Impacts of browsing on regeneration and recruitment of palatable broadleaves in boreal forests

Ungulate browsing is widely regarded as a major constraint on the recruitment of broadleaves important as carriers of biodiversity. Here, we combine observational data from 123 Moose Management Areas (MMAs) and 30 experimental exclosure pairs to evaluate the recruitment targets set by the Swedish Forest Agency and Swedish Environmental Protection Agency for rowan (Sorbus aucuparia), aspen (Populus tremula), willows (Salix spp.), and oaks (Quercus spp.) (RAWO) in Swedish moose management. We investigated goal fulfilment and predictors of recruitment using national monitoring data. Targets were met for only ∼20% of Sweden. Site productivity (+) was the strongest predictor of recruitment, while moose and deer densities had little influence. Experimental exclusions of browsers primarily affected the transition of seedlings into competitive size classes, not initial establishment, with growth stalling after the first 3–4 years when browsers were present. In an experiment on intermediate-productivity soils, RAWO grew slower than pine and recruitment fell below targets, even in exclosures without ungulate browsing. In a second experiment on high-productivity soils, browsing constrained RAWO growth but competitive RAWO stem density remained well above the target, even with browsing. Without browsing, combined measures of RAWO kept up with conifers. Responses to browsing and competition differed between RAWO species, such that rowan, willow and oak were more affected than aspen. Our results indicate that while browsing limits RAWO recruitment, site productivity and competition are also important. We suggest that the current quantitative targets may have little relevance and may be inappropriate for setting harvest quotas in MMAs in Sweden.