Understanding the adaptive basis for age and size-related trends in conifer ecophysiology

white pineThe productivity of forest trees has traditionally been measured by the increase in their trunk wood over time. The result is a near universal trend of decreasing productivity that begins somewhat before the midpoint of a tree’s expected lifespan and becomes stronger as the tree enters an old-growth life-stage. This trend is used by forest managers to determine when trees should be harvested to achieve an expected return on investment, and will be used to quantify the rates of carbon sequestration in determining the value of a forest in a future carbon-credits market. The classic approach of measuring forest productivity by stem wood increment suggests that young forests, harvested near their peak of stem wood production, maximizes use of forest land for both purposes. The down side of adopting the classic model is that forests composed largely of younger trees lack many old-forest characteristics required by many species of plants and animals, and may decrease outputs of ecosystem services such as water resources, recreation and non-timber products. However, recent findings suggest that the classic stem-increment approach is an incomplete metric of tree productivity and simply results from a shift in the carbon allocation priorities of older or larger trees, which may retain high levels of productivity for decades or even centuries beyond the age of maximum stem wood production rates. This project examines the shifting carbon allocation patterns as conifer trees, the major commercial component of Maine’s forest, age. Understanding these trends will allow biomass production and carbon sequestration models to accurately reflect the true productivity value of old forests and silvicultural management systems that retain older and larger trees as components of uneven-aged forests. Additionally, this project will provide an understanding of the seasonal dynamics of carbon reserves in red spruce, one of the most important timber species in Maine and adjacent states. A clear picture of annual carbon dynamics will permit a better assessment of the impacts on this species of climate change and seasonal climate shifts. Analysis of stress resistance through age/size specific allocation strategies will describe age/size differences in the ability of red spruce to withstand drought and other abiotic and biotic stresses. In combination, the results of this research will translate into a better understanding of the effects of harvesting approaches on different age/size-classes of red spruce, and provide a physiological basis directing further advances for understanding and even manipulating the genomic and hormonal systems that control age/size-related trends.

Investigator: Day, M.

Unit: School of Forest Resources

Termination Date: 30-Sep-16