Greenhouse Gas Emissions from Land Use Change in the United States during 1900-2019

Abstract:

Greenhouse gases (GHGs), including mainly CO₂, CH₄, and N₂O, are the major driver of the ongoing climate warming. Terrestrial ecosystems have been intensively studied in terms of their dynamics and underlying mechanisms for acting as a sink or source of the three GHGs and their feedback to the climate system. However, the impacts of anthropogenic activities, especially large-scale land use change (LUC) and management actions, on GHG emissions of terrestrial ecosystems are still highly uncertain. This is partly caused by insufficient long-term observations of land use change effects across multiple types of ecosystems. But more importantly, there still lacks proficient modeling tools that can simulate three GHGs together. Here, we improve the Dynamic Land Ecosystem Model (DLEM) in representing land conversion and the accompanied carbon and nitrogen dynamics and apply it to the contiguous United States to assess the spatial and temporal patterns of LUC-caused GHG emissions during 1900-2019. A particular focus in on the impacts of plantations in the southeast U.S., which rank second in the world in the land area of forest plantation. The results show that deforestation can stimulate short-term GHGs emissions but following cropland or pasture management practices can significantly increase N₂O emissions. Reforestation like plantations can emit more N₂O but absorb more CO₂. This study provides insights into the multifaceted influences of land use change on the carbon and nitrogen cycles.