Patterns of shrub diversity and tree regeneration across topographic and stand-structural gradients in a Mediterranean forest

Abstract

Aim of study: This study aimed to determine the influence of topography and stand-structure on the characteristics of shrub communities and tree regeneration in a Mediterranean forest. Area of study: The Navahondona forest in Cazorla mountain range (SE Spain). Material and Methods: Data from 298 inventory plots were analysed by means of Generalized Linear Models (GLM) to test the effects of aspect, altitude and stand basal area on shrub cover and diversity. Likewise, the effects of these three factors plus shrub cover on the recruitment of Spanish black pine (Pinus nigra spp. salzmannii) and two oak species (Quercus ilex and Q. faginea) were analysed by GLMs. Additionally, the influence of topography and forest structure on the specific distribution of shrub species was analysed with multivariate methods. Main results: Shrub cover and diversity were generally low and did not change across the topographic gradient. Tree density was the only study variable affecting (negatively) shrub cover. However, shrub composition changed with aspect and altitude. Both pine and oak regeneration benefited from partial tree cover at intermediate values of stand density, but only oak regeneration was facilitated by shrubs. Research highlights: Altitude, aspect and stand basal area influence the characteristics of shrub communities and tree regeneration. Proactive management of dense pinewoods might be needed to increase shrub and tree diversity.