Is intraspecific variability an advantage in mountain invasions? Comparing functional trait variation in an invasive and a native woody species along multiple environmental gradients

Alien plants that expand towards high elevations from surrounding lowlands must simultaneously tolerate climatic harshness and shifting environmental conditions over short distances. Intraspecific functional variability is expected to underlie their success. Yet, the importance of this mechanism in mountain invasion by woody species remains understudied. We explicitly tested intraspecific functional variability by comparing a woody invasive species with a broad elevational range, Cotoneaster franchetii, with the dominant woody native, Polylepis australis, in a mountain located in Central Argentina. We selected 20 individuals of each species along a local topo-edaphic gradient at four elevations, from 1200 to 2100 m a.s.l. We assessed functional strategies and their variation by measuring eight traits indicative of resource-use and water-transport strategies in each individual, during two consecutive growing seasons. The invasive species presented more conservative attributes than the native. Contrary to our expectation, the invasive species did not adjust its functional attributes to the elevational or topo-edaphic gradients, nor did it exhibit more intraspecific variation than the native. The variation of C. franchetii traits along the gradients showed little association with its performance (growth rate and potential germination), which remained almost constant throughout the study area. In contrast, P. australis seemed to adjust its attributes along gradients, with this trait variation being related to its performance. Our findings do not support intraspecific variability of functional strategies as a mechanism underlying woody mountain invasion success. However, our results support the hypothesis that invasive species have wide environmental tolerance, probably triggered by a more conservative functional strategy than natives and a relatively high and stable performance along the multiple environmental gradients.