Latitudinal gradients of associations between beta and gamma diversity of trees in forest communities in the New World

We analyze two continental data sets of forest communities from across the New World to examine the latitudinal gradients of beta diversity after accounting for gamma diversity and the latitudinal gradient of gamma diversity after accounting for beta diversity. Correlation and regression analyses were used to relate beta and gamma diversity to latitude along two latitudinal gradients in the New World (one including 72 forest sites located south of the equator and the other including 79 forest sites located north of the equator). Beta diversity and gamma diversity were negatively correlated with latitude. Beta diversity was strongly and positively correlated with gamma diversity (Pearson's correlation coefficient: 0.783 for New World North and 0.848 for New World South). When beta diversity was regressed on latitude and gamma diversity, 69.8 and 85.7% of the variation in beta diversity were explained, respectively, for New World North and New World South. When gamma diversity was regressed on latitude and beta diversity, 81.8 and 84.3% of the variation in gamma diversity were explained, respectively, for New World North and New World South. After statistically removing the relationship between beta and gamma diversity, latitude has weak or no relationships with beta and gamma diversity. However, strong positive correlations between beta and gamma diversity may not be considered as evidence of one driving the other along a latitudinal gradient.