Literature Review: Forest Tree Diversity

by Carl Strang

One of the fundamental questions of community ecology is: why are there so many species? This question comes in many forms, and two papers published in the past year addressed a narrowly focused version of it. Given that trees are competing for just a few kinds of resources (light, soil moisture, nutrients), how is it that so many different kinds of them can coexist in forests? Why don’t the best competitors just push the rest out of the picture? One study looked at a temperate forest (Clark, James S. 2010. Individuals and the variation needed for high species diversity in forest trees. Science 327:1129-1132).

The other study had some personal interest because it was done at the famous Barro Colorado Island field station in Panama, which I got the chance to visit as a graduate student in 1975 (Comita, Liza S. Helene C. Muller-Landau, Salomón Aguilar, Stephen P. Hubbell. 2010. Asymmetric density dependence shapes species abundances in a tropical tree community. Science 329: 330-332).

Both studies followed the careers of hundreds of individual trees of the various species present, considering their growth and survival with respect to their neighbors. Despite the differences in physical environmental conditions, similar results came out. The bottom line in each case was that trees compete most strongly with (and therefore suppress most strongly) members of their own species. Clark pointed out that this is not shown when species are taken as wholes. Individual careers, particularly variations in size or age, need to be followed to obtain this result. Comita et al. in addition obtained the interesting finding that intraspecific suppression increased with species’ rarity, contributing significantly to the structure and diversity of the tropical forest tree community.


1 Comment

  1. Michelle said,

    November 26, 2010 at 12:47 pm

    Very educational post, thank you for sharing!

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