|Cladonia stygia||C. stellaris|
|© Sylvia and Stephen Sharnoff|
Cladonia arbuscula, shrubby reindeer lichen, tree reindeer lichen, woodland reindeer lichen
Cladonia mitis, green reindeer lichen, spineless reindeer lichen
Cladonia rangiferina, gray reindeer lichen, graygreen reindeer lichen
Cladonia stellaris, alpine reindeer lichen, star reindeer lichen, star-tipped reindeer lichen
As explained in greater detail by Stenroos and others , the taxonomic status of Cladonia spp. has been debated, with some authorities using the genus Cladina, while others have given Cladina subgenus status within the Cladonia genus.
A study of phylogenetic relationships within Cladonia and Cladina species based on DNA sequences, morphological data, and chemical analyses led some researchers to conclude that Cladina is best treated as a subgenus of Cladonia . Ahti and DePriest  also conclude, based on molecular phylogenetic results, that lichens previously placed in the genus Cladina should instead be included within the Cladonia genus. This summary provides information on the 5 Cladonia species listed below:
Cladonia arbuscula (Wallr.) Flotow [4,122]
Cladonia arbuscula subsp. arbuscula (Wallr.) Flot. 
Cladonia arbuscula subsp. beringiana (Ahti) N.S. Golubk. [3,23]
Cladonia mitis Sandst.
Cladonia rangiferina (L.) F.H. Wig.
Cladonia stellaris (Opiz) Pouzar & Vĕzda
Cladonia stygia (Fr.) Ruoss [4,122]
for Cladonia mitis Sandst.:
Cladina mitis (Sandst.) Hustich 
for Cladonia rangiferina (L.) F.H. Wig.:
Cladina rangiferina (L.) Nyl. 
for Cladonia stellaris (Opiz) Pouzar & Vĕzda:
Cladonia alpestris (L.) Rabenh. 
Cladina stellaris (Opiz) Brodo 
for Cladonia stygia (Fr.) Ruoss:
Cladina stygia (Fr.) Ahti 
Cladonia arbuscula is widely distributed in Canada and the northern half of the United States. In western North America, C. arbuscula occurs in Alaska [11,12] and western Canada  south to Oregon and west to Idaho, western Montana, Wyoming [83,84], and Colorado . Cladonia arbuscula is uncommon in the Pacific Northwest and rare in the Southwest . In eastern North America, C. arbuscula occurs as far south as the northern Great Lakes states [131,141] and New England [37,47]. Cladonia arbuscula occurs as far east as Labrador  and Newfoundland . Although C. arbuscula was reported from North Carolina's coastal plain in 1931 , more recent sightings were lacking as of 2008.
Cladonia mitis occurs in Alaska, Canada, and the northern fringe of the United States [18,83,115,125]. In western North America, C. mitis occurs as far south as the southern Willamette Valley [61,84], the northern Cascade Range , Idaho, western Montana, and Wyoming [83,84]. Cladonia mitis is uncommon in the Pacific Northwest and rare in the Southwest . In eastern North America, C. mitis occurs in the northern Great Lakes region [64,131,141], New Jersey , southeastern New York , Labrador , Newfoundland , Quebec [48,89], and the boreal and arctic vegetation zones in Ontario .
Cladonia rangiferina is relatively widespread in the arctic and temperate zones of the United States and Canada [3,23]. There are reports of C. rangiferina near its apparent southern distributional limits of Oregon, Montana , Minnesota , Wisconsin , Michigan [62,141], West Virginia , and New Jersey .
Cladonia stellaris and C. stygia are widespread in the arctic and boreal regions of North America [3,23]. Cladonia stellaris is rare along maritime coasts  but is reported in New Jersey , Michigan's Upper Peninsula , and Wisconsin . Cladonia stygia is most common at the northern boreal timberline zone. It occupies habitats from Kodiak Island, Alaska, east to Newfoundland and south to Queen Charlotte Islands, British Columbia, Idaho, northern Minnesota, the Appalachian Mountains, and western North Carolina [5,141].There are also reports of reindeer lichens in southwestern Illinois, western Kentucky, western Tennessee , and on Nantucket Island, Massachusetts . However, species were not identified. As of 2008, distributional maps of reindeer lichens were lacking. NatureServe provides a partial list of states and provinces where reindeer lichens, including the 5 species featured in this summary, occur.
HABITAT TYPES AND PLANT COMMUNITIES:
C. rangiferina in oak-pine litter
© Charles S. Lewallen
Reindeer lichens are also noted in oak (Quercus spp.) woodlands in southwestern Illinois, western Kentucky, and western Tennessee  and in grassland-heathland communities on Nantucket Island, Massachusetts .
The vegetation classifications listed below describe plant communities in which reindeer lichens are dominant.North America (general):
Most descriptions of reindeer lichens highlight their dense, mat-forming, richly branched podetia, which range from 1.6 to 4.7 inches (4-12 cm) tall and 0.6-1.8 mm wide. While there was much overlap in the size ranges reported for patches of reindeer lichens in the literature, maxima were typically largest for C. stygia and C. rangiferina and lowest for C. stellaris [23,84]. In northern Ontario, a 16 × 33-foot (5 × 10 m) patch of C. stellaris had an estimated 35,000 podetia .
Lichens absorb water and minerals from the air through the outer surface of the thallus and thus are not as dependent on soil as are vascular plants . Also, lichens gain and lose moisture in close tandem with changes atmospheric moisture levels. Diurnal changes in the moisture content of reindeer lichens closely track diurnal changes in relative humidity . Reindeer lichen moisture requirements and anchoring substrates are discussed in greater detail in Moisture and Substrate.
