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Research Project Summary: The effects of experimental fires in an Alaskan black spruce/feather moss community

• FIRE MANAGEMENT IMPLICATIONS
• STUDY LOCATION
• SITE DESCRIPTION
• PREFIRE PLANT COMMUNITY AND FUELS
• PLANT PHENOLOGY
• FIRE SEASON AND SEVERITY CLASSIFICATION
• FIRE DESCRIPTION AND EFFECT ON FUELS AND SOIL
• FIRE EFFECTS ON PLANT COMMUNITY
• APPENDIX: SPECIES INCLUDED IN THE SUMMARY
• REFERENCES

Source:
Unless otherwise indicated, the information in this Research Project Summary comes from the following paper:

Viereck, Leslie A.; Foote, Joan; Dyrness, C. T.; Van Cleve, Keith; Kane, Douglas; Seifert, Richard. 1979. Preliminary results of experimental fires in the black spruce type of interior Alaska. Res. Note PNW-332. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Forest and Range Experiment Station. 27 p.

• Prescribed fires on small units can simulate at least moderately severe wildfires in black spruce stands: The experimental fires generally spread and crowned quickly. They burned in a mosaic, similar to patterns observed in nearby areas burned by wildfires.
• Aboveground vegetation was "almost completely" killed or top-killed. The forest floor was consumed to varying depths, with thickness reduced by 24% to 62 %. Consequently, the forest floor displayed a mosaic of different fire severities.
• The moisture content of forest floor materials is extremely important in controlling fire severity in black spruce/feather moss stands.
• Fuel load enhancement was unnecessary to achieve desired fire severities; "unloaded" units burned at intensities similar to those of units with added fuels.
• Fuels were too moist to meet prescription for most of the summer. Although aboveground conditions were similar on the 2 burning days, depth of burning into the soil organic layer was considerably less in the late July vs. the late August fires. This was attributed to moister conditions of the forest floor in July. On 22 July, soil moisture content was about 60% by volume 15 cm below the forest floor. On 26 August, it was about 30%.
• Black spruce was expected to regenerate successfully after these fires. Its seedfall began shortly after the fires. Abundant seedling establishment was expected, beginning in postfire year 1.

STUDY LOCATION:
The study was conducted at the Washington Creek Fire Study and Training Area, about 40 km north of Fairbanks, Alaska (latitude 64.20 longitude -149.49 radius 10 km).

SITE DESCRIPTION:
The burned area was on a ridgetop that sloped to the southeast. Elevation was approximately 520 m. The soil was a shallow silt loam with shattered bedrock and stones at a depth of 20 to 50 cm. No permafrost was present. The study area was divided into 5 units, 4 of which were burned (Units 1L, 2, 3, and 4L). Units ranged in size from 0.09 to 0.15 ha, separated by firelines. Total area burned was 1 ha.

PREFIRE PLANT COMMUNITY AND FUELS:
The prefire community was a 70-year-old stand of black spruce/feather moss with some paper birch, American green alder, feltleaf willow, and Scouler willow. Trees grew in scattered clumps, with density ranging from 2,226 to 5,468 trees/ha. Mean tree DBH ranged from 4.3 to 4.9 cm, but some trees were 9 to 10 cm DBH and up to 6.5 m tall. Shrubs grew in open areas between tree clumps. Low shrubs included bog blueberry, bog Labrador-tea, and lingonberry. Lichen mats grew beneath the shrubs. Feather mosses were abundant throughout the stand, with cover of 72% to 85%. Reindeer lichens were most common in the lichen mats; dominant feather moss species included fire moss, splendid feather moss, and juniper haircap moss. Combined, lichen and feather moss cover was "nearly continuous".

The study site is classified in the following plant community and probably historically experienced this fire regime:

PLANT PHENOLOGY:
The fires were conducted during the growing season.

