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Tree cover and seasonal precipitation drive understorey flammability in alpine mountain forests
Author(s) -
Fréjaville Thibaut,
Curt Thomas,
Carcaillet Christopher
Publication year - 2016
Publication title -
journal of biogeography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 158
eISSN - 1365-2699
pISSN - 0305-0270
DOI - 10.1111/jbi.12745
Subject(s) - environmental science , understory , shrub , biomass (ecology) , litter , flammability , vegetation (pathology) , ecology , plant litter , canopy , atmospheric sciences , ecosystem , biology , geology , medicine , physics , pathology , thermodynamics
Aim Little is known about the understorey flammability of European mountain forests. The aim of this study was to determine the relative effects of climate, 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 measured in the litter, grass and shrub layers. Simulation outputs were used to compare understorey flammability between different forest ecosystem types ( FET ). The FET s were characterized by using a co‐inertia analysis between composition and the environment (vegetation structure and climate). The relationships 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 intensity also increased as a result of seasonal precipitation patterns (differential distribution between the seasons): rainy springs enhanced biomass growth, whereas dry climates, especially in autumn, promoted shrub biomass and stimulated litter accumulation and residence (higher litterfall and lower decomposition 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 seasonality 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.