Identification of site-types important for rare ferns in an area of deciduous woodland in northwest Spain

Abstract

The Eume woods in northwest Spain are an important refuge for a number of endangered ferns, including Culcita macrocarpa, Cystopteris diaphana, Dryopteris aemula, Dryopteris guanchica, Hymenophyllum tunbrigense and Woodwardia radicans. Because some of these species are inconspicuous or difficult to identify in the field, we attempted to develop simple floristic criteria to identify sites important or potentially important for these species (‘high-value sites’). Having drawn up field-layer vascular plant inventories for 44 plots in the study area, we considered two major strategies. Under strategy 1, we looked for those conspicuous species which best discriminated between plots containing the endangered species (‘current-high-value plots’) and all other plots. Under strategy 2, we first carried out a global plots-by-species classification using indicator species analysis (Hill et al. 1975) and then looked for those conspicuous species which best discriminated between groups containing current-high-value plots and all other groups. For our data set, the second strategy proved more effective. The best criterion identified was ‘If two or more of Luzula sylvatica, Viola riviniana and Rubus spp. are present, then that plot is high-value’. We include a listing of a BASIC program for the discriminant analysis algorithm, which we consider to have a number of potential applications in vegetation science and biogeography.