Grasslands and Prairies

Saturday, October 22 at 1:00-2:40 pm, Oak Room

Session Description: California grasslands are among the most endangered ecosystems in the United States and are important subjects of ecological research and experimentation. This session focuses on native grassland research and management including biodiversity enhancement, invasive species, livestock grazing, and restoration within our unique California grassland/prairie ecosystems.

Session Chairs: Jennifer Buck-Diaz (California Native Plant Society, Sacramento, CA, USA) and Valerie Eviner (University of California, Davis, Davis, CA, USA)

44.1    Mojave Desert grasslands: 40 years of collecting historical ecological evidence of past and present native plant community diversity

Laura Cunningham (Western Watersheds Project, CA, USA)

Through extensive examination of reference sites across the Mojave Desert of California and Nevada since the 1980s, supplemented with historical record searches, and the study of herbaria collections, a diversity of native arid grassland components can be reconstructed among current native plant communities. Grassland communities may have been a more common part of deserts, intermixing with Mojave Desert scrub, Joshua tree savannas, and wetlands. Distinct desert grassland communities are evidenced in the West Mojave Desert region, southern Mojave lowland and upland areas, uplands in the Mojave National Preserve and southern Nevada ranges, and a distinctive desert grassland type in the northern Mojave. Details of the native grass species diversity in these geographic regions are reviewed. Cool season grasses dominate western Mojave Desert regions, transitioning to warm season grasses in eastern Mojave regions. Warm-season grasses are known as C4 plants, as they use the four-carbon compound PEP carboxylase in photosynthesis. PEP carboxylase is a photosynthetic enzyme that can “attract” CO₂ more efficiently than C3 plants, and allows the stomates of the plant to be closed more often—an adaptation to drought. Historic and ongoing impacts such as livestock grazing, invasive non-native grasses and forbs, habitat development and disturbance, and climate change have greatly reduced native grasses. Given the importance of cover from predation to Agassiz desert tortoise (Gopherus agassizii), a better understanding of this component of Mojave Desert plant communities is recommended, especially when considering mitigation measures and restoration activities of desert habitats.

44.2    Grassland restoration increases native plant cover but facilitates biotic homogenization

Justin C. Luong (University of California, Davis, Davis, CA, USA), Daniel M. Press (Santa Clara University, Santa Clara, CA, USA), Karen D. Holl (University of California, Santa Cruz, Santa Cruz, CA, USA)

There are large monetary investments for restoration globally and achieving goals are important for limiting biodiversity loss, but outcomes are not often assessed. Combining ecological and management surveys, we assessed the outcomes of 37 restored California coastal grasslands along a 1000-km N-S climate gradient, 3-30 years post-implementation. Restoration efforts were successful at achieving original project goals (95%) and a standard metric (80%) for native cover, but management interviews suggest practices could lead to regional biotic homogenization. Invasive species were indicated as the largest barrier to achieving project goals which was further supported by a relationship between non-native cover and post-implementation project age. High labor investment resulted in projects with higher native richness and lower non-native cover. Future restoration efforts may benefit from regional government restoration agencies that coordinate species use across projects to limit biotic homogenization.

44.3    Conserving native coastal prairie on Martin Griffin Preserve: reintroduction of fire as a disturbance process

Brian Peterson (Audubon Canyon Ranch’s Fire Forward Program, Marin County, CA, USA)

Coastal grasslands are among the most threatened ecosystems in California, and they are rapidly disappearing under encroaching forest and scrubland. Martin Griffin Preserve, located on the Marin coast, has had an estimated 91.5 percent reduction in grassland since 1962. However, remnant native bunchgrass stands, the foundation of coastal prairie ecosystems, remain scattered throughout these encroached areas. Audubon Canyon Ranch’s Fire Forward program has been working on Martin Griffin Preserve to reverse this encroachment and conserve these remaining bunchgrass grasslands by restoring fire as a natural process using a cycle of mapping, manual cutting, burning, and planting.

44.4    Using fine-scale grassland mapping for conservation and management

Shelly Benson (Benson Biological Consulting, Sebastopol, CA, USA), Dina Robertson (East Bay Regional Park District, Oakland, CA, USA) 

California grasslands that have high native species richness or cover are uncommon and warrant further study, protections, and special consideration for management. In order to best manage these native grasslands, we need to map their locations and describe them, and when possible, monitor them over time. Fine-scale vegetation maps are the best tool to inventory these resources and are essential for conservation and management. Most of the vegetation mapping efforts being conducted across the state are unable to map herbaceous communities at a fine-scale (alliance or association) due to limitations in remote mapping techniques. At this point in time, ground-based mapping is the only accurate method for mapping grassland communities. In this presentation we will describe the management goals and results of recent mapping efforts in Alameda County at Pleasanton Ridge and Garin Regional Parks, East Bay Regional Park District.

44.5    Native plants play a critical role in the resilience of California grasslands under a changing environment

Valerie Eviner (University of California, Davis, Davis, CA, USA)

As California experiences increasing frequency of drought, and increasing frequency and size of wildfires, it is critical to understand how to maintain ecosystem resilience. Research in California grasslands has highlighted the critical role of native grasses and forbs in providing resilience to these disturbances. Forbs are the “emergency first responders” after wildfire and during droughts—they often dominate under conditions when the annual exotic grasses decrease in cover. Even when forbs were relatively rare in vegetation cover before disturbance, their seedbank allows them to persist over the long-term and survive fires and other disturbances. However, there is concern that the seedbank of forbs is declining due to multiple factors, including long-term climate change and lack of disturbances. Promoting occasional disturbances in grasslands (e.g. grazing, mowing, prescribed fires) may be critical to maintaining the forb seedbank, and thus resilience of grasslands to disturbances. Native perennial grasses are also important for resilience of California’s grasslands. Once established, they can persist during multi-year droughts, and resprout quickly after wildfires. Their deep roots also increase deep soil carbon and water-holding capacity, increasing water availability for all grassland plants during dry periods. Even with relatively low cover of native grasses and forbs in California grasslands, they can become dominant and play a critical role in ecosystem resilience under a changing climate.