Age-class Mosaics and Wind-driven Fire: Further Fuel for the Debate

Authors

Jan L. Beyers, U.S. Forest Service
Philip J. Riggan, U.S. Forest Service
David Weise, U.S. Forest Service
Timothy Paysen, U.S. Forest Service
Marcia Narog, U.S. Forest Service

Date of this Version

2012

Document Type

Article

Citation

Final Report. JFSP Project Number 07-1-2-10

Comments

US government work.

Abstract

In 2006 the Santa Ana wind-driven Esperanza fire burned through the North Mountain Experimental Area (NMEA) and vicinity, including the scars of 10 previous fires. Multiple images of the fire’s progression were taken using PSW Research Station’s airborne FireMapper thermal-imaging system. Existing fuels data and historic NMEA maps plus new fire images were used to investigate relationships between vegetation history, fire behavior and severity, and fuel consumption. Soil samples were collected at a subset of fire severity sample points to assess seed bank survival. Coordinated documentation of vegetation recovery addressed the effects of age class and fire severity on chaparral regeneration and non-native species invasion. Ground sampling of fuel characteristics combined with remote sensing demonstrated that the multispectral FireMapper instrument can provide an improved means to acquire the needed pre and post-fire fuels data necessary for quantitative, high-resolution measurement of wildland fire. Detailed analysis of the field data and remotely sensed data showed that the standard fire behavior fuel models for chaparral and grass did not capture the range of fuel loading associated with elevation and stand age. Fuel loading showed a general correspondence with observed fire behavior (radiant heat release (W m-2). Southwestern spread of the Esperanza Fire was contained near boundaries of previous fires and young fuels. Fuel, fire perimeter, and energy release data from FireMapper roughly agreed with simulation results from the CAWFE model. We were able to use FireMapper imagery to identify and differentiate various landscape features on vegetation plots to transect resolution. This included separation of general plant characteristics such as large compared to small leafed species. Sequential images reflected the increased plant cover observed from repeated measurements of vegetation plots. This technology appears to have utility for monitoring general plant cover recovery for large and/or remote areas. Areas containing older chaparral stands (>50 years since last fire at the time of the Esperanza fire) and higher fuel loading corresponded to areas of higher burn severity (as determined by ground crews). Species richness was greatest in mid-age burns (11-50 years since previous fire). At three years post-fire, non-native grasses were the most abundant cover type. Non-native species dominated both burned and unburned fuel breaks.