Investigators:
J.Morgan Varner
Grants:
"Predicting fire behavior and fire effects resulting from elevated atmospheric [CO2]", Humboldt State University RSCA Grant, $4,700, 2006 - 2007
Description:
Questions addressed:
We are using model-estimated fire behavior and small lab burns to compare fire behavior between ambient and elevated CO2 atmospheres.Protocol:
Project design consists of approximately 20 plots in each of the ambient and elevated [CO2] sites, which will include measurements for fuel loading, stand structure and collection of litter samples. Location, distance between plots and direction of sampling plane will be randomly selected and fuel measurement procedures will follow standard non-destructive field procedures (Brown 1974). Total transect length will be 12 m and will include measurements of all time-lag classes, litter (Oi horizon) depth, duff (Oe + Oa) depth, and fuel height (see figure 2). Fuel loading calculated from these data will be input into BehavePlus and FOFEM modeling programs.Stand structure will be characterized by measuring the two closest trees to plot center at each plot. Tree height, crown base height, and diameter (dbh) values will be recorded for use in the NEXUS simulation-modeling program.
Samples of forest floor litter will be collected at every other designated plot and will be located 0.5 m from plot center at a 90° angle. Samples will be collected using a 30 x 30 cm frame and placed into sealed polyethylene bags. Collected fuels will be cooled and transported to the Humboldt State University's Fire Lab for oven-drying (60° C) to determine moisture content. Oven-dried fuels will be exposed to the lab atmosphere to reach 5% moisture content (dry wt. basis) prior to burning. All collected fuels will be arranged on the burn platform in 15 g (dry wt.) fuelbeds at bulk density values that approximate field conditions at FACE. Fuels will be ignited with a standard ignition source (xylene-soaked cotton string matrix above the fuelbed) and monitored for duration of burn. Fire behavior characteristics to be recorded are outlined in the data analysis section of this proposal.
Data Analysis
To predict fire behavior under elevated [CO2] regimes, we will use BehavePlus 3.0.1 (Andrews et al. 2003) and NEXUS (Scott 1999) fire simulation programs. BehavePlus uses fuel, topographic, and weather inputs to simulate rate of fire spread, spotting distance, and fire intensity. NEXUS uses similar inputs along with vegetation data (canopy bulk density, canopy base height, and foliar moisture content) to estimate canopy ignition and crown fire spread. To estimate deviations due to climate change we will use both published and collected data on fuel loading and predicted shifts in ambient weather. Data will be analyzed using standard ANOVA comparing ambient and elevated fire behavior under 5 different moisture scenario simulations.
To predict the effects of fire on altered vegetation, we will use the simulation program FOFEM 5.0 (Reinhardt et al. 1997). FOFEM uses fuel loads and vegetation composition and structure to predict tree mortality, smoke production, and soil heating. To simulate these fire effects, we will input published (e.g., Davis et al. 2002) and collected fuel loading data from Duke's FACE site. Fire effects data will be analyzed using standard ANOVA comparing ambient and elevated fire effects (tree mortality, smoke production, and soil temperatures) under 5 different moisture scenario simulations.
We will compare simulation results with results gathered from mesocosm fires using collected litter from Duke's FACE site, where ecosystems were grown in ambient and elevated (range 650-720 ppm) [CO2]. The Humboldt Fire Lab facility consists of a 1.2 m x 2.4 m platform beneath an adjustable draw hood that can be raised or lowered over constructed fuelbeds. On the platform, fuels are ignited with a standard ignition source (xylene-soaked cotton string matrix above the fuelbed). For each burn, we will measure flame height (=fire intensity), duration of flaming, duration of smoldering, total burn time, and residual ash (% consumed). Comparisons will be made between litter fuels grown at ambient and elevated CO2. We will use ANOVA to evaluate treatment effects of elevated [CO2] on flame length, flame time, smolder time, total burn time, and percent fuel consumed by experimental fires.