Distribution and species diversity patterns of Vitex negundo var. heterophylla shrublands in North China

Aims To explore the factors controlling the spatial distribution, as well as the species diversity, of the Vitex negundo var. heterophylla shrublands in North China.
Methods We investigated the species composition and environments for 370 shrubland plots of Vitex negundo var. heterophylla shrublands in North China. We calculated biodiversity indices (Shannon-Wiener index, Simpson index and Pielou’s evenness index) and then applied multivariate regression trees (MRT), analysis of variance (ANOVA), Pearson correlation analysis to disentangle distribution of the Vitex negundo var. heterophylla community and patterns of species diversity along both horizontal and elevational gradients.
Important findings The results showed that Vitex negundo var. heterophylla shrublands distributed in a large area stretching for more than 10° of both latitude and longitude, together with an elevational range of more than 1 000 m (117 m to 1 248 m). The Shannon-Wiener index, Simpson index and Pielou’s evenness index were higher in the herbaceous layer than those in the shrub layers. The species diversity of shrub layer increased with latitude but decreased with elevation. In contrast, that of the herbaceous layer decreased with latitude but increased with elevation. The Shannon-Wiener indexes of both layers were significantly correlated with environmental factors. The results of Pearson correlation analysis indicated that the Shannon-Wiener indexes of shrub layer had a significantly negative relationship with its temperature and slope position, and a significantly positive relationship with its precipitation. However, that of herb layer showed opposite trends.