Spatio-temporal Patterns of Pollinator Persistence in Temperate Coniferous Forests: Implications for Forest Management and Pollinator Conservation

Abstract

Managed forests may serve as havens for native pollinators. However, very little is known about the abundance, diversity, and distribution of forest pollinators at the landscape-scale necessary to design effective long term conservation strategies. This research aims to shed light on the spatiotemporal dynamics of pollinator communities in response to various managed forest features and seasonal shifts in resource availability, elucidate the pathways pollinators use to move through the forest, and predict long term outcomes of alternative management scenarios. Data were collected using a network of blue vane traps dispersed throughout Gifford Pinchot National Forest – a 1.3-million-acre managed forest in Washington State – sampled bimonthly over the active seasons of most pollinators in temperate ecosystems for three years. To gain finer scale insight into the movement of pollinators through forest environments, I deployed a new method of in situ pollen tracking, applying quantum dot nanotechnology to trace the insect mediated dispersal of individual pollen grains over an extensive and successionally varied forest landscape. Analysis revealed distinct communities emerging at varying spatial and temporal scales, indicating the sensitivity of pollinators to landscape, stand, and within-stand level conditions facilitated by managed forests. Pollinators’ foraging pathways were also influenced by forest landscape structure and exemplified the effective use of quantum dots as pollen analogues and the importance of floral resources to support pollinators in otherwise sparsely populated areas. To understand the practical implications of this research, I used a combination of occupancy and detection models and spatial simulation to characterize the habitat niches of wild bees – an important group of forest pollinators – and predict their presence across virtual landscapes representing alternative harvesting regimes. These simulations revealed that, at the temporal resolution of observed harvest rotations (i.e., 80-100 years), landscapes with large (350 acre) and small (50 acre) harvest patches both displayed a synchronized shift to mid succession forest and wild-bee communities exhibited a similar large-scale homogenization and loss of diversity over the harvest regime. Whereas moderate sized harvests (100 acres) maintained successional heterogeneity and wild-bee communities similarly sustained diversity. Collectively, this research supports the potential for managed forests as pollinator conservation havens if managed conscientiously and provides evidence for simple yet effective management practices – such as daylighting and seeding roadsides and maintaining moderate harvest sizes – to preserve the pollination services and persistence of wild pollinators over future forest landscapes.