In this U.S.-Mexico project researchers from the U.S. and Mexico will gain a preliminary understanding of the consequences of tropical afforestation and its spatial configuration across the landscape for nitrogen cycling, and to identify and model landscapes where plantation establishment is likely to have the greatest impact on nitrogen biogeochemistry. In this pilot study baseline measurements of nitrogen fluxes and nitrogen cycling will be conducted, and the ratios of carbon to nitrogen to phosphorus (C:N:P) in the litter and soils of pine plantations and grasslands will be examined. By quantifying differences in nitrogen cycling between pine plantations and grasslands, the research will shed light on ecosystem response to afforestation, whether natural or intentional, and to increasing levels of nitrogen deposition. Such investigations are needed in order to scale ecosystem process rates such as nitrification across spatially heterogeneous landscapes and to predict watershed nitrogen losses more accurately. This pilot will be carried out by an interdisciplinary team of researchers from two U.S. institutions, the University of North Texas and Cary Institute of Ecosystem Studies, in conjunction with colleagues from Universidad Veracruzana in Mexico.

This project affords a valuable opportunity to answer important questions at the intersection of ecosystem science, global change, and land-cover change. This project should enable the researchers to confirm previous findings and develop a model of the nitrogen-cycling effects of afforestation, especially within the context of land-use change, increased nitrogen deposition from urbanization, and phosphorus-limited forests of tropical developing countries worldwide. The results of this study will provide the foundations for a future international collaborative research proposal that can provide important data for policy makers considering the implications of reforestation and afforestation and the potential trade-offs and unintended consequences of each. Graduate students and early-career scientists from underrepresented groups will benefit from inclusion in these studies with international research partners. Involvement of young researchers in collaborative international activities is a major goal of OISE.

Project Report

Forests within and around urban areas provide multiple environmental benefits to urban residents. Of crucial importance, montane forests maintain water quality by reducing erosion and sediment inputs to streams; they also retain nutrients and pollutants deposited from the atmosphere, such as nitrogen, in vegetation and in soils. Given their role in protecting urban drinking water supplies and aquatic ecosystems, montane forests around the world are being targeted for conservation and restoration. However, as urban areas continue to expand, so do nitrogen emissions and deposition, with potentially negative effects on soils and streams. In this study, researchers investigated the effects of nitrogen deposition on nitrogen cycling in Atlantic montane forests in southeastern Brazil. Although more than 85% of this ecosystem has been cleared, streams draining Atlantic montane forests still supply drinking water to millions of urban residents in São Paulo and Rio de Janeiro metropolitan areas. In this study, nitrogen inputs, soil nitrogen availability, and indices of soil leaching losses were measured in forests in and around Rio de Janeiro: (1) on an island 100 km west of Rio de Janeiro; (2) in the coastal city of Rio de Janeiro; and (3) in a protected area 40 km inland from Rio de Janeiro. Contrary to expectation, the researchers found that the protected national forest inland of Rio de Janeiro received nearly two times more nitrogen than both the urban and island forests, highlighting the vulnerability of protected areas to urban air pollution. Several indicators showed, however, that nitrate losses from the urban and downwind forests were similar and far higher than those measured at the island forest. This finding suggests that chronic exposure to nitrogen pollution from urban areas decreases the capacity of forests to retain nitrate, which is likely to end up in surface waters. Overall, findings from the study show that forests closer to urban areas––under higher levels of N pollution––exhibit clear alterations in N cycling. This project contributed to the development of new international collaborations and broadened participation in science by involving several undergraduate and graduate students and technicians from underrepresented groups.

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Institute of Ecosystem Studies
United States
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