Comparison of climatic conditions (a: mean annual temperature; b: annual precipitation) between the Chinese and North American locations of Ulmus pumila. Wilcoxon rank sum tests were used to test for differences between both ranges. Mean annual temperatures are significantly higher for locations from the U.S. (W = 7, p < 0.05). Annual precipitation is marginal higher in the invasive populations compared to the native populations (W = 9, p = 0.05). Significant differences are symbolized by different lowercases above the boxes.