Book excerpt: Forests constitute a significant global carbon sink that continues to expand in size, in addition to supporting a range of environmental, economic, and social co-benefits. Forests interact with the overlying atmosphere through exchanges of carbon, water, and energy, and because of the climatic relevance of these fluxes, processes related to terrestrial ecology and land use have a considerable impact on global climate. The comparatively large size of the forest carbon sink in combination with the complimentary climate feedbacks it provides give it significant potential as an avenue for climate mitigation through management practices designed to enhance carbon sequestration. However, anthropogenic management and shifting environmental conditions due to climate change modify forest structure and function, which fundamentally alters land-atmosphere exchanges and the resultant feedbacks with climate. Gaps remain in our understanding of how forest management, structure, function, and climate change interact across long timescales, and whether relationships are spatially dependent, particularly with regards to vulnerabilities of forest function to climate change. These knowledge gaps manifest as substantial uncertainty surrounding the future of the terrestrial carbon sink and other ecosystem services, and the viability of improved forest management as a climate mitigation strategy hinges on addressing these uncertainties. Here, we sought to address three overarching questions: 1) What is the mechanistic relationship between forest structure and function? 2) What is the primary driver of future shifts in forest function? And 3) How does management impact the stability of forest function in the face of climate change? Observational data from the Chequamegon Heterogeneous Ecosystem Energy-balance Study Enabled by a High-density Extensive Array of Detectors 2019 (CHEESEHEAD19) field campaign was used to construct simplified models of the mechanistic relationships between forest structure and function and evaluate spatial dependence. We found that the mechanistic relationship between forest structure and function is mediated by resource use efficiency, is dependent upon the spatial resolution used to calculate structural complexity metrics, and that structural metrics representing the degree of vertical heterogeneity are the most influential productivity drivers for heterogeneous temperate forests. Next, a process-based model was employed to simulate multi-decadal projections of vegetation demographics in response to management, using data from National Ecological Observatory Network (NEON) core terrestrial sites in two U.S. regions. Additionally, downscaled global climate model (GCM) output under two future radiative forcing scenarios (RCP4.5 and RCP8.5) was used to drive model meteorology, allowing for the approximation of vegetation responses to shifting climatic conditions, and facilitating understanding of how management might moderate those responses. With this approach, we showed that management is the strongest driver of future variability in forest function at the regional scale, but that at broader spatial scales gradients in future climate become critical. The narrow precedence of climate over management as a driver of forest function at the sub-continental scale suggests that their effects are likely not independent of one another. We also found that temporal stability is driven primarily by climate, while resilience is shaped by management, but that the impact of management on forest functional stability is regionally dependent and varies by management intensity and severity. These findings allow us to improve representation in ecosystem models of how structural complexity impacts light and water-sensitive processes, and ultimately productivity. Improved models enhance our capacity to accurately simulate forest responses to management, furthering our ability to assess climate mitigation strategies. Additionally, these findings highlight the regional dependency of the response of forest function to management and climate change, and caution that the same management approach is not necessarily viable everywhere, meaning that the durability of management related Nature-based Climate Solutions have to be assessed at the regional scale. This information can help forest managers evaluate trade offs between ecosystem goods and services, assess climate risks of applying management practices in different regions, and potentially identify specific components of ecosystem function to bolster through targeted management practices.