C. rangiferina podetia
Vegetative regeneration is considered the predominant method of reindeer lichen reproduction. Thallus fragments or microscopic particles with both algal and fungal components can potentially produce a new lichen body. Given the complex reproductive biology and very small size of lichen reproductive structures or fragments, natural regeneration studies and observations are difficult. Webb  indicated that reindeer lichen regeneration in burned or logged boreal forests occurred through propagules or surviving fragments that were usually too small to see. Johnson  reported that C. mitis and C. rangiferina regeneration in the first years after fire was likely from thallus fragments .
Dispersal: Lichen fragments and microscopic fungal and algal particles can be dispersed by wind, water, or animals . In grasslands and forests of northeastern Germany, most dried lichen thallus fragments dispersed less than 8 inches (20 cm) from the parent source. The maximum wind-dispersal distance of C. arbuscula fragments was 14 inches (35 cm) in a dry sandy grassland and 27 inches (68 cm) in an open, early-seral Scots pine (Pinus sylvestris) forest. Lichen cushions disturbed and/or moved by animals dispersed a maximum distance of 32 feet (9.7 m) .
Growth: Reindeer lichens are slow growing and long lived. Average growth rates of 4.8 to 11.1 mm/year  and average ages of over 100 years  have been reported. Growth rates do, however, vary with lichen age, lichen species, site conditions, and herbivory.
Three growth stages exist throughout the reindeer lichen lifespan. The 1st stage, the growth-accumulation period, lasts an average of 10 years but can vary from 6 to 25 years. During this stage, size increases every year, and no part of the podetium dies. In this 1st period of growth, internodes grow 10 to 15 times the height attained in the 1st year of life. During the 2nd stage, the renovation period, podetium height still increases, but internode death occurs at the base. Since decay of the internode is not immediate, height still increases some. This stage may continue for several decades and may exceed 100 years. During the 3rd stage, the withering period, the podetium decays at the base faster than internodes lengthen. This stage of growth lasts approximately 10 to 20 years .
Slow reindeer lichen growth has been documented in several locations in the northern hemisphere. On the Seward Peninsula of northwestern Alaska, the average growth rates for C. stellaris, C. rangiferina, and C. arbuscula were 5.0 mm/year, 5.3 mm/year, and 5.4 mm/year, respectively. The growth-accumulation period averaged 11.1 years for C. stellaris, 5.9 years for C. rangiferina, and 10.7 years for C. arbuscula . In forested peatlands of northern Alberta, C. mitis grew an average of 4.8 mm/year . In diverse areas of northern Russia, the average annual height growth was 3.9 mm/year for C. stellaris, 5.9 mm/year for C. rangiferina, and 4.5 mm/year for C. arbuscula. Growth-accumulation periods averaged 12 to 14 years for C. stellaris, 8 to 9 years for C. rangiferina, and 9 to 11 years for C. arbuscula (des Andreev 1939, cited in ).
Reindeer lichen growth is greatest on ungrazed, humid, somewhat sheltered sites with relatively long growing seasons. In Newfoundland, the average height of reindeer lichens was greatest in heath stands, followed by shrub-dominated subalpine barrens, and then black spruce forests. Reindeer lichens were shortest in bog stands. Within similar habitat types, ungrazed stands were typically taller than grazed stands (review by Ahti ). Nevertheless, reindeer lichen growth following sublethal disturbances may be relatively rapid compared with the growth of newly established individuals. In Sweden, Skunke  simulated the effect of reindeer grazing on C. stellaris by clipping to varying heights. Six to 8 years after cutting mats to 0.8 to 1 inch (2-3 cm) heights, C. stellaris recovered to a "completely grazable" condition. When clipped down to the "gelatinous material", C. stellaris was not "grazable" 14 years later .SITE CHARACTERISTICS:
Climate: In general, reindeer lichens occur in cool to cold climates. McCune and Geiser  indicated that reindeer lichens occurred on cool, moist sites in the Pacific Northwest. In Canada, reindeer lichens occur in tundra, boreal, cool-temperate, and cool meso-thermal climates . In Quebec, reindeer lichen are subject to short, cool summers and long, cold winters . Cladonia stellaris is an indicator of alpine tundra and boreal climates in coastal British Columbia . Cladonia mitis occurs in arctic to temperate climates with continental tendencies .
Species-specific differences exist among reindeer lichens in their relative affinities for maritime and continental climates. In British Columbia, Goward and Ahti  found C. arbuscula subsp. beringiana and C. rangiferina "to be indifferent to continentality" and "present in coastal and highly continental inland regions alike". However, Ahti  indicated that C. mitis is much less common in maritime-influenced than in continental climates of Newfoundland.
Most literature suggests reindeer lichen abundance is greatest on dry sites, although a review by Ahti and Hepburn  indicated that high relative humidity is important to reindeer lichen growth, and McCune and Geiser  indicated that reindeer lichens occupied cool, moist sites in the Pacific Northwest. As of this writing (2008), research relating reindeer lichen abundance to precipitation data was lacking.
Moisture: Although reindeer lichens require a relatively humid climate, their ability to absorb water directly from the atmosphere allows them to colonize and even dominate habitats with soils that are too droughty, and often too cold, to support vascular plants . Much of the available literature indicates that reindeer lichen abundance is greatest on dry sites. However, reindeer lichens in Newfoundland can be found on sites ranging from dry to wet and from very poor to moderately rich in fertility .
