Integrating silvopasture, biochar, and understory seeding to improve forage productivity, invasive buckthorn management, and oak savanna restoration

Commodities

Practices

Silvopasture - the integration of grazing livestock, trees, and pasture - can simultaneously provide food, timber, and wildlife habitat. In the Upper Midwest, imperiled oak savannas are major restoration priorities and potential sites for silvopasture, yet restoration is challenged by woody invasives. Common buckthorn (Rhamnus cathartica) is especially problematic: it suppresses native species and degrades soil quality. Buckthorn is also the primary alternate host of major crop pests such as soybean aphid, which cause severe economic damage, yield losses, and threats to food supply.

Integrating rotational grazing into oak savannas is a promising practice that can provide forage and shade to livestock while reducing buckthorn. However, there is a lack of research-backed management practices that achieve the multiple goals of enhancing on-farm woodlands to suppress buckthorn, improve soil health, and provide high-quality forage.

On-farm biochar production- a soil organic matter-rich product produced under high heat and low oxygen conditions- from cleared woody invasives may be an additional strategy to improve soil conditions to favor forage regeneration and suppress buckthorn. While there is increasing farmer interest in biochar production, and prior research suggests that soil organic matter amendments like biochar can suppress invasive species and improve plant productivity, the effects of biochar on buckthorn and silvopasture establishment haven't been tested.

Research objective: The proposed project will assess the efficacy of rotational grazing, native seed mixes, and soil biochar amendments on buckthorn suppression, forage production, and oak savanna restoration in Sherburne County, Minnesota. I will test the following hypotheses:

1) Rotational cattle grazing will reduce buckthorn reemergence after clearing by trampling resprouts and consuming leaves;

2) Biochar application and understory native seeding will reduce buckthorn reemergence by reducing nitrogen (N) mineralization;

3) Biochar will improve native forage productivity via increasing in soil properties linked to plant productivity, including microbial biomass, cation exchange capacity, water holding capacity, and soil organic matter.

In a two-year, full factorial experiment, I will test three treatments: grazing, biochar, and native seed addition. I will sample vegetation before and after grazing for two grazing events per year and sample soil annually.

Outreach and evaluation: In partnership with the rancher-collaborators, Minnesota Board of Water and Soil Resources, University of Minnesota Extension, and the Savanna Institute, we will develop three workshops and educational materials to increase knowledge of and interest in silvopasture and biochar for producers and resource professionals. Participant surveys will evaluate learning, knowledge gaps, and future research directions.

Research objective: The proposed project will develop science-backed management strategies for converting buckthorn-invaded oak savannas into silvopasture and assesses the efficacy of rotational grazing, native understory seeding, and soil biochar amendments on buckthorn suppression, forage production, and habitat restoration.

Outreach: Through collaboration with the Minnesota Board of Water and Soil Resources (BWSR), the Savanna Institute, and University of Minnesota (UMN) Extension, we will produce educational materials and facilitate three workshops on silvopasture and restoration for producers and county-level resource professionals (which may include Soil and Water Conservation District (SWCD) staff, extension agents, and NRCS staff). At the workshops, we will share results from the proposed study and related research and facilitate exchange of ideas and questions between participants.

Learning outcome 1: Resource professionals and producers will learn about rotational grazing, seeding, and biochar impacts on buckthorn management, soil quality, forage production, and habitat restoration.

Action outcome 1: Collaborating ranchers will expand rotational grazing and buckthorn management plans on the approximately 85 woodland acres they manage, utilizing understory seeding and biochar amendments if appropriate. They will share their experiences with other ranchers.

Action outcome 2: SWCD staff and other resource professionals will incorporate rotational grazing, seeding, and/or biochar into management plans for silvopasture establishment and oak savanna restoration. They will share resources for on-site biochar production with interested farmers and ranchers.