Environmental Assessment

AFFECTED ENVIRONMENT & ENVIRONMENTAL CONSEQUENCES CHAPTER 3
Fuel models 2, 5, and 6 are the predominate models in the planning area. Fuel models 8, 9, and 10 are
present. The slash fuel models - 11, 12, and 13 (light, medium, and heavy slash respectively) - are not
present due to treatments in previously harvested areas. Fuel models 1, 3, 4, and 7 do not exist in the
planning area.
Fuel models 6 and 10 are rated as high or extreme for fire behavior potential. Collectively they
encompass 33 percent of the planning area or approximately 18,491 acres. Fuel models 2 and 9, rated
moderate for fire behavior potential encompass 51 percent of the planning area or approximately 27,751
acres. These four fuel models collectively include 84 percent of the planning area acres or 46,242 acres.
A typical fire season on the Bend-Fort Rock Ranger District is defined as from May 15 th through
September 30 th . The analysis of the effects of a fire burning under the three alternatives is based on 90 th
percentile day 47 weather conditions. The 90 th percentile day weather conditions are based on observations
obtained from a weather station located within northwest corner of the planning area, located within the
planning area boundary. Based on observations from that station, the following conditions are considered
to be representative of weather for the planning area on the 90 th percentile day:
air temperature of 90 degrees Fahrenheit;
relative humidity of 13 percent;
wind speeds of 12 miles per hour measured 20 feet above the tallest vegetation;
1-hour fuel moistures of 3.4 percent;
10-hour fuel moistures of 4.9 percent;
100-hour fuel moistures of 10.8 percent;
live herbaceous fuel moistures of 50 percent; and
live woody fuel moistures of 60.7 percent.
The above information/assumptions were used to model expected fire behavior in the planning area using
the BEHAVE program. Models 2 and 6, representative of the ponderosa pine/grass understory and xeric
shrub habitats respectively, were used to model the existing condition as they represent approximately 71
percent of the planning area acres. Model 9, which represents stands of ponderosa pine characteristic of
conditions found at the time of Euro-American settlement, was run to represent the desired conditions,
both in terms of vegetation and expected fire behavior.
Table 3-23 displays the results of the BEHAVE model runs for the Opine planning area.
Table 3-23 Selected Fire Behavior Conditions
Fuel Model Flame Length (feet) Rate of Spread (maximum) ch/h
Fuel Model 6 6.8 feet 36 chains per hour
Fuel Model 9 3.2 feet 9 chains per hour
Fuel Model 2 7.0 feet 38 chains per hour
Under conditions of the 90 th percentile day, flame lengths can range from three (3) to 7 feet. When flame
lengths exceed four (4) feet in length, fires are too intense for direct attack and require mechanized
equipment and/or retardant drops for effective control. Based on observations from the Skeleton fire we
may expect even higher flame lengths.
47 During a typical fire season, 90 percent of days have weather conditions that are cooler, have higher relative humidities, and
lower wind speeds than the 90 percentile day. The remaining 10 percent of the days are warmer, have lower relative humidities,
and higher wind speeds.
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