Many studies suggest that reindeer lichens are most common on dry or well-drained sites [2,30,32,81]. In coastal British Columbia  and in open-canopy forests in northern Canada , reindeer lichens are common on well-drained, water-shedding sites. In central British Columbia's Rocky Mountain lodgepole pine (Pinus contorta var. latifolia) forests, reindeer lichens occurred on mesic and xeric 50- to 100-year-old burned sites. Cover on mesic sites did not change appreciably after 100 years; however, on xeric sites, reindeer lichen cover increased with stand age, and researchers doubted "an equilibrium state had been attained" . The Rocky Mountain lodgepole pine/velvetleaf blueberry/reindeer lichen forest type in west-central Alberta was restricted to sandy, well-drained, coarse-textured soils . In the boreal zone of central and western Ontario, reindeer lichens were more common on shallow, dry soils or rocky outcrops than on poorly drained soils. On the Slate Islands of Lake Superior, reindeer lichens were more than twice as frequent and more than 10 times as abundant in forests with "dry" moisture regimes than those with "medium" moisture regimes . In the Great Lake states, reindeer lichens are considered characteristic groudlayer components only in the driest, least productive jack pine forests . Similarly, in Newfoundland, the black spruce/sheep-laurel/reindeer lichen forest type is characteristic of the driest, least fertile sites .
Rarely do reindeer lichens occur in standing water or on saturated substrates. In relatively wet habitats, reindeer lichens typically occupy only the driest microsites, often exploiting subtle topographic variations . Within black spruce muskegs in western Alaska's upper Kuskokwim River region, reindeer lichens occur on hummocks and other dry sites . In British Columbia, reindeer lichens occur occasionally in nutrient-poor wetlands on "topographic prominences subjected to regular desiccation" . A review of indicator plants in Canada states that "in wet areas and peatlands, reindeer lichens occupy micro-topographic prominences subject to regular desiccation, such as the tops of sphagnum hummocks" . In West Virginia heath bogs, C. rangiferina occurs on slightly raised areas of peat subject to periodic drought .
Several published accounts suggest there are interspecific differences in reindeer lichen abundance relative to site moisture. Cladonia arbuscula, although frequently found mixed with C. mitis in northern Ontario, is more common in moist habitats . Rowe  characterized C. rangiferina as a xerophytic species in the southern boreal forests of Saskatchewan and Manitoba. According to Ahti , C. rangiferina may be the most moisture-tolerant of the reindeer lichens in Newfoundland but also occupies the driest sites. In southeastern Labrador, C. rangiferina is more abundant than C. mitis on moist sites . A review suggests that C. stellaris prefers the driest sites, while moisture tolerances of other reindeer lichens are broader . Cladonia stygia has been confused with C. rangiferina and the two are often found together; however, based on observations made in Sweden, C. stygia may be more tolerant of moisture, even enduring seasonal inundation .
Although evidence clearly indicates that reindeer lichen colonize and persist on dry sites, presence of dense lichen mats may alter soil surface moisture conditions. Rouse and Kershaw  found that soil moisture under lichen mats in mature northern Ontario black spruce forests was at least 40% greater than soil moisture in adjacent 3- and 16-year-old burns with minimal lichen cover, suggesting that lichen ground cover reduced soil moisture evaporation.
Substrate: Since lichens absorb water and mineral nutrients from the air through the outer surface of the thallus, they are not as dependent on soil as vascular plants. Published accounts of substrates bearing reindeer lichens in North America include mineral rock [3,83,84], soil, humus [84,105], duff , raised peat , organic debris , and coarse woody material [3,50,105]. According to Ahti and Hepburn , reindeer lichens require at least a thin soil layer for attachment, so they cannot colonize bare rock. Cooper  indicated that establishment of reindeer lichen mats on rock surfaces on Isle Royale, northern Michigan, may be facilitated by prior establishment of rhacomitrium moss (Rhacomitrium canescens). Apparently, the moss provides a means of attachment for the lichen mat on rock surfaces with few crevices .
The literature reports several instances of possible reindeer lichen affinities for specific substrates. Cladonia stellaris has an affinity for infertile sand or bedrock substrates, while other reindeer lichens have somewhat broader substrate tolerances . A study in east-central Alberta examined the diversity and abundance of lichens on downed woody debris in boreal quaking aspen (Populus tremuloides)-mixed-conifer forests. The frequency of C. mitis was as high as 20% on downed woody debris in the most advanced stage of decay, with nearly 100% humification. Frequency of C. mitis was lower, usually less than 5%, on downed woody debris in less advanced stages of decomposition . In boreal forests of northwestern Ontario, reindeer lichen (C. rangiferina, C. mitis, and C. stellaris) establishment after fire and logging occurred almost exclusively on organic materials such as conifer needles, cone scales, woody debris, dead moss, crustose lichens, overturned ground cover, accumulations of fine organic matter, or shallow organic soils. Cladonia rangiferina occasionally colonized textured rock faces. Reindeer lichens were not observed on mineral soil on sites disturbed 2 to 16 years earlier . On an 8-year-old burned site in northern Minnesota, C. mitis and C. rangiferina "preferred" dead wood .
Reindeer lichens often grow in soils and substrates ill-suited for other plants and bryophytes. Reindeer lichens may be found in habitats underlain by permafrost [13,24,46,136,137]. In recently abandoned agricultural fields in eastern Minnesota, C. mitis and C. rangiferina occurred on sandy, low-nutrient soils with delayed successional advancement . Throughout Canadian forests, reindeer lichens are good indicators of acidic, nutrient-poor, coarse-textured, shallow, extremely dry to very dry soils [71,105]. Nevertheless, reindeer lichens in Newfoundland can be found, albeit at reduced abundance, on sites moderately rich in fertility .
