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

What is it about?

What causes gradients in species richness? Many hypotheses have been proposed but one of the oldest and most compelling is that environmental stresses or harshness acts as an ecological filter on the range of species traits and thus also species richness that is viable in a particular site.The difficulty has been that you need to be able to measure harshness in a way that is independent of richness to test this hypothesis. We argue that maximum tree height is a way responds to harshness on many stress gradients and is thus a convenient proxy for harshness. We show that as the harshness hypothesis would predict tree species richness in North America is predicted remarkably well by maximum tree height.

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Why is it important?

Conservation planners often lack detailed species richness data on the scale of individual land parcels. In the absence of richness data, maximum tree height data which is quickly becoming widely available through remote sensing is an alternative. Moreover the tallest forests also contain the most carbon. Thus the approach of focusing on tree height could serve multiple conservation goals.