Tuesday, February 22, 2011

Independence of leaf and stem traits

Multivariate relationships between leaf and stem traits for 600+ Neotropical tree species. 
Before reading Baraloto et al. in Ecology Letters, I think the best assumption for how leaves and stems correspond is that plants with high-activity leaves (low tissue density, high N concentrations, low leaf longevity) would be associated with low density wood. Pioneer species are typically thought of this way--think Cecropia. Essentially cheap leaves come with cheap stems. Late-successional species typically have low-activity leaves and high wood density.

Yet, if you think about it a bit more, pines and firs have low wood density, yet their leaves live a long time. So what is the pattern? Do leaf and stem traits correlate or are they independent.

Baraloto et al. compared key leaf and stem functional traits for over 600 tropical tree species. The authors convincingly show that leaf and stem economic axes are orthogonal. Species with low leaf tissue density and high foliar nitrogen concentrations are equally as likely to be associated with high stem density as low. In short, cheap leaves can be born on expensive stems. 

The factorial ecology of leaf and stem economics has still to be worked out and the obvious next question is to reexamine patterns with roots, but the paper is an excellent example of the power of sampling large numbers of species and distilling data to a clear, simple message.

Baraloto, C., C. E. Timothy Paine, L. Poorter, J. Beauchene, D. Bonal, A. M. Domenach, B. Herault, S. Patino, J. C. Roggy, and J. Chave. 2010. Decoupled leaf and stem economics in rain forest trees. Ecology Letters 13:1338-1347.

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