PS 17-235 - CANCELLED - Fire may increase biodiversity and stability of plant-pollinator networks in fire-suppressed forests of the Sierra Nevada, California

Abstract: Fire regimes are altered by climate change, land use, and management, resulting in fires that burn outside of the natural range of variation in frequency, severity, or extent, with cascading effects on community structure. Historically, fire in mixed conifer forests and meadows created habitat for plant-pollinator communities by releasing flowering plants from competition, thereby increasing nectar and pollen resources for pollinators. However, effective fire suppression and climate change have altered the fire regime such that fires burn less frequently, but at higher severity, with unknown impacts on plant-pollinator communities. To better understand the effects of high-severity fire on plant-pollinator communities, we observed interactions among all plant-pollinator species in unburned and severely burned meadows and unburned, moderately burned, and highly burned forests of the King fire in the Sierra Nevada, CA. We compared plant-pollinator networks in the burn-habitat classes using null models and network-level topographical metrics of nestedness, the tendency of specialists to interact with a subset of actors that more generalist species interact with, and specialization, a measure of selectiveness that indicates how much the network deviates from expectations based on relative abundance. The effects of fire depended on the habitat, with more profound effects in forests than meadows. Networks in unburned meadows were more nested than in burned meadows but did not differ significantly in specialization. Networks in both highly burned or moderately burned forests were significantly more generalized and nested than networks in unburned forest. Networks with more generalized and nested architecture may have less competition, more coexisting species, and more redundancy, suggesting that even large, high-severity fire in forests is important to maintaining biodiversity of plant-pollinator communities.