Longterm recovery of ecosystem services reveals non-linear tradeoffs following forest harvest
Management of ecosystem services (ES) requires understanding the interactions among multiple services, and how these interactions change over time. Coastal temperate forests provide a model system for studying long-term ES interactions such as tradeoffs from timber harvesting. Timber harvesting provides near-term services (such as wood products), but can be responsible for declines in other services such as carbon storage or wild edible foods, which may take decades or even centuries to recover. We used a 250-year forest chronosequence dataset in a novel way to estimate long-term post-harvest recovery of eight ecosystem services on Vancouver Island, BC, Canada. We estimated ES using forest structural attributes and quantify their non-linear recovery trajectories using generalized additive models. Our main objective is to determine at what rate and along what trajectory do multiple ecosystem services recover following forest harvest. ES examined include: wood volume, carbon storage, large heritage trees, large cedar trees for First Nations carving, snags, coarse woody debris, habitat for species-at-risk as well as wild edible berries. We expected ES recovery trajectories to be unique for each service and to depend on the known processes of forest development that unfold over decades to centuries following timber harvest.
ES recovered at markedly different rates and along varying non-linear trajectories. Wood volume, snags, and carbon storage recovered along sigmoidal trajectories linked closely to biological rates of biomass recovery. These three recovery curves reached an inflection point after ~65 years; whereas they reached baseline levels at varying times (wood volume = 160 years; snags = 140 years; carbon storage = 212 years). In contrast, recovery of wild edible berries, large heritage trees and habitat for the at-risk marbled murrelet was generally slower and recovered along other trajectories, including u-shaped and delayed sigmoidal trajectories. Our observation of non-linear recovery suggests that tradeoffs from timber harvest change through time as some services recover relatively quickly and other much more slowly. Recognizing these tradeoffs can help inform silviculture or restoration treatments needed to speed recovery of desired services. Evidence of prolonged, persistent tradeoffs among some services support conservation planning for remaining old-growth forests on Vancouver Island and can help managers to plan length of harvest rotations to support the provision of multiple ES valued by society.