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The biomass of intact tropical forests must be known in order to quantify C pools and emissions arising from biomass burning associated with deforestation, land conversion, or fragmentation. To address this need, the study quantified the total aboveground biomass (TAGB) and forest structure in 20 intact tropical forest sites in western Brazil. The sites were located in open, dense, and ecotone (to savanna) forest types. The TAGB of open forest ranged from 288 to 346 Mg ha-1, with a mean of 313 Mg ha-1; dense forest TAGB ranged from 298 to 533 Mg ha-1, with a mean of 377 Mg ha-1; and ecotone forests TAGB ranged from 298 to 422 Mg ha-1, with a mean of 350 Mg ha-1. Mean TAGB for all 20 sites was 341 Mg ha-1. "live trees" (broad-leaved trees) comprised most of TAGB, averaging 280 Mg ha-1. Mean aboveground biomass of trees 10 cm diameter at breast height (dbh) differed between open (239 Mg ha-1) and dense forests (307 Mg ha-1). Mean biomass of live "non-tree" components (predominantly palms) for all 20 sites was 22 Mg ha-1. The combined biomass of coarse wood debris, forest floor (litter/root mat), and standing dead plants (trees, palms and vines) averaged 38 Mg ha-1 or 12% of the TAGB. Forest structure and biomass distribution were not uniform among sites or forest types. For example, non-tree components ranged from 41% of the TAGB in one ecotone forest to as low as 7% in a dense forest site. Non-tree components comprised 22% of TAGB. This is noteworthy because the non-tree components are often omitted from forest biomass/carbon pool estimates.

Tropical rainforests are a significant global terrestrial C pool, thus, deforestation/land conversion contributes to rising levels of greenhouse gases in the atmosphere. Information on total aboveground biomass (TAGB) is scarce for Amazonian forests. Indirect estimates based on commercial volume from forest inventory data (Brown and Lugo, 1992; Fearnside and Fearnside, 1992b), as well as direct field measurements of individual trees have been used to predict TAGB ( Jordan; Klinge; Russell, 1983 and Higuchi et al., 1994). Estimates for TAGB in the Brazilian Amazon have ranged from 155 to 555 Mg ha-1 (Revilla Cardinas et al., 1982 and Brown).

Differences in estimates of TAGB arise in part from the methods used to measure it, as well as from the heterogeneity of the forests. Early studies involved destructive sampling to develop predictive models for tree biomass estimations based on combinations of tree diameter at breast height (dbh), specific gravity (sg), and height (h) (Jordan; Klinge; Russell, 1983 and Higuchi et al., 1994). The models for individual tree biomass were then applied to measurements from trees. The application of destructive and field measurements is limited by the time and cost associated with collecting field data over a large area of tropical forests. To reduce the dependence on destructive or direct field measurements, commercial volumes derived from forest inventories have been used to estimate total tree biomass at large scales (Brown; Brown and Brown, 1997). Based on a compilation of results from nine studies for which direct measurements of biomass were made, as well the indirect estimates of Brown and Lugo (1992), Fearnside (1992b) estimated the average TAGB for the Brazilian Legal Amazon at 335 Mg ha-1. In another set of studies, Kauffman et al. (1995) and Guild et al. (1998) quantified TAGB for six slashed primary forests. Their biomass estimates ranged from 293 to 436 Mg ha-1, with a mean of 362 Mg ha-1. Although the tierra firme forest sampled by Jordan and Uhl (1978) was considered to be of low stature and biomass (335 Mg ha-1) for the Amazon, their estimate was almost 100 Mg ha-1 more than the mean biomass for Amazonia (227 Mg ha-1) that Brown and Lugo (1992) calculated through models based on forest inventories. However, the Brown and Lugo (1992) estimates ignored components of TAGB other than trees 10 cm dbh. Laurance et al. (1997) calculated TAGB and biomass losses from forest inventories by assuming that all non-tree biomass and trees <10 cm dbh made up 12% of the overstory (trees >10 cm dbh).
Yet, in Amazonian forests studied by Kauffman et al. (1998), there was a significant negative relationship between overstory and understory biomass. Nevertheless, TAGB is often estimated by assuming a constant proportion between overstory trees and other biomass components ( Fearnside, 1992a).

