Williamson, G. Bruce. 1988.

Michael C. Wiemann y G. Bruce Williamson. 1988. Extreme radial changes in wood specific gravity in some tropical pioneers. Wood and Fiber Science, 20(3), 1988, pp. 344-349^[1] )

Abstract

(tomado del artículo)
Twelve Hampea appendiculata, six Heliocarpus appendiculatus, and twelve Ochroma pyramidale trees from tropical wet forest in Costa Rica were sampled across their radii. Wood from all three species increased linearly in specific gravity^[2] ,^[3] from pith to bark. The magnitude of the increase was about 0.1 units of specific gravity per 10 cm of radius, although there were differences between the species and between trees within each species. All three species colonize clearings and disturbed sites, and these extreme changes in specific gravity may be associated with the pioneer habit in the wet forest.^[4]

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Apostillas

1. ^ . G.B. Williamson (PhD Indiana U, post doc en UofMichigan y Assistant Prof. at USFlorida) developed his doctoral diss. about the ecological significance of specific gravity of wood (or wood density expressed in g/cm³). The central points are:
   – slow-growing spp accumulate more wood/unit time than fast-growing spp, thereby, have a higher wood density
   – the average wood density of a forest (mean of spp abundance times wood density of each spp) reflects the age of the forest (if there is no selective logging). The higher the mean wood density the older the forest.
   ∂_k = (∑ ∂_in_i)/∑n_i
   Where:
   ∂_k = mean density of the k_th forest
   ∂_i = wood density of the i_th species
   n_i = abundance of the i_th species
   Luis Carlos García Lozano has a copy (paper) of Williamson's dissertation. It can be scanned or photocopied upon request.
2. ^ . Rather ample lists of wood density values compliled from the ecological lierature, can be seen in:
   – ICRAF Database - Wood Density
   – Estimating Biomass and Biomass Change of Tropical Forests: a Primer. (FAO Forestry Paper - 134, 1997)
   – Wood Densities of Tropical Tree Species
3. ^ . Wood density is a specific property (a given sp of tree has a wood density value relatively constant accross the natural range of the sp); however, there is variance to this value: some of it is phenotypic (incomplete expression of genetically determined density), some ontogenic (younger individuals differ from older ones in terms of density) and also, in the case of the paper here cited, young wood differs from older wood (within the same individual).
4. ^ . Besides the present paper, the basic references to Williamson's work are:
   – Williamson, G. B. 1975. Pattern and sera! composition in an old-growth beech-maple forest. Ecology 56(3):727-731.
   – Williamson, G. B. 1984. Gradients in wood specific gravity of trees. Bull. Torrey Bot. Club 111(1):51-55.