Hoover, Coeli (USDA-Forest Service, Forestry Sciences Lab, PO Box 640, Durham, NH, 03824; Phone: 603-749-1477; Email: choover@fs.fed.us)

Thinning and Carbon Sequestration in Allegheny Hardwoods: Results from One Thinning Cycle

C.M. Hoover*

Ongoing climate change negotiations have focused attention on the role of forests in the global carbon cycle; this role is also important in international sustainability agreements such as the Montreal Process. Consequently, understanding the effects of management on forest carbon cycles is a high priority. Thinning forest stands is a commonly employed silvicultural technique that is used to achieve a variety of objectives: concentrating resources on selected stems, improving stand structure, and improving species composition, among others. This analysis uses data from one thinning cycle of a large study in Northwestern PA. Fourteen plots in five blocks of the study were used: seven unthinned control plots, and seven plots thinned to 60% relative density. Twelve plots were in the Allegheny hardwood forest type (cherry-maple), while two plots were in stands dominated by sugar maple. Age at thinning ranged from 50-80 years since establishment; all plots are located in even aged stands. Different blocks of the study were established in different years; this study presents the results from the first fifteen years since thinning in each block, regardless of date of establishment. Carbon stocks were estimated for each five year period for the following pools: aboveground biomass of woody stems (greater than 2.5 cm dbh), coarse root biomass, dead aboveground biomass, logging slash, and products. From the carbon stock estimates, average annual change over the fifteen year study period was also computed for each stand. Carbon stocks in thinned plots were less variable across study blocks than carbon in control plots and less biomass was lost to mortality in thinned plots, indicating that the treatments were achieving their primary objectives. All plots had positive values for average annual change in carbon stocks, demonstrating that carbon was sequestered. However, the average increase in carbon stocks was lower in thinned stands than control stands, indicating lower carbon sequestration rates. The plots will continue to be inventoried as stand age increases and the second thinning cycle is entered, providing a more detailed picture of the effects of thinning treatments on carbon sequestration in Allegheny hardwood stands.