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References:
Brown, J.K., 1974. Handbook for Inventorying Downed Woody Material. USDA Forest Service, Ogden, UT, 25 pp.
Brown, S., 1997. Estimating Biomass and Biomass Change of Tropical Forests: A Primer. Forestry Paper 134, FAO, Rome.
Brown, S. and Lugo, A.E., 1984. Biomass of tropical forests: a new estimate based on forest volumes. Science 223, pp. 1290¯1293. Abstract-GEOBASE
Brown, S., Lugo, A.E., 1990. Biomass estimates for Brazil's Amazonian moist forests. In: Forest'90: Annals of the First International Symposium on Environmental Studies on Tropical Rain Forests, Manaus, Brazil, pp.46¯52.
Brown, S. and Lugo, A.E., 1992. Aboveground biomass estimates for tropical moist forests of the Brazilian Amazon. Interciencia 17, pp. 8¯18.
Brown, S., Lugo, A.E. and Iverson, L.R., 1992. Processes and lands for sequestering carbon in the tropical forest landscape. Water Air Soil Pollut. 64, pp.139¯155. Abstract-Compendex | Abstract-GEOBASE | Abstract-EMBASE
Brown, I.F., Nepstad, D.C., Pires, O., Luz, L.M. and Alechandre, A.S., 1992. Carbon storage and land-use in extractive reserves, Acre, Brazil. Environ. Conserv. 19, pp. 307¯315. Abstract-GEOBASE
Brown, I.F., Martinelli, L.A., Thomas, W.W., Moreira, M.Z., Ferreira, C.A. and Victoria, R.A., 1995. Uncertainty in the biomass of Amazonian forests: an example from Rondônia, Brazil. Forest Ecol. Mgmt. 75, pp. 175¯189. Abstract | PDF (1041 K)
Fearnside, P.M., 1985. Brazil's Amazon forest and the global carbon problem. Interciencia 10, pp. 179¯186.
Fearnside, P.M., 1986. Brazil's Amazon forest and the global carbon problem: reply to Lugo and Brown. Interciencia 11, pp. 58¯64.
Fearnside, P.M., 1992. Forest biomass in Brazilian Amazonia: comments on the estimate by Brown and Lugo. Interciencia 17, pp. 19¯27.
Fearnside, P.M., 1997. Wood density for estimating forest biomass in Brazilian Amazonia. Forest Ecol. Mgmt. 90, pp. 59¯87. Abstract | PDF (1489 K)
Fearnside, P.M., 2000. Global warming and tropical land-use change: greenhouse gas emissions from biomass burning, decomposition and soils in forest conversion, shifting cultivation and secondary vegetation. Climatic Change 46, pp. 115¯158. Abstract-GEOBASE | Abstract-Elsevier BIOBASE | Abstract-BIOTECHNOBASE | Full Text via CrossRef
Fearnside, P.M. and Barbosa, R.I., 1998. Soil carbon changes from conversion of forest to pasture in Brazilian Amazonia. Forest Ecol. Mgmt. 108, pp. 147¯166. SummaryPlus | Full Text + Links | PDF (198 K)
Laurance, W.F., Laurance, S.G., Ferreira, L.V., Rankin-de Merona, J.M., Gascon, C. and Lovejoy, T.E., 1997. Biomass collapse in Amazonian forest fragments. Science 278, pp. 1117¯1118. Abstract-EMBASE |Abstract-GEOBASE | Full Text via CrossRef
Laurance, W.F., Fearnside, P.M., Laurance, S.G., Delamonica, P., Lovejoy, T.E., Rankin-de Merona, J.M., Chambers, J.Q. and Gascon, C., 1999. Relationship between soils and Amazon forest biomass: a landscape-scale study. Forest Ecol. Mgmt. 118, pp. 127¯138. SummaryPlus | Full Text + Links | PDF (164 K)
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