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An Assessment of Fuel Treatment Effects on Fire Behavior, Suppression Effectiveness, and Structure Ignition on the Angora Fire

Description Of Fire Environment

Fuel and Topology

Fuel types within and adjacent to the fire perimeter vary by vegetation types. Most of the fire area is characterized by multi-storied mixed conifer stands with moderate and heavy dead woody fuel and mixed brush in the under story. A variety of vegetation and fuel management activities have occurred throughout the area.

Image of typical conditions in stand which havenot recieve fuel treatment

Figure 2: Typical conditions in stands which had not received fuel treatments

Conditions in untreated stands varied but were mostly dense, multi-storied stands with abundant ladder fuel (Figure 2). Live surface fuel consisted mostly of manzanita, bitterbrush, and sage brush. Heavy dead woody fuel loadings were present in the south part of the Angora Creek Stream Environment Zone (SEZ), and in the areas not actively managed. Fuel was sparser on the southwest perimeter and the southeast slope of Tahoe Mountain, where the terrain is steep and rocky.

Image of fuel treatment area southwest of Cayuga Circle

Figure 3: fuel treatment area southwest of Cayuga Circle (see Residential Area Street Map in Appendix A)

Where vegetation and fuel management activities have been implemented, stands were less dense, with fewer small trees, and greater numbers of large Jeffrey Pine. Surface fuel in these managed stands consisted of pine needles and brush, with small amounts of large decayed wood (Figure 3).

The topography within the fire perimeter varies from flat on the southeast flank to steep (>40%) on the south and southeast aspects and on the west side of Angora Ridge and Tahoe Mountain.

Table 1: Treatments types and approximate acres within Angora Fire perimeter. Source data is the LTBMU Geographic Information system Staff.
General Treatment Types Acres
USFS Fuel Treatments 480
USFS Other Vegetation Treatments 850
USFS Urban Lot Treatments 42
USFS Non Treatment 1,366
State CTC Urban Lot Treatments 24
California State Park Treatment 3
California State Park Non treatment 17
State Ownership, Non Treatment 79
Private and other 211
Total 3,072

Fire Danger and Fire Weather

The Angora fire started on Sunday, June 24, 2007, burning all of the structures and most of the acres in the first burning period. Fire danger was listed as "Very High." The Meyers Remote Automated Weather Station (RAWS) data showed the Energy Release Component (ERC), a measure of fuel dryness, was above the 90th percentile for the season, and set a record for the day (Appendix C). The large dead fuel moisture was 9%, and live woody fuel moistures were 73%, near record lows for the date. The minimum relative humidity was 8%, a record for the date and the maximum temperature was 80 degrees. Winds were initially southwest, and then changed to more westerly later in the day. Wind speeds were recorded at Meyers RAWS at 12 mph with gusts to 22 mph. Local Fire Danger experts indicated that the Meyers RAWS did not reliably indicate windspeed and direction. Firefighters and other eyewitnesses estimated wind gusts on the fire as high as 40 mph.