Since pre-settlement times over 90% of native North American grasslands have declined, primarily due to agricultural conversion. Thus, much of grassland restoration efforts occur in the context of agroecosystems. Today, grasslands provide essential habitat for many rare and endangered plant and animal species; including native bees and spiders. Grassland bees increase pollination of native plants and neighboring crops while spiders enhance pest control. Yet it is unclear whether much of grassland restoration has resulted in restoration of native bee and spider diversity and function. A recent realization of the importance of grassland habitats has led to an increased number of restoration projects in eastern Oregon such as The Nature Conservancy Boardman Grasslands and Zumwalt Prairie and The Umatilla National Wildlife Refuge, all sites that were previously grazed and invaded by annual grasses. The primary goal of this study is to use three years of observational data to understand how grassland restoration impacts native bee and spider diversity and determine if restoration returns diversity and richness to native levels by comparing restored, native, and degraded sites.
Native bees and spiders were collected 2014-2016 from June to September. Native bees were collected via pan traps and handnetting and spiders were collected via pitfalls. All floral resources were counted and identified in addition to using vegetative characteristics to estimate habitat quality. Results from 2014 indicate strong temporal patterns for both native bees and floral resources—with significantly less native bees but higher abundances and diversity of available floral resources seen later in the field season. Over 50% of the native bees collected were Agapostemon spp. followed by Melissodes spp.; the only genera that increased in abundance throughout the season. Major families of spiders collected include: Lycosidae, Gnaphosidae, Salticiade, and Theridiiade. Ground hunting spiders including Lycosidae were closely associated with degraded grassland sites, while web-spinners were more closely associated with native grassland sites. Ultimately, this research will result in management recommendations that can increase the number and diversity of beneficial invertebrates and the ecosystem services they provide in restored grasslands of the Pacific Northwest.