Sheep Grazing as a Tool for Vernal Pool Stewardship

View the project final report

• 2006 annual report
• 2007 annual report

Commodities

• Animals: sheep

Practices

• Animal Production: range improvement
• Education and Training: demonstration
• Natural Resources/Environment: biodiversity, habitat enhancement, wetlands
• Pest Management: weed ecology
• Production Systems: agroecosystems, holistic management
• Sustainable Communities: partnerships, urban/rural integration

In this project we tested the effectiveness of livestock grazing as a management tool for vernal pool lands. Vernal pools are unique seasonal wetlands that provide essential habitat for many rare and endangered plant and animal species. Recent anecdotal evidence has suggested that livestock grazing on vernal pool grasslands in California may help maintain native plant diversity by suppressing the non-native annual grasses that typically surround these pools. In collaboration with local ranchers, we tested this idea by introducing sheep grazing to a site with vernal pools in Sonoma County, California. Exclusionary fencing on half of each pool allowed us to compare the plant community composition of grazed and ungrazed plots each spring from 2005 (before grazing was introduced) through 2008. We found that spring sheep grazing at the experimental site did not significantly increase native plant cover or richness. Sheep grazed heavily in pool bottoms once pools dried, contrary to management goals. However, sheep grazing did reduce cover of an invasive late-season forb, and increased cover of an early-season native aquatic forb. Sheep grazing may be effective at enhancing natives if done while pools are still inundated, or after natives have senesced. A companion study showed that high-productivity vernal pools grazed by cattle did have greater native richness and cover than ungrazed pools. Further study will help refine these conclusions, but land managers in Sonoma County are already looking for local ranchers with whom to partner to steward vernal pool lands. We have presented our results in a number of forums, we hosted a highly successful workshop bringing local ranchers and land managers together to discuss vernal pool grazing, and we are working on a manuscript for publication in a scientific journal.

Introduction

Vernal pools are temporary wetlands that once occurred throughout California grasslands and provided habitat for many rare and endemic organisms. Today, less than 10% of pool habitat remains, and native pool species across California are in decline. Anecdotal evidence indicates that pools on active ranchlands often have healthier native plant populations than do those from which livestock grazing was removed in recent decades. Land managers in Sonoma County and elsewhere in California are poised to reintroduce managed grazing to pools in hopes of encouraging natives, but have hesitated for lack of careful research on which to base their management plans.
To address this gap in knowledge, we carried out a sheep-grazing experiment in collaboration with local ranchers. At a Sonoma County site with vernal pools, half of each pool was fenced to exclude grazing; the other halves were unfenced and readily accessible to sheep. We monitored and compared the hydrology and vegetation of grazed and ungrazed plots, and presented our results in a number of forums. We organized a field workshop to share our results with local ranchers and land managers. We are in the process of preparing a manuscript describing our results for submission to a peer-reviewed scientific journal focusing on applied ecology.

Our objectives for the first four months of the grant period (fall 2006) were to analyze preliminary data, present preliminary results at a grasslands management conference, and begin monitoring vernal pool inundation. Our objectives for 2007 were to continue experimental sheep grazing, monitor vegetation of grazed and ungrazed plots, monitor vernal pool hydrology, analyze the resulting new data, begin manuscript preparation, and plan for an educational field session. Our objectives for 2008 were to continue experimental sheep grazing and vegetation monitoring for a final season, to host a field session sharing our results and informing ranchers and land managers about vernal pool grazing, and to complete and submit a manuscript to an ecological journal.