The SoMar Silvopasture field demonstration project is located in northern Marin County within the Chileno Creek and greater Walker Creek Watersheds.
Much of northwest Marin County is mixed annual-perennial grassland. Tree cover is minimal, and generally associated with certain soil types, north-facing slopes, riparian areas, or historic windbreaks. Integrated forest and grazing lands are rare, generally limited to small stands of oak or bay woodlands.
As excessive heat days have increased in recent years, rancher concerns about heat stress to livestock have also grown. Shade trees are rare and often found along fencelines or creek corridors. Where shade does exist within pastures, livestock often crowd beneath lone trees, concentrating grazing impacts in relatively small areas. Few producers in this area have explored the possibility of adding trees to grasslands to increase shade cover and improve livestock distribution. By adding trees to grazing areas, livestock are given multiple places to retreat from heat, reducing the wear and tear on any one area. This can ultimately encourage better livestock distribution and more even forage consumption.
By prioritizing oaks and other native tree species in silvopasture systems, managers are also provided a unique opportunity to build valuable habitat on Marin County working lands. Open woodland or savanna ecosystems—and the countless species that depend on them—are increasingly rare throughout Northern California. Silvopastures featuring native tree species mimic these ecosystems, increasing tree cover and edge habit.
There is a need to build regional knowledge about silvopasture systems, particularly “silvopasture by addition,” or adding trees to grazing systems. This demonstration will help landowners to assess trade-offs and evaluate common concerns associated with mixed agroforestry-grazing systems. For example, land managers frequently express concerns about a loss of forage with increased shade in pastures. Research tends to suggest that sparse tree canopies (less than 25% canopy cover) typically have little effect on forage production, particularly when systems feature deciduous hardwood species that cast minimal shade during the early growing season when cool-season grass growth is highest. Further, these tree canopies may harbor “islands of fertility” in semi-arid grassland: areas with higher organic matter and moisture retention where green forage lingers even after the surrounding landscape has dried out. In addition to forage impacts, concerns around efficacy and maintenance are common. This project seeks to fill this regional knowledge gap, broadening a local understanding of effective design, installation, and maintenance.
Silvopasture: The demonstration project centers around the creation of a silvopasture system by integrating trees and other woody vegetation into active grazing land. Because trees are not established at a prescribed or uniform density however, the project design may better fit the NRCS CPS 612 – Tree and Shrub Establishment: “Establishing woody plants by planting, direct seeding, or through natural regeneration.”
SoMar Farms consists of over 600 acres of rangeland characterized by annual and perennial grasses and forbs, with scattered bay laurel trees (Umbellularia californica), coastal live oak (Quercus agrifolia), California buckeye (Aesculus californica), and eucalyptus (Eucalyptus globulus). The property primarily supports livestock grazing and finishing grass-fed beef, although the landowner also raises grass-fed lamb. The landowner is actively engaged in a variety of restoration activities on the property as a whole. They are proud to produce delicious and nutritious food for their community by using regenerative agricultural practices that prioritize the well-being of the planet, animals, and people involved.
SoMar Farms received a Carbon Farm Plan in 2018, and they have been working to accomplish goals of increased carbon sequestration including increasing year-round above-ground biomass, increasing forage quality, improving soil health and water holding capacity, and operating as a model of good stewardship and business sustainability. This practice is one of many that they are working on that work to contribute to those goals. This landowner is interested in trying new things and contributing to the “good stewardship model”, and thus was a great candidate for this demonstration project. They are excited to increase shelter for cattle from high winds and heat and look forward to the potential of observing any effects on forage within that pasture, whether directly or indirectly supported by this project.
The SoMar Silvopasture demonstration project is located in a region known locally as the “Petaluma Gap.” Characterized by rolling open grasslands, this part of northern Marin and southwest Sonoma County is characterized by gentle topography and coastal influence, including onshore wind and summer fog. A mild climate and summer fog favor annual grasslands and coastal prairies, and predominant land uses in this area are cattle grazing (typically cow-calf operations), silage production, and dairying.
