Non-natives are linked to higher plant diversity across spatial scales

Abstract

Although non-native and invasive plants often pose a significant threat to biodiversity, global-scale studies have yet to conclusively demonstrate a systematic pattern of reduced native plant diversity in areas affected by these invasions. Here, we aim to explore the association of non-native and invasive plants with the species richness and evenness of plant communities from the local to global scale. We use the world's largest vegetation plot repository—sPlot—to compare species richness and community evenness between invaded (by invasive or non-natives) and native plots of equal size, paired within 32 km2 grid cells distributed across all continents. Aggregating plots at the cell, biome and global level, we also quantified differences in gamma diversity at different spatial scales. We found that invaded plots had higher species richness and similar community evenness, a trend largely consistent across biomes. The higher total species richness was not the result of additional invasive or non-native species, as the number of native species was also higher in invaded plots. These patterns persisted at larger spatial scales. Cell, biome and global gamma species richness of invaded plots were consistently higher than of native plots. All these patterns held regardless of whether the non-native species in a plot were invasive or non-invasive. Our study reveals a globally consistent pattern: plant diversity, both total and native, is higher when invasive or non-native plants are present, spanning spatial scales from local to global. Although we cannot infer causal effects, our results challenge the prevailing hypothesis that non-native and invasive species universally depress plant diversity.