Research

Understanding and managing community and ecosystem dynamics in annual-dominated grasslands

Collaborators: Mary Cadenasso (UC Davis), Hopland Research & Extension Center, Pepperwood Preserve, 

Understanding and managing for the resilience of California’s grasslands is particularly challenging because they are dominated by annual species. The annual nature of this system makes it extremely sensitive to fluctuations in abiotic and biotic controllers and requires persistent management to meet conservation and production goals. It is critical to develop a framework by which we can understand, manage, and predict the response of these grasslands to multiple environmental and management activities, because current frameworks from other grasslands aren’t applicable to this “novel ecosystem”. 

Our research is building a conceptual framework for understanding, predicting, and managing annual-dominated grassland systems. Particularly for understanding the resilience of these systems, it is critical to better understand how the system “resets” each year, through the high seed production and seed germination rates, unique to annual systems, and how many factors influence seed production and seedling survival, including: annual weather conditions, soil, plant neighborhood, grazing, fire, and small mammals.

Much of this research focuses on how to manage grasslands for resilience to fire, drought, and climate change.

Controls over restoration success and failure

To improve restoration success, it is important to:

• Select sites well-suited to restoration, by identifying the site conditions that benefit restoration of specific species
• Improve site conditions before restoration plantings to enhance plant success
  • Improve our understanding of how specific site amendments can benefit or harm specific restoration species 
  • Use certain plant species to enhance site conditions (e.g. deep-rooted plants to increase soil drainage)

In California's grasslands, oak woodlands, and riparian systems, we are assessing the conditions that influence restoration success and failure, including: soil conditions, local hydrology, weather conditions during establishment, pathogens, herbivores, and management practices (including pre- and post-restoration). 

This work includes a project specifically focused on controls over California sycamore seed production and seedling establishment.

Plant species effects on multiple ecosystem processes: variations due to time, environmental conditions, and neighboring species

Plant community composition can alter most soil properties and processes, and thus vegetation manipulations have been commonly used to provide critical soil services in managed landscapes. While there is a strong conceptual background for predicting the average impacts a plant community has on soil, managers need to employ site-specific understanding because the effects of a given plant community change across environmental conditions and management practices. This is particularly true as we work to understand the ecosystem effects of different plant functional groups, and of native vs. exotic species.

We seek to develop a mechanistic understanding of plant impacts on multiple soil processes, and how these impacts change across space and time. These goals are pursued using experimental and observational approaches from plot to landscape scales. In all of these approaches, we investigate soil water, carbon and nitrogen dynamics. 

Impacts of precipitation change, nutrient deposition, and grazing management on community interactions between native grasses, exotic forage, and exotic noxious weeds in California grasslands

Collaborators: Carolyn Malmstrom (Michigan State U.), Kevin Rice (UC Davis)

Plant composition and ecosystem dynamics in semi-arid systems are strongly impacted by the timing and quantity of precipitation. Current precipitation patterns vary across sites and years in California grasslands, and climate change models predict that California grasslands will either experience wetter, longer growing seasons, or shorter drier seasons. In this study, we investigate:

1. How predicted shifts in precipitation impact plant community composition and diversity, particularly the presence of noxious weeds (recent invaders), annual forage species (invaded 200-300 years ago), and native grasses and forbs. In particular, we are interested in how these patterns are influenced by initial plant composition, nitrogen deposition, and timing of grazing.
2. What mechanisms underlie plant community responses? We will investigate the mechanisms driving community responses, focusing on the role of species differences in demographic traits and phenology of resource uptake.
3. How do plant species shifts influence the timing and magnitude of water, carbon, and nutrient fluxes under different precipitation regimes? Do these plant effects feedback to further alter vegetation dynamics?

Plant effects on soils feedback to alter success of restoration and invasion

Collaborators: Christine Hawkes (North Carolina State University), Sarah Hoskinson (UCD), Sarah Gaffney (UC Davis, Hopland Research & Extension Center)

In long-term plantings of native vs. exotic grasses in California, we have demonstrated that exotic and native grasses differ in their impacts on the timing, location, amount, and form of soil resources, and in the composition of the microbial community. We are investigating:

1. To what extent do species’ effects on soil feedback to alter competitive dynamics between natives and exotics?
2. The relative importance of the multiple feedback mechanisms in mediating competitive dynamics.
3. The extent to which different soil properties need to be altered to enhance restoration success.

Graduate student projects

Current graduate students in the lab are involved in research projects that are independent of those listed above. These include:

• David Mitchell: Impacts of soil amendments on soil conditions, soil microbial communities, Phytophthora, and riparian restoration success

Past graduate student projects include:

• Jill Baty: Effects of plant species on the role of soil foodwebs in litter decomposition, and how global change factors will alter these impacts.
• Evan Batzer: The impacts of nitrogen deposition on spatial patterns of vegetation composition and diversity in California annual grasslands.
• Tracy Erwin: Understanding ecotypic differences among populations of the rare species, Cordylanthus palmatus, and how these can be applied to conservation and restoration management.
• Sarah Gaffney: Effects of native grassland restoration on suppression of weeds, and the impacts of plant-soil interactions on restoration success.
• Kelly Garbach: Spatial dimensions of the ecosystem services provided by conservation plantings in agroecosystems in Costa Rica, as part of the payment for ecosystem services program.
• Liz Goebel: Controls over distribution of remnant stands of native grasses, and importance of grass-oak interactions in maintaining native oak savannah communities.
• Sarah Hoskinson: Effects of the proportion of plant species in mixture on ecosystem processes and plant-soil feedbacks.
• Marguerite Mauritz: Community interactions in Coastal Sage Scrub as mediated by plant-soil-water interactions and fire.
• Julia Michaels: The impacts of current and past livestock grazing on vegetation composition and beta-diversity in California’s vernal pools.
• Sophie Noda: Effectiveness of burn piles on control of coyote brush, and restoration of coastal prairie
• Isaiah Thalmayer: Woody seedling restoration success, as influenced by soil inoculations from drier vs. wetter sites.
• Ben Waitman: Effects of nitrogen deposition on interactions between plants, ectomycorrhizae, and soil processes.
• Rebecca Wynd: Effects of grazing on forb diversity and composition.