functional attributes, deforestation, edge effect, phenotypic plasticity, land use

Riparian forests are critical in protecting biodiversity and water resources and are a priority for conservation in anthropized landscapes, but fragmentation associated with the expansion of agriculture in the tropics threatens their ecological integrity. In this context, we compared the structure, diversity, and functional attributes of tropical riparian forests within intact watersheds (n=4) and in agricultural landscapes (n=6) in a region of intense soybean production in the southern Brazilian Amazon. We studied riparian forest plots distributed in ten watersheds, ranging in width from 120 to 210 m, with forests in agricultural landscapes maintained to comply with Federal Law 12.651, which deals with the protection of native vegetation. We found that riparian forests in agricultural landscapes had fewer tree and sapling species and had higher proportions of opportunistic and pioneer tree species compared to intact riparian forests. We also found greater variation in tree species composition and greater internal dissimilarity in areas in agricultural landscapes compared to intact forests. Forests closer to streams in agricultural landscapes and watersheds with intact forests were more similar to each other. We analyzed 123 species for their functional attributes, with 52% common to both environments, 27% restricted to agricultural landscapes, and 21% to intact forests. Leaf thickness and potassium concentration were the functional attributes with the greatest phenotypic plasticity for species common to both environments. Species restricted to intact forests had greater specific leaf area compared to species restricted to agricultural landscapes. We further note that in intact forests species tend to adopt acquisitive strategies and in forests situated in agricultural landscapes resource-conservative strategies predominate. Our results suggest that in agricultural landscapes, wider strips than required by Law would be necessary to maintain the structure, diversity, and functional attributes of riparian forest tree species in southern Amazonia. Thus, the minimum 30 m riparian strips required by the Law may therefore be insufficient to prevent long-term changes in the composition, structure, and functional attributes of these forests.