Table 4 Factors used to estimate probabilities of the occurrence (random events) or impact (cyclical events) of each type of event. Temperature and precipitation values are based on Oregon Climate Division 7 descriptive statistics for water years 1885 to 1886 through 2007 to 2008. Fire occurrence records cover 1980 to 2006 fire years for Lakeview and Burns Bureau of Land Management districts and Hart Mountain Refuge. Wind frequency is based on 10-minute average wind speeds in August from 12 remote automated weather stations located within the Malheur High Plateau area. Reynolds Creek Experiment Range snow data cover 1967 to 1968 through 1996 to 1997 water years.

Stand-replacing fire

WM (0.0085)

Frequency of May monthly temperature ≥13 °C multiplied by frequency of winds ≥24 km hr⁻¹ in August.

Reduced by 25 % to account for sufficient fuel but lack of ignition. Decreased in low and average fire years. Increased in high and extreme years.

Swetnam and Betancourt 1990, 1998, Rorig and Fergusson 1999, Grissino-Mayer and Swetnam 2000, Heyerdahl et al. 2002, Rollins et al. 2002 (probability basis, ignition adjustment) Oregon Climate Division 7 records (precipitation and temperature) Remote Automated Weather Station (RAWS) records (wind) Fire occurrence records (frequency of low, average, high, and extreme fire years) Expert opinion (ignition and grazing adjustments)

CM (0.0062)

Combined frequency of spring precipitation ≥75^th percentile and summer precipitation ≤25^th percentile multiplied by frequency of winds ≥24 km hr⁻¹ in August.

WD (0.0046)

Combined frequency of spring precipitation ≥75^th percentile and average June temperature ≤13 °C multiplied by frequency of winds ≥24 km hr⁻¹ in August.

SD (0.0046)

Same as WD Group.

Mosaic fire

WM (0.0645)

Frequency of May monthly temperature ≥13 °C minus stand-replacing fire frequency.

Reduced by 25 % to account for sufficient fuel but lack of ignition. Decreased in low and average fire years. Increased in high and extreme years.

Same as above

CM (0.0497)

Combined frequency of spring precipitation ≥75^th percentile and summer precipitation ≤25^th percentile minus stand-replacing fire frequency.

WD (0.0352)

Combined frequency of spring precipitation ≥75^th percentile and average June temperature ≤13 °C minus stand replacing fire frequency.

SD (0.0046)

Same as stand-replacing fire in WD Group.

Drought*

All (0.0375)

Literature

None

Cook et al. 2004, Stahle et al. 2007 (cycle and impact)

Insect Outbreaks

All (0.2943 for buildup and crash) (0.4388 for peak)

Literature

None

Gates 1964, Hall 1965, Speer et al. 2001, Speer and Jenson 2003 (cycle and impact)

Pronghorn herbivory

WD, SD (0.0199)

Combined frequency of winter precipitation ≥129.0 mm plus winter average temperature <−1.07 °C.

Reduced by 75 % to account for limited area of impact.

Kindschy et al. 1982, Verts and Carraway 1998, Keating 2002, Yoakum 2006

Freezekill

CM (0.0088)

Combined frequency of winter precipitation ≤68 mm plus January average temperature≥0.89 ^°C.

Reduced by 75 % to account for limited area of impact.

Hanson et al. 1982, Walser et al. 1990, Hardy et al. 2001 Oregon Climate Division 7 (precipitation and temperature) Expert opinion (adjustment factor)

Snow mold

CM (0.0177)

Combined frequency of winter >179 days, snow depth >2087 mm, snow melt date laterthan 25 May.

Reduced by 75 % to account for limited area of impact.

Sturges 1986, 1989 Reynolds Creek Experimental Range data (winter length, snow depth, snow melt date) Expert opinion (adjustment factor)

Vole Outbreaks

CM (0.036 for MSO) (0.0785 for LSO) (0.01 for LSC)

Literature

Reduced by 90 % to account for limited area of impact.

Murray 1965, Frischknecht and Baker 1972, Parmenter et al. 1987 (cycle and impact) Expert opinion (adjustment factor)