FIRE DESCRIPTION AND EFFECT ON FUELS AND SOIL:
Objectives: The fire management objectives were to: 1) measure fire behavior under prescribed conditions in the black spruce/feather moss type of interior Alaska and 2) determine the effects of fires of different severities on vegetation, the soil organic layer, and soil nutrients. This was the first prescribed fire study conducted in a black spruce community of interior Alaska for which fire prescription and fire effects data were published. All 4 burn units experienced a combination of ground, surface, and crown fire. The fire prescription was:

fuel stick moisture content = 5% to 20%
relative humidity = 20% to 45%
wind speed and direction = 0 to 4.5 m/s, southwest to southeast
air temperature = 10 °C to 27 °C

Fire Descriptions: Four prescribed fires were set, 1 in July and 3 in August.
Late July fire:
Unit 2 was burned on 22 July 1976, following a rainless period from 16 to 22 July. The soil organic layer was high in water content from previous heavy rains. Burning conditions just before ignition were:

fuel stick moisture content = 6.6%
relative humidity = 32%
wind speed and direction = 0 to 2.2 m/s, south-southeast
air temperature = 24 °C

Burning in Unit 2: The fire was ignited at 11:52 am. Heat developed rapidly, and the fire quickly spread to the crowns. The fire moved across the unit in 7 minutes. Mean fire temperatures were higher at 0 to 3 m above the ground than within the forest floor. Little of the soil organic layer was consumed. Based on heat-sensitive paint, temperatures ranged from <43 to 454 °C at 0 to 15 cm above the forest floor and 43 to 288 °C at depths of 2 to 3 cm within the soil organic layer.

Late August fires:
The other 3 units were burned in the afternoon on 26 August 1976. A total of 16 mm of precipitation fell between 1 August and 26 August, which delayed firing these units for more than a month after Unit 2 was ignited. To measure the effects of high-severity fire, 2 of the units (1L and 4L) had previously been loaded with additional fuels. Black spruce cut from the bordering firelines was laid in rows within Units 1L and 4L in June 1975, more than 1 year before burning. Fuels were enhanced by about 26,500 kg/ha on Unit 1L and by about 15,600 kg/ha on Unit 4L. Unfortunately, cut black spruce had dropped their needles by the time of the prescribed fires, which reduced the flammability of these enhanced fuels. Conditions just before ignition were:

fuel stick moisture content = 6.6%
relative humidity = 40%
wind speed and direction = 2.7 to 3.6 m/s, south-southeast
air temperature = 19 °C

Burning in Unit 1L: This unit was ignited at 12:42 pm. Fire spread to tree crowns within 1 minute. Crowning was spotty except in the center of the unit. In one area, crown flames were 16 m long. Most active flaming was over within 16 minutes, but fire continued to burn in the soil organic layer for several hours. A few spots smoldered and periodically flamed for several days. The authors suggested that the 26,000 kg/ha of fuels added to this unit did not contribute to fire intensity but caused the ground fire to persist. Temperature measurements from heat-sensitive paints were lower on this unit than on the 3 others.

Burning in Unit 4L: This unit was ignited at 2:13 pm. The fire completed its run across the unit in 6 minutes. Spotting occurred into the already burned Unit 1L. Unit 4L burned hotter than the other units. The authors suggested that the 15,600 kg/ha of extra fuel apparently added to the spread and intensity of the fire and depth of burning into the organic layer. Nearly 90% of live black spruces had at least 50% of their needles consumed, and nearly 70% of groundlayer vegetation burned at moderate to high severity.

Burning in Unit 3: This unit was ignited at 3:01 pm, and it burned primarily as a slowly moving ground fire with some spotting. The fire took 29 minutes to burn across the unit. This fire consumed the lowest percentage of black spruce needles, and heat-sensitive paints indicated this was the coolest of the 4 fires. However, ground fire continued for several days, eventually burning about 50% of groundlayer vegetation at moderate to high severity.

Burning data for all units: Indicators of fire intensity and severity for all units are presented in Table 4 and Table 5.

Fire Effects on the Forest Floor and on Fuels:
Unit 2 was burned a month earlier than the other 3 burn units, when moisture content of the soil organic layer was higher. Consequently, although the crown fire burned hot and moved quickly, the fire consumed only a few centimeters of the soil organic layer, and forest floor thickness was reduced by only 24%. Fire behavior varied among the 3 units burned in August. Unit 3 had a mostly creeping, patchy ground fire that left "many green trees and an appreciable portion of the forest floor" unburned. In contrast, Unit 4L had an intense fire that crowned quickly, burning almost the entire unit and charring the forest floor deeply. Although mean consumption of the forest floor was similar on units 3 and 4L, the ground fire burned down to mineral soil on most burned portions of Unit 3.

