Project Highlight: Willamette Valley Prairie Pollinator Studies

By Kylie Baker

Restoring Pollinator Communities to Save Endangered Species: The Willamette Valley Pollinator Project

Since 2019, the Institute for Applied Ecology (IAE) has been collaborating with the U.S. Army Corps of Engineers (USACE) to address a crucial conservation challenge: restoring pollinator communities in Oregon’s rapidly disappearing Willamette Valley prairies. IAE researchers Tom Kaye, J. Christina Mitchell, and Scott Harris are the co-principal investigators. This partnership, through the Pacific Northwest Cooperative Ecosystem Studies Unit (PNW CESU), extended into a second phase with additional funding in 2022, reveals the critical connections between endangered plant species and their pollinators—insights essential for effective prairie restoration.

The journey began with the Willamette daisy (Erigeron decumbens), a federally listed endangered plant with a dwindling population. Before this project, very little was known about its pollinators or basic biology, apart from small, localized studies. The Army Corps of Engineers, which owns and manages land supporting the daisy, was keen to improve its habitat management and understand which pollinators were key to the plant’s survival.

A Vital Partnership: Plants and Pollinators

One of the project’s most striking discoveries was that the Willamette daisy cannot reproduce without insects, meaning that pollinators are essential for the recovery of this species. Without pollinators, there’s virtually no seed production. This finding highlighted just how crucial it is to not only focus on the endangered plant itself but to also restore the broader prairie ecosystem in which it thrives.

The team surveyed multiple daisy populations across the Willamette Valley to identify which insects visited these plants and how their presence affected overall reproduction. These sites included lands managed by the U.S. Army Corps of Engineers, Bureau of Land Management (BLM), U.S. Fish and Wildlife Service (USFWS), and private lands. As the project progressed, they expanded their research to two other threatened species—golden paintbrush (Castilleja levisecta) and Kincaid’s lupine (Lupinus oreganus)—asking similar questions about pollinator relationships and broader ecosystem interactions.

The challenge? Prairie ecosystems in the Willamette Valley today cover less than one percent of their historical range. The need to understand what remains of these communities—and how to restore them—drives the project forward.

Understanding Pollinator Networks

IAE researchers take a methodical approach to their work. Their protocol cycles through every two weeks, but they’re out in the field almost every day from April to July completing field work. They head into the prairies to document which plant species are flowering and how many flowers are present. From there, they target patches of abundant flowers for pollinator sampling, using nets to catch insects as they visit the flowers. Each insect that touches the reproductive structures of the flower is a potential pollinator.

These “network surveys” not only reveal which pollinators visit endangered plants like the Willamette daisy, but also which other species those pollinators are interacting with. It’s a community-wide approach—researchers are learning that to support one species of endangered plant, you need to restore a whole community of plants and pollinators. After all, many of these pollinators visit a variety of plants, making it essential to preserve a diversity of species.

Digging Deeper: Pollen Supplementation and Species-Specific Observations

Alongside network surveys, the team has also been conducting pollen supplementation experiments. These experiments test whether the existing pollinator community is providing enough service for plant reproduction or if there are gaps. In general, they’ve found that most sites exhibit some level of pollination deficiency—plants set more seeds when pollen is manually supplemented, indicating that pollinators alone aren’t doing quite enough.

**Example of conducting pollen supplementation trials with a) golden paintbrush (*Castilleja levisecta*) and b) Kincaid’s lupine (*Lupinus oreganus)*.**

This information has been critical for managers, as it highlights the importance of maintaining dense patches of plants to attract and sustain pollinators. Pollinators prefer large, concentrated resources, so smaller, isolated patches of plants often struggle to reproduce at the same rate.

The focus on pollen supplementation has recently expanded to include golden paintbrush and Kincaid’s lupine. While analysis of their data is ongoing, early observations suggest that different species of pollinators may be visiting these plants compared to the Willamette daisy.

A Broader Impact on Prairie Restoration

The work has revealed a rich diversity of insect life in the prairies, with over 100 species of pollinators visiting the Willamette daisy alone. Their findings indicate that while bees are the most effective pollinators, many species contribute to these networks, including flies, beetles, and butterflies. Over the course of five years, the team identified over 80 bee taxa and 45 fly taxa visiting the Willamette daisy alone. Sweat bees (Halictidae), bumblebees (Apidae), and leafcutter bees (Megachilidae) are among the most common visitors, providing essential pollination services.

Various pollinators for the Willamette daisy.

One striking discovery is that pollinator diversity varies greatly across sites and seasons. This underscores the need to preserve multiple prairie habitats across the region to capture the full range of pollinators and their interactions with endangered plants. The variation observed in pollinator communities suggests that no single site or season can represent the full complexity of these relationships—long-term, multi-site studies are essential to inform conservation efforts.

The insights gained through this work have ripple effects across prairie restoration and management efforts. With input from agencies like the U.S. Fish and Wildlife Service, the Bureau of Land Management, and private landowners, the project aims to refine conservation practices to better support pollinators. The research also informs land management practices like controlled burns, which can influence both plant and pollinator communities.

IAE is also working with a key collaborator in Washington, Susan Waters of Quamash EcoResearch, to develop a comprehensive and long-term dataset on prairie plant-pollinator networks in the Pacific Northwest. With the Oregon State Arthropod Collection, Oregon Bee Atlas, and entomologist David Cappeart, IAE is also establishing a reference collection and creating regional identification keys, providing valuable resources for future conservation work. Other critical partners include the U.S. Fish and Wildlife Service, the Bureau of Land Management, and private landowners; who have provided input, additional funding, and access to sites they manage.

Looking Ahead

As the project continues, a full field season is planned for 2025, with ongoing research into the broader pollinator communities and their relationship to endangered plant species. The team will also continue refining management practices to ensure the best possible outcomes for both plants and their insect partners.

In the world of applied ecology, this project exemplifies the intersection of science and on-the-ground conservation. By bringing together researchers, land managers, and conservationists, the Willamette Prairie pollinator project is changing the way we think about saving species—not just one at a time, but as interconnected parts of a broader ecosystem.

A special thank you to Tom Kaye, J. Christina Mitchell, Scott Harris, Susan Waters, David Cappeart, Wendy Jones (USACE), Christine Calhoun (BLM), and Graham Evans-Peters (USFWS) for their critical contributions to this project.