Comparison of understory plant community composition and soil characteristics in Quercus pyrenaica stands with different human uses

Abstract

The species composition of the plant community and the soil characteristics in Quercus pyrenaica ecosystems according to the degree of disturbance and the type of human intervention (burning, cutting, livestock grazing) were compared. Four types of oak communities were selected, each with five replicates: oak shrublands (SL), dehesas (DE) or open woodlands used for grazing, and two types of mature oak forest, one with abundant shrub biomass in the understory (FS) and the other with little shrub biomass in the understory (FO). A total of 175 species were found in the 20 sites studied, 52 appeared in a single site. The dehesas were the most different regarding species composition, with 30 species only found there. This was verified by a qualitative similarity analysis, in which the five dehesas formed a group clearly distinguishable from the other sites; the oak shrublands also formed a group, but it was not possible to distinguish between the mature oak forests with and without a shrubby understory. However, the soil characteristics were similar across all sites and differences could only be detected in organic matter and nitrogen content, which were significantly higher in the mature forests without a shrubby understory. When the plant community and soil characteristics were analysed as a whole using a canonical correspondence analysis, the separation of the dehesas was observed on the first axis, due to its greater richness and abundance in herb species, especially annuals. The other sites were ordered on the second axis, with greater differences between the oak shrublands, associated with higher shrub species cover, and the mature open forests, associated with forest herb species and a soil with a higher nitrogen, organic matter and cation exchange content. The mature forests with abundant shrub biomass were in an intermediate position. Therefore, although the differences in soil were not important and many species were common to all types of Q. pyrenaica communities, the type of human intervention did determine changes, as shown by the results of the multifactorial analyses. In addition, given that all the community types presented some species which were not found in the other types, greater biodiversity would be attained by preserving all of them.