More info for the terms: backfire, bog, crown fire, density, duff, fire severity, frequency, fuel, headfire, high-severity fire, lichen, natural, peat, severity, shrubs, taiga, tree
Bog Labrador tea is commonly present in even early postfire communities regardless of fire
severity or season. Typically bog Labrador tea coverage, occurrence, frequency, and
density are lower on burned than unburned sites for the 1st postfire years. However,
comparisons of 5-year-old burned and adjacent unburned sites revealed greater bog Labrador
tea frequency, 100%, on burned than on unburned, 94.4%, sites in southeastern Labrador.
Fire severity or conditions at the time of burning were not described [53]. Bog Labrador tea
was present on all 11 sites burned between 3 and 110 years prior in well-drained black spruce-
or jack pine-dominated lichen forests in northern Quebec's James Bay area. Bog Labrador tea
was reportedly "expanding." No information as to fire severity or season was given
[50].
In the Agassiz Provincial Forest of Manitoba, a mid-May forest fire burned white spruce-dominated
stands. The fire was considered severe and top-killed all above ground vegetation. By 16 months
postfire, bog Labrador tea was widespread on burned sites, but abundance estimates were not provided
[70]. Bog Labrador tea was also considered abundant on "lightly" burned sites following
a summer fire in interior Alaska's mature, open black spruce-lichen forests. The "light"
fire removed an average of 2 inches (5 cm) of the forest floor [41]. In the taiga of north-central
Canada, Labrador tea growth was sparse on sites burned 1 year prior, but common on 2 to 3-year-old
burned sites, and dense on sites burned 3 to 17 years ago. This study comprised a large area and many
past fires. Fire season or severity were not described. Sparse, common, and dense were also undefined
[116].
The frequency of bog Labrador tea was lower on burned than unburned 2nd growth mixed conifer-hardwood
stands in Lake County, Minnesota. The Heart Lake area burned on 28 April 1952 when the ground was cold
and moist and winds were strong. The Keeley Creek area burned 11 July 1955 in a fire described only
as "hot." Bog Labrador tea frequency on burned sites was lower than on unburned sites even
14 years postfire. The frequency of bog Labrador tea on thirty plots, each 100-foot²(10-m²), is summarized
below [93].
Burned areaUnburnedHeart Lake
(spring fire)Keeley Lake
(summer fire)Canopy vegetation46% black spruce, 23% jack pine, 23% paper birch60% black spruce-balsam fir, 16% jack pine, 14%
swamp45% black spruce, 35% jack pine, 5% balsam firTime since fire (sample year)195619653 years (1954)5 years (1956)14 years (1965)2 years (1956)5 years (1959)11 years (1965)Frequency (%)3330232323131713
By the 10th postfire year, bog Labrador tea coverage was greater on burned than unburned
sites in Alaska's interior black spruce/feather moss-reindeer lichen forests. The Wickersham
fire burned with moderate severity in June 1971. Measurements on burned sites were made 2, 5,
and 10 years postfire. The maximum thaw depth was 16 to 20 inches (40-50 cm) during the course of
the study on unburned sites. Thaw depth increased each year on burned sites, reaching a maximum
of 73.6 inches (187 cm) in the 10th postfire year. Bog Labrador tea coverage on burned sites was
double that on unburned sites in the 10th postfire year. The recovery of bog Labrador tea on burned
and fireline sites is summarized below. Bog Labrador tea recovery was also monitored on the fireline in
this study; for that information see the earlier
Fire and other disturbances section [193].
Unburned
Burned
Postfire year2510bog Labrador tea coverage (%)112321
Bog Labrador tea frequency increased with each successive postfire sampling in black spruce/lichen
and jack pine/lichen forests of northern Quebec's Ecomiak Lake area that burned in the summer of 1989.
The postfire frequency of bog Labrador tea was higher in the black spruce than in jack pine forests.
The sampling of multiple seasons in the 3rd postfire year suggests that the timing of postfire sampling
may affect results. The percent frequency of bog Labrador tea in both forest types at increasing time
since fire is provided below [167].
Sampling periodJuly 1990June 1991July 1991August 1991July 1992July 1993Black spruce/lichen1.21.22.23.18.09.1Jack pine/lichen<0.5<0.5<0.50.51.11.2
Sites with longer recovery time had greater bog Labrador tea coverage and frequency
in black spruce/Schreber's big red stem moss habitat types of western and central Quebec.
