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50 For more details on the administrative requirements of logging concessions, seeMiranda et al., All That Glitters is Not Gold: Balancing Conservation andDevelopment in Venezuela’s Frontier Forests (Washington, DC: WRI, 1998), p.14.51 Our data are based on surveys and interviews with sawmill operators and wewere unable to independently verify the results52 Ramiro Silva, Venezuelan forestry expert, personal communication, 22November, 200053 J.G. Collomb et al., An Overview of Logging in Cameroon (Washington, DC:WRI, 2000), p. 20.54 Extraction rates in Guyana, French Guiana, and Suriname vary between 5-15m 3 /ha and in some forest blocks extraction rates can reach up to 60-100 m 3 /ha.See H. ter Steege and D.S. Hammond, “Forest Management in the Guianas:Ecological and Evolutionary Constraints on Timber Production,” BOSNiEuWSLETTER 15 (1996): 63; extraction rates in the Brazilian Amazone varyaccording to three intensity levels i) low –14-24 m 3 /ha and 1 tree/ha; ii) moderate–24-32 m 3 /ha and 1-3 trees/ha; and iii) high –32-35 m 3 /ha and 5-10 trees/ha.See D. Nepstad, et al., “Large-scale impoverishment of Amazonian Forests bylogging and fire,” Nature (in press); C. Uhl et al., “ Natural ResourceManagement in the Brazilian Amazon: an integrated approach,” BioScience 47,3 (1997): 160-168.55 The official cubic meter is derived by a formula established by the Ministry ofEnvironment: V-MARN=0.605 * D 2 * L, where V-MARN = the volume in m 3 ;0.605 = conversion constant; D= cutting diameter at breast height in meters; L=commercial height in meters. For more details on the official cubic meter, seeJ. C. Centeno, Estrategia para el Desarrollo Forestal de Venezuela (Report commissionedby WRI, June 1995), p. 29.56 J. C. Centeno, Estrategia para el Desarrollo Forestal de Venezuela (Report commissionedby WRI, June 1995), p. 2957 According to data collected from management plans of concessionaires operatingin Guayana region. See Annex 1 for details.58 Ramiro Silva, Venezuelan forestry expert, personal communication, 22November, 2000.59 J. Ochoa G., “Análisis preliminar de los efectos del aprovechamiento demaderas sobre la composición y estructura de bosques en la GuayanaVenezolana,” Interciencia 23 (1998): 197-207.60 C. Uhl and I. Vieira, “Ecological Impacts of Selective Logging in the BrazilianAmazon: A Case Study from the Paragominas Region of the State of Pará,”Biotropica 21, 2 (1989): 98-106; R. J. Buschbacher, “Natural Forest Managementin the Humid Tropics: Ecological, Social, and Economic Considerations,”Ambio 19, 5 (1990): 253-257.61 J. C. Centeno, Estrategia para el Desarrollo Forestal de Venezuela (Report commissionedby WRI, June 1995), p. 37.78