Retrofitting is the process of using primary data from independent experiments to test hypotheses beyond the scope of the original studies. We used this approach to compile and analyze data from long-term silviculture experiments on several USDA Forest Service experimental forests. These studies originated between the 1920s and 1950s and were designed to address management problems in specific forest types. Criteria such as study duration and management history were used to select candidate sites in the northeastern quadrant of the U.S., resulting in five sites with more than 100,000 tree records spanning eight decades, five ecoregions, and a gradient of site conditions. These data were stratified and subset to answer the questions: What are the relative influences of climate, silviculture treatment, and site on net aboveground biomass increment? What are the carbon sequestration implications of these findings?
Results/Conclusions
We found a range of important influential factors that varied by treatment, including diversity, composition, density, and climate in unmanaged forests and density and climate in managed forests. These results suggest that management treatment simplified the influential factors on growth and therefore live-tree carbon sequestration. Climatic factors were important in all models, but the positive effect of favorable growing environment was greater in managed forests. Specifically, the climatic factor mean annual precipitation had a greater positive influence on net aboveground biomass increment in managed than unmanaged stands. This may reflect management-induced changes in competitive relationships affecting resource use. Given the difficulty and expense of collecting and maintaining long-term data from manipulative studies, the value and need for retrofitting will likely increase with time. This work demonstrates the potential of synthesized long-term data from silviculture experiments to broadly address questions related to the functioning and management of forest ecosystems, such as biomass increment and carbon sequestration, and is generally applicable to other sites and fields of study.