For the Dieppe study area, comparisons were made on sites burned in a June crown fire 21
years earlier and on unburned sites. In the Mathieu study area, the regeneration of bog
Labrador tea was evaluated on sites burned in a June crown fire 14 years prior and on
unburned sites. No other fire severity or behavior characteristics were provided. On neither
of the burned sites did coverage or frequency of bog Labrador tea reach that of unburned
sites. The coverage and frequency of bog Labrador tea on burned and similar unburned sites
are summarized below [122]:
SiteDieppe Mathieu Time since fire21 years 14 yearsStatusunburnedburnedunburnedburnedFrequency (%)75596119Cover (%)6572
Bog Labrador tea was an early invader of a 1-acre (0.4-ha) plot of black spruce/bog
Labrador tea/reindeer lichen vegetation burned on 18 July 1972 in north-central Alberta.
The prescription fire burned in a 50-year-old stand where tree density was 597/ha. There
was no precipitation for 6 days prior to the fire. Average air temperature was 73 °F (22.8
°C), relative humidity was 38%, and winds averaged 12 mi/h (19.3 km/h). The Canadian fire
weather indices suggested moderate to extreme fire potential. The maximum headfire spread
rate was 22 feet/min (6.6 m/min), while the backfire spread rate was just 1.8 feet/min
(0.5 m/min). The prefire fuel loadings of bog Labrador tea foliage and woody material were
0.11 kg/m² and 0.22 kg/m² and moisture contents were 92% and 54% of oven-dried
weight, respectively. The fire consumed all bog Labrador tea above ground
biomass. The researcher estimated that bog Labrador tea height would be 1 foot
(0.3 m) by 10 to 15 years postfire. Fuels in this area would likely recover and
be able to support another fire in approximately 25 years given moderate burning conditions
[90].
Fire and other disturbances:
Several studies provide information on bog Labrador tea recovery following fire on
previously disturbed sites. Typically bog Labrador tea quickly appears on burned
sites however, prefire or unburned coverage and frequency are not typically reached
until 5 or more years following fire.
Bog Labrador tea plants were smaller on burned sites following a high-severity
fire in the Northwest Territories, but the frequency of small-sized shrubs had nearly
reached prefire and unburned levels by the 3rd postfire year. The fire burned over a
research site in the Northwest Territories, and allowed researchers to compare recovery
of disturbed and undisturbed burned sites. The research area was previously disturbed
when seismic lines and right of ways (ROW) were created. The ROW required the removal
of all trees and shrubs in 1985. The seismic line created in 1972 and 1973 was used as
a winter road from 1983 to 1985 and was still used for snowmobile and ATV travel at the
time of the study. Before these disturbances the area was primarily open black spruce-lichen
forest, and the oldest trees were approximately 300 years old. A "high intensity crown
fire" burned on 6 June 1995 with temperatures hot enough to melt aluminum boat engine
blocks and deform small aluminum and sheet metal animal traps that were in its path. Below
is the percent frequency of bog Labrador tea on the ROW, forest, seismic line, and unburned
areas. Prefire data was collected in 1987 (after ROW creation), and postfire data was collected
in the 3rd postfire year (1997) [124].
Bog Labrador tea size classROWBurned forest Seismic LineUnburned forestPostfire yearprefire 3prefire 333/NA0.3-1 m73.3050.00033.30-0.3 m97.460.510084.286.893.3
Using a propane torch, recently clearcut bogs of the Acadian forest were burned in the spring,
summer, and fall. Twenty-five 7Ã7 feet (2Ã2 m) sites were burned, and all green material was
blackened. A temperature of 130 °F (55 °C) was maintained for 5 minutes at a 0.8 inch (2 cm)
depth in the consolidated duff layer. After burning, hot spots and smoldering were discouraged
with water treatments. Clearcuts were dominated by leatherleaf (Chamaedaphne calyculata),
rhodora (Rhododendron canadense), and bog Labrador tea before burning. By 5 months postfire,
there were no significant (p=0.05) relative abundance differences in bog Labrador tea regrowth on
spring, summer, or fall burning treatments, and no burned plot densities had recovered to preburn
densities by the 5th postfire month. Regrowth was initially slowest on the spring-burned sites;
however, by the 5th postfire month, regrowth on spring-burned sites exceeded that of both summer-
and fall-burned sites [48].
