Over the past millennium, more than half of the globe’s natural vegetation has been transformed by humans for agriculture, forestry, and other land uses. This reconfiguration of the Earth’s surface has changed the composition of the atmosphere, the planetary energy balance, and as a result, the climate. The associated changes in temperature and precipitation patterns will continue to have cascading impacts on terrestrial ecosystems through a myriad of interrelated mechanisms. Opportunities exist for preparing more climate-resilient ecosystems and employing land in climate mitigation efforts. In this dissertation I quantify the causes, consequences and solutions associated with radiative forcing and land use change. In Chapter 1 I provide a comprehensive regional assessment in southwest Michigan, USA, of the radiative forcing, or climate impacts, of both historical land use change and the adoption of nature based climate solutions ranging from conservation agriculture to managed forestry and natural forest regeneration. I found that the globally significant radiative forcing caused by historical deforestation of the region (1851 +/- 71 μW m-2) can be partially mitigated by the adoption of conservation agriculture (0 to -62 +/- 50 μW m-2), managed forestry (-322 to -674 +/- 71 μW m-2), and natural forest regeneration (-1359 +/- 71 μW m-2). In Chapter 2 I quantify the response of soil greenhouse gas fluxes to projected climate changes by experimentally increasing precipitation variability or inducing a growing season drought across conventionally tilled row-crops, no-till row-crops and an early successional plant community. I found that the resulting changes to soil water content were largely able to predict the responses of soil N2O and CH4 fluxes, but that CO2 fluxes exhibited higher than expected emissions following pulse rewetting events. The overall finding is that increased precipitation variability and drought caused equal or reduced radiative forcing, respectively. In Chapter 3, I present a mechanistic understanding of the response of atmospheric nitrogen fixation in legumes to increased precipitation variability and drought. Using stable isotope techniques, leaf level gas exchange measurements, remote sensing and soil microbial assays, I found that plant and microbial nitrogen cycling were resistant to increased precipitation variability, but not to drought. Chapter 4 focuses on a climate change solution called bioenergy with carbon capture and storage. I compared three common methods of quantifying the net ecosystem carbon balance of the fields where bioenergy crops were established, namely 1) eddy covariance flux measurements, 2) plant and soil carbon inventories, and 3) a process-based ecosystem model. I took these different estimates and put them in the context of the other radiative forcing budget components, namely, soil N2O and CH4 fluxes, land surface albedo, farming-related fossil fuel emissions, and geologically stored carbon from the bioenergy processing facilities. I found that each method agreed that bioenergy with carbon capture and storage can provide significant negative radiative forcing, or cooling effects, but that methods sometimes did not agree on the magnitude of this effect. While this work highlights the complex and nuanced relationships between land and climate, it also shows how resilient ecosystems can be to some climate extremes as well as how nature can play a significant role in cooling the Earth.
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