Assessing layer-specific vegetation diversity responses to environmental gradients in a riparian corridor

Riparian ecosystems are critical landscape components characterized by high biological diversity, shaped by the simultaneous influence of topographic, hydrological, and microclimatic gradients. This study is aimed at examining vegetation diversity responses to environmental gradients in riparian corridors of Yozgat Province using a layer-specific analytical approach. Field surveys conducted across 70 sampling sites resulted in the identification of 191 plant taxa, and species abundance data were used to calculate the Shannon diversity index. Vegetation was classified into tree, shrub, and herbaceous layers, and analyses were performed by considering different layer combinations. Environmental variables were represented by spectral indices (NDVI, SAVI, LST, and SMI) derived from Landsat 8 OLI imagery using the Google Earth Engine platform, as well as topographic and hydrological variables (elevation, slope, Aspect Suitability Index, and Topographic Wetness Index) generated in an ArcGIS environment. Relationships between vegetation diversity and environmental variables were analyzed using Generalized Additive Models (GAMs), while the multidimensional structure of environmental variables was assessed through Principal Component Analysis (PCA). The results revealed that slope and elevation exert statistically significant and nonlinear effects on vegetation diversity, with these effects varying according to vegetation layer structure. Remote sensing-based spectral indices exhibited weaker individual relationships with diversity; however, when evaluated in conjunction with topographic variables, they played a complementary role in riparian ecosystem monitoring. This study underscores the importance of layer-specific and multivariate approaches in the assessment and monitoring of riparian ecosystems and provides a comprehensive, application-oriented framework for riparian landscape evaluation.