Do native plant species functionally similar to invasive species suffer more impacts from the invasion in seasonally dry tropical forests?

Abstract

We tested the hypothesis that of the species studied in the Brazilian Semiarid, the ones most functionally similar to tree Azadirachta indica would be more affected by this exotic species during germination and early development. At first, we produced a crude extract of A. indica fresh leaves in six different dilutions. We placed 25 seeds of four native species (Cenostigma pyramidale, Libidibia ferrea, Mimosacaesalpiniifolia, and Amburana cearensis) to germinate in Petri dishes for each dilution, with four replicates for each species. We assessed: radicle length, emergence percentage, emergence speed index, and mean emergence time. We conducted an experiment in a greenhouse to assess how the exotic plant affected the development of individual plants of the studied species. We planted five seeds of each native species alone and five in interaction with the exotic species using ten 20-l buckets. The experiment lasted four months, and the functional attributes of the individuals were collected. Among the native species analyzed, according to the cluster analysis using the functional attributes of the species planted alone, M. caesalpiniifolia, C. pyramidale and L. ferrea were functionally more similar to the exotic species. In the germination experiment, the extract affected only root length, regardless of the functional similarity. We noticed that only M. caesalpiniifolia had its early development strongly inhibited when planted in interaction with the exotic species. Although the functional similarity between the exotic and the native species did not influence germination, it negatively affected the development.