Effects of dead wood on arthropods in managed pine forests in Sweden

Sammanfattning: Forests provide humans with a range of valuable ecosystem services, but current forest management practices may increase susceptibility to damage from disturbances such as pest insects. One such practise is the harvesting of residue, which decreases the amount of dead wood in the forest. Dead wood has been shown to be of importance for biodiversity and could decrease vulnerability to biotic disturbances. Sustainable forest management and conservation of biological diversity is required to maintain ecologically healthy forests. I aimed to investigate if biodiversity connected to dead wood could contribute to insect pest mitigation. I sampled ground-dwelling arthropods with pitfall traps in monoculture pine stands in Central Sweden on plots where dead wood had been either added or removed. To relate catches from pitfall traps to predation pressure of pest insects, I used plasticine model larvae to measure the attack rate. Contrary to my expectations, total arthropod abundance was higher when dead wood had been removed. Furthermore, the presence of dead wood had no effect on total arthropod diversity and diversity and abundance of predators. There was no relationship between predator catches and attack rates on plasticine model larvae. My results contradict previous findings that dead wood promotes biodiversity and pest mitigation. This highlights the need for studies targeting the more specific effects of different types of dead wood, in different types of forest stands on specific taxonomic groups and ecological processes, as results do not appear to be uniform across studies.