Beyond carbon: The net climate impact of forested, agricultural, and residential land cover in a suburbanizing landscape

Background/Question/Methods

Policy initiatives aimed at offsetting climate change through land management typically promote carbon sequestration through practices such as no-till agriculture and forest protection.  Often not considered is that these practices bear climate consequences through other mechanisms.  Carbon stored in untilled soils can result in higher emissions of greenhouse gases like nitrous oxide, while forest preservation results in lower albedo tree canopies as compared to residential lawns.  Our goal was to go beyond this carbon-centric approach and quantify the net climate impact of forested, agricultural, and residential land cover, considering greenhouse gas emissions, albedo, and surface heat exchange, as well as carbon stocks.  The research took place in a 12 × 12 km, multiple land use, suburbanizing landscape surrounding Durham, NH, USA.  It combined field measurements, remote sensing imagery, and process based modeling to make spatially continuous estimates of carbon pools, greenhouse gas emissions, shortwave surface albedo, and surface heat flux.  Each of these variables was converted into a common radiative forcing unit (W m^-2) to determine how agricultural, residential, and forested land cover influences climate. 

Results/Conclusions

Our measurements and models outputs indicate that forests are net sinks of greenhouse gases—including carbon—while pastures and cultivated fields are net sources.  However, the picture becomes more complicated when also considering albedo.  Forest-to-lawn or forest-to-pasture conversion releases greenhouse gases but also results in higher albedo surfaces that can offset these emissions, even 100 years following deforestation.  Overall, our findings suggest that biophysical factors such as albedo influence climate forcing at least as much as biological processes such as carbon storage and greenhouse gas emissions. As a result, the current policy focus on carbon sequestration may be too narrow for developing comprehensive approaches for mitigating climate change across mixed land use landscapes.