Using Native Forb Species to Enhance Forage Diversity for Livestock and Pollinators

Two pasture trials were established in the fall of 2022 to investigate the capacity of organic forage production to increase native pollinator plant species. This collaborative effort began through the work of a small group of professionals and producers interested in adding pollinator habitat to farms and agricultural lands in the San Juan Islands, WA. New Hannah Farm, Catkin Design and Consulting, San Juan County Land Bank, and Washington State University San Juan County Extension (WSU SJC Extension) worked together with Natural Plant Solutions to direct seed a local native pollinator plant seed mix into pastures. The same experimental design was used to evaluate the success of site preparation and impacts on forage biomass and quality in both trial locations.

This proposal builds on the work of this small “pasture-prairie” group to expand the current scope of work and track the establishment of previously seeded pollinator plants, most of which are perennials and were not likely detected during the pilot phase of this study. If funded, this work would expand to characterize the effects of site preparation and seeding methods on forage quantity and quality. Year 1 trial data and methodologies will inform the design of this study. The seeding treatment will be modified to increase the likelihood of seeding establishment at each site. Initial trial results to date will inform seed mix selection for mesic and more xeric sites to improve overall establishment response and better inform management recommendations.

In this study, we characterize the efficacy of several factors in the establishment of native pollinator plants into pastures or hayfield and the effect of site preparation and species enrichment on forage for livestock in organic agricultural systems. Combining farmer interest in more diverse and multipurpose pastures, professional observations during previous pasture studies, and results from similar work, this project joins pasture management and pollinator habitat to assist producers in making informed decisions about livestock forage and pollinator conservation. In this study we ask:

Does the incorporation of native pollinator plants into organic livestock forage production improve native habitat for pollinators?

Null hypothesis (H₀): Livestock forage production does not accommodate an increase in native plant species making up the pollinator habitat found in the herbaceous layer of the forage system.

Alternative hypothesis (H₁): The incorporation of native pollinator plants into forage grasses and forbs can improve native habitat and livestock forage production.

Project Goals:

1. To establish native pollinator habitat in organic pastures;
2. To quantify the effect of enhancing pollinator habitat on forage biomass and quality;
3. To detect a shift in pasture species composition based on management treatments; and
4. To expand pollinator habitat for a rare, endangered species.

Project Objectives:

• Test seeding method to determine if there is a difference in outcome between no-till and broadcast seeding;
• Test the effects of tilling during site preparation on native pollinator plant establishment; and
• Test early-season mowing to determine if increased mowing in the spring over multiple years can influence forb establishment among competitive pasture grasses.

To address our research question, hypotheses, project goals, and objectives, we will establish two additional new pasture trials with two new producers and continue to sample previously established trials. We will continue to design and implement trials using a full-factorial randomized split-block design to test the response of native pollinator plant seedling diversity and forage productivity and quality to three treatments used as part of a strategy to enhance organic pasture with native pollinator species. These three treatments include:

• Seeding method (planting)
• Tillage (site preparation)
• Mowing (post-planting management)

Seeding treatments will be compared to determine if a difference can be determined between the the control, no-till, and broadcast treatments. We will test treatment effects to evaluate differences in terms of pollinator plant seedling establishment. No seeds will be planted in control plots, while a no-till seed drill will be used to plant seeds in no-till plots, and seeds will be broadcast by hand for broadcast treatments. Natural Plant Solutions will be contracted again to seed plots using a no-till seed drill for all trials in the study.

Site preparation will employ a tillage treatment to expose bare ground and create a seed bed for seeding native pollinator plants. This will be employed for each seeding treatments combination to test the effects of site preparation. The use of synthetic herbicides to reduce weeds is common when establishing native plant species where introduced pasture grasses are growing, but this option is not available to organic producers, so tillage represents a suitable choice for organic growers when introducing forbs into pastures. We will determine if a difference is observed when comparing a control in which no soil has been tilled and tilled subplots where a walk behind tractor has been used to turn the soil, remove weeds, and expose soil for seed contact. This will allow us to either accept or reject the null hypothesis to establish the effect of tillage on either native pollinator plant seed establishment or forage productivity in this study.

Post-planting management is incorporated into the study as a mowing treatment. This mowing treatment is used to reduce competition between the sown native plant seed mix and pre-existing, introduced pasture plants including grasses, forbs, and weeds. We will test mowing treatments to determine if there is a difference between the control and mowed subplots in terms of response of both native pollinator plant diversity and forage biomass and quality as plant biomass begins to increase during the spring and pre-existing pasture species may outcompete seeded prairie or native species for sunlight and other resources, subplots assigned to the mowing treatments will be mowed in after spring emergence of seeded pollinator plant species. This will provide native species with access to sunlight and resources to reduce the growth and use of resources by introduced pasture competitors. 

We will evaluate pollinator plant species richness and the percent cover of these focal native prairie plant species at each trial location in the spring (in April). We will also estimate percent cover of functional groups during this early-season sampling date prior to flowering of grass species. During early to mid-June, when grasses are in flower and can be identified, we will return to each trial site to record plant species diversity and species percent cover for all species found in trial plots to document potential species composition change. Forage biomass will be assessed by cutting, weighing, and drying samples. Forage samples will be dried before being sent to a laboratory for forage analysis to determine a final dried weight and forage quality including crude protein, relative feed value, and neutral detergent fiber among other nutrients and feed quality index values. At the end of each spring growing season, when forage is ready to be cut for hay, the entire plot will be mowed during haying and all forage or hay removed from the trial plot. 

Statistical analysis will be performed to determine the effects of trial management treatments using the R language. Data will be collected and analyzed using a split plot design with linear mixed models to accept or reject the study null hypothesis. Main and random effects will be analyzed to determine the effects of seeding and pre-and post-seeding site preparation and management. Inferences drawn from this study will allow us to determine management recommendations for farmers and agricultural specialists interested in providing pollinator habitat in pastures. This will help to fill a key gap in the San Juan Islands and help develop recommendations and best management practices to producers and landowners. Continued interest in converting pastures consisting of introduced grasses to pollinator-friendly multi-purpose pasture environments provides ample opportunity for our study results to be applied to management practices.