Road paving, fire regime feedbacks, and the future of Amazon forests

doi:10.1016/S0378-1127(01)00511-4

Forest Ecology and Management

Volume 154, Issue 3, 1 December 2001, Pages 395-407

https://doi.org/10.1016/S0378-1127(01)00511-4 Get rights and content

Abstract

Fire poses the greatest threat to the forests of Amazônia. The magnitude of this threat is amplified by three positive feedback loops that drive the expansion of forest fire in the region: (1) Fire promotes drought, and therefore more fire, by releasing smoke into the atmosphere, thus reducing rainfall. Fire-assisted conversion of forests to pastures may also promote drought by increasing albedo and decreasing water vapor flux to the atmosphere, further inhibiting rainfall. (2) Fire increases the susceptibility of forests to recurrent burning by killing trees, thereby allowing sunlight to penetrate the forest interior, and increasing the fuel load on the forest floor. (3) Finally, fires also self-perpetuate by burning agricultural and forestry systems, discouraging landholders from making those fire-sensitive investments in their land that would allow them to move beyond their dependence upon fire as a management tool.

The long-term reduction of Amazon fire, and its substantial costs to society, is most likely to emerge through investments and policy change that stimulate permanent agricultural and forestry production systems within existing frontiers while slowing the rate of frontier expansion. But the Brazilian government’s plan to pave, recuperate or construct 6245 km of roads in the Amazon may have the opposite effect. We present research findings that the government plan would nearly double the area of forestland that is accessible by paved highways, including 192,000 km² of fire-prone forest. Our analysis finds that these roads will stimulate 120,000–270,000 km² of additional deforestation, and forest impoverishment through logging and understory fire, if the historical relationship between road paving and forest alteration by humans continues. Infrastructural investments are urgently needed in Amazônia to help integrate isolated urban centers into the market economy, to improve the quality of life for millions of rural Amazonians, and to improve the profitability of agribusiness in Brazil’s agricultural belt. But as currently planned, these investments will have the ancillary effects of accelerating deforestation, logging, forest fire, smoke-related illness, and the displacement of small-scale farmers.

Section snippets

Introduction: fire as chronic emergency

Amazon fires were world news in 1998, 1997,1995, 1992 and 1988. During the severe drought of the 1998 El Niño episode, understory fires that creep along the ground burned at least 20,000 km² of standing forest in Roraima and southeastern Pará, beyond the scope of Brazil’s deforestation monitoring program (Nepstad et al., 1999a); another 1.5 million km² of forest became susceptible to burning during this period but most did not burn because of a shortage of ignition sources (Fig. 1). The total area

The economic feedback

Amazon fires are a “chronic emergency” (Nepstad et al., 1999b) because they are deeply imbedded in the culture and economic logic of four million rural Amazonians trying to survive or grow wealthy on the agricultural frontier. Faced with acid-infertile soil, abundant, inexpensive forestland, and a shortage of labor and capital, the forest itself is the most logical substitute for fertilizer, pesticides and farm machinery. A farmer can prepare an ash-fertilized field, with few pests or weeds,

The forest flammability feedback

The dense, high-canopy forests of Amazônia extend like giant firebreaks across the landscape during most years (Uhl and Kauffman, 1990), partly because of their remarkable capacity to avoid drought-induced leaf-shedding by absorbing soil water stored to depths of more than 10 m (Jipp et al., 1998, Nepstad et al., 1994). But during severe droughts such as that provoked by the 1997–1998 El Niño episode, even deep soil moisture supplies are depleted and forest trees shed their leaves, allowing the

The climatic feedback

The climate of Amazônia is tightly coupled to the forest, which provides water vapor to the atmosphere throughout the year, and which absorbs solar energy, thereby heating parcels of humid air that then rise to become cumulus clouds (Nobre et al., 1991). Large-scale cattle ranching and slash-and-burn agriculture inhibit rainfall by replacing forest with cattle pasture and crop fields, reducing the amount of water that evaporates from the land and diminishing the amount of solar radiation that

Implications for Amazônia

These three positive feedback cycles threaten to transform about half of the forests of Amazônia into fire-prone scrub vegetation and cattle pastures through the interaction of forest conversion to pasture and cropland, logging, and severe drought (Fig. 2, Fig. 3, Fig. 4). The possibility of widespread, sustainable production systems (agroforestry, tree crops, tree plantations, forest management for timber) is reduced through this transformation because of the high risk that investments in the

Breaking the feedbacks

Amazônia will continue to incur large, possibly expanding, ecological and economic losses through fire unless these positive feedback cycles are broken. Beyond the palliative “chronic-emergency” responses to these fires, involving troops and aircraft, long-lasting reduction in accidental fires must address the causes, and not just the symptoms, of the burning problem. We hypothesize that one of the key processes by which the positive fire feedbacks of Amazônia can be uncoupled is through a

Roads to fire

Roads are the single most robust predictor of frontier expansion and accompanying deforestation in tropical forest regions (reviewed by Kaimowitz and Angelsen, 1998). More than two-thirds of Amazon deforestation has taken place within 50 km of major paved highways (Alves, in press; and this study, Table 2). Avança Brasil, the Brazilian government’s national economic development plan, would rapidly increase the supply of inexpensive forestland through the paving of 6245 km of roads in Amazônia (

Acknowledgements

Funding for this research was provided by the US Agency for International Development, NASA-LBA Ecology, the AVINA Foundation and the Tinker Foundation. We thank A. Moreira, D. Zarin, and two anonymous reviewers for comments on this manuscript, P. Schlesinger for assistance with data analysis, M. Ernst for assistance with graphics, and K. Schwalbe.

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