Functional traits of acquisitive invasive woody species differ from conservative invasive and native species

One of the most important sources of invasiveness is species' functional traits and their variability. However, there are still few studies on invasive tree species traits conducted along resource gradients that allow for a comparison of acquisitive and conservative strategies. We aimed to assess the differences in trait variation among native, alien conservative and alien acquisitive tree species along resource availability gradients (soil fertility and light availability) and to assess the traits variability of the species studied along resources availability gradients. Our study compared invasive tree species in Europe (Prunus serotina Ehrh., Quercus rubra L. and Robinia pseudoacacia L.) with their native competitors (Ater pseudoplatanus L., A. platanoides L., Quercus petraea (Matt.) Liebl. and Fagus sylvatica L). The study was conducted on 1329 seedlings and saplings collected in a system of 372 study plots in W Poland. For each individual we assessed leaf, stem and root mass ratios, total biomass, leaf area ratio, specific leaf area and projected leaf area. Two invasive species (P. serotina and R. pseueloacacia) represented a more acquisitive strategy than native species - along litter pH and light availability gradients these species had higher leaf mass fraction, specific leaf area and leaf area ratio. In contrast, Q. rubra had the highest total biomass and root mass fraction. Alien species usually had higher coefficients of variation of studied traits. This suggests that relatively high projected leaf area, as a way of filling space and outcompeting native species, may be reached in two ways - biomass allocation to leaves and control of leaf morphology or by overall growth rate. High variability of invasive species traits also suggests randomness in seedling survival, which similarly to the neutral theory of invasion, highlights the necessity of including randomness in modelling biological invasions.