COS 88-5 - Prescribed fire increases plant-pollinator network robustness to losses of rare native forbs

Abstract: Restoration efforts often focus on changing the composition and structure of invaded plant communities, with the tacit hope that restored communities will be more resilient to future stressors. However, the impact of restoration activities such as prescribed fire on plant-pollinator interaction network structure and in turn, network robustness is incompletely understood. We examined the effects of restoration-focused prescribed fire and native forb replanting on plant-pollinator network structure in a restoration chronosequence in Pacific Northwest prairies. We then simulated the effects of three plant species loss/removal scenarios on secondary extinction cascades in the networks. Specifically, we explored three management-relevant plant loss scenarios (removal of an abundant exotic forb, removal of an abundant forb designated a noxious weed, and loss of the rarest native forb) and compared them to control scenarios.

Pyrodiversity, proportion of area recently burned, and cumulative replanting effort (plugging and seeding) over the prior 10 years increased the abundance and diversity of floral resources as well as the frequency and diversity of pollinator visits. Pyrodiversity also decreased network connectance and nestedness, increased modularity, and buffered networks against secondary extinction cascades. Rare forbs contributed disproportionately to network robustness in less restored prairies, while removal of typical “problem” plants like exotic and noxious species had relatively small impacts on network robustness, particularly in prairies with a long history of restoration activities. Restoration actions aimed mainly at improving the diversity and abundance of pollinator-provisioning plants may also produce plant-pollinator networks with increased resilience to plant species losses.