Fire recurrence effects on biodiversity and community structure in Sanabria Natural Park (Spain)

Abstract

The aim of this study was to determine the effect of fire recurrence on the structural characteristics, in particular biodiversity, of different communities in Sanabria Natural Park (Castilla y Leon Region, Spain). Fourteen sites, ten Erica australis heathlands and four Quercus pyrenaica stands, two mature oak forests and two oak shrublands, were chosen. All of them had different levels of fire recurrence and different ages since the last fire. Data on fires occurring in the study area since 1990 are available. Sampling was carried out in July 2005. A 10 x 10 m plot was located in the centre of each site; in each plot, ten 1m 2 quadrats were studied and all the species present were quantified as visual cover percentage. A sampling by layers was also carried out in the same quadrats, estimating total plant cover in each layer. Plant species diversity was measured as richness (number of species). Alpha diversity (diversity/m 2 ), gamma diversity (diversity/plot), and beta or pattern diversity (S beta = S gamma / mean S alpha) were analysed. Structural diversity was calculated by the Shannon index, using plant cover data in the different layers. An affinity analysis was carried out considering all the species present. The dendrogram showed two groups: Erica australis heathlands and Quercus pyrenaica oak stands. The effect of fire recurrence on species composition was not observed in either case. A PCA was carried out in order to determine whether recurrence or the time elapsed since the last fire had any effect on species diversity or community structural diversity. Differentiation between the oak stands and the heathlands was also observed in this case. There was higher herbaceous species richness and more structural diversity in the oak stands. Stratification was noticeably lower in the heathlands, although they usually had higher woody species richness. No ordination depending on the time elapsed since the previous fire or recurrence was observed. Therefore, changes in community structure caused by fire recurrence in a relatively short period, such as that considered (15 years), are not noticeable in areas adapted to frequent fires. Nevertheless, repeated fire impedes the progress of succession and slows down its initial immature stages. These recover by autosuccession following repeated fire and persist as heathlands or oak shrublands. Although fires occur in mature oak forests, only the understory is affected, thus maintaining greater diversity and structural complexity.