Elevation: Few elevational ranges for reindeer lichens have been reported. McCune and Geiser  indicated that C. rangiferina is found mostly at "low to middle" elevations in the Pacific Northwest, while C. mitis and C. arbuscula are typically limited to "low" elevations. Cladonia stygia occurs between 33 and 490 feet (10-150 m) on British Columbia's Queen Charlotte Islands .SUCCESSIONAL STATUS:
Shade tolerance: Reindeer lichens are generally considered shade intolerant, and their importance typically decreases with increasing canopy cover [19,71]. In the Slate Islands of Lake Superior, Ontario, reindeer lichen frequency was more than 10% in "dry regime" forests with less than 45% crown cover, while frequency was 2% or less in forests with greater than 65% crown cover . On black spruce-dominated sites in northern Manitoba, reindeer lichens formed a nearly continuous carpet in openings, in sparsely wooded areas, and/or where trees were small. In denser areas, other lichens and mosses dominated . In late-seral lodgepole pine/reindeer lichen forests of north-central British Columbia, splendid feather moss dominated microsites with a canopy leaf area indices that were significantly greater (P<0.05) than those of reindeer lichen-dominated microsites .
Cladonia rangiferina may be the most shade tolerant of the reindeer lichens [19,51]. However, in Rocky Mountain lodgepole pine forests in west-central Alberta, cover of C. rangiferina and C. mitis were not significantly different (P<0.05) between sites with 45.3% to 52.3% canopy cover and those with 72.8 to 87.0% canopy cover . Tegler and Kershaw  suggest that heat tolerance and not shade tolerance dictates differences in C. stellaris and C. rangiferina distributions. Cladonia stellaris is more likely to grow in hot, open habitats, while C. rangiferina is more likely to grow in cool, shady habitats. In the pine barrens of south-central Wisconsin, C. mitis occurred in moderately open, warm microsites somewhat protected from xeric conditions by surrounding vegetation, while C. rangiferina occurred in relatively shady, cool microsites with mesic conditions .
General: Available literature suggests that reindeer lichens tolerate the later stages of primary succession in some locations and nearly all stages of secondary succession, although some species-specific preferences exist. On Isle Royale in northern Michigan, reindeer lichens, including C. arbuscula, C. rangiferina, and C. stellaris, were dominant in the late stages of rock-surface succession. These species remained, more or less, through subsequent stages of succession on rockshore habitats that were developing from heath communities to jack pine-black spruce forests. In more mesophytic forest sites, reindeer lichens were likely to be replaced by mosses. In xerophytic areas with sparse jack pine, reindeer lichens were likely to remain abundant on rocky surfaces in tree interspaces .
Several studies report reindeer lichens in early-seral forests. In quaking aspen woodlands of east-central Alberta, C. mitis is characterized as an early-seral species . In jack pine-black spruce forests in northern Ontario, C. stellaris is typically replaced by splendid feather moss beginning around 40 to 50 years after fire . About 40 to 60 years after stand initiation in Alaskan upland black spruce forests, reindeer lichens invade and may cover up to 20% of the ground layer. In this successional stage, trees are replacing tall shrubs, and there may be as many as 6,000 saplings and mature trees per ha and 12,000 seedlings per ha .
Many studies report reindeer lichens in mid- and late-seral communities. A review indicates that in central and southern North American black spruce/lichen forests, a "well-developed lichen carpet" of primarily C. mitis, C. rangiferina, and C. stellaris characterizes the intermediate successional stage . In upland white spruce forests of Alaska's interior, reindeer lichens are generally common in stands over 170 years old . In lowlands of east-central Ontario, C. rangiferina was associated with unlogged and old logged stands . Where site conditions restrict tree establishment and growth, reindeer lichens may persist for extremely long periods without fire. In west-central Alberta, the lodgepole pine/velvetleaf blueberry/reindeer lichen forest type was considered an "edaphic climax" on droughty soils where spruce and fir regeneration were lacking . Payette  found dense black spruce/reindeer lichen krummholz sites in northern Quebec that had not burned for 1,500 years or more. Laboratory experiments indicated that reindeer lichen ash may promote nutrient leaching in subarctic spruce-lichen woodlands and thus slow postfire regeneration . For more on reindeer lichen postfire succession, see Fire as a regeneration process and Discussion and Qualification of Lichen Response.
Generally, C. mitis occupies earlier seral habitats than C. rangiferina and C. stellaris. A review reports that mature northern boreal lichen woodlands in Canada "have a ground cover of almost pure C. stellaris". Isolated C. mitis and C. rangiferina podetia occur in the mats, but C. mitis and C. rangiferina are more important in earlier succession, possibly because of the relatively slow growth rate of C. stellaris . In eastern Canada, C. rangiferina is the last species of three (C. mitis, C. stellaris, and C. rangiferina) to drop out as light levels diminish under increasing canopy cover . During succession from bare sand to white spruce/lichen woodlands along the east coast of Hudson Bay, C. mitis established earlier than C. stellaris, which eventually succeeded it in groundlayer dominance . In northern Ontario, C. stellaris is more abundant in later than in earlier stages of lichen woodland succession. Outside of maritime coastal habitats and sites disturbed by fire and caribou grazing, C. stellaris generally succeeds other reindeer lichens and is dominant in "climax" stands . Miller  indicated that C. stellaris and C. rangiferina were climax species that appeared 40 or more years after fire in the taiga, but that C. mitis may establish earlier.
Many suggest that reindeer lichens may help maintain forest openings. In different-aged burned sites within northern Quebec's black spruce/lichen woodlands, Morneau and Payette  suggested that continuous lichen mats preserved canopy openings by restricting black spruce recruitment. Sedia and Ehrenfeld  also found that reindeer lichen mats within severely burned portions of New Jersey's pitch pine forests restricted vascular plant colonization and development, maintaining canopy openings for many decades.
As of 2008, published information on the seasonal development of reindeer lichens was apparently lacking.
