How is carbon affected by active forest management for old-growth forest conditions?

Background/Question/Methods

Changes in forest carbon (C) associated with ecological restoration activities in temperate rainforests are poorly understood. Management practices restoring late-seral forest conditions in southwest Washington, represent an opportunity to examine how active management can interface with forest C dynamics. Forest thinning can accelerate development of structural complexity toward old-growth conditions, but could paradoxically reduce C storage in forests. Here, we model 100 years of change in forest C using the Forest Vegetation Simulator (FVS) in combination with fourteen-year repeat measurements of aboveground forest conditions and soil organic matter (OM) at the Ellsworth Creek Preserve, WA (USA). The repeat measurements were used to refine model behavior and generate forecasts of forest C in control and active management basins. We hypothesized that 1) aboveground C storage would remain depressed under active management; 2) soil OM C would decrease in managed plots, driven by the removal of forest litter inputs; and 3) the magnitude of soil OM losses would be greater in younger stands, due to C losses from soil respiration being greater than C uptake from regrowth.

Results/Conclusions

Preliminary results show reduced C pool aboveground in most active management scenarios, and reduced soil OM C in response to thinning operations. A comparison of soil OM depth and mass from 2022 field measurements similarly suggests reduced OM C in soils. Our results highlight the trade-offs of ecological restoration practices and elucidate stand conditions that favor preservation of soil OM C in western temperate rainforest systems. Additionally, these findings illustrate the need for improvements in modeling capabilities, especially regarding soil properties and forest C dynamics.