Infodoc : Sciences, Techniques et Culture

A better understanding of the reasons for variation in tropical rain forest (TRF) structure is important for quantifying global above-ground biomass (AGBM). We used three data sets to estimate stem number, basal area, and AGBM over a 600-ha old-growth TRF landscape (La Selva, N.E. Costa Rica). We analyzed the effects of soil type, slope angle, topographic position, and different sample designs and measurement techniques on these estimates. All three data sets were for woody stems ≥10 cm in diameter. Estimated AGBM was determined from stand-level measurements using Brown's (Brown, 1997) allometric equation for Tropical Wet Forest trees. One data set was from three subjectively-sited 4-ha plots (the 'OTS plots'), another was based on 1170 0.01 ha plots spaced on a regular grid (the Vege[...]

A better understanding of the reasons for variation in tropical rain forest (TRF) structure is important for quantifying global above-ground biomass (AGBM). We used three data sets to estimate stem number, basal area, and AGBM over a 600-ha old-growth TRF landscape (La Selva, N.E. Costa Rica). We analyzed the effects of soil type, slope angle, topographic position, and different sample designs and measurement techniques on these estimates. All three data sets were for woody stems ≥10 cm in diameter. Estimated AGBM was determined from stand-level measurements using Brown's (Brown, 1997) allometric equation for Tropical Wet Forest trees. One data set was from three subjectively-sited 4-ha plots (the 'OTS plots'), another was based on 1170 0.01 ha plots spaced on a regular grid (the Vegetation map plots'), and the third was from 18 0.5 ha plots (the 'Carbono plots') sited to provide unbiased samples of three edaphic conditions: flat inceptisol old alluvial terraces; flat ultisol hill-tops; and steep ultisol slopes. Basal area, estimated AGBM and the contributions of major life forms were similar among studies, in spite of the differences in sampling design and measurement techniques. Although the Carbono plots on flat inceptisols had significantly larger and fewer trees than those on ultisols, AGBM did not vary over the relatively small edaphic gradient in upland areas at La Selva. On residual soils, the largest trees were on the flattest topographic positions. Slope angle per se was not correlated with basal area or AGBM within the residual soils. Errors introduced by palm and liana life forms, as well as hollow trees, did not significantly affect AGBM estimates. In contrast, the methods used to measure buttressed trees had a large impact. Plot sizes of 0.35-0.5 ha were sufficient to achieve coefficients of variation of + -