Can Shrub Flammability be Affected by Goat Grazing? Flammability Parameters of Mediterranean Shrub Species under Grazing

Abstract

In this study, we evaluated changes in the potential flammability of different Mediterranean shrub species in a pine (Pinus pinea) forest in the Doñana Natural Park (of SW Spain) as a result of goat grazing. Plant height, total biomass, fine fuel biomass and leaves/wood ratio were measured in individual plants of each species in both grazed and ungrazed areas. Moisture content, mean time of ignition, mean time of combustion, gross heat of combustion (GHC) and flammability class of the studied shrub species were determined in the laboratory. The results of this experiment showed that grazing influenced the flammability characteristics of the studied shrub species. However, the strength of this effect was insufficient to modify the flammability index of these plants, except in the case of Myrtus communis, in which grazed plants presented a lower flammability index. According to Valette’s classification, Cistus salviifolius, Halimium halimifolium and Pistacea lentiscus are flammable species, Rosmarinus officinalis is a flammable-highly flammable species, and M. communis is non-flammable. The GHC values obtained were generally “intermediate”, except for those of R. officinalis, which were classified as “high”. The flammability parameters of the study species did not show a very marked trend in relation to grazing, but the vertical structure of plants did change by presenting reduced biomass of leaves and fine twigs. This change altered the physical characteristics of these plants and possibly acted to reduce the inherent fire risk of the shrublands.