Changes in vegetation structure and fuel characteristics along post-fire succession promote alternative stable states and positive fire-vegetation feedbacks

KITZBERGER, THOMAS; MORALES, JUAN MANUEL; TIRIBELLI, FLORENCIA

JOURNAL OF VEGETATION SCIENCE

WILEY-BLACKWELL PUBLISHING, INC

Año: 2018 vol. 29 p. 147 - 156

1100-9233

Aims: Structural and compositional changes along post-firesuccession modify plantcommunity proneness to burn (flammability). The dominant regeneration strategiesand life forms, and their interactions along post-firesuccession, modulate thesechanges by affecting density, amount and connectivity of fuels. Depending on howflammability evolves during post-firesuccession it may feed back negatively, neutrallyor positively into fire probability and behaviour. Negative fire?vegetation feedbacksarise when communities increase flammability as stands age, while positivefeedbacks occur where early stages have higher flammability than later stages. Wecharacterized changes in vegetation structure and fuel characteristics with timesince fire in sites where either resprouters maintained dominance (shrublands), orwhere colonizer trees reached the sites and dominate later post-firestages (forests).Location: Northwestern Patagonia, Argentina.Methods: We measured vegetation structure and characterized fine fuels with theintercept pole method in stands of different post-fireage in 18 shrublands (range1?115 years) and 18 forests (range 7?216 years).Results: In shrublands fuel amount quickly recovered after fire to a relatively constantvalue and fine fuel density remained high. Conversely, in forests, fuel amountrapidly increased during early post-firestages (when resprouting shrubs dominatethe community), peaked at c. 30?50 years (related to the co-existenceof resproutersand young trees) and decreased to a relatively constant value (when tall trees dominatethe community and suppress resprouters). Moreover, forest fuel density decreasedwith time. These changes in fuel characteristics were largely linked tochanges in vegetation structure, which in turn were modulated by the dominant regenerationstrategies and life forms.Conclusions: Our results provide evidence of a positive fire?vegetation feedback forthe community dominated by colonizer trees, while the community dominated byresprouter shrubs showed a neutral feedback. Given the co-existenceof flammableshrublands bordering fire-sensitiveforests and their low tree regeneration rates, weargue that forest communities are especially sensitive to changes in fire frequencyand severity driven by global change. Anthropogenic or climate-drivenchanges inignitions are threatening these landscapes, which may undergo potentially rapidtransformations, as seen in other temperate ecosystems.