Map Unit | Slope | Soil Texture | Organic Matter (%) | AWHC (cm/cm) | Depth to Root Restrictive Layer (inches) |
140 | 5-15% | Loam | 2.48 | 0.16 | 97 |
209 | 15-30% | Clay Loam | 1.20 | 0.20 | 130 |
Establishment activities, including irrigation, weeding and browse protection, will be carried out for 3 years post installation. Pending funding, RCD staff hope to revisit this site to conduct sampling per Point Blue’s Range-C protocol.
Silvopasture at SoMar Farms was designed to increase biodiversity and structural diversity by installing clusters of native trees in a rangeland system. Native tree species were selected based on adaptation to local soils and climate, and their ability to provide long-term carbon sequestration, wildlife habitat, and other ecosystem services. Ten 16’ x 16’ “pod” livestock exclosures were constructed with hog panels and t-posts. Each tree “pod” contains 5 individuals. Plants were planted via seed and nursery stock. All plants were installed with de-galvanized seed baskets to reduce predation during establishment. Species include coast live oak (Quercus agrifolia), California sycamore (Platanus racemosa), box elder, (Acer negundo), California buckeye (Aesculus californica), bay laurel (Umbellaria californica), valley oak (Quercus lobata).
Variable(s) | Sampling Method | Sampling Equipment Used | Timing/Frequency | Analysis Method | Sampler |
Soil Bulk Density | soil core to 6 inches | AMS 2 ½“ soil core on slide hammer | Fall 2024 | Oregon State University | Marin RCD |
pH, EC, organic matter estimate, total C and N, nitrate-N, P, K, Mg, Ca, texture, potentially mineralizable nitrogen, active carbon, wet aggregate stability, microbial respiration | Soil sample to 12 inches | AMS 2 ½“ soil core on slide hammer | Fall 2024 | Oregon State University Complete Soil Health + Microbial Biomass | Marin RCD |
Plant survival, height, vigor | Visual, photographic | Monitored for the entirety of the summer seasons for 3 years (~1x/week) |
| Point Blue STRAW staff |
Pre-Restoration, Post-Installation, and Year 1 monitoring photos. Pre-restoration photos were taken in October of 2024, while Year 1 photos were taken in September of 2025.
Establishing native plants in a rangeland setting presents challenges from livestock pressure, especially when plants are young and most vulnerable to damage. Hog panel enclosures were built for each planting pod to provide robust protection from cattle while also facilitating easy access for establishment and monitoring activities.
The silvopasture planting area is located on steep slopes that are not easily accessible by vehicle, particularly during planting months. This necessitated hauling all tools and materials into the individual pods on foot, requiring more labor hours to complete the project. The same access constraints applied to the maintenance and irrigation design of the project, which required installation of a 1000 ft temporary mainline to convey water to each individual pod, as typical methods of watering similar sized smaller plantings were not feasible (e.g. hand watering via a water trailer).
This area of Marin County adjacent to the coast is prone to high sustained winds, which affects plant ranges and growth forms, especially for wood species with large canopies. To mitigate this, planting locations were strategically selected to maximize leeward effects and to mirror site characteristics of local naturally-occurring tree stands, which are primarily found on north facing slopes.
Due to the nature of silvopasture and the effects on measured variables, this project will be sampled on a longer-term return interval (3-5 years) pending appropriate funding sources.
Pre-Restoration Data Collection (Fall 2024)
Across Control and Treatment sites Pre-Planting:
Preston Duncan, Marin RCD
preston@marinrcd.org
415.787.7440
The Gamble Ranch Field Trial, located in the Oakville AVA in the middle of Napa Valley, incorporates the Mainardi plow with compost application and green manure cover cropping, and monitors the effects on soil properties and vineyard productivity.
Napa County RCD’s Huichica Creek Vineyard trial sought to demonstrate conservation practices including those to promote soil health, carbon sequestration, erosion control, water conservation, and irrigation scheduling.
This Sonoma County Vineyard trial seeks to investigate the economic and soil health tradeoffs of compost application in combination with common tillage practices.
Our quarterly publication is full of curated and self-published articles sharing our experience, achievements, noteworthy field news, helpful tips, tutorials, and more.
