CAREER: Land Use and Environmental Controls on Soil Carbon in Human-Dominated Tropical Landscapes

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One of the major uncertainties in predicting changes in earth's climate is how one of the world's largest terrestrial carbon reservoirs, soils, responds to environmental change. Changes in land use and land cover, such as deforestation for agriculture or pasture use, or forest regrowth after agricultural abandonment, affect the exchange of carbon between soils and the atmosphere, with implications for climate and soil fertility. Past human activities can influence the quantity and dynamics of carbon in soils. Despite this, and the fact that an increasing proportion of the Earth's surface is covered by human-modified landscapes, few regional-scale assessments of soil carbon incorporate historical land use. This project will focus on how historical and environmental factors affect how much carbon is stored in tropical soils and its vulnerability to disturbance. Tropical regions are experiencing dynamic changes in land cover and increasing human population growth, yet our understanding of how tropical soils respond to global change is limited to few soil environments which are not representative of the global tropics. The proposed field research will take place in the U.S. Caribbean island of Puerto Rico. Puerto Rico is a model system to study interactions between environmental and human factors in the tropics because it represents a diversity of climatic regions, ecosystem and soil types. The proposed educational activities will provide students with interdisciplinary research and career skills training and field experience and will increase participation of underrepresented communities in geography and the geosciences, in particular women and Hispanic students. Collaborations with agency scientists will facilitate broad dissemination of research results to managers and policymakers. This project aims to measure legacy effects of past human activities on tropical soil carbon dynamics by taking advantage of an extraordinary natural laboratory in Puerto Rico with a rich diversity of geologic substrates, precipitation gradients, and well-documented land-use history. The project will quantify carbon storage (amount and turnover) under different land uses across environmental gradients with a long history of human management through the collection of new data and integration of archived data to increase the geographic representation of tropical soil environments. The project will evaluate the magnitude and persistence of historical land use legacy effects on soil carbon with time across different soil types using carbon isotope depth profiles and field chronosequences. Improved mechanistic understanding of the effects of soil type, climate and land use on soil organic matter retention to will be accomplished through physical fractionation approaches that investigate the sensitivity of different soil carbon pools to disturbance and the use of natural abundance radiocarbon isotopes to measure carbon storage effectiveness. The research and educational activities will provide students with training in field, lab, geospatial and data analysis skills. The integration of research and educational activities will create new opportunities for collaborations between social and physical scientists, especially through the development of a mixed-methods field course focused on environmental challenges in human-dominated tropical landscapes.