Risk of bark beetle damage in relation to forest management practice

I projektet undersöks kopplingen mellan utbrott av granbarkborre och olika alternativa skogsskötselmetoder. Målet är att ge skogsägare underlag för hur skogen kan skötas för att minska risken för framtida angrepp.

The outbreaks of the spruce bark beetle after drought or storm-felling makes damage as unpredictable as the weather event it follows. As it is a notorious outbreak species in Europe, researchers follow population developments in response to climate change. Observations show more frequent and larger outbreaks in the most recent decades. Following last year’s drought, the spruce bark beetle has reached outbreak levels killing more trees during an individual year than during any other outbreak in recent history in Sweden.

Forestry in Sweden is changing toward more variation rich forest management. From an ecological perspective, this could decrease susceptibility to abiotic and biotic disturbances, such as insect outbreaks. Research shows that increased variation can lead to higher predation and stronger tree defence, thus lowering survival of pest species. We propose to investigate the performance of the spruce bark beetle in relation to alternative forest management methods.
Mixed and uneven-aged forest stands are ecologically more diverse in tree species, understory and age structure than even-aged monoculture stands. More diverse stands are expected to support higher and more stable populations of generalist predators, potentially leading to better pest control and less dramatic population increase following disturbances. Similar effects on pest control are expected from trees having stronger defences in more diverse stands due to lower intraspecific competition. We aim to test the relationship between stand type and spruce bark beetle abundance, tree defence and natural enemy abundance and efficiency.

Our project will provide arguments for risk management using different types of forest management. It will inform us about the underlying mechanisms, thus about the potential to suppress bark beetle populations in different forest types. Our findings will help the forest owner to make decisions reducing the risk for spruce bark beetle outbreaks in the future.