Abstract
AbstractForest management practices emphasizing stand 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 part of a long‐term study evaluating silvicultural treatments that promote late‐successional forest characteristics in northern hardwood‐conifer forests. We are testing the hypothesis that aboveground biomass development (carbon storage) is greater in structural complexity enhancement (SCE) treatments when compared to conventional uneven‐aged treatments. Structural complexity enhancement treatments were compared against selection systems (single‐tree and group) modified to retain elevated structure. Manipulations and controls were replicated across 2‐ha treatment units at two study areas in Vermont, United States. Data on aboveground biomass pools (live trees, standing dead, and downed wood) were collected pre‐ and post‐treatment, then again a decade later. Species group‐specific allometric equations were used to estimate live and standing dead biomass, and downed log biomass was estimated volumetrically. We used the Forest Vegetation Simulator to project “no‐treatment” baselines specific to treatment units, allowing measured carbon responses to be normalized against differences in site characteristics affecting tree growth and pre‐treatment stand structure. Results indicate that biomass development and carbon storage 10 yr post‐treatment were greatest in SCE treatments compared to conventional treatments, with the greatest increases in coarse woody material (CWM) pools. Structural complexity enhancement treatments contained 12.67 Mg/ha carbon in CWM compared to 6.62 Mg/ha in conventional treatments and 8.84 Mg/ha in areas with no treatment. Percentage differences between post‐treatment carbon and simulated/projected baseline values indicate that carbon pool values in SCE treatments returned closest to pre‐harvest or untreated levels over conventional treatments. Total carbon storage in SCE aboveground pools was 15.90% less than that projected for no‐treatment compared to 44.94% less in conventionally treated areas. Results from classification and regression tree models indicated treatment as the strongest predictor of aboveground C storage followed by site‐specific variables, suggesting a strong influence of both on carbon pools. Structural enhancement treatments have the potential to increase carbon storage in managed northern hardwoods. They offer an alternative for sustainable management integrating carbon, associated climate change mitigation benefits, and late‐successional forest structure and habitat.
Highlights
Forests globally function as a significant carbon sink, storing ~45% of terrestrial carbon (Bonan2008), yet are a leading source of carbon emissions due to deforestation and forest degradation (Keith et al 2009)
Carbon responses post-treatment Our results support the hypothesis that structural complexity enhancement (SCE) carbon recovery 10 yr post-treatment would be greatest relative to pre-treatment or no-management baseline values when compared to conventional treatments
Carbon stocking in aboveground biomass pools in northern hardwood forests has the potential to increase with silvicultural prescriptions that retain elements of stand structure, increase horizontal and vertical complexity, and elevate the availability of coarse woody material (CWM)
Summary
Forests globally function as a significant carbon sink, storing ~45% of terrestrial carbon (Bonan2008), yet are a leading source of carbon emissions due to deforestation and forest degradation (Keith et al 2009). It is widely acknowledged that forest ecosystems of greater maturity and structural complexity maintain high levels of carbon storage (Harmon et al 1990, Luyssaert et al 2008, Keeton et al 2011, Gunn et al 2014), there is ongoing debate regarding the effects of different silvicultural approaches on carbon storage (Ruddell et al 2007, Thomas et al 2007, Nunery and Keeton 2010). We quantified aboveground biomass and carbon storage in northern hardwood-conifer forests over a 10-yr period following an experimental silvicultural treatment, called structural complexity enhancement (SCE), and determined how this compared both to conventional selection harvesting systems and passive (no-harvest) management. This study provides an opportunity to validate earlier projections (Keeton 2006) and other model simulations (Nunery and Keeton 2010) using empirical data
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