Leaf economic traits of Hawaiian species are independent of geographic distribution
Non-native invasive species pose a significant threat to global biodiversity, yet there is still debate about the mechanisms that explain why some non-native species become invasive and others do not. In the forests of Hawaii, non-native species outnumber natives, and non-native invasive species continue to expand their ranges at alarming rates. Previous studies have proposed that Hawaii’s native species are more conservative at gathering and spending resources than invasive species, making them poor competitors. We sought to test the hypothesis that Hawaii’s native woody plants are more conservative than invasive plants by examining traits associated with the leaf economic spectrum, which posits that species separate based on the speed with which they achieve a return on investments of nutrients and dry mass in leaves (a fast-slow continuum). To test whether the Hawaiian species cluster together when compared to a global dataset of leaf traits, and whether there are differences among the Hawaiian species based on their geographic distributions, we collected functional trait data on over 80 species and 900 woody plants across the Hawaiian Islands. We used a principal components analysis to look for evidence of niche differentiation based on specific leaf area, photosynthesis, transpiration, carbon:nitrogen ratio, and percent phosphorus.We detected no evidence of niche differentiation between native and non-native species, and no evidence that the Hawaiian species were clustered within the global dataset. There is also no separation by species distribution (indigenous, endemic, non-native, invasive non-native), and native species are not generally more conservative than non-native species or invasive non-native species in their functional traits. We also found no evidence of separation among our species when grouped by land cover type, and no clear patterns arose with regards to performance across resource gradients. Despite the strong phylogenetic relatedness among the native species in our dataset, we found only moderate evidence of a phylogenetic signal on the functional traits, specifically, photosynthesis and carbon:nitrogen. Our results suggest that within Hawaii, native and invasive woody plant species overlap in their functional traits, and that across environments, native species do not appear to be more conservative than non-native species in their leaf economics. In conclusion, the success of non-native invaders in Hawaii does not appear to be driven by differences in leaf traits, and may instead depend on wood traits, belowground traits and belowground interactions, and recruitment success.