PARENT SESSION
Contributed Oral Session 148: Biogeochemistry: Nutrient Dynamics
Friday, August 12, 8:00 AM - 11:30 AM, Meeting Room 511 B, Level 5, Palais des congrès de Montréal
Season of burning: the differential effects of spring and fall prescribed fire on soil nitrogen and carbon fluxes.
Hamman, Sarah *,1, Burke, Ingrid 1, Knapp, Eric2, 1 Forest, Range, Watershed Stewardship Department, Fort Collins, CO, USA2 U.S. Forest Service Pacific Southwest Research Station, Redding, CA, USA
ABSTRACT- Historically, most fires in the mixed conifer forests of the Sierra Nevadas burned late in the growing season. Today, maintaining a fire regime that incorporates late season burning is extremely difficult due to limited number of prescription days and considerable air quality concerns. Conducting prescribed burns earlier in the growing season, when environmental conditions are more suitable, is a potential solution, but spring burning may have significantly different effects on soil properties and processes. We quantified differences between fall and spring burning effects, relative to controls, on soil carbon and nitrogen turnover rates two years post-fire in the Giant Forest region of Sequoia National Park, California. We conducted soil respiration and net nitrogen mineralization measurements and assessed several environmental parameters that influence these nutrient turnover rates (soil moisture, temperature and pH). Spring burning did not alter soil moisture levels but fall burning significantly decreased soil moisture relative to the control. Soil temperature was significantly higher relative to the control in both the spring and fall burn sites and soil pH increased more in fall burns sites than in spring burn sites. All of these parameters can impact the turnover rate of the labile soil organic matter and, hence, the nutrient availability in the soil. We found significantly lower soil respiration rates with burning but there was no differentiation between spring and fall burning. Relative to the control, the average net nitrogen mineralization rate was lower in spring burn sites and higher in fall burn sites, suggesting differing rates of microbial immobilization in the two treatments. Based on these results, any management decisions involving seasonal prescribed fire should consider the relative impacts on soil nutrient turnover and availability.
Key words: fire ecology, soil nitrogen mineralization, soil respiration