Relationships between tree height and tree species richness at small scales

Tree height and tree species richness are both essential to characterize forest structure. Previous research showed that maximum tree height is a strong predictor of tree species richness at forests on a large scale. However, it is unknown whether this relationship exists in a forest at small scales. Here the intensively surveyed data from 1 ha of forest plot in northern Alabama was used to exam this relationship at small scales (e.g., 1 m x 1 m, 2 m x 2 m, ..., and 50 m x 50 m). The results indicated that there was no significant correlation between the maximum tree height and tree species richness across small scales. Majority trees with the highest tree height at the small scales were oaks and hickories, which are dominant trees in this forest community through succession. A weak negative spatial autocorrelation existed in tree heights. Tree height distribution across the small scales followed power-laws but with varied scaling exponents. These scaling exponents were significantly correlated with tree species richness when the scales were no less than 1000 m(2), which was equivalent to have about 15 tree species in the study area. The results may explain the complicated relationship between tree species diversity and tree height. This study may provide implications for forest structure management and conservation.