FIRE ECOLOGY OR ADAPTATIONS:
Fire adaptations: Reindeer lichens typically colonize burned sites from thallus fragments dispersed from unburned areas. While colonization by microscopic particles with both algal and fungal components may be possible, it was not reported in the literature and likely is not easily detected. According to Yarranton , initial postfire colonization occurs by "long range" dispersal of thallus fragments from populations outside the burned area. Once established, reindeer lichens expand vegetatively. After prescribed fires in Sweden, there was very little reindeer lichen colonization of burned sites by the 5th postfire year, but researchers noted "a few small fragments that dispersed onto some of the burned plots from unburned surroundings" .
Many studies have reported reindeer lichen survival in protected sites that were either missed by fire or burned with extremely low severity [27,107,114]. For more on reindeer lichen regeneration and/or survival on burned plots, see Fire Effects.
Fire regimes: Reindeer lichens are an easily ignitable surface fuel that aids in fire spread; however, these surface fuels alone rarely support extreme fire behavior or high-severity fires. Periodic fire maintains canopy openings and the early- to midseral habitats that reindeer lichens prefer. In many habitats, reindeer lichens are eventually replaced, often within 100 years, by mosses, other lichens, and/or vascular plants. However, in some habitats, tree regeneration is restricted by site conditions, so reindeer lichens may persist indefinitely in the absence of fire. Differences in site conditions may partially explain why mean fire-return intervals in reindeer lichen habitats range from 40 to over 500 years.
Fuel characteristics/fire behavior: Reindeer lichens dry readily, becoming a highly flammable fuel during warm, dry conditions . In park-like forests, sun exposure to the "well-aerated (reindeer lichen) tubular body with a high surface-to-volume ratio" makes reindeer lichen potentially the most rapidly desiccated surface fuel in Canadian forests. When submerged in water, reindeer lichen moisture content can increase by 400%, and when drying in shaded conditions, as much as 63% of its moisture can be lost in less than 2 hours (Van Wagner 1969, cited in ). In bogs of southeastern Labrador, researchers report that "fire tends to burn preferentially along the lichen-covered ridges and hummocks" . Observations and experiments have shown that reindeer lichens dry much more rapidly than associated moss and snow lichen species [6,91]. In the laboratory, C. rangiferina dried "rapidly" after soaking when compared to associated moss-layer bryophytes from the New Jersey pine barrens , and the drying rate of reindeer lichen samples was 1.7 times that of the wetting rate . Based on estimations from measurements made during diurnal wetting and drying, Pech  determined that in the absence of cloud cover, C. rangiferina moisture content was reduced to the previous day's minimum by 10:00 am, when overnight dew was light, or by noon, when dew was heavy .
Although reindeer lichens burn readily when dry and form a substantial component of the surface fuel bed, fire severity and behavior are strongly dependent on the species and density of the overstory.
Experimental fires in primarily black spruce/lichen forests in the Northwest Territories indicated that potential fire spread rates and severity depend on overstory characteristics. Continuous lichen cover in these forests is flammable but does not, by itself, produce high fireline intensity even during favorable burning conditions. In canopy openings, the spread rate through the lichen mat is generally slow. Lichen bulk density is generally too low to support downward heat sufficient to ignite the entire surface layer before the flaming front passes and too high to support rapid fire spread. Even with wind, "a high-intensity flame-radiation surface fire does not develop". Typical residence times are 30 seconds or less. However, high-intensity fires can be produced when black spruce are ignited. In open black spruce stands, trees typically produce branches that extend to ground level. When black spruce moisture content declines to its typical summer moisture content of 80%, flames from surface fires burn quickly into the crowns under dry, windy conditions. Winds help to spread surface fires and ignite spot fires. Crown fires preheat lichen mats beyond the fire front, increasing the fire spread rate .
Jack pine/lichen forests rarely burn in the high-intensity fires described for black spruce stands. Self-pruning in aging jack pines produces crowns well above the surface. Fires in the lichen layer rarely produce surface fire intensities capable of igniting crowns or causing tree mortality .
Findings were similar during experimental fires in lodgepole pine stands in British Columbia, some of which contained a substantial reindeer lichen surface fuel component. While reindeer lichens were easily ignited and able to carry fire on the surface, the fire had low intensity and severity. When compared to mosses and lodgepole pine needles, reindeer lichens had the lowest bulk density, lowest surface-to-volume ratio, and lowest heat content. Surface fuels containing a substantial reindeer lichen component carried fire better than those without reindeer lichens, but fires in forests with reindeer lichens were of low severity and exposed very little mineral soil. The researcher concluded that lodgepole pine stands with primarily moss and lichen surface fuels were at low risk of crown fire in the absence of strong winds and/or ladder fuels .
Fire as a regeneration process: In the majority of reindeer lichen habitats, periodic fire is necessary to maintain groundlayer dominance in canopy openings. Reindeer lichen persistence in the absence of fire depends on forest and site conditions. Where site conditions restrict tree establishment and growth, reindeer lichens may persist for extremely long periods without fire. Payette  found dense black spruce/reindeer lichen krummholz sites in northern Quebec that had not burned for 1,500 years or more.
Eventual replacement of reindeer lichens by mosses and other associated lichens is described in black spruce habitats from the Northwest Territories to Newfoundland and Labrador. On sites sampled in a postfire chronosequence in western Labrador, reindeer lichen cover was greatest, 54%, on 40-year-old sites. Cover was much lower, 11%, in 20-year-old stands. Reindeer lichen cover was 1.3% in 140-year-old stands; reindeer lichen had been replaced successionally by Schreber's moss and knight's plume moss (Ptilium crista-castrensis) . On rich, moist, black spruce forest sites in Newfoundland, reindeer lichens are generally succeeded by mosses and may even be excluded from postfire succession once vascular plants and mosses establish. However, in dry forests near the alpine or maritime treeline, reindeer lichens may be long-lasting after fire . Replacement by mosses is described in 2 reviews: Damman and Johnston  suggested that without recurring fire, black spruce/lichen forests eventually become closed-canopy black spruce/feather moss (Hylocomiaceae) forests; Kershaw  similarly reported that in the absence of fire, tree density increases and eventually eliminates lichen ground cover. However, both reviews indicated that black spruce/lichen forests burn readily, and rarely are fires so infrequent that closed canopies develop [34,68].
