Position on slope,disturbance, and tree species coexistence in a Seasonal Semideciduous Forest in SE Brazil |
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Authors: | Roque Cielo-Filho Mario Antonio Gneri Fernando Roberto Martins |
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Institution: | (1) Graduate Course of Plant Biology, Department of Botany, Institute of Biology, Campinas State University, Caixa postal 6109, Campinas, 13083-970, SP, Brazil;(2) Section of Timber and Forest Products—D. Bento Pickel Herbarium (SPSF), Forest Institute, Caixa Postal 1322, Sao Paulo, 01059-970, SP, Brazil;(3) Department of Statistics, Institute of Mathematics, Statistics and Computer Science, Campinas State University, Caixa postal 6065, Campinas, 13083-970, SP, Brazil |
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Abstract: | We investigated the influence of position on a slope (plot relative elevation) and vegetation disturbance (the tallest tree
height per plot) on community composition and diversity in a SE Brazilian Seasonal Semideciduous Forest (46°55′ W, 22°50′
S). Trees with dbh ≥5 cm were sampled in one hundred 10 × 10 m plots randomly placed in a 6.5-ha stand. Through partial
Mantel test, floristic dissimilarities among plots (Jaccard index computed with species abundance in each plot) were correlated
with environmental distances among plots (Euclidian distance index computed with relative elevation and the tallest tree height
values in each plot). Relative elevation and the tallest tree per plot height were individually correlated with floristic
gradients expressed by PCA axes scores using Pearson’s correlation coefficient. Through resampling, we compared diversity
(richness, Berger-Parker D and Shannon H′) among plots in the drier (up) and moister (low) ends of the slope. Floristic dissimilarities were significantly correlated
with environmental distances even after geographic distances among plots have been partialled out (r
m = 0.1274, p < 0.001). The first two PCA axes accounted for 22% of the total variance. After Bonferroni and Dutilleul’s corrections, axis
1 showed a marginally significant correlation with plot relative elevation (r = − 0.4097, p = 0.0309), and axis 2 was significantly correlated with the tallest tree height per plot (r = 0.2953, p = 0.0106). Position on the slope and vegetation disturbance were reliable predictors of community composition, thus suggesting
the operation of niche assembly organizing processes. Richness and diversity (H′) decreased and dominance (D) increased with elevation on the slope. Dominance increase from D
(300) = 0.11 (confidence interval = 0.091–0.131) to D
(300) = 0.19 (CI = 0.165–0.210) surpassed the expected dominance increase based on the reduction of richness alone: D
(300) = 0.13 (CI = 0.110–0.140), thus highlighting the niche partitioning assembly of the community, especially among abundant species. Given
the great amount of floristic variability remaining unexplained, stochastic processes, such as those related to dispersal
limitation, may also have influence on the community composition. Therefore, both niche assembly and chance events can operate
even on a fine local scale. |
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Keywords: | Environmental heterogeneity Diversity Neutral theory Topography |
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