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 forestacross landscape units. In this study, the composition and structure ofriparian and adjacent forest were compared in a humid and a semiarid ecoregionin northwestern Argentina: the Yungas forest and the Western Chaco. We expectedthat differences between riparian and adjacent zones could be less marked inhumid than in semiarid regions. Ten sites were surveyed with a block design; An Importance Value Index, Rank-Abundance curves, Analysis of Similarity and multivariate analyses (NMDS) were performed to evaluate differences between forests. Stream and floodplain widths, lateral and longitudinal slopes of streamsidewere analyzed by a principal components analysis (PCA). NMDS and PCA axes werecorrelated to analyze relations among physical and biological arrangements. Results revealed that riparian forest may be very different from the adjacent in bothecoregions. However, marked differences in geomorphological and physica lfeatures 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 inboth sectors by the widest rivers could indicate that the dimensions of theriparian 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.