2.6 Influence of landscape on genetic diversity
To reveal the influence of the composition of the landscape types around each sampling point on the genetic diversity, Arcgis10.2 (ESRI) was used to create circular buffers with radii of 300 m, 800 m, and 1,000 m and with each sample point as the center. Then, the proportions of P. massoniana , C. lanceolata , P. elliottii , mixed forest (including some hosts), broad-leaved forest, urban, farmland, road, water, and nudation landscape types in each circular buffer were calculated. The db-RDA model (Legendre & Anderson, 1999)was used to analyze whether the ten landscape types at the three scales could explain the genetic diversity. In addition, to explain the nonlinear relationship in the db-RDA analysis and explore whether those variables inhibited or facilitated the genetic diversity of M. alternatus , a flexible fitting method (GAM) (Lengyel & Podani, 2015)was used to map the explanatory variables over the first two principal coordinates analysis (PCoA) axes.