Rehabilitation forestry and carbon market access on overharvested, former industrial northern hardwood-conifer forests

Background/Question/Methods

Many former industrial timberlands in the Northeast experienced decades of heavy cutting, including the unsustainable removal of valuable trees with little thought to regeneration. These practices yield immediate monetary returns, but jeopardize long-term forest productivity and ecosystem functioning. Today, thousands of hectares of timberland remain less than fully stocked. Finding economical rehabilitation methods is critical to restoring these forests, yet few studies have examined specific approaches. This study evaluates the effectiveness of 13 distinct rehabilitation treatments on 400 hectares of overharvested timberland in northern Vermont. The overarching goal is to quantify how these approaches impact long-term dynamics and opportunities for carbon market participation. Forest structure and composition were inventoried using 155 prism plots stratified among four 30-246 ha stands. The effects of 13 silvicultural treatments, including different combinations of passive restoration, initial stand improvement cutting, intermediate thinning, and regeneration harvesting were modeled over 100 years using the Forest Vegetation Simulator. Stand structural metrics, carbon sequestration and net present value of timber harvests were compared for each treatment using related measures ANOVA and Tukey’s HSD post-hoc tests. Carbon offset credits were quantified following the specific requirements of the Climate Action Reserve and the American Carbon Registry voluntary offset programs.

Results/Conclusions

An ANOVA comparing the 13 rehabilitation strategies indicates that a long-term strategy of limited or no harvesting achieves significantly (p<0.05) greater carbon storage, averaging 75-94 Mg C/ha over 100 years in live and dead trees and harvested wood products. However, a range of initial actions may be used with this long-term strategy without significantly reducing carbon storage. This includes silvicultural clearcuts and targeted, variable density thinning. While the latter improves stand structure and species composition, it requires substantial financial investment with little or no initial return. The former generates substantial return, but could be in conflict with some offset standards. When offset credits are taken into account, natural recovery becomes appealing because it can generate credits 10-30 years earlier than other treatments. This approach also achieves the greatest total number credits at 222 Mg CO₂/ha when paired with no future harvesting. However, if commercial timber management is a priority then initial recovery followed by low-intensity, individual tree selection harvests can achieve credits of 89 Mg CO₂/ha. Although overharvested forests face distinct challenges, it is possible in some cases to simultaneously restore productivity, generate carbon credits and commercially harvest timber. These results are relevant to thousands of hectares across the Northeast.