The effects of harvest practices and intensity on carbon sequestration in Douglas-fir forests of western Washington, USA

Background/Question/Methods

Managing forests for multiple ecosystem services including carbon (C) storage is of interest to forest managers, conservation groups, and ecologists.  Quantifying C is challenging but provides a potential alternative to revenue from timber extraction through the sale of C credits. This study quantifies C sequestration associated with various forest management practices. We used stand level survey data from nearly 400 plots measured across a 1,740-hectare forest in western Washington to initialize simulated stands.  Stand-by-stand forest growth projections and simulated harvest were forecasted 30 years into the future under different management scenarios using the Forest Service Forest Vegetation Simulator (FVS).  Scenarios included: a regional common practice of clearcut harvesting with a 45-year rotation; 65- and 105-year rotations based on the Forest Stewardship Council’s (FSC) Pacific Coast Standard (requiring 10 or 30% basal area retention and green-up and harvest restrictions); a thinning only prescription, and a no harvest scenario. Multi-objective optimization was used to maximize net present timber value, while constraining the harvest schedule to increase C above the baseline across a 30-year period.  Carbon was calculated using FVS outputs and allometric equations specific to species and region sorted by: above- and below-ground biomass, snags, woody debris, and harvested wood products.

Results/Conclusions

A baseline inventory of 305 Gg C was determined and all forest planning scenarios increased C-storage due to model constraints. The profit maximizing scenario, using clearcut harvests on a 45-year rotation, sequestered 353 Gg of on-site C (GgC) forest-wide over the 30-years. Less intensive management regimes sequestered increasing amounts of C: FSC-65 y rotation (388 Gg), FSC-105 y rotation (406 Gg), thinning only (506 Gg), however all were less than the no harvest scenario (528 Gg).   A 45-year rotation clearcut management scenario where an additional 40.5 hectare habitat reserve was established sequestered as much C (389 Gg) as the FSC-65 year rotation scenario but with much greater projected timber revenue.  The FSC-105 scenario provided essentially a break-even scenario while the thinning only scenario results in negative cash flow, indicating surprising trade-offs between management practices, revenue streams, and C sequestration. Non-production reserves may offer a more efficient way to store C than adherence to less-intensive harvesting practices.