Summary Sustainable development requires that population and consumption remain within the limits of carrying capacity, while preventing a decline in the carrying capacity of an area requires that productive systems implanted through development be sustainable. Zoning can be a valuable tool in influencing land-use decisions, but we cannot expect government decrees to be capable of causing the landscape to evolve toward the sustainable patterns which have been rec- ommended through zoning. A prerequisite for influ- encing land-use change is understanding the social processes involved in land-use decisions, beginning with deforestation dynamics. Work to estimate carry- ing capacity needs to embrace the wide variety of pro- duction systems used and contemplated for Amazonia and to be able to interpret this information at scales ranging from local communities to the region as a whole. This will require not only studies of different land-use systems in rural areas, but also integration with studies of energy use and support limits of urban populations. Risks of environmental impacts must be quantified under different development scenarios, and limits of acceptable risk identified and integrated into analyses of carrying capacity. Tapping the value of environmental services of standing forest represents a promising means of sus- taining Amazonia’s population over the long term, but numerous obstacles exist. These include halting defor- estation before opportunities are lost and supporting the population in non-damaging ways while the insti- tutional groundwork is laid for using the environmen- tal services involved. Research is needed to quantify the magnitude of services and the appropriate mone- tary value per unit of service. Diplomatic agreement must be reached on these values, which can be ex- pected to be quite different from estimates of the ‘true’ values based on research. A series of social arrange- ments must be proposed and implemented if the value derived from environmental services is to fulfil its dual role of maintaining both the forest and the human population in Amazonia. Keywords : human carrying capacity, Brazil, Amazonia, human population, tropical agriculture, rain forest Introduction Sustainable development and carrying capacity Here I explore the relationship between carrying capacity and sustainable development and the challenges to estimating carrying capacity and to applying carrying capacity findings to influence the course of development in the region. An im- portant factor for the future will be the extent to which the potential value of environmental services can be tapped as a basis for supporting the population. Forests in Brazil’s 5 million km 2 ‘Legal Amazon’ region (Fig. 1) represent a tremendous potential resource for sus- tainable development, but only if the forests remain standing. ‘Sustainable development’ means different things to different people, but here will be used in the sense of creation of a basis for lasting support of a population. Sustainable development requires specification of the minimum acceptable levels of consumption and environmental quality, and the maximum acceptable risk that these standards will not be met. In order to be ‘development’, the population involved must be sup- ported in the region in question, which in this case is Human carrying capacity estimation in Brazilian Amazonia as a basis for sustainable development PHILIP M. FEARNSIDE* N ational I nstitute for Research in the Amaz on ( I N PA) , CP 478, 69011–970 M anaus, Amaz onas, Braz il Date submitted: 17 December 1996 Date accepted: 12 June 1997 *Correspondence: Dr Philip M. Fearnside Fax: +55 92 236–3822 T el: +55 92 642–3300 ext. 314 email: pmfearn@cr–am.rnp.br* Environmental Conservation 24 (3): 271–282 © 1997 Foundation for Environmental Conservation Figure 1 Brazil’s Legal Amazon region.