Reindeer lichens dominated the ground flora in black spruce/lichen forests burned between 20 and 60 years ago but declined and were replaced by snow lichen when stands reached about 130 years old in the Abitau-Dunvegan Lakes region of Northwest Territories . In taiga habitats of north-central Canada, fire is considered important to reindeer lichen regeneration. In late stages of succession, reindeer lichens are replaced by vascular plants and feather mosses due, at least in part, to increased amounts of surface litter. Fire removes litter as well as much of the late-successional vegetation; after this clearing process lichens can reestablish and eventually flourish . While the time required for lichen establishment and dominance were not given in these papers, this topic is addressed in other reports (see Discussion and Qualification of Lichen Response).
Insect outbreaks and fire may work in concert to maintain canopy openings and reindeer lichen dominance. In southeastern Quebec, black spruce/reindeer lichen forest patches within a closed-canopy black spruce/feather moss forest were created by the combined effects of fire together with defoliating spruce budworm and European sawfly outbreaks . The insects severely restrict black spruce reproduction, since they preferentially feed on reproductive buds . Fires in infested stands thus cause tree mortality during a time when regeneration potential is low, producing open stands. Recurrent fire in these stands would likely maintain the black spruce/reindeer lichen type, whereas fire exclusion would likely advance development of the black spruce/feather moss forest . Temporal scales were not described in the paper.
In some cases, canopy closure is restricted by factors other than fire; in these cases, reindeer lichens may not be replaced by mosses or vascular plants even after extremely long fire-free intervals. On several sites in northern Canada, reindeer lichen abundance appeared to be increasing after a century without fire. In black spruce/bog blueberry forests near Inuvik in the Northwest Territories, reindeer lichens were only abundant on sites with fire-return intervals substantially longer than 100 years. Cladonia mitis became dominant in stands burned 120 to 200 years ago, and C. stellaris and C. rangiferina were dominant in stands over 200 years old . On burned black spruce/C. stellaris forests in northern Quebec, C. stellaris biomass was about 2,500 kg/ha on 47-year-old burned sites, nearly 6,000 kg/ha on 110-year-old burned sites, and 6,677 kg/ha on 140-year-old burned sites . In burned areas of northern Saskatchewan, northern Manitoba, and the Northwest Territories, the average biomass of "high-value" lichens, including C. stellaris, C. mitis, and C. rangiferina, was nearly twice as great in stands over 120 years old as in stands 76 to 120 years old . In northern Quebec, a dendro-ecological investigation indicated that a black spruce/lichen krummholz type was converted to a tundra/lichen community due to a lack of black spruce regeneration. Before a fire in 1750, the site was occupied by krummholz black spruce that regenerated primarily through layering. Postfire seedling establishment was severely limited. The subsequent development of a thick lichen mat may have further inhibited black spruce establishment .
Fire frequency/ecology: The few studies reporting average fire-return intervals in reindeer lichen habitats indicate a large range, about 40 to over 500 years. In jack pine/reindeer lichen forests in the Athabasca Plains region in northern Saskatchewan/northeastern Alberta, the mean fire-return interval averaged 40.4 years for 6 study sites. Fire scars spanned dates from 1783 to 1972. Average fire-return intervals calculated for individual sites ranged from 28 to 54 years, suggesting somewhat patchy burn patterns . Mean fire-return intervals were similar in jack pine and black spruce forests near the northern boreal forest-tundra boundary in northern Quebec. Ground layers were dominated by either C. mitis or C. stellaris at the 18 study sites. Eight fires occurred between 1773 and 1988, including both crown fires and surface fires, although crown fires were considered more common. Mean fire-free intervals ranged from 41 to 85 years for individual sites; the overall mean fire-free interval was 54.8 years. On average, 1.4% of the study area burned each year, indicating a fire-rotation period of 70 years. After 1851, three fires accounted for more than 60% of the burned area, while the other fires were much smaller and burned less than 10% of the area. At the time of the study (1988), stand ages ranged from 35 to 150 years, and 67-year-old stands were most common . Fire-return intervals may exceed 500 years in reindeer lichen habitats in coastal Labrador ( and sources therein).
The following table provides fire regime information that may be relevant to reindeer lichens. Included are only those vegetation communities for which published information confirms, or strongly implies, reindeer lichen occurrence. Because site tolerances and distributions for reindeer lichens are incomplete and many reindeer lichen habitats do not burn, such as rocky outcrops and talus slopes, other reindeer lichen habitats may also be missing from the fire regime table. If you are interested in a community not listed below, please consult the complete FEIS Fire Regime Table.
