A novel view of salvage logging in Europe’s spruce forests

In their recently published research, Laura Dobor, Tomáš Hlásny and colleagues investigate how different levels of intensity in salvage logging affect both bark beetle outbreaks and  landscape-scale carbon storage.

Salvage logging – the removal of trees killed by wind, insects and other agents – is one of the most frequently applied management responses to forest disturbances worldwide. In European Norway spruce forests, salvaging of windfelled trees is often applied to prevent subsequent bark beetle outbreaks. For example, windthrown trees are a highly suitable breeding material for the European spruce bark beetle and often trigger outbreaks.

By preventing bark beetle outbreaks, salvage logging can also conserve carbon (C) in live trees, and thus contribute to climate change mitigation. At the same time, salvage logging removes carbon from the ecosystem and could thus lead to an overall reduction of the C stored in the forest.

European spruce bark beetle - Gilles San Martin
A likely culprit for bark beetle outbreaks. Windthrown trees make great breeding material for the European spruce bark beetle. Photo: Gilles San Martin

Despite the long and large-scale application of salvage logging in forestry, aspects such as their potential to prevent bark beetle outbreaks as well as their effects on C storage remain poorly quantified. We investigated how different salvaging intensities of windfelled trees affect bark beetle dynamics and landscape-scale carbon storage.

We found that climate change resulted in a two- to three-fold increase in bark beetle disturbances throughout the 21st Century. Removing >95 % of windfelled trees can effectively dampen bark beetle infestations and increase the amount of carbon in live trees. However, realistic rates of salvaging (<95 % of windfelled trees detected and removed) had no significant effect on bark beetle dynamics and live tree carbon, and reduced the total carbon stored in the landscape.

Accelerated development of bark beetles under warmer temperatures further compromised the efficiency of salvaging. Furthermore, the intense suppression of bark beetle infestations increased the share of dense and mature Norway spruce forests on the landscape, which, in turn, are more susceptible to future wind disturbances. Hence, positive effects of high-intensity salvaging were partly offset by increasing wind disturbances.

We conclude that salvage harvesting is primarily meaningful in small and concentrated disturbances where very high salvaging intensities are feasible in practice. Considering that an increase in the frequency and size of disturbances due to climate change makes the timely detection and removal of disturbed trees operationally challenging, we conclude that alternative management approaches are needed in the face of changing disturbance regimes.

Read the full article, Is salvage logging effectively dampening bark beetle outbreaks and preserving forest carbon stocks, in Journal of Applied Ecology.

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