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Question: Can grazing by goats eliminate potentially combustible plant biomass and thereby change the flammability of mediterranean vegetation? Location: Doñ ana Natural Park, SW Spain.Methods: The effect of goat grazing was evaluated, over a period of 42 mo, in 100 ha of pine forest understorey with an average density of 217 trees·ha À1 . Grazing by large herbivores was halted temporarily in the study area, with wild deer excluded from 1970, and domestic goats excluded from 2002. However, following the creation of grazing exclusion plots and sampling of the vegetation within as a control, adult female Payoya goats were introduced to the area in spring 2007. Vegetation was sampled twice yearly using the point-intercept method, and data of frequency, cover and phytovolume obtained. The study was completed with an analysis of change in the flammability of the study area (determined using data on the phytovolume and flammability of species). Changes in species richness and species diversity were determined.Results: After 42 mo, the phytovolume of the ungrazed vegetation had increased significantly by 32%, while bare soil had decreased by 5%. This gave rise to a significant increase in flammability of 25%. Within the grazed area, species phytovolume decreased significantly by 34%, leading to a significant increase in bare soil of 51%, while the flammability of the area decreased by 22%. The number of species remained constant throughout the study at 20 species. Significant differences in species diversity were observed between grazed and ungrazed areas after 42 mo of grazing (species diversity index after 42 mo of exclusion = 1.59 ± 0.17, species diversity index after 42 mo of grazing = 0.95 ± 0.13).Conclusions: Monitoring of the scrub understorey has shown the positive impact of grazing goats: the resulting decrease in the quantity of total phytovolume (easily combustible vegetation) induces changes in species diversity without lowering species richness and reduces the risk of fire.

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