|Fire regime information on vegetation communities in which reindeer lichens may occur. For each community, fire regime characteristics are taken from the LANDFIRE Rapid Assessment Vegetation Models . These vegetation models were developed by local experts using available literature, local data, and expert opinion as documented in the PDF file linked from the name of each Potential Natural Vegetation Group listed below. Cells are blank where information is not available in the Rapid Assessment Vegetation Model.|
|Vegetation Community (Potential Natural Vegetation Group)||Fire severity*||Fire regime characteristics|
|Percent of fires||Mean interval
|Alpine and subalpine meadows and grasslands||Replacement||68%||350||200||500|
|Lodgepole pine (pumice soils)||Replacement||78%||125||65||200|
|Vegetation Community (Potential Natural Vegetation Group)||Fire severity*||Fire regime characteristics|
|Percent of fires||Mean interval
|Northern Rockies Forested|
|Persistent lodgepole pine||Replacement||89%||450||300||600|
|Whitebark pine-lodgepole pine (upper subalpine, Northern and Central Rockies)||Replacement||38%||360|
|Lower subalpine lodgepole pine||Replacement||73%||170||50||200|
|Lower subalpine (Wyoming and Central Rockies)||Replacement||100%||175||30||300|
|Vegetation Community (Potential Natural Vegetation Group)||Fire severity*||Fire regime characteristics|
|Percent of fires||Mean interval
|Great Lakes Woodland|
|Jack pine-open lands (frequent fire-return interval)||Replacement||83%||26||10||100|
|Northern oak savanna||Replacement||4%||110||50||500|
|Surface or low||87%||5||1||20|
|Great Lakes Forested|
|Northern hardwood maple-beech-eastern hemlock||Replacement||60%||>1,000|
|Conifer lowland (embedded in fire-prone system)||Replacement||45%||120||90||220|
|Great Lakes spruce-fir||Replacement||100%||85||50||200|
|Great Lakes pine forest, jack pine||Replacement||67%||50|
|Surface or low||10%||333|
|Surface or low||81%||85|
|Red pine-white pine (frequent fire)||Replacement||38%||56|
|Surface or low||26%||84|
|Red pine-white pine (less frequent fire)||Replacement||30%||166|
|Surface or low||23%||220|
|Great Lakes pine forest, eastern white pine-eastern hemlock (frequent fire)||Replacement||52%||260|
|Surface or low||35%||385|
|Vegetation Community (Potential Natural Vegetation Group)||Fire severity*||Fire regime characteristics|
|Percent of fires||Mean interval
|Eastern woodland mosaic||Replacement||2%||200||100||300|
|Surface or low||89%||4||1||7|
|Rocky outcrop pine (Northeast)||Replacement||16%||128|
|Surface or low||52%||40|
|Surface or low||65%||12|
|Oak-pine (eastern dry-xeric)||Replacement||4%||185|
|Surface or low||90%||8|
|Vegetation Community (Potential Natural Vegetation Group)||Fire severity*||Fire regime characteristics|
|Percent of fires||Mean interval
|South-central US Woodland|
|Interior Highlands dry oak/bluestem woodland and glade||Replacement||16%||25||10||100|
|Surface or low||80%||5||2||7|
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 [58,73].
Studies suggest reindeer lichen survival on burned sites is most likely in moist, protected refugia and/or during a quickly burning fire. Rouse  reported that "the lichen mat is always consumed when fire reaches it, but if the fire is fast-moving, patches are often missed." In burned black spruce stands in northern Saskatchewan, some C. stellaris and C. rangiferina survival occurred in "small relic areas that had escaped fire" . In jack pine/reindeer lichen woodlands of northeastern Alberta and northern Saskatchewan, surface and surface/crown fires generally resulted in lichen mortality but some survival occurred near the fire margin and in moist depressions . The moisture-retaining properties of reindeer lichen mats may increase reindeer lichen survival potential. In northwestern Alaska, reindeer lichens commonly grow in or on a moss layer, which retains some moisture even under dry conditions. Reindeer lichen pieces dislodged by caribou trampling are more susceptible to drying and may be more susceptible to fire-caused mortality than undisturbed mats, which retain some moisture at the base .
Very low-severity fire may kill only the top portion of the lichen mat, allowing for some reindeer lichen survival. In a Scots pine forest in Sweden, burning treatments were evaluated on a continuous reindeer lichen layer. In the lowest-severity treatment, fire spread over the plot, but smoldering combustion was immediately extinguished with a thick blanket. Although appearing dead, by the end of the 5-year observation period new basal growth was observed in C. rangiferina in the lowest-severity treatment. Additional treatments that allowed smoldering for 5 minutes, 15 minutes, and 1 hour completely consumed the reindeer lichen mat, and no subsequent reindeer lichen growth was observed . While experimental treatments may or may not represent realistic conditions, it is possible some reindeer lichens survive after extremely low-severity fires. However, 1 to 11 years after "low intensity" surface fires in Scots pine stands in Lithuania, C. rangiferina and C. arbuscula were present only in adjacent unburned plots .LICHEN RESPONSE TO FIRE:
It is often difficult to ascertain from fire studies whether or not postfire reindeer lichen recovery is the result of off-site dispersal or expansion of small surviving pieces in the burned area. Given the potential small size of regenerating or surviving pieces and slow increase in size and abundance of reindeer lichens, they may be overlooked in early postfire communities . Miller  indicated that during initial regeneration after removal of all vegetation, including reindeer lichens, primary thalli were inconspicuous and scattered. Vascular plant sampling techniques may not be sufficient to detect early postfire reindeer lichen regeneration.DISCUSSION AND QUALIFICATION OF LICHEN RESPONSE:
Many other fire studies indicate that reindeer lichens may not appear on burned sites for a decade or more. A European review reported that while small reindeer lichen thalli may occur 10 years after a fire, between 25 and 40 years were required before reindeer lichens were fully developed . In burned black spruce forests of northern Saskatchewan, C. stellaris and C. rangiferina were rare in areas burned less than 30 years earlier . When a chronosequence of 10 burned black spruce/C. stellaris stands was visited in northern Quebec, a 47-year-old stand was the youngest on which C. stellaris was recorded . In forested peatlands of northern Alberta, where C. mitis was the dominant lichen, sites burned within 20 years of sampling had 0% to 20% lichen cover. Average lichen cover in 25- to 65-year-old burned sites was not significantly different (P>0.05) from that on mature sites (over 70 years old). Despite substantial variation in lichen cover among sites of all ages, postfire recolonization on peatlands was considered rapid compared to that on other sites .
