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Understory recovery after low- and high-intensity fires in ponderosa pine forests of northern Idaho

Compiler(s): Corey L. Gucker, Roberta A. Walsh, Janet L. Fryer
Year Published: 2017

Researchers compared early postfire vegetation recovery on sites burned with different intensities in seral ponderosa pine communities of the Douglas-fir/mallow ninebark habitat type. The plots were burned over 30 days burned under varying conditions of temperature, fuel moisture, and relative humidity, resulting in fires of varying intensity [1,2]. Mean prefire fuel load on burned sites was 58,200 kg/ha, nearly half of which was duff [3]. Three replicated high-intensity burns, low-intensity burns, and unburned sites were sampled. High- and low-intensity fires had significantly different (P<0.05) fireline intensities. Energy released by high-intensity fires was between 30 to 3,034 kcal/m/s and averaged 781 kcal/m/s; energy released by low-intensity fires averaged 127 kcal/m/s and ranged from 25 to 194 kcal/m/s. Flame lengths averaged 0.9 m and ranged from 0.1 to 1.7 m on all sites. On average, duff smoldered longer on high-intensity plots than on low-intensity plots. Significantly more duff was consumed on the high-intensity fire plots (80%) than on low-intensity fire plots (40%). Postfire depth of duff averaged 6.6 cm on unburned plots, 4.0 cm on low-intensity plots, and 1.3 cm on high-intensity plots [1,2]. FIRE EFFECTS ON PLANT COMMUNITY: Researchers measured cover and frequency on burned and unburned plots for 3 consecutive posttreatment years (1979-1981). Shrub canopy estimates came from line intercept sampling using five 10-m transects in macroplots (15×15 m). Cover and frequency of herbaceous vegetation was measured in 10 microplots (20×50 cm) at the edge of the shrub transects. Level of significance was set at P<0.1 for all variables that follow [1,2]. Graminoid coverage was significantly lower on high-intensity plots than on unburned plots during all 3 years of treatments [1,2], although it increased significantly from the 1st to the 3rd postfire year on burned plots. Significantly more duff was removed on plots burned at high intensity. The authors attributed low coverage of graminoids on high-intensity plots to prolonged duff smoldering, which killed graminoid rhizomes and root crowns [1]. Forb coverage was greatest on low-intensity plots, and researchers noted that increases in forb coverage on burned plots were significantly greater than on unburned plots for all 3 postfire years. Shrub coverage was not significantly different between treatments [2].

Citation: Gucker, Corey L.; Walsh, Roberta A.; Fryer, Janet L., compilers. 2017. Research Project Summary: Understory recovery after low- and high-intensity fires in ponderosa pine forests of northern Idaho. In: Fire Effects Information System, [Online]. Missoula, MT: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer).
Topic(s): Fire Effects, Ecological - Second Order, Vegetation, Fuels, Fuels Inventory & Monitoring, Post-fire Management
Ecosystem(s): None
Document Type: Synthesis
NRFSN number: 18266
Record updated: Nov 5, 2018