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Lourens Poorter talks with and answers a few questions about this month's Fast Moving Front in the field of Geosciences. The author has also sent along images of their work.
Article: Wood mechanics, allometry, and life-history variation in a tropical rain forest tree community
Authors: van Gelder, HA;Poorter, L;Sterck, FJ
Journal: NEW PHYTOL, 171 (2): 367-378 2006
Addresses: Univ Wageningen & Res Ctr, Forest Ecol & Forest Management Grp, POB 47, NL-6700 AA Wageningen, Netherlands.
Univ Wageningen & Res Ctr, Forest Ecol & Forest Management Grp, NL-6700 AA Wageningen, Netherlands.
Inst Boliviano Invest Forestal, Santa Cruz, CA USA.

 Why do you think your paper is highly cited?

The paper addresses the importance of wood characteristics for the life history variation of tropical trees. Wood density is emerging as a core trait in functional plant ecology, because of its importance for the biomechanics, architecture, water relations, and carbon gain of trees. The unique contribution of the paper is that we evaluated wood properties for a large number of coexisting tree species in a tropical rain forest community, and we showed that they were closely associated with the shade tolerance of tree species.

 Does it describe a new discovery, methodology, or synthesis of knowledge?

Figure 1:
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Arnold van Gelder

Wood density is often assumed to be an indicator of the shade tolerance of tree species, but empirical evidence for this is sparse. The nice thing is that we had a quantitative index of the shade tolerance of the species, and we found that wood density was closely and positively associated with the ability of species to persist in the shade.

The mechanisms that led to an increase in the survival of high-wood density species in the shade were unclear, and it is thought that tree biomechanics can play a role. What we did was to measure the biomechanical wood properties of small trees in the field. This was a novel approach, because normally this is only determined for dried adult wood of a few commercial tree species.

 Would you summarize the significance of your paper in layman's terms?

Species that are typically found in the shaded forest understory grow slowly, and have to survive for a long time if they eventually want to make it to the forest canopy. As much as 25% of all plants in the forest understory are annually hit by falling branches, or broken off by mammals. We found that species adapted to those conditions had dense and stiff wood, which breaks less easily under falling debris, and enhances tree stability.

Species that are typically found in bright, open places in the forest have to grow very fast in order to outcompete their neighbors and attain maturity. These species have low density wood, which is very cheap to construct, thus enabling fast stem height and diameter growth. These different wood characteristics allow species therefore to occupy different light "niches," which is thought to contribute to the high species richness of the tropical rain forest.

 How did you become involved in this research and were there any particular problems encountered along the way?

The focus of my research is on the importance of functional trait variation for species coexistence. I was especially interested in the importance of traits for plant survival, a very much understudied component.

Arnold van Gelder, the lead author, is a civil engineer, who was interested in doing his thesis on tree biomechanics. Frank Sterck, the other coauthor, was interested in including these biomechanical traits in a tree model. In combination, this was an ideal research team. We had the good luck to work together with Jose Chuvina, an indigenous paratoxonomist who helped us with the identification in the field, and with forest engineer Gregorio Cerrogrande from the local Bolivian university, who helped us to determine wood properties with a beautiful and well-working loading equipment machine from the sixties.

Specific problems encountered: it rained for days, the river level was two meters higher than the bridge, and in the end we had to cross the river with a motorbike on a canoe to finally get to the field and finish the research.

 Where do you see your research leading in the future?

We are now working on the importance of wood traits for drought tolerance; how they facilitate water transport in the xylem in the wet season, and how they prevent embolism and tree dysfunction in the dry season. Another interesting aspect would be to model the implications of wood traits for tree growth and survival.

 Do you foresee any social or political implications for your research?

Locally, the people are interested in these wood material properties, because tropical rain forests harbor a tremendous amount of tree species, whereas currently only a few species are commercially harvested for timber. Many other species might be potentially interesting as well, as long as we know their wood properties. In addition, tropical forests are an important storehouse for carbon, and the potential for carbon storage is, amongst others, determined by the wood density of the species. Insight into how wood density varies across species, along with species composition, is therefore needed if we want to make more accurate estimates about how much carbon is stored within these forests.

Dr. Ir. Lourens Poorter
Forest Ecology and Forest Management Group and Resource Ecology Group
Center for Ecosystem Studies
Wageningen University
Wageningen, The Netherlands

Figure 1:

Figure 1: Coauthor Arnold van Gelder doing the bending test.

Keywords: Lourens Poorter, functional plant ecology, wood characteristics, wood traits, life history variation of tropical trees, wood density, carbon gain of trees, high-wood density species, tree biomechanics, tree stability, high species richness of the tropical rain forest, drought tolerance.

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2008 : November 2008 - Fast Moving Fronts : Lourens Poorter