Assessing riparian vegetation structure and the influence of land use using landscape metrics and geostatistical tools

Abstract

The present work aims to identify potential landscape metrics that best describe and quantify the riparian structure and evaluate its response to land use pressure. The study was conducted in four rivers of the Tagus fluvial system Data was achieved from the on-screen photo interpretation of airborne digital images. Eight landscape metrics related with the spatial configuration, isolation, inter-connectivity and distribution of riparian vegetation were calculated for the tree, shrub and herbaceous strata. The influence of proximal and distal land use (30 m and 200 m buffers, respectively) in the riparian structure was analysed using redundancy analysis. Geostatistical analysis were used to describe and incorporate the spatial component of the data and to assess the spatial autocorrelation of the riparian structure. The results showed that the combined interpretation of metric values can consistently describe the patterns of riparian structure especially for the tree cover class. Disturbed riparian woods due to major land use pressure, such as agriculture, presented a low number of small patches with simple and homogenous shapes, reduced patch connectivity and a non interspersed patch distribution. Also it is shown that the proximal land use is more determinant in shaping within-stand riparian structure, therefore protection areas should both envelop riparian zones and an adjacent buffer.