COS 8-4
Managing northern hardwood forests for carbon storage through structural complexity enhancement: Effects on aboveground carbon pools
Forest management practices emphasizing structural complexity are of interest across the northern forest region of the United States because of their potential to enhance carbon storage. Our research is nested within a long-term study testing how disturbance-based silvicultural treatments affect aboveground biomass development and carbon fluxes in northern hardwood forests. We are testing the hypothesis that biomass development (carbon storage) will be greater in structural complexity enhancement (SCE) treatments when compared to conventional uneven-aged treatments. SCE treatments were compared against selection systems (single- tree and group) modified to retain elevated structure. Manipulations and controls were replicated across 2-hectare treatment units at two study areas in Vermont, USA. Data on aboveground biomass pools (live trees and coarse woody material, standing and downed) were collected pre- and post-harvest then again a decade later in 2013. Species-specific allometric equations were used to estimate biomass. We used the Forest Vegetation Simulator to project “no-treatment” baselines specific to treatment units, allowing measured carbon responses to be normalized relative to differences in site-specific characteristics and pre-treatment conditions. The relative influence of treatment versus alternative sources of variability in carbon responses were evaluated through AIC analysis.
Results/Conclusions
Results suggest that 10 years post-harvest, downed log and standing dead (coarse woody material) carbon pools are significantly (P=0.014) greater in SCE treated areas than in conventionally treated and untreated areas. Structural complexity enhancement treatments contained 12.67 Mg ha-1 carbon in coarse woody material (CWM) compared to 6.61 Mg ha-1 in conventional treatments and 8.84 Mg ha-1 in areas with no treatment. This produced a 66% increase in the amount of CWM carbon in SCE treatments over conventional treatments and 36% increase over areas with no treatment. Total aboveground biomass (live tree and CWM) 10 years post-harvest was 110.88 Mg ha-1 in SCE treatments, 80.80 Mg ha-1 in conventional treatments, and 132.66 Mg ha-1 in untreated controls. Aboveground biomass in SCE units was 17% below that of untreated areas compared to conventional treatment aboveground biomass, which was 49% below areas with no treatment. Top ranked AIC models predicting aboveground carbon storage included treatment as well as site-specific variables, suggesting a strong influence of both on carbon pools. These results suggest the ability of structural enhancement silvicultural treatments to increase carbon storage in aboveground biomass pools relative to conventional treatments. Structural complexity enhancement offers an alternative for sustainable forest management integrating carbon storage, associated climate change mitigation benefits, and late-successional biodiversity.