Effects of the recent land-use history on the postfire vegetation of uplands in Central Spain

Abstract

Land-use change has been one of the main drivers of landscape changes in the Mediterranean region during the last decades. Many of the formerly intensively cultivated or grazed areas were converted to forest and wilderness through afforestation or abandonment. Understanding the threats to such lands in their process of recovery to less intensively managed systems is important to have a proper understanding of the effects of land-use change on the ecosystem. Our aim was to determine how land-use history could affect postfire vegetation. In 1986, a large fire occurred in Sierra de Gredos (Central Spain) and affected an area of 6652 ha which had had different land-use histories in the preceding decades. Land-use history was reconstructed from aerial photographs taken in 1956, 1972 and 1982. Within the crown-fire area of the burn, we chose areas that were cultivated, abandoned (matorral) or pine ( Pinus pinaster) woodlands in 1956. Their status was later assessed in 1972 and in 1982. We selected three groups of plots that underwent different types of land-use history: that had not changed since 1956, or that changed in land-use type between 1956 and 1972, or between 1972 and 1982. Only two land-use types were considered in 1982: abandoned land (i.e. matorral) and pine woodland. Plots remained like this until 1986 when they burned. Five years after the fire vegetation was sampled: at each plot, shrubby plants were measured on 10 5 m transects, and herbaceous plants were measured on 50 30 cm×30 cm squares regularly distributed within the transects. The effect of land-use history on the postfire vegetation was analyzed by one-way ANOVA and a posteriori multiple comparisons. After the fire, the shrubby vegetation was dominated by the legume Cytisus striatus subsp. eriocarpus. P. pinaster was very scarce. The herbaceous flora was composed of mostly annual species of Gramineae, Compositae and Leguminosae. The abundance of shrubs or herbs was not significantly different among different land-use histories. Similar results were obtained when species richness was analyzed, except that plots burned as matorral developed a greater abundance of hemicryptophytes, and less of herbaceous legumes. Plots that had been cultivated had a richer flora of annuals than those that remained matorral for a longer time. Overall, the recent land-use history accounted for few effects on the structure and composition of this plant community. Fires may act as a homogenizing agent of vegetation and, therefore, could further contribute to increase fire hazard.