Browsing damage in planted silver birch (Betula pendula Roth) stands

Abstract

Herbivory is a source of damage for Fennoscandia commercial stands. Silver birch (Betula pendula Roth) plantations are of increased interest to address the climate and biodiversity crises, but there are concerns about browsing risk. We inventoried 92 planted silver birch stands from a survey focused on browsing variables (e.g. symptom, severity, cause, and position), and one on tree measurements. We estimated ungulate density from national surveys and pellets observation. We assessed landscape characteristics (neighbouring land use/land cover classes and distance to roads). We observed considerable browsing risk for silver birch plantations, with 38 ± 35% and 23 ± 19% of planted birches browsed in younger and older stands, respectively, with mean height <5 and >5 m. Moose were considered responsible for almost half of browsing (44%), while other species accounted for a small amount (4.1%), the majority by unidentified cervids. Especially, crown damage in younger stands developed into vertical branches in older stands, leading to low stem external quality. In a model predicting the number of browsed stems at stand level, damage occurrences were dependent only on stand characteristics and abundance of browsing animals. Our analysis could not provide site selection recommendations for lower browsing risk sites. However, avoiding early damage seems the most crucial step.