1. A single basin-wide estimate for basic density of wood (0.69) has been employed to map above-ground biomass and carbon stocks across Amazonia (Fearnside 1997, Houghton et al. 2001). But forest types occupying much of the Arc of Deforestation may have wood of lower density, because more fertile soils and natural disturbance by lianas and climbing bamboos both favor faster-growing trees. In open and in dry forests trees may also be shorter at any given diameter, compared with the dense forests where Amazon tree biomass allometry has been developed. The magnitude of theses two effects on above-ground stand biomass was examined for two forest types in the SW Amazon, near Sena Madureira, Acre. These were a dense forest on relatively fertile soil and an open bamboo-dominated forest on the same soil. METHODS (1) Biomass was first estimated for each forest type using an allometric relationship between diameter at breast height (DBH) and standing above ground dry biomass for trees > 5 cm DBH, developed for dense forest in the Central Amazon near Manaus (Chambers et al. 2001). (2) Average stand wood basic density at breast height (dry weight at 103 o C divided by fresh volume with bark) and the height-diameter relationship were determined in small felled samples (100-300 trees) for each of the two SW Amazon forest types and for the dense forest of the Central Amazon. (3) Corrections for height and wood density differences were applied to large scale inventories of the two forest types in the SW Amazon. Yc = f(DBH) · Ch · Cd, where: Yc = corrected above-ground dry weight of an inventoried tree; f(DBH) = biomass of each tree using Central Amazon model of Chambers et al. (2001), with DBH as the only input; Ch = effect of lower total height on each tree’s biomass in test forest, compared with Central Amazon; Cd = effect of lower wood density on tree biomass in test forest, compared with Central Amazon. Effects of wood density and the height-x-diameter relationship on biomass differences between three Amazon forest types RESUMO/ABSTRACT N o 528; Authors: Bruce W. Nelson (1), Mabiane B. França (2), Euler M. Nogueira (3) & Átila C.A. de Oliveira (4) (1) Ecology Dept, INPA – Instituto Nacional de Pesquisas da Amazônia, Manaus, Brazil, bnelson@inpa.gov.br; (2) Forest Science Graduate Program – INPA (former student); (3) Forest Science Graduate Program – INPA; (4) Ecology Graduate Program – INPA (former student)bnelson@inpa.gov.br TREE HEIGHT EFFECT Trees tend to be shorter at any given diameter in each of the SW Amazon forests, compared with the Central Amazon forest. Regression slopes are homogeneous and intercepts are different within each figure. Only the effect on trunk weight is considered (~66% of tree biomass), since crowns may be just as large as in Central Amazon. The subtractive biomass correction due to different heights, Cs, is given by: Cs = (1 - H 1d /H 2d ))*0.66, where H 1d = Expected height in SW Amazon forest, at diameter d; H 2d = Expected height in Central Amazon dense forest, at same diameter d. The multiplicative correction factor for lower tree height (lower left graph) is: Ch = 1 - (0.66 - 0.66*(H 1d /H 2d )) Tree-height effect on estimated biomass (Ch) varies with DBH in non-linear fashion: – SW Amazon dense forest; – SW Amazon open bamboo-dominated forest. WOOD DENSITY EFFECT Forest type Average wood density Correction to biomass +/- 2 std errors Central Amazon dense0.7041.0 SW Amazon dense0.5930.843 +/- 0.0482 SW Amazon open0.5060.718 +/- 0.0534 COMBINED EFFECTS (in large scale forest biomass inventories) CONCLUSIONS Lower wood density and shorter tree height -- compared with sites where biomass allometries have been developed -- cannot be ignored when estimating carbon emissions in the Arc of Deforestation. Compared with a Central Amazon site, these two effects alone reduce estimates of stand biomass by: 40% in a SW Amazon open forest 22% in a SW Amazon dense forest NOTES: Central Amazon allometric model of Chambers et al. (2001) for estimating above ground dry weight of trees >5 cm DBH is: LN(DW) = -0.370 + 0.333*LN(DBH) + 0.933[LN(DBH)]^2 - 0.122[LN(DBH)]^3 References: Chambers, JQ; dos Santos, J; Ribeiro, RJ & Higuchi, N. 2001. Tree damage, allometric relationships, and above-ground net primary production in Central Amazon forest. Forest Ecology and Management 152: 73-84. Fearnside PM. 1997. Wood density for estimating forest biomass in Brazilian Amazonia Forest Ecology and Manangement, 90, 59-87. Houghton RA, Lawrence KT, Hackler JL, Brown S. 2001. The spatial distribution of forest biomass in the Brazilian Amazon: a comparison of estimates. Global Change Biology, 7, 731-746. Open and dry forests dominate most of the Arc of Deforestation Terra firme dry forest Terra firme open forest Terra firme dense forest Manaus Belém Sena Madureira