Scatterplot of elevation and non-native plant species richness and cover derived from 1,662 plots in Death Valley National Park, Mojave National Preserve, and Lake Mead National Recreation Area in the Mojave Desert, southwestern USA. There was no relationship between elevation and non-native richness or cover (Pearson r = 0.00). The inset graph in (b) shows percentages of plots infested by either non-native grasses or forbs, or both (‘neither’ signifies 18% of plots not invaded and 2% invaded only by woody species).