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Tree cover and seasonal precipitation drive understorey flammability in alpine mountain forests

Abstract : Aim Little is known about the understorey flammability of European moun- tain forests. The aim of this study was to determine the relative effects of cli- mate, vegetation structure and composition on the fuel-driven variation in fire spread and intensity. Location The western Alps. Methods Fire spread and intensity were simulated under constant moisture and weather conditions for a wide range of understorey fuel parameters mea- sured in the litter, grass and shrub layers. Simulation outputs were used to compare understorey flammability between different forest ecosystem types (FET). The FETs were characterized by using a co-inertia analysis between composition and the environment (vegetation structure and climate). The rela- tionships between these factors, fuel properties and understorey flammability were then tested using partial regression analyses. Results The most flammable forests displayed an open canopy (dry-subalpine and open-mediterranean) and grew in areas with dry autumns and wet and cold springs. Fire spread and intensity were controlled by the trade-off between tree cover and dead (litter) and live (grass and shrub) biomass load. Fire inten- sity also increased as a result of seasonal precipitation patterns (differential dis- tribution between the seasons): rainy springs enhanced biomass growth, whereas dry climates, especially in autumn, promoted shrub biomass and stim- ulated litter accumulation and residence (higher litterfall and lower decomposi- tion rates). Interestingly, we found a positive relationship between fire intensity and the proportion of conifers that disappeared after accounting for tree cover, indicating that, in the Alps, the open canopy structure of needle-leaved forests makes them potentially more flammable than broad-leaved forests because of the higher load and continuity of surface fuels. Main conclusions Inter-relationships between tree cover, precipitation sea- sonality and species composition govern the understorey flammability of mountain forests. We also found evidence that tree cover strongly constrains fire spread by driving the amount and type of surface fuel, which suggests that land use change can have a strong influence on flammability patterns.
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Contributor : Nathalie Lyvet Connect in order to contact the contributor
Submitted on : Wednesday, September 14, 2016 - 2:40:13 PM
Last modification on : Friday, September 30, 2022 - 11:12:08 AM

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Thibaut Fréjaville, Thomas Curt, Christopher Carcaillet. Tree cover and seasonal precipitation drive understorey flammability in alpine mountain forests. Journal of Biogeography, 2016, 43 (9), pp.1869-1880. ⟨10.1111/jbi.12745⟩. ⟨hal-01366349⟩



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