G. Bruce Williamson
Professor of Tropical Ecology,
Dept. of Biological Sciences, Louisiana State University, Baton Rouge, LA 70808
Coordenação de Pesquisas em Ecologia, Instituto Nacional de Pesquisas da Amazônia,
Manaus, Amazonas, BR
[Bruce is former Biotropica Curator]
Recent article in BIOTROPICA
About Bruce Williamson's study
The Pioneers Project of the Biological Dynamics of Forest Fragments Project (BDFFP) is focused on tropical forest regeneration, the functional traits of trees, and the land use patterns that interact with natural processes to determine local species assemblies and successional trajectories. One trait, wood specific gravity (SG), is a powerful predictor of plant growth rates, trunk strength properties and tree survival rates because it measures the allocation of biomass per unit volume to support. Tropical pioneer species exhibit exceptionally low wood specific gravities, less than one-third the SG of mature forest species. Furthermore, pioneers produce even lower SG wood as juveniles, leaving them at greater risk of structural failure; subsequently, SG increases into adulthood, achieving greater stability later in life.
In tropical wet forests, pioneers such as Ochroma, Cecropia and Trema, increase wood SG 2-3 fold from saplings to adults. Recently we suggested that this radial variation in wood SG is regulated by tree age, not by tree size, during development (Williamson & Wiemann 2010, Biotropica 42:590-597). Age versus size dependence has significant consequences for standing biomass estimates, forest regeneration rates, and tropical plantation forestry.
In our studies of succession, we share cross-site collaborations with groups working in Mexico, Costa Rica and Brazil, in order to determine generalities and differences across the neotropics. What trends are shared and what patterns are unique in tropical successions? (see www.neoselvas.org)
Williamson, G.B., & M.C. Wiemann. 2010. Age-dependent radial increases in wood specific gravity of tropical pioneers. Biotropica
42: 590-597. Abstract
Williamson, G. B., & M. C. Wiemann. 2010. Measuring wood specific gravity...correctly. American Journal of Botany 97: 519-524.
R.C.G. Mesquita, K. Ickes, G. Ganade, & G.B. Williamson. 2001. Alternative successional pathways following deforestation in the Amazon Basin. Journal of Ecology 89:528-537.
Castro, F. de, G.B. Williamson, & R. Moraes de Jesus. 1993. Radial variation in the wood specific gravity of Joannesia Princeps
: the role of age and diameter. Biotropica
25: 176-182. JSTOR
Rueda, R., & G.B. Williamson. 1992. Radial and vertical wood specific gravity in Ochroma pyramidale
(Cav. ex Lam.) Urb. (Bombacaceae). Biotropica
24: 512-518. JSTOR
Wiemann, M.C., & G.B. Williamson. 1989. Radial gradients in the specific gravity ofwood in some tropical and temperate trees. Forest Science 35: 197-210.
Wiemann, M.C., & G.B. Williamson. 1989. Wood specific gravity gradients in tropical dry and montane rain forest trees. American Journal of Botany 76: 924-928.
Photo captions: Top : Bruce Williamson (bottom of photo) boring a large Bursera simaruba near Cauhita, Costa Rica. Left : Bruce Williamson (left) and Mike Wiemann (right) examine a recently extracted wood sample to ascertain it's completeness, pith to bark; Right : large balsa (Ochroma pyramidale) 1.0 m dbh in Corcovado National Park, Costa Rica, recently bored by the authors.
Successional perspective: active pasture (foreground), a monogeneric stand of Vismia species in a 5-year old abandoned pasture (intermediate) and primary forest at the Biological Dynamics of Forest Fragments Project, Amazonas, Brazil (background). (© B. Williamson)