes.

1. Fires in savannas limit tree cover, thereby promoting flammable grass accumulation and fuelling further frequent fires. Meanwhile, forests and thickets form dense canopies that reduce C4 grass fuel loads and creating a humid microclimate, thereby excluding fires under typical climatic conditions. However, extreme fires occasionally burn into these closed-canopy systems. Although these rare fires cause substantial tree mortality and can make repeat fires more likely, the long-term consequences of an extreme fire for closed-canopy vegetation structure and potential to convert to savanna (hereafter 'savannization') remain largely unknown.2. Here, we analysed whether an extreme fire could, alone, alter species composition, vegetation structure and fire regimes of closed-canopy ecosystems in an intact savanna-forest-thicket mosaic, or whether successive fires after an initial extreme fire were necessary to trigger a biome transition from forest to savanna.3. We found that forests that only burned once recovered, whereas those that burned again following an initial extreme fire transitioned from closed-canopy forests towards open, grassy savannas. While thickets had less tree mortality in fires than forests, repeat fires nonetheless precipitated a transition towards savannas. Colonization of the savanna tree community lagged behind the grass community, but also began to transition. 4. Synthesis. Our results suggest that rare extreme fires, followed by repeated burning can indeed result in savannization in places where savanna and forest represent alternative stable states.