Using VF To Establish Valley Oaks On Rangeland

Oaks are keystone species in the California foothills, providing essential habitat and resources for a wide range of wildlife. For over a century, there has been growing concern that certain native California oak species—specifically blue oak, valley oak, and Engelmann oak—are failing to regenerate adequately to maintain their current population levels and stand densities. This issue is driven by several factors, including development, competition for water and nutrients from annual grasses, altered fire regimes that once controlled competing vegetation, and grazing pressure from livestock. Young saplings under 6.5 feet are particularly vulnerable to browsing damage from livestock, which can kill or stunt their growth (McCreary and George, 2005).

Successful oak regeneration on rangeland often requires active management, such as protecting seedlings with physical barriers, controlling competing vegetation, and providing irrigation. Without these interventions, long-term survival is limited.

Virtual fencing (VF), typically used to confine livestock within a designated area, can also serve to exclude them from specific zones. VF exclusions can be placed around newly planted oak plantations to protect young oaks and allow them to establish and grow undisturbed until they reach adequate heights.

In November 2023, we established a valley oak (Quercus lobata) plantation on annual rangeland, following guidelines from Regeneration Rangeland Oaks in California (McCreery 2001)). We collected 600 acorns from a local valley oak, sorted out damaged seeds, and stratified them in a refrigerator for a month. In January 2024, acorns were planted in a 57-acre pasture, which was divided into four half-acre plantation sites to mimic the natural clustered growth of oak stands. Each site had 40 planting spots, where we prepared 2-by-2-foot patches by removing competing vegetation. In each planting spot, we dug a one-inch hole and buried three acorns on their sides for sprouting redundancy. Within each plantation, half of the planting sites were left bare, while the other half were protected with tree shelters.

By March, the first acorns began to sprout, with roughly equal numbers emerging from both bare and sheltered sites. However, by August, the hottest month, only 35 healthy seedlings remained, all of which were in tree shelters. Seedlings that had sprouted at bare sites had disappeared, likely due to ground squirrels, gophers, voles or other vertebrates.

To support their growth through the summer heat, each tree received a single application of water from a 5-gallon bucket with a drip line, as recommended by (Redboot). Our next step involves allowing cattle to graze in the area with exclusions around two of the four plantations to assess whether the trees remain undisturbed.