The Value of Forests to Pollinating Insects Varies with Forest Structure, Composition, and Age

Forests play an essential role in conserving pollinating insects and supporting pollination services in mixed-use landscapes and are particularly important to species that require resources restricted to forests. However, some forests provide higher quality habitat for these organisms than others. The primary objectives of this article are to 1) review how pollinator communities are influenced by changes in forest structure, composition, and age, 2) explore how these patterns differ between conifer and broadleaf forests, and 3) provide recommendations for managers interested in optimizing forest conditions for pollinating insects. Although biodiversity generally increases as forests mature and become more structurally and compositionally complex, patterns exhibited by pollinating insects vary depending on forest type and prevailing disturbance regimes. For example, conifer forests can either sustain pollinator diversity comparable to open habitats or experience reduced pollinator diversity depending on the openness of the canopy. In broadleaf forests, pollinator diversity often increases with age (following the stem exclusion stage) and increasing tree diversity, and diversity in these areas can exceed what is observed in open habitats even under closed-canopy conditions. Such patterns likely reflect the importance of flowering broadleaf trees to pollinators, including many forest-dependent species, and suggest that optimal management practices for conserving pollinators differ between conifer and broadleaf forests. We conclude that: 1) the quality of forests to pollinating insects is a function of forest structure and composition as mediated by forest age and disturbance history and 2) best management practices need to be developed separately for conserving pollinators in conifer and broadleaf forests. Research aimed at better understanding the value of different broadleaf tree taxa to pollinators, especially forest-dependent species, is needed.