Effects of Grassland Restoration on Native Bee and Spider Communities in a Pacific Northwestern Agroecosystem

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• 2016 annual report

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Since pre-settlement times, 90% of native grasslands have declined in North America, primarily due to agricultural conversion. Today, grasslands are a top priority for restoration as they provide essential habitat for many rare and endangered species. Restoration efforts vary from large scale projects (e.g., tens of hectares) to small scale projects (e.g., field margins or roadsides), and while many endangered species are monitored in restored grasslands, native beneficial invertebrates are rarely examined. The purpose of this study is to determine how grassland restoration affects native bee and spider communities in Pacific Northwestern agroecosystems and create a low-maintenance protocol to successfully restore field margins to enhance potential ecosystem services, restore native grasslands, and improve farm sustainability. My research questions are: How does grassland restoration affect native bee and spider communities? How quickly are invertebrate responses manifested? Does the time since restoration affect invertebrate diversity? What are the factors driving responses, and can restoration ecologists use this knowledge to increase beneficial invertebrates and the services they provide? Will beneficial insects from nearby restored grasslands provide services to adjacent farms? Is there a low maintenance protocol that can be used to restore field margins and increase invertebrate-mediated ecosystem services? Is it possible for growers to use this protocol? Grassland invertebrates provide ecosystem services such as pollination, nutrient cycling, food for vertebrates, and pest control; however, agricultural cultivation can negatively impact invertebrate abundance and diversity and associated ecological functions. It is unclear whether much of the grassland restoration occurring in the United States has resulted in restoration of invertebrate diversity and function. This is particularly true of grasslands in the Pacific Northwest, where very little research has studied the effects of restoration on invertebrate diversity in arid agroecosystems. For example, in Oregon, nearly 28% of land is used for agriculture, with the majority of acreage in large production farms in eastern Oregon. These farms are center pivot-irrigated surrounded by field margins, the relatively small corners of crop circles that are widely unmanaged. However, there is a growing interest in restoring these areas so they can be used to increase native plant biodiversity and invertebrate facilitated ecosystem services such as crop pollination and pest control. In eastern Oregon many of the beneficial invertebrates such as native bees that pollinate crops and spiders that manage crop pests live in arid grasslands. Managing and conserving field margins to native grasslands could increase invertebrate diversity and augment pollination and pest predation in surrounding crops. My plan is to determine if grassland restoration enhances beneficial invertebrate communities and to create a low maintenance protocol to restore field margins to native grasslands while also educating the surrounding community about the benefits invertebrates provide to us.

All objectives will assist in determining how grassland restoration impacts native bee and spider communities and in producing a low-maintenance protocol that farmers in eastern Oregon could use to restore field margins and enhance farm sustainability.  

1. 1. Determine how grassland restoration affects native bee and spider communities in eastern Oregon by comparing native bee and spider diversity and abundance in restored, native, and degraded grasslands.

Hypothesis 1: Bee and spider diversity and abundance is expected to be higher in undisturbed or restored grassland than degraded grasslands.

2. 2. Investigate the role of restoration project age on native bee and spider responses by comparing native bee and spider communities across sites that were restored at different times.

Hypothesis 1: Bee and spider diversity and abundance is expected to be greater in restoration plots that have the longest time to recover. 

3. 3. Assess which factors are most strongly associated with native bee and spider diversity and abundance by evaluating what floral resources and vegetative structure are available at each site.

Hypothesis 1: Flowering plant diversity and abundance is expected to be a major driver of native bee diversity and abundance.

Hypothesis 2: Plant structure is expected to be a major driver of spider diversity and abundance.

4. 4. Determine if native bees and spiders can enhance pollination and pest control for growers by measuring how far and which species can travel from restored grasslands to neighboring farms.

Hypothesis 1: Native bees and spiders will be more abundant near restored grassland edge and less abundant farther from grassland edge and farther into farm.

5. 5. Produce a low maintenance protocol that can be used to restore field margins to previous grasslands, decrease field erosion, control crop weeds, and increase invertebrate-mediated ecosystem services by planting different native plant combinations in field margins. All plants will be native to surrounding grasslands, including native bunchgrasses and forbs. 

Hypothesis 1: Bee and spider diversity and abundance is expected to be greater in restoration plots with the most diverse plantings. 

6. 6. In the educational component of my project, I will educate growers and people in the Hermiston area about the important ecosystem services that invertebrates provide and present a low-maintenance protocol to enhance these services through restoring field margins. I will present my results at field days on the Hermiston Agricultural Research and Extension Center, through an educational project for children ages 5 to 18, and will provide brochures and presentations at the annual Hermiston Farm Fair.  I will also present results to the science community through peer-reviewed journals and posters and presentations at conferences. The entire research process will be documented on a blog (grasslandrestoration.weebly.com) that will educate people interested in restoring invertebrate diversity in field margins and in native grasslands.