Weedy fields and forests: interactions between land use and the composition of plant communities in the Peruvian Amazon

Slash-and-burn agriculture is a sequence of interactions between farmers and ecosystems, which includes forest, cropping, fallow, and cropping after fallow. In sampling across this sequence in Pucallpa, Peru, 235 plant species were recorded in the forest, of which 143 were not found in any successive land use. However, plants not occurring in the forest colonized fields and fallow. In total, 595 species were identified across treatments. Changes in communities generally reflected the replacement of shade-tolerant plants, with seed dispersed by bats, other mammals, ants, and larger birds, and by pioneer plants adapted to open conditions and producing larger numbers of small seed, dispersed by smaller birds and the wind. Each form of land use hosted 7-25% of the original forest species, plus 13-66 plant species adapted to that land use. As field conditions changed over time, different sets of more competitive weeds emerged. As a response, farmers changed crops, fallowed fields, and cleared more forest. Farmers were most concerned about Rottboellia cochinchinensis (Lour.) Clayton in fields after fallow, and Imperata brasilinesis Trin., an indicator of land degradation. Older fallow was similar to forest in many respects, although species composition differed. Farmers named useful species across treatments, but counts of these were very low, suggesting high human intervention in the forest and heavy pressure on such species in all land uses. (C) 2000 Elsevier Science B.V. All rights reserved.