16. Chaparral Resilience and Future Concerns 2

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Chaparral Resilience and Future Concerns 2

Friday, October 21 at 10:00-11:40 am, Donner Room

*note alternate instance of this session – Thursday at 10am

Session Description: Chaparral contains 24 percent of California’s native plant species, and more of these plants are considered rare here than in any other plant community. Since chaparral exists in every single county, chaparral represents the most accessible native plant experience to the greatest number of Californians and visitors to our state, and it provides unique research and educational opportunities. Due to the uniqueness of chaparral it presents major challenges to fire managers concerned with balancing fire hazard reduction and resource conservation. This session will explore the remarkable biodiversity, resilience, and value that chaparral provides to all the life forms and the need to address threats to vegetation type conversion in light of many global changes.

Session Chair: Jon E. Keeley (U.S. Geological Survey, University of California, Los Angeles, CA, USA) and Tom Parker (San Francisco State University, CA, USA)

16.2 Balancing fuel management goals and the ecological impacts of fuel modification

Robert Fitch (University of California, Santa Barbara, Santa Barbara, CA, USA), Carla D’Antonio (University of California, Santa Barbara, Santa Barbara, CA, USA), Nicole Molinari (USDA Forest Service)

In California, fuel breaks in chaparral habitat become invaded by non-native annual grasses which along with anthropogenic wildfire, pose direct threats to shrubland ecosystems. Thus, there is a need to balance the goals of human safety and the ecological impacts of wildland management. Our goal is to understand how to reduce the ecological consequences of fuel modification by eco-engineering fuel breaks with native herbaceous species to limit the impacts of non-native species, reduce ignition risk, and support desired ecosystem functions. In order to understand how native plant communities could differ in desirable ecological traits and fuel characteristics from the current vegetation that dominates fuel breaks, non-native annual grasses, we started a plot-scale restoration experiment in a fuel-modified habitat in the Los Padres National Forest, Santa Barbara, California. Plots were restored by either seeding a community of annual forbs, or by hand planting a community of bunchgrasses and perennial forbs. Control plots were established nearby which contained non-native annual grasses and forbs. For three years, the different plant communities were monitored including metrics for wildfire spread and ignition potential, live fuel moisture, fuel load, live/dead biomass, and litter depth, as well as ecological traits, invasion resistance, and floral availability. Native species communities retained live fuel moisture over the summer and created less litter, whereas the non-native community lost all live fuel moisture in spring and generated more litter. Thus, the native communities would likely be more difficult to ignite and propagate fire. Therefore, the native herbaceous communities potentially created more favorable fuel conditions than the non-native community, giving creditability to using native species on fuel breaks to meet fuel management goals, while supporting desirable ecosystem services.

16.3 The effect of deer browsing on post-fire recovery of seedlings from three endemic chaparral taxa on Santa Catalina Island: Results from 13 years of plot surveys

Brandon Pratt (California State University, Bakersfield, CA, USA)

The islands of southern California contain a rich woody flora with many rare and endemic species. Introduction of megaherbivores has dramatically altered these ecosystems. On Santa Catalina Island, mule deer and American Bison are the current two introduced megaherbivores. The deer are browsers and vigorously consume many chaparral shrubs species. Small seedlings may be especially sensitive to herbivory, thus post-fire chaparral seeders may be uniquely vulnerable to introduced herbivores. Following the 2007 Avalon Fire, we established plots at four sites to examine seedling recruitment of three endemic chaparral post-fire obligate seeders on Catalina Island including Ceanothus arboreus (2 sites), C. megacarpus, and Arctostaphylos catalinae. Each site contained plots with seedlings exposed to deer browsing and plots that were protected by fencing. After fire, abundant seedlings germinated, and densities ranged from an average of 26-225 seedlings/m2, which contrasts with the very few adults that were present prefire. Mortality ranged between 72% and 99.5% as of July 2021, with the highest mortalities occurring for C. arboreus and A. catalinae. Mortality due to deer browsing and trampling has been apparent in all unprotected plots, whereas mortality due to drought and density dependent competition appeared common for protected plants. At more mesic sites, fences have promoted a more robust chaparral recovery than the paired unprotected sites, whereas at the drier sites, mortality in the protected plots has matched those unprotected. Deer browsing has resulted in dramatically shorter individuals and more open habitat with lower leaf area index. Seed bank measures suggest that if another fire occurs, unprotected plots will not recover. Herbivory and disturbance from introduced megaherbivores are important factors promoting loss of shrub cover and conversion of chaparral shrublands into more open habitats.

16.4 Chaparral shrub wood structure illustrates diverse hydraulic strategies and differential susceptibility to drought

Anna L. Jacobsen (California State University, Bakersfield, CA, USA)

Chaparral shrub species differ in the way they use water (hydraulic strategies). Co-occurring shrub species may include those that are deep and shallow rooting; evergreen, semi-deciduous, and deciduous; have low and high wood density; and are relatively fast and slow growing. Species are also highly diverse in their wood structure, and anatomy. The characteristics of vessels, which are the cells specialized to transport water in wood, are particularly important in understanding water transport and hydraulics. Species fall into different categories: those with generally narrow vessels, generally wide vessels, and heterogeneous vessel diameters. These vessel structural traits are associated with hydraulic strategies of resistance or avoidance, with each of these differing in how susceptible they may be to drought-associated mortality. Globally, chaparral species include some of the most drought tolerant species recorded, but some of those same species are also vulnerable to drought-induced mortality, which can drastically alter community composition following extreme drought events. Understanding diverse chaparral hydraulic strategies is key to predicting differential susceptibility of species to future extreme events and climate change.

16.5 Got Bots? A survey of latent fungal pathogens and dieback in big berry manzanita during an historic southern California drought

Laura Drake-Schultheis (UC Santa Barbara, Santa Barbara, CA, USA; Westmont College, Santa Barbara, CA, USA), Ryoko Oono (UC Santa Barbara, Santa Barbara, CA, USA), Carla M. D’Antonio (UC Santa Barbara, Santa Barbara, CA, USA)Dieback and mortality in wildland plant species due to climate change has been on the rise in recent decades, and latent fungal pathogens may play a significant role in these events. During a severe multi-year drought, canopy dieback associated with latent pathogens in the Botryosphaeriaceae (Bot.) family was observed in stands of a dominant shrub species, big berry manzanita (Arctostaphylos glauca), across chaparral landscapes in California. These fungi are significant pathogens of woody agricultural species, especially in hosts experiencing stress, and have become a threat to economically important crops worldwide. However, little is known regarding their occurrence, distribution and impacts in wildland systems. We conducted a field survey of three hundred A. glauca shrubs across an elevational gradient to identify Bot. infection as it relates to a) A. glauca dieback severity and b) landscape variables associated with plant drought stress. We found Bot. widely infecting A. glauca across the landscape. Two Bot. species, Neofusicoccum australe and Botryosphaeria dothidea, were most abundant, with N. australe being the most common and, based on haplotype analysis, likely the most recently introduced of the two. The level of Bot. infection did not vary significantly across the landscape or with dieback; however, elevation was shown to be a strong predictor of dieback severity in generalized linear models, suggesting infected shrubs at lower elevations are most susceptible. Our results confirm the wide distribution of latent Bot. fungi in a wild shrubland system, and provide valuable insight into areas of greatest risk for shrub dieback and mortality. These findings may be particularly useful for informing future wildlands management strategies with regard to introduced latent pathogens.

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