Viereck 1979

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

This document summarizes information from a research project conducted in the summer of 1976 in a black spruce forest community near Fairbanks, Alaska. It is intended to:

1. provide concise information about the effects of particular fire treatments on a specific plant community and
2. supplement FEIS reviews of individual species with detailed information on specific treatments and effects in a particular location. The studies summarized in FEIS Research Project Summaries are selected based on their integration of fire effects information with relatively complete descriptions of burned and unburned vegetation, burning conditions, fire weather, and fire behavior.

Common names are used throughout this summary. For a complete list of the common and scientific names of species discussed in this summary and for links to FEIS species reviews, see the Appendix.

Citation for this Summary:
Fryer, Janet L., compiler. 2013. (Revised from Uchytil, Ronald J., compiler, 1991.) Research Project Summary: The effects of experimental fires in an Alaskan black spruce/feather moss community. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: [].

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.

These studies quantified the short-term effects of fires of different severities on the organic soil layer and plant species in a black spruce/feather moss type of interior Alaska. Key findings are listed here. Details and documentation are in the sections that follow. For a longer-term investigation of fire effects and postfire responses of vegetation in this black spruce/feather moss community, see the Research Project Summary of Zasada and others' [2,6,7] later studies in the Washington Creek Fire Study and Training Area.

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).

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.

The prefire community was a 70-year-old stand of black spruce/feather moss with some paper birch, American green alder, Alaska 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 mountain cranberry. 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".

Table 1. Prefire stand structure on the 4 burn units [5]
Burn unit
1L 2 3 4L
Mean density (stems/ha) (SD)
black spruce trees     
3,398 (497) 5,468 (1,878) 4,179 (707) 2,226 (939)
paper birch trees     
0 741 (497) 78 (110) 117 (55)
black spruce saplings*     
1,490 (432) 1,953 (1,761) 8,758 (1,933) 1,874 (111)
paper birch saplings     
0 78 (110) 0 0
dead trees     
156 (0) 703 (110) 468 (110) 156 (110)
Mean height of black spruce (m) 3.4 3.4 3.5 3.1
Mean DBH of black spruce (cm) 4.8 4.8 5.0 4.3
Estimated biomass of live black spruce (kg/ha)**
total aboveground     
19,020 23,780 18,250 6,560
4,040 4,030 3,844 1,530
2,530 3,160 2,420 900
620 780 600 210
live branches     
2,350 2,940 2,250 850
dead branches     
850 1,060 810 310
6,650 8,310 7,980 2,740
*Saplings are <2.5 cm DBH.
**Biomass determined by regression equation models.

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

Table 2. Fire regime information on the vegetation community studied in this Research Project Summary. Fire regime characteristics are based on the LANDFIRE Biophysical Settings data layer [4]. This vegetation model was developed by local experts using literature and expert estimate as documented in the PDF file linked from the BioPhysical Settings Group name listed below.
Vegetation Community Mean interval
Fire severity* Percent of fires
Western North American boreal black spruce wet-mesic slope woodland 76 Replacement 46
Mixed 54
Surface or low 0
*Fire Severities:
Replacement=Any fire that causes greater than 75% top removal of a vegetation-fuel type, resulting in general replacement of existing vegetation; may or may not cause a lethal effect on the plants.
Mixed=Any fire burning more than 5% of an area that does not qualify as a replacement, surface, or low-severity fire; includes mosaic and other fires that are intermediate in effects.
Surface or low=Any fire that causes less than 25% upper layer replacement and/or removal in a vegetation-fuel class but burns 5% or more of the area [1,3].

The fires were conducted during the growing season.

Season: summer (late July and late August)
Severity: mosaic of fire severity classes from unburned to high severity (see Table 3).

Table 3. Fire severity descriptions [5]
Severity class Description
Unburned plant parts green & unchanged
Scorched moss & other plants yellow or brown but species identifiable
Low lightly burned, plants charred but original form of mosses & twigs visible
Moderate shallow ash layer present, organic layer partially consumed, parts of woody twigs remain
High ash layer present, organic material in the soil consumed or nearly consumed, no discernible plant parts remain

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.

Table 4. Mean highest temperatures recorded and water evaporation during prescribed burning on 4 burn units [5]
Burn unit
1L 2 3 4L
Highest temperature recorded by heat-sensitive paints (°C)
          Height above forest floor:
2.75 m     
66 288 66 454
2.25 m     
66 288 66 454
1.75 m     
66 288 121 454
1.25 m     
121 288 121 660
0.75 m     
121 288 121 660
0.25 m     
288 288 288 660
6-15 cm     
288 288 288 454
0-5 cm     
288 121 288 454
          2-3 cm in organic layer: no data 43 288 121
Highest temperature recorded by heat-sensitive pellets (°C)
          Depth in organic soil layer:        
0 cm (surface)     
>83 >83 >83 >83
5 cm     
43 43 43 69
10 cm     
<43 <43 <43 <73
Water evaporated from 250-ml cans*
65 ml 5 ml 16 ml 107 ml
0-70 ml 0-10 ml 0-30 ml 20-210 ml
*Cans were set next to heat-sensitive paints. Water-evaporation data are averaged for all heights above the forest floor.

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.

Table 5. Fire effects on the forest floor [5]
Burn unit
1L 2 3 4L
Forest floor thickness
Mean thickness before burning (cm)     
21.6 19.8 23.2 22.4
Mean thickness after burning (cm)     
11.6 14.9 7.8 7.2
Reduction in thickness (%)     
43 24 61 62
Percent of forest floor in fire severity classes
Based on ten 1-m² plots:     
6.0 0 0 0
7.5 0.7 1.8 0
37.5 97.1 49.3 34.5
25.0 0.2 11.9 6.1
24.0 2.0 37.0 49.4
Based on ten 1-m transects:     
7.7 0 1.7 0
1.0 6.9 4.5 0.1
36.1 75.0 42.0 24.9
21.0 16.0 16.0 17.0
34.2 2.1 36.8 58.0

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.

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).

Table 6. Needle consumption by prescribed fires on 4 burn units [5]
Burn unit
1L 2 3 4L
Percentage of saplings
0-25% needle consumption 0 14 2 0
26-50% needle consumption 8 8 17 2
51-75% needle consumption 16 15 38 20
76-100% needle consumption 76 62 43 78
Percentage of trees
0-25% needle consumption 7 14 9 0
26-50% needle consumption 28 22 44 6
51-75% needle consumption 32 16 38 55
76-100% needle consumption 33 47 9 39

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, pinegrass 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.

Qualitative monitoring in postfire years 2 and 3 showed fireweed, fire moss, and common liverwort colonized severely burned plots. Pinegrass, bog blueberry, and bog Labrador tea dominated plots burned at low severity.
The species below occurred within the black spruce/feather moss community described in this Research Project Summary. For further information on fire effects, follow the highlighted links to the FEIS reviews of these taxa.

Scientific name Common name
Cladonia spp. reindeer lichens
Ceratodon purpureus fire moss
Hylocomiaceae feather mosses
Hylocomium splendens splendid feather moss
Marchantia polymorpha common liverwort
Polytrichum juniperinum juniper haircap moss
Calamagrostis canadensis pinegrass
Chamerion angustifolium fireweed
Alnus viridis subsp. crispa American green alder
Ledum groenlandicum bog Labrador tea
Salix alaxensis Alaska willow
Salix scouleriana Scouler willow
Salix spp. willows
Vaccinium uliginosum bog blueberry
Vaccinium vitis-idaea mountain cranberry
Betula papyrifera paper birch
Picea mariana black spruce
Populus tremuloides quaking aspen


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: [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: [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: [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]

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