Simultaneous competition and environmental filtering in woody communities of the understory of Eucalyptus plantations in the Cerrado

Dense and species-rich understory communities have been commonly found in old or abandoned stands of Eucalyptus plantations in the Cerrado domain presenting plant species and ecological niches that suggest a repository of the original biodiversity. This repository depends on the largely unknown effect of Eucalyptus plantations on their understories. We addressed this issue by testing if the effect of Eucalyptus trees on the assembly of Cerrado communities causes environmental filtering or competitive exclusion. For the test, 40 plots (20 inside stands and 20 outside) were allocated and all woody plants with a circumference at the ground level equal to or greater than 10 cm were sampled. Species richness, diversity indexes and species turnover were determined. The phylogenetic structure was evaluated at different scales using the values of Mean Pairwise Distance (MPD), the Mean Nearest Taxon Distance (MNTD), the Net Relatedness Index (NRI) and the Nearest Taxon Index (NTI), as well as phylobetadiversity indices. The metrics of alpha and beta phylogenetic diversity (NTI, MNTD, NRI and MPD, betaMPD and betaMNTD) fell within the random expectation in each plant community, suggesting a phylogenetic uniformity, but fewer plants of the Fabaceae family than expected by chance were detected outside Eucalyptus stands suggesting that this family is filtered in inside Eucalyptus stands. Species richness is lower inside than outside Eucalyptus stands. The pattern is congruent with simultaneous environmental filtering and competitive exclusion in a context of niche conservatism which means that functional traits are conserved within phylogenetic lineages.