Abstract
Moose browsing is a major source of damage in Swedish forests. Tree growth is stunted and trees can be deformed when apical shoots are browsed. Positive correlations between moose browsing and insect herbivory exist but the combined effect on trees has not been quantified. Whether the frequency and severity of combined effects of several pests on trees will change with global change is unknown. We intend to study the combined effects of moose browsing and insect herbivory on trees by using an existing field experiment with moose exclosures run by Holmen AB. The experiment will be used to quantify (1) the combined direct effect of moose browsing and insect herbivory on tree growth, (2) the indirect effect of moose browsing on insect diversity, damage and performance through plant quality, (3) the effect of habitat modification by moose on insect mortality rates. In addition, long-term data collected by Skogsstyrelsen on moose damage in Sweden will be used to address (1) and (2) in gradients of moose browsing and site productivity. We will use two study systems; birch - winter moth and pine - pine sawfly. Additionally, we will collect data on fungal pathogen damage in the sites, to establish whether moose-insect-pathogen damage act together in stunting tree growth. The overarching goals are to bring forward knowledge on tree responses to multiple biotic stressors and provide forest owners with information for decision-making regarding forest management.
Sweden