Tree diversity, tree height and environmental harshness in eastern and western North America

Abstract

Does variation in environmental harshness explain local and regional species diversity gradients? We hypothesise that for a given life form like trees, greater harshness leads to a smaller range of traits that are viable and thereby also to lower species diversity. On the basis of a strong dependence of maximum tree height on site productivity and other measures of site quality, we propose maximum tree height as an inverse measure of environmental harshness for trees. Our results show that tree species richness is strongly positively correlated with maximum tree height across multiple spatial scales in forests of both eastern and western North America. Maximum tree height co-varied with species richness along gradients from benign to harsh environmental conditions, which supports the hypothesis that harshness may be a general mechanism limiting local diversity and explaining diversity gradients within a biogeographic region.

Climate‐ and successional‐related changes in functional composition of European forests are strongly driven by tree mortality

“…Functional diversity and water availability were the main drivers of the changes in maximum tree height, particularly in broad‐leaved and Mediterranean coniferous forests. At high diversity, we found generally an increase in maximum tree height (see also Marks, Muller‐Landau, & Tilman, ), which might be reflecting the expected secondary succession trajectory. In wet sites (i.e.…”

Tropical cyclones disrupt the relationship between tree height and species diversity: Comment

“…), supporting the harshness hypothesis (Marks et al. , ). In contrast, in Taiwan, where tropical cyclones occur annually, tree species richness decreased but maximum tree height increased with increasing elevation, the opposite of the predictions of the harshness hypothesis (Fig.…”

“…In a recent report on the patterns of tree species richness in eastern and western North America, Marks et al. () claimed to have identified an operational indicator of environmental harshness (maximum tree height) and concluded that environmental stressors that limit tree height also act as ecological filters on species richness. Marks et al.…”

Global patterns and determinants of forest canopy height

“…Marks et al. () found relatively lower maximum tree height in southern Florida, which can be partly attributed to the increases in the soil water‐logging tolerance of trees. More importantly, using forest inventory data from China and USA, we found that forest canopy heights decreased with very high water availability (Fig.…”