Road building in South America is difficult to monitor, both because of the rate at which roads are constructed, and because new roads are often built, legally or illegally, without the support and oversight of local governments. With high growth rates of the road network in Brazil expected to continue for the next 30-40 years, understanding the environmental impacts of road building is important in informing regulation or advocacy efforts. The objective of this study was to explore how road building in tropical forest ecosystems impacts the water stress of nearby vegetation. We combined a previously compiled dataset on roads built in the Brazilian Amazon between 1982 and 2012 with remotely sensed estimates of canopy leaf water content expressed as the Normalized Difference Water Index (NDWI) in a paired-plot design for areas directly adjacent to roads and areas more distant from the road network to provide a reference condition. Using Google Earth Engine, we explored the effective impact distance of roads, road building in different land use types, differential impacts based on road type, and temporal changes to NDWI adjacent to roads.
Initial results suggested that road edge impacts are observable to a distance of 150 meters, and that a reference area from 150 to 500 m is appropriate. Applying these buffer distances to a larger subset of roads, we compared roads built in ecological stations, national parks, state parks, biological reserves, extractive reserves, and unprotected areas. The largest apparent impacts were from roads built in national parks and extractive reserves. Looking at roads across Brazil built in these two land designations, we found significant changes (p < 0.05) to the relationship between adjacent and reference NDWI values when comparing pre-road conditions (more than 3 years before road building) with the post-road condition. This suggests that road building may act as a catalyst for impacting plant water stress on adjacent areas. These results have implications for road building and management in Brazil, and suggest that roads should be routed around parks and extractive reserves when possible. Additional work is warranted to utilize Google Earth Engine to explore other landscape changes associated with Brazilian road construction.