Taxonomic and functional diversity of woody plant communities on opposing slopes of inselbergs in southern Brazil

AbstractBackground: Inselbergs are known to influence vegetation patterns worldwide. In extra-tropical areas, opposing slopes of inselbergs have different exposures to solar radiation; for example, in southern South America, north-facing slopes are more exposed to solar radiation than south-facing slopes, both in terms of angle and period of incidence.Aims: We aim to verify whether species diversity and composition and trait convergence and divergence in woody plant communities are associated with differences in the relative solar radiation intercepted by opposing slopes of inselbergs.Methods: We estimated the relative solar radiation intercepted by opposing slopes of seven inselbergs in southern Brazilian Pampa, applying hill shading estimation (HSE) to a digital elevation model. We recorded woody individuals with a diameter at breast height ≥5 cm in 13 plots placed on north- and south-facing slopes. We tested for the association of species diversity and composition and trait convergence and divergence with HSE.Results: Variation in species diversity and composition was associated with HSE. Less exposed slopes were taxonomically more diverse than more exposed slopes. Convergence and divergence of leaf traits were associated with slope exposure.Conclusions: The low-diversity communities on more exposed slopes likely resulted from filtering by environmental variables associated with slope exposure. The higher diversity of tree communities on less exposed slopes might be attributed to diversification of strategies for resource capture and capacity of supporting more niches due to potentially higher water availability. These findings advanced our understanding of the role of slope exposure for plant community assembly in the extra-tropical South America.Keywords: aspectdiversity profileenvironmental filteringhill shadingPampa biomerocky outcropslope exposuresolar radiationtrait convergencetrait divergence AcknowledgementsData collection was funded with resources from CAPES-Brazil (PROF), FAPERGS (grant 11/2185-0) and CNPq-Brazil (grants 479083/2008-8 and 563271/2010-8). CAPES provided M.Sc. fellowships (2009-2011) to M.B.C., V.A.G.B. and J.H.M., and Ph.D. fellowships to G.S.H. and V.A.G.B.; CNPq provided Ph.D. fellowships to G.I. and M.B.C. and PQ fellowships to L.D.S.D., S.M.H. and S.C.M.. We are very grateful to Mark Leithead, who kindly revised English language and content of this paper. We also thank László Orlóci, Valério D. Pillar, Marcela Pinillos G. and Fernanda Z. Teixeira for valuable suggestions on data analyses; Luiz Flamarion B. Oliveira, Chris Kettle, Laszlo Nagy and two anonymous reviewers for valuable suggestions on previous versions of this manuscript; Martin Grings for helping with species identification; Eliseu J. Weber for a valuable discussion on hill shading estimation; and V.D. Pillar for facilitating the use of species trait data. We thank Seu Decinho for permitting data collection at his property.Additional informationNotes on contributorsMarcos B. CarlucciAll the authors of the paper are researchers of the Graduate Programme in Ecology at the Federal University of Rio Grande do Sul (UFRGS). Marcos Carlucci, Vinícius Bastazini, Gabriel Hofmann, Josielma Macedo, and Graziela Iob are (or were) graduate students, while Leandro Duarte, Sandra Hartz and Sandra Müller are professors. The common interest of the group is to understand the assembly of ecological communities from the perspective of the niche theory.