Exploring the causes of high biodiversity of Iberian dehesas: the importance of wood pastures and marginal habitats
2016
In extensive low input farming and in
agroforestrysystems, the importance for biodiversity of managed productive fields with respect to unmanaged marginal
habitatsthat occupy a low proportion of farm surface, is still poorly understood, contrasting with the well-known key importance of marginal
habitatsin intensive systems. We analyzed the importance of open and
wood pasturesand marginal
habitatsfor species richness of Iberian dehesas in Central-Western Spain. We sampled 155 plots classified into 9 general
habitatcategories:
wood pastures(n = 41 plots); open
pasturesdominated by
annual plants(n = 11), by
perennial plants(n = 15) and co-dominated by annuals and
perennial plants(n = 16);
shrublands(n = 19); agricultural crops (n = 12); herbaceous strips (n = 10); woody strips (n = 11); and water bodies (n = 10). In each plot we measured the abundance and species richness of four taxonomic groups: vascular plants, bees, spiders, and
earthworms. We detected 431 plant species (37 ± 2.5 CI95 in 100 m2 on average), 60 bee species (3.1 ± 1.1 in 600 m2), 128 spider species (7.4 ± 1.2 in 1.5 m2) and 18
earthwormspecies (2.5 ± 1.0 in 0.27 m2) in 145 sampling plots.
Wood pasturessupported fewer species of spiders and
earthwormsat the plot level, but more plants and
earthwormspecies at the landscape level than open
pastures. The low proportion of shared species among
habitatsand among plots within each
habitattype, and the high proportion of species found in unique plots or
habitatsindicated that every
habitatcontributes to farm biodiversity. Overall, our extensive survey confirms the hypothesis that the high diversity of dehesas depends on the coexistence within farms of a wide mosaic of
habitats, including marginal
habitats, which seemed to harbor a disproportionately high number of species as compared to their small extent. Results support policy measures for the maintenance of farm keystone structures such as linear features, small wood/shrub patches and ponds, and reveal that these measures should not be exclusively applied to more
intensive farmingsystems.
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