Aims Structural and compositional changes along post‐fire succession modify plant community proneness to burn (flammability). The dominant regeneration strategies and life forms, and their interactions along post‐fire succession, modulate these changes by affecting density, amount and connectivity of fuels. Depending on how flammability evolves during post‐fire succession it may feed back negatively, neutrally or positively into fire probability and behaviour. Negative fire–vegetation feedbacks arise when communities increase flammability as stands age, while positive feedbacks occur where early stages have higher flammability than later stages. We characterized changes in vegetation structure and fuel characteristics with time since fire in sites where either resprouters maintained dominance (shrublands), or where colonizer trees reached the sites and dominate later post‐fire stages (forests). Location Northwestern Patagonia, Argentina. Methods We measured vegetation structure and characterized fine fuels with the intercept pole method in stands of different post‐fire age in 18 shrublands (range 1–115 years) and 18 forests (range 7–216 years). Results In shrublands fuel amount quickly recovered after fire to a relatively constant value and fine fuel density remained high. Conversely, in forests, fuel amount rapidly increased during early post‐fire stages (when resprouting shrubs dominate the community), peaked at c. 30–50 years (related to the co‐existence of resprouters and young trees) and decreased to a relatively constant value (when tall trees dominate the community and suppress resprouters). Moreover, forest fuel density decreased with time. These changes in fuel characteristics were largely linked to changes in vegetation structure, which in turn were modulated by the dominant regeneration strategies and life forms. Conclusions Our results provide evidence of a positive fire–vegetation feedback for the community dominated by colonizer trees, while the community dominated by resprouter shrubs showed a neutral feedback. Given the co‐existence of flammable shrublands bordering fire‐sensitive forests and their low tree regeneration rates, we argue that forest communities are especially sensitive to changes in fire frequency and severity driven by global change. Anthropogenic or climate‐driven changes in ignitions are threatening these landscapes, which may undergo potentially rapid transformations, as seen in other temperate ecosystems.

Summary Ecological memory, often determined by the extent and type of retained biological legacies present following disturbance, may produce persistent landscape patterns. However, after fire, the persistence or switch to an alternative state may depend on the complex interplay of ecological memory (biological legacies) and potential effects of new external factors influencing the post‐fire environment. The current study assesses both the strength of ecological memory resulting from biological legacies of pre‐burn vegetation types as well as post‐fire effects of livestock. Following a severe fire in 1999, we set up a network of long‐term exclosures to examine the effects of legacies and cumulative herbivory by cattle on fuel types, amounts, distribution, flammability and microenvironmental conditions in two post‐fire communities representing alternative fire‐driven states: pyrophobic Nothofagus pumilio subalpine forests and pyrophytic Nothofagus antarctica tall shrublands in northwestern Patagonia, Argentina. Our results show that the retained post‐disturbance legacies of tall shrublands and subalpine forests largely determine fuel and flammability traits of the post‐fire plant communities 16 years after fire. The importance of biological legacies retained from the unburned plant communities was reflected by the substantially higher amounts of total fine fuel, greater vertical and horizontal fuel continuity and the higher temperatures reached during experimental tissue combustion at post‐fire shrubland compared to post‐fire forest sites. We show that herbivores may produce antagonistic effects on flammability by decreasing tissue ignitability, total fine fuel and litter depth, and disrupting the vertical and horizontal fine fuel continuity, therefore reducing the probability of fire propagation. However, cattle can increase ratios of dead to live fine fuels, reduce soil moisture, and inhibit tree height growth to canopy size, consequently impeding the development of a closed pyrophobic forest canopy. Synthesis. Our results support the hypothesis that biological legacies, most importantly the dominance by pyrophytic woody plants that resprout vigorously vs. the dominance by pyrophobic obligate seeders, favour fuel and flammability characteristics at the community level which reinforce the mechanisms maintaining pyrophytic shrublands vs. pyrophobic forests. Herbivory by introduced cattle can partially blur sharp pyrophobic/pyrophytic state boundaries by promoting the development of novel post‐fire transitional states.

Questions: Increased wildfire activity is resulting in plant community-type conversions worldwide. In some regions, fire-sensitive forests are being replaced by flammable fire-resilient communities, increasing the likelihood of reburning due to positive fire feedbacks. Here we evaluated whether fire severity affects post-fire plant community flammability attributes that lead to community-type conversions and changes in the likelihood of reburning. Specifically, we assessed how fire severity, the dominant pre-fire vegetation, and distance to unburned remnant forest may shape post-fire community properties and flammability trajectories in northwestern Patagonia. Location: Northwestern Patagonia, Argentina. Methods: We repeated sampling of Nothofagus pumilio, Nothofagus dombeyi, and Austrocedrus chilensis forests and native shrublands (composed of multiple shrub species) two and 18 years after fires that burned at low-to very high-severity levels, and measured community structure and flammability attributes. Results: Eighteen years after fire, forests that burned at moderate to very high severity were unable to recover and were replaced by more flammable shrublands and grasslands. Following low-severity fire, fine-fuel density was lower and forest recovery was enhanced by greater survival of remnant seed trees. Burnt shrublands increased in abundance across all severity classes but attained highest fine-fuel production after moderate-to very high-severity fire. Conclusions: Low fire severity, by enabling regeneration of forests that are less flammable than shrublands, diminishes the likelihood of reburning, thus establishing a negative feedback favorable to forest perpetuation. Conversely, moderate to very high fire severity leads to a positive feedback by promoting conversion to shrublands and greater fine-fuel accumulation. This increases the likelihood of reburning, reinforcing the persistence of pyrophytic communities and favoring landscape-scale loss of fire-sensitive forests. This fire severity-mediated positive feedback may in many regions worldwide further amplify warming-related wildfire activity increases, posing serious threats to the persistence of fire-sensitive ecosystems.