Bog Labrador tea was removed from a white spruce/bog Labrador tea-mountain cranberry
(Vaccinium vitis-idaea)/splendid feather moss community for at least the
first 2 years following slash fires in a clearcut area. Bog Labrador tea coverage and
frequency in undisturbed forests were 31.8% and 65%, respectively. The fire was described
as severe enough to kill above and below ground portions of most species, and immediately
following the fire 6% of mineral soil was exposed; this amount increased to 30% in the 1st
postfire year [42].
Researchers assessed the recovery of Charlevoix Highlands vegetation in southern Quebec
following several disturbances. Some sites within the black spruce-dominated forests were
clear cut in 1946, others in 1954. Spruce budworm infected stands from the late 1970s to
the mid-1980s, and all sites burned in a June 1991 fire. At the time of the fire, greater
than 90% of trees were less than 4 inches (10 cm) in diameter. Bog Labrador tea coverage
on burned sites that were logged in 1946 ranged from 10% to 20% and on sites logged in 1954
ranged from 1% to 40% in the 8th postfire year [129].
Fire chronosequences:
Bog Labrador tea frequency and coverage are typically low immediately after fire but normally
increase as time since fire increases. However, as time since fire increases beyond 20 or more
years, trends are no longer consistent.
In burned areas of the Newfoundland's barren range, bog Labrador tea coverage and frequency
were compared on sites burned at different times. All fires were natural and assumed to burn
during dry conditions, but no other information of fire severity, season, or behavior was
given. Bog Labrador tea coverage was greatest on sites burned 10 to 19 years prior but frequency
was greatest on sites burned 20 to 36 years ago. Bog Labrador tea coverage and frequency on
past-burned areas are summarized below [134]:
Time since fire (years)0.5-12-56-910-1920-3637Coverage (%)trace13543Frequency (%)112439385945
On peat and lichen plateaus of Chick Lake Basin, Northwest Territories, bog
Labrador tea coverage was compared on different aged burned sites. Fire
characteristics were not reported. The coverage of bog Labrador tea on peat
plateaus burned 4 years earlier was 18%, on sites burned 53 years prior was 7%,
and on sites burned 92 years ago was 8%. On lichen plateaus, coverage of bog
Labrador tea was 2% on sites burned 44 years earlier, 3% on sites burned 47
years prior, and 0% on sites burned 100 years prior to the study [154].
Bog Labrador tea coverage was greatest on black spruce/sphagnum sites burned
8 years prior in northeastern British Columbia when past burned areas were
evaluated. The study included several forest types in areas burned between 8
and 24 years prior. Bog Labrador tea coverage was typically greater in forests
burned more recently. However the inclusion of different forest types with different
time since fire introduced confounding factors. It is likely that site conditions
associated with the different forest types affected bog Labrador tea recovery. Below
are the forest types, time since fire, and postfire bog Labrador tea coverage from
single plots evaluated in this study [127]:
Forest typeTime since fire in years (seasonality)Bog Labrador tea coverage (%)Additional informationBlack spruce/sphagnum8 (May fire)80%bog Labrador tea coverage in similar unburned stands (old trees
117-160 yrs.) was 50%Black spruce/feather moss10 (June fire)50%----Lodgepole pine-black spruce19 (August fire)40%plot located in Muncho Lake Provincial ParkHardwood (quaking aspen, balsam poplar)-lodgepole pine-white
spruce24 (season not given)25%plot above Moose Lake
After visiting 130 white spruce- and black spruce-dominated stands that burned between
1 month and 200 years earlier in the taiga of interior Alaska, Foote [49] summarized changes
in bog Labrador tea coverage and frequency. In white spruce stands, bog Labrador tea coverage
and frequency were greatest on sites burned an average of 15 and 36 years earlier, respectively.
In past-burned black spruce stands the frequency and coverage of bog Labrador tea did not follow
any trend. Fire severity was not reported, and it is likely that unknown differences in sampled
communities may have been as important as time since fire in resulting bog Labrador tea coverage.
A summary of the data is presented below [49].
Mean time since fire ± s
(number of stands sampled)Frequency (%)Coverage (%)White spruce-dominated stands6 ± 7 months (n=4)004 ± 2 years (n=8)2215 ± 8 years (n=9)3836 ± 7 years (n=5)22387 ± 38 years (n=11)71170 ± 70 years (n=4)00Mesic black spruce-dominated stands5 ± 0 weeks (n=3)3772 ± 2 years (n=19)65310 ± 6 years (n=21)39648 ± 9 years (n=12)68670 ± 26 years (n=11)352121 ± 56 years (n=4)588