Tamm review: Does salvage logging mitigate subsequent forest disturbances?

Abstract

After natural forest disturbances such as wildfires, windstorms and insect outbreaks, salvage logging is commonly applied to reduce economic losses and mitigate subsequent disturbance risk. However, this practice is controversial due to its potential ecological impacts, and its capacity to mitigate or increase the risk of subsequent disturbances remains unclear. Salvage logging removes and alters the legacies remaining after natural disturbances, and it produces additional management legacies. Consequently, salvage logging has the potential to alter the functional connection between natural disturbances and also produce new functional connections to additional disturbances. We reviewed the efficacy of salvage logging in mitigating the risk of subsequent wildfire, insect outbreaks, hydrologic disturbances, mass movements, windthrow, browsing, and microclimatic stress. We asked: (1) Does salvage logging modify resistance to subsequent disturbances? (2) Through what mechanisms do such effects operate? Based on 96 publications, salvage logging can reduce total ecosystem fuels but increase small ground fuels and produce drier fuels in the short term, reduce bark beetle host trees and beetle-tree connectivity (though with little evidence for outbreak mitigation), magnify erosion and flood impacts of disturbance but with uncertain watershed-scale implications, increase susceptibility to windthrow at artificially created stand edges, remove the protective function of deadwood in preventing rockfall and avalanches, alter browsing pressure by modifying forage availability and hiding cover for herbivores and predators, and increase microclimatic stress due to greater radiation and temperature fluctuations. We propose a decision-making framework to evaluate the suitability of salvage logging to manage subsequent disturbances. It contemplates the likelihood and impacts of both salvage logging and the subsequent disturbances. In summary, salvage logging does not necessarily prevent subsequent disturbances, and sometimes it may increase disturbance likelihood and magnitude. Forecasting the suitability of salvage logging for management goals requires assessing the mechanisms through which salvage logging effects operate under local conditions, balanced with its impacts as a disturbance itself. Managing to foster the highest-priority functions and services –such as biodiversity conservation, pest mitigation or economic return– across different parts of disturbed forest landscapes based on decision-making procedures such as the one proposed may constitute the best response to uncertain subsequent disturbances.