Green infrastructure maintenance is more than land cover: Large herbivores limit recruitment of key-stone tree species in Sweden

Due to anthropogenic alteration of stand composition and landscape pattern in Swedish forest landscapes managed for industrial wood production, remnant patches of deciduous forests and woodlands do not form a functional green infrastructure for biodiversity conservation. We assessed if large herbivore browsing hampers the restoration of deciduous forest as green infrastructure by reducing the recruitment of boreal and temperate deciduous tree species of particular importance for biodiversity conservation. A natural experiment approach was applied in the distinct Swedish temperate-boreal forest gradient in Sweden. We measured the potential for saplings of aspen, rowan, sallow and oak to become recruited into the population of ecologically mature trees, as well as the amount of tree and field layer food. Sampling was made in forest stands representing four strata of managed forest landscapes accessible to large herbivores (experiment) and human settlements avoided by large herbivores (control). All four focal deciduous tree species had lower damage levels in controls (towns and villages) compared to experimental (forest) sites. While tree forage was much more abundant in controls, field layer forage in controls was not different from experimental stands. For all tree species except aspen we found a positive relationship between damage levels and large herbivore abundance, to which moose contributed > 89%. We discuss the role of research design for assessing the impact of large herbivores on plants, and highlight the need for integration of multi-species wildlife management as well as conservation planning and management.