Natural resource managers in California have the ambitious goal of treating for fire prevention one million acres of forestland annually by the year 2025. Meeting this goal will require using all available tools that are effective in reducing wildfire severity. Prescribed fire is arguably the most appealing tool because it is relatively inexpensive and aligned with the disturbance regime to which California’s forest ecosystems are most adapted. However, prescribed fire is operationally challenging because burning is restricted to a limited number of days. As fuels dry out, optimal conditions for prescribed fires typically occur in the spring. But because fires historically occur during the summer and fall, there is concern around burning in the spring given uncertain ecological effects. In particular, an area of critical uncertainty is how spring burns will affect tree mortality and cascading effects on soil microbial communities that drive soil carbon (C) storage and greenhouse gas (GHG) emissions. This is because most research has focused on fire impacts on aboveground C stocks despite most C being stored belowground. Indeed, soils store ~1500 Gt C, which is more than vegetation (~560 Gt) and the atmosphere (~750 Gt) combined. These large terrestrial soil C stocks are correlated with soil microbial biomass, suggesting that soil C storage is driven by microbes. Our team will provide critical information to determine if conducting prescribed fires in spring reduces or exacerbates tree mortality and the effects on the microbes that control C sequestration and GHG emissions. Thus, we ask: how do spring vs fall fires affect tree mortality, their associated soil microbial communities and, in turn, soil C storage and GHG emissions?

Seasonal burn effects on vegetation have been studied in mature forests and indicate that spring fires may induce higher plant mortality than fall fires. This may be due to spring burns being concurrent with bark beetle emergence as well as tree vulnerabilities related to higher live fuel moistures and active cambial growth. Fire seasonality effects on young forests, however, are uncertain, and is in unclear if studies from mature forests translate to young forests. Most importantly, how burn season affects soil microbial communities and their influence on soil C storage, remains a large knowledge gap. The net impact of fires on soil C sequestration likely depends on the season in which the fire burns and how seasonality impacts soil microbial resilience—the rate at which microbial composition returns to its original state after a disturbance. Resilience is likely to be affected by fire season since microbial dispersal and growth rates are strongly affected by timing of precipitation and soil moisture. Thus, if spring fires cause higher plant mortality in both mature and young forests, then likely they cause higher mortality for associated soil microbes, not only because they are killed by heat but also because they lose photosynthetic C inputs from dead trees.

Here, we leverage and vastly expand in scope the existing the Treatment Alternatives for Young Stand Resilience (TAYSR) study in the California Sierra Nevada to address a wide knowledge gap: the effect of prescribed burn season on tree survival, microbial communities, and their impacts on C cycling and GHG emissions. To this end, we use advanced biogeochemistry and molecular tools to answer the following questions:

What is the influence of burn season (spring vs fall) and stand age (young vs mature) on:
1) Crown scorch of mixed conifer tree species during similar dead fuel moisture and air temperature conditions, and tree mortality post-fire?
2) Resilience of bacterial and fungal biomass, richness, and composition?
3) The fate of soil carbon?
4) Trace gas (NO) and GHG (CO2, N2O) emissions?

No publications at this time.

For more information on this project please visit:

The Glassman Lab website: 
https://sydneyglassman.wordpress.com/

Contact Information:

Sydney Glassman, Ph.D. (PI)
sydneyg@ucr.edu

CAL FIRE Forest Health Research Program
FHResearch@fire.ca.gov