Rubber agroforests at the Tapajos river, Brazilian Amazon--environmentally benign land use systems in an old forest frontier region

Scientific and public attention concerned with natural rubber (Hevea brasiliensis) production in the Amazon has focused on the high-tech practice of double-grafted, leaf blight resistant and high-yielding rubber clones on the one hand, and the low-tech practice of extractive use of natural rubber stands on the other. The intermediate, traditional practice of enriching slash-and-burn plots with rubber trees and managing them in a secondary forest environment, in association with other timber and non-timber species, has largely been overlooked. We present results from a survey of 51 farmer families conducted on the eastern bank of the Tapajos river in the central Brazilian Amazon, focusing on the population zone of the Tapajos National Forest and its northern vicinity. Actively managed rubber agroforests were most common on the sandy river banks and on humus- and clay-rich and ferralitic soils near the edge of the plateau at a few kilometers from the river. There was a gradient in management intensity between the proximity of the villages at the river, where rubber was often a component of homegardens, and the distant groves on the plateau, which often resembled secondary forests. The spatial separation of access to water at the river and more fertile soils on the plateau, the historical practice of abandoning the rubber groves at times of low rubber prices, and a substantial risk of losing plantations to abiotic and biotic threats, especially fire, are identified as factors that have presumably favored the development of agroforests with low management intensity in the region. Although about half of the interviewed farmers expressed a preference for weeded plantations, almost 90% of them extracted vegetal products other than rubber from the agroforests or used them as hunting grounds, and 80% believed that associated vegetation had no negative influence on rubber yields. The often good health of old rubber trees in Amazonian agroforests is explained with lower pressure from root rots, the periodic abandonment and especially a tapping technique that is well adapted to a moist forest environment.