Fig. 1

Maps depicting (a) the distribution extent of the 11 conifer species sampled in this study. The color ramp represents the concentration of species per cell. The black box in a describes the focus area of this study. The enlarged map (b) depicts the field sites where branch samples were collected across Montana and Idaho, USA. The elevation gradient of each site is shown in four categories, from blue (500–1000 m), light blue (1000–1500 m), pink (1500–2000 m), and red (2000–2500 m). The branches sampled at each site are listed via the abbreviations, which are available in Table 1. The grey scale depicts the counties that were used as boundaries to extract Forest Inventory Analysis (FIA) data. Spatial data for a were extracted from a digitized version of Little and Viereck (1971)