By postfire year 3, woody fuel loading on Unit 4L—the most severely burned—was reduced by more than 50% compared to before the fire. The other 3 units showed no significant reduction of woody fuels. On Unit 3, total fuel load increased after fire due to treefall. All units showed decreases in twigs <0.64 cm in diameter.

FIRE EFFECTS ON PLANT COMMUNITY:
Black spruce: Black spruce recovery was monitored in September 1976, at the end of the 1st postfire growing season. Because it was difficult to tell if trees were dead or alive that soon after the fires, damage to black spruce trees and saplings was recorded as a percentage of needles consumed, rather than mortality. Unit 3—which experienced mostly ground fire—had the least percentage of needles consumed, while units 2 and 4L—which had the highest aboveground temperatures—had the greatest amount of needles consumed (see Table 6).

In general, more needles were consumed on saplings than on tall trees, indicating that the crown fires were hottest below tree crown levels (see Table 4.).

The fires caused black spruce cones to open and shed seed. Seedfall began almost immediately after the fires. Seedfall in Unit 4L was much lower than in the unburned unit. The Unit 4L fire may have been severe enough to consume many cones and kill the seed. In the other units, seedfall in September and October was higher than on the unburned unit.

Other species: Paper birches, American green alders, and willows were apparently top-killed. On Unit 2, which was burned in July, bluejoint and Scouler willow were sprouting by September. Scouler willow had reached 30 cm tall by then, with an approximate 70% browse rate by black-tailed jackrabbits. In units burned in August, no postfire growth was apparent by September.

REFERENCES:

1. Barrett, S.; Havlina, D.; Jones, J.; Hann, W.; Frame, C.; Hamilton, D.; Schon, K.; Demeo, T.; Hutter, L.; Menakis, J. 2010. Interagency Fire Regime Condition Class Guidebook. Version 3.0, [Online]. In: Interagency Fire Regime Condition Class (FRCC). U.S. Department of Agriculture, Forest Service; U.S. Department of the Interior; The Nature Conservancy (Producers). Available: http://www.frcc.gov/ [2013, May 13]. [85876]

2. Dyrness, C. T.; Norum, Rodney A. 1983. The effects of experimental fires on black spruce forest floors in interior Alaska. Canadian Journal of Forest Research. 13(5): 879-893. [7299]

3. LANDFIRE Rapid Assessment. 2005. Reference condition modeling manual (Version 2.1), [Online]. In: LANDFIRE. Cooperative Agreement 04-CA-11132543-189. Boulder, CO: The Nature Conservancy; U.S. Department of Agriculture, Forest Service; U.S. Department of the Interior (Producers). 72 p. Available: http://www.landfire.gov/downloadfile.php?file=RA_Modeling_Manual_v2_1.pdf [2007, May 24]. [66741]

4. LANDFIRE. 2008. Alaska refresh (LANDFIRE 1.1.0). Biophysical settings layer. In: LANDFIRE data distribution site, [Online]. In: LANDFIRE. Washington, DC: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory; U.S. Geological Survey; Arlington, VA: The Nature Conservancy (Producers). Available: http://landfire.cr.usgs.gov/viewer/ [2013, April 10]. [86808]

5. Viereck, Leslie A.; Foote, Joan; Dyrness, C. T.; Van Cleve, Keith; Kane, Douglas; Seifert, Richard. 1979. Preliminary results of experimental fires in the black spruce type of interior Alaska. Res. Note PNW-332. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Forest and Range Experiment Station. 27 p. [7077]

6. Zasada, John C.; Norum, Rodney A.; Teutsch, Christian E.; Densmore, Roseann. 1987. Survival and growth of planted black spruce, alder, aspen and willow after fire on black spruce/feather moss sites in interior Alaska. The Forestry Chronicle. 63(2): 84-88. [85354]

7. Zasada, John C.; Norum, Rodney A.; Van Veldhuizen, Robert M.; Teutsch, Christian E. 1983. Artificial regeneration of trees and tall shrubs in experimentally burned upland black spruce/feather moss stands in Alaska. Canadian Journal of Forest Research. 13: 903-913. [6991]