Riparian and adjacent forests differ both in the humid mountainous ecoregion and the semiarid lowland

Abstract

Few studies have quantified changes in riparian and adjacent forest across landscape units. In this study, the composition and structure of riparian and adjacent forest were compared in a humid and a semiarid ecoregion in northwestern Argentina: the Yungas forest and the Western Chaco. We expected that differences between riparian and adjacent zones could be less marked in humid than in semiarid regions. Ten sites were surveyed with a block design. An Importance Value Index, Rank-Abundance curves, and Analysis of Similarity and multivariate analyzes (NMDS) were performed to evaluate differences between forests. Stream and floodplain widths, lateral, and longitudinal slopes of streamside were analyzed by a principal components analysis (PCA). NMDS and PCA axes were correlated to analyze the relations among physical and biological arrangements. Results revealed that riparian forest may be very different from the adjacent in both ecoregions. Marked differences in geomorphological and physical features of streamsides were found between ecoregions and they were strongly associated with assemblage distribution. In Yungas forest, dominant species were different at all sites, according to the altitudinal stratification of this region. Within Western Chaco the species Salix humboldtiana Willd. and Tessaria integrifolia Ruiz and Pav., were commonly dominant in riparian sectors. The dominance of these species in both sectors by the widest rivers could indicate that the dimensions of the riparian zone in those sites are greater than those by the smaller streams. Our study reinforced the concept of riparian zones as dynamic ecosystems and we propose considering a landscape perspective in managerial decision making.