Environmental filtering explains a U-shape latitudinal pattern in regional β-deviation for eastern North American trees.

The underlying drivers of β-diversity along latitudinal gradients have been unclear. Previous studies have focused on β-diversities calculated at a local scale and shed limited light on regional β-diversity. We tested the much-debated effects of range size vs. environmental filtering on the β-gradient using data from the US Forest Inventory Analysis Program. We showed that the drivers of the β-gradient were scale dependent. At the local scale species spatial patterns contributed little to the β-gradient, whereas at the regional scale spatial patterns dominated the gradient and a U-shape latitudinal relationship for the standardised β-diversity deviation was revealed. The relationship can be explained by spatial variation in climate and soil texture, thus supporting the environmental filtering hypothesis. But it is inconsistent with Rapoport's rule about the effect of range size on β-gradient. These results resolve the debate on whether species spatial distributions contribute to β-gradient and attest the importance of environmental filtering in determining regional β-diversity.