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Grassland Restoration Action Science and Stewardship Network (GRASS-Net)

The goal of GRASS-Net is simple: provide evidence-based recommendations to land managers for restoring drought resilient grasslands in California. Current grassland restoration practices lead to biological homogenization as practitioners use the same 7 native species that are known to succeed. In collaboration with several other CSU campuses, our lab is quantifying a novel lethal drought index (e.g., soil moisture at 50% population mortality) for 20+ native species to expand the species selection pool utilized by restoration practitioners. We're also measuring several plant functional traits (e.g., specific leaf area, turgor loss point, and leaf nitrogen content) to determine whether functional traits can act as proxies of plant mortality. Click here to learn more about GRASS-NET and ongoing developments in the network.

Assessing post-wildfire drought impacts on California seed banks

California’s ecosystems are facing a trifecta of global change drivers: wildfire, drought, and biological invasions. This project aims to understand the synergistic effects of these stressors on belowground seed banks. Preliminary data from the Big Chico Creek Ecological Reserve (BCCER) suggests high frequency prescribed fire promotes native plant diversity and reduces the spread of invasive species. These preliminary data were collected 3 months prior to the Park Fire, which ignited in July 2024 and rapidly spread to become the 4th largest wildfire in the state’s history, burning >420,000 acres. Tragically, much of BCCER was burned, including the sites where we've surveyed seed bank diversity. In 2025, we will be assessing seed bank recovery from this historic wildfire as well as post-wildfire drought impacts.

Grassland Sensitivity to Extreme Drought

​Globally, all ecosystems will be impacted to some extent by changes in climate means and more frequent and severe periods of climatic extremes. The goal of the Extreme Drought in Grasslands Experiment (EDGE) was to understand how and why grassland ecosystems differ in their sensitivity to extreme drought. EDGE employed large rainfall exclusion shelters across six grasslands within the central US from desert grasslands to tallgrass prairie. The shelters intercepted ~66% of incoming precipitation over a 4 year period. The sensitivity of above- and below-ground primary productivity, species composition, and plant functional traits were assessed annually throughout the project.

Key findings

• Drought sensitive grassland sites were characterized by both low community functional diversity (i.e. trait dissimilarity between species) and a scarcity of drought tolerant species.​ Additionally, the four-year experimental drought shifted community functional composition towards reduced drought tolerance and increased functional diversity. Published in Journal of Ecology - download here
• Our experimental drought reproduced the paradoxical responses that were observed during the 1930's Dust Bowl – warm-season C4 grasses replaced by cool-season C3 grasses – which we attribute to changes in precipitation seasonality during drought. Published in PNAS - download here
• These results were presented to the UC Davis Plant Science Department in February 2024 - click to view the seminar

Mechanisms of Plant Invasions

Understanding the mechanisms of competitive superiority of invasive plants over native species is a priority for the preservation of global biodiversity. We've conducted a home-away range comparison of photosynthetic performance and leaf N allocation patterns of plant invaders, involving 27 woody and herbaceous invaders sampled across populations in France, Japan, and central New York, including those common in forests and fields of low- and high-light regimes. The global scale of this project allowed us to test the hypothesis that invader advantage in the non-native range is a result of shifting N allocation away from leaf structure or defenses (e.g., cell wall proteins and secondary metabolites) and towards photosynthetic machinery (e.g., Rubisco or proteins involved in light harvesting and the associated electron transport chain). 

Key Findings

• A case study of Japanese knotweed (published in Biological Invasions - download here) as well as preliminary analyses across the entire dataset suggest leaf N allocation shifts in the invaded range for invaders, facilitating greater assimilation rates compared to natives, and shifts are consistent with optimal leaf N partitioning in sun versus shade environments. 

Functional Traits of Grasses

Grassland in the SF Bay Area (Photo credit: Brody Sandel)

Plant traits include any morphological, physiological, or phenological characteristics which impacts plant fitness via their effects on growth, reproduction or survival. Plant traits can influence both their response to environmental change and their effect on climate and ecosystem processes. The global grass trait database (pioneered by Brody Sandel at Santa Clara University) is a growing dataset of plant traits for grass species (family: Poaceae) including >120 species. Our goal for this dataset it to assess how functional traits vary within species (intraspecific variation) and respond to spatial and temporal variation in climate. Grasses are a highly successful group of plants from an evolutionary perspective with ~ 11,500 species worldwide. They are the dominant growth form of grasslands, which cover 52 million square kilometers, or roughly 40% of Earth’s terrestrial land surface, and make a significant contribution to the terrestrial carbon sink. Humans are heavily dependent on grasses for food (e.g. corn, rice and wheat), building materials (e.g. bamboo) and forage for livestock. Despite their ecological, economic and cultural importance, grasses have received relatively little attention in functional trait studies, and we hope to fill that gap

Ecological Responses to Rainfall Variability

​Climate Change is expected to alter precipitation patterns across the Great Plains region leading to fewer but larger rainfall events with longer dry intervals between events. Results from past precipitation manipulation experiments suggest that this shift in rainfall patterns will lead to increases in net primary production in arid grasslands. These past experiments often use weekly watering treatments which fail to represent the natural stochastic patterns of precipitation. With a separate rainfall manipulation experiment in a semi-arid grassland in Colorado, I mimicked the rainfall pattern of a historically variable growing season. Using irrigation treatments, I then deconstructed this ambient precipitation pattern to eliminate growing-season variability in (1) rainfall event size, (2) event timing, or (3) both event size and timing while keeping total precipitation amount equal across treatments. Whole ecosystem responses as well as physiological responses of the dominant grass species were measured within each treatment. 

Example shelter in the shortgrass steppe of Colorado receiving irrigation treatments

Key Findings

• Removing variability in both rainfall event size and timing increased net primary production and reduced variability in soil CO2 flux, both of which were associated with more frequent soil moisture pulses and reduced physiological stress of the dominant grass species ​(published in Journal of Ecology - download here)