As global demand for protein and commodity crops increases so will pressures on tropical regions, which contain the largest remaining land pool suitable for the expansion of crop production. By protecting riparian forest buffers at a continental scale, the Brazilian Forest Code (FC) has the potential to mitigate some of the climatic and ecological impacts associated with intensive agricultural production. Here, we evaluate the multi-scale role of riparian forests in maintaining freshwater ecosystem functions by: (1) mitigating the local effects of deforestation on stream temperature and habitat connectivity, and 2) modulating regional climate impacts via evapotranspiration. We used a combination of remotely sensed satellite observations, field measurements, and modeling to investigate how the FC’s riparian forest conservation requirements influence in-stream habitat quality and regional climate. Since the FC prescribes buffer widths based on stream channel width, we first calculated the Strahler stream order based on the Brazilian National Water Agency’s (ANA) stream hydrography data for Brazil. We estimated stream width based on stream order and assigned riparian buffer widths based on FC guidelines for Riparian Preservation Areas. We derived evapotranspiration rates based on published estimates.
Results/Conclusions
Satellite-based measurements indicate that the transition from tropical forest to croplands or pastures increases land surface temperature by 4-6oC. Our field measurements in the SE Amazon’s agricultural frontier confirm that riparian forests play a critical role in buffering small streams against this substantial local increase in temperature by shading stream channels in agricultural watersheds. Clearing of riparian forests can warm headwater streams by as much as 4oC, compared with forested streams. The Brazilian FC protects riparian buffers along an estimated 1.9M km of streams, occupying an area of 155,000 km2. Most of these riparian zones (124,000 km2 along 1.5M km of streams) occur in the Amazon, Cerrado, and Atlantic Forest biomes – the region responsible for the vast majority of Brazil’s agricultural output. These forests have the potential to recycle 166 km3yr-1 of water to the atmosphere via ET, of which the Amazon contributes 64% (107 km3yr-1), the Cerrado 20% (33 km3yr-1), and the Atlantic Forest 8.5% (14 km3yr-1). If fully implemented, the FC could thus protect a forest area larger than the state of Louisiana, helping to buffer regional climate, hydrological connectivity, and freshwater ecosystem integrity over large areas of the agricultural frontier.