Studies have documented substantial variation, ranging from decades to centuries, in the time required to reach prefire abundance, peak levels of abundance, or surface layer dominance following fire. In a postfire black spruce/lichen chronosequence in the Abitau-Dunvegan Lakes region of the Northwest Territories, reindeer lichens dominated ground flora between roughly 20 and 60 years after fire, while the ground layer was dominated by snow lichen in 61- to 130-year-old stands and by mosses in stands older than 130 years . In another black spruce/lichen chronosequence that spanned 3 to 70 postfire years in the southeastern Northwest Territories, C. stellaris was present (0.1% cover) in 12-year-old stands but had greatest cover (46-47%) in 49- and 70-year-old stands . Maximum lichen cover where C. mitis dominated the ground layer occurred about 45 years after fire in jack pine/reindeer lichen woodlands of the Athabasca Plains region in northern Saskatchewan/northeastern Alberta . In eastern Newfoundland, reindeer lichen cover was much greater on 38-year-old than 23-year-old burned black spruce-sheep-laurel stands. Reindeer lichen cover was low in early postfire succession, averaging 5% in 23-year-old stands, but increased to 79% in 38-year-old stands . In subarctic black spruce forests in western Labrador, reindeer lichen cover was greatest, 54%, in 40-year-old burned stands when compared to 2-year-old, 18-year-old, 80-year-old, and 140-year old burned stands .
Studies indicate that fire severity, moisture conditions, grazing intensity, and vegetation type can affect postfire recovery of reindeer lichens. Investigations after a prescribed fire in young jack pine stands in northern Ontario indicated that C. rangiferina recovery may be affected by fire severity. Although initially "eliminated" by the fire, plots with less than 1.2 inches (3 cm) of duff removal had some C. rangiferina regeneration 6 to 10 years after fire. Plots with more than 1.2 inches (3 cm) of duff removed had no C. rangiferina in the same time frame . In Rocky Mountain lodgepole pine forests in central British Columbia, reindeer lichens occurred on mesic and xeric 50- to 100-year-old burned sites. Cover on mesic sites did not change much after 100 years; however, on xeric sites, reindeer lichen cover progressively increased with stand age, and researchers doubted that "an equilibrium state had been attained" . After years of studying caribou in the Kaminuriak Lake region of Nunavut, Miller  suggested that fire severity and intensity of caribou grazing may affect reindeer lichen recovery on burned sites more than time since fire.
Only 1 study to date (2008) compares reindeer lichen responses to fire from different vegetation types: This research, conducted in New Brunswick, suggests vegetation type may affect reindeer lichen recovery patterns and timing. Cladonia rangiferina was more abundant and occupied more ground cover earlier in burned jack pine than in mixed-hardwood stands. Average cover was 18% in 37-year-old jack pine stands and less than 0.5% in 37-year-old mixed-hardwood stands .
Species-specific responses: Within a vegetation type, species-specific differences in recovery patterns after fire are evident. In studies that compared reindeer lichen species recovery or establishment on burned sites, C. mitis was typically found earliest on burned sites. Generally, C. rangiferina occupied sites soon after C. mitis colonization. The pattern and timing of the appearance of C. stellaris and C. arbuscula on burned sites were less clear. Uggla  considered postfire recovery faster by C. rangiferina and C. arbuscula than by C. stellaris.
Treeless bogs: In a study of 4 bog hummocks in southeastern Labrador burned 6 to 83 years earlier, C. mitis and C. rangiferina were first recorded in a 22-year-old burn, and C. stellaris was first recorded in a 50-year-old burn .
Lodgepole pine: In burned lodgepole pine stands in north-central British Columbia, C. mitis and C. rangiferina occurred in 0- to-50-year-old stands, becoming groundlayer dominants in 50- to-150-year-old stands. Cladonia stellaris was present, but less abundant, in young and medium aged stands. In the 100- to 150-year-old and over 150-year old stands, C. arbuscula occurred with low abundance. The importance of C. mitis and C. rangiferina decreased as stand age exceeded 150 years .
Spruce: Cladonia mitis was often the first reindeer lichen to colonize and eventually dominate burned spruce forests. In black spruce/bog blueberry forests near Inuvik, Northwest Territories, C. mitis became dominant around 120 to 200 years after fire. Cladonia stellaris and C. rangiferina did not dominate until 200 or more years after fire . In northern Saskatchewan black spruce forests, C. stellaris and C. rangiferina may reach prefire abundance within 90 to 120 years of fire .
In burned spruce/lichen stands in northern Quebec, C. mitis occurred on 4-year-old burned sites. Cladonia rangiferina and C. stellaris were not detected until 14 years after fire. A continuous C. mitis lichen carpet occurred on a 38-year-old burned site, but cover was greatest on the 65-year-old burned site and declined in older stands. Cladonia stellaris cover was relatively low in early postfire stands but reached 70% to 80% on 130- and 250-year-old burned sites .
A postfire chronosequence in tundra, boreal forest, and ecotone habitats in northern Quebec showed that C. mitis dominated in the first 50 years after fire but was replaced by C. stellaris on sites unburned for 90 years or more .
|Average percent cover of reindeer lichens in northern Quebec |
|Years since fire||0-30||31-50||51-90||>90|
|Number of sites||5||10||12||38|
Cladonia mitis, C. rangiferina, and C. arbuscula appeared earlier in postfire succession than did C. stellaris in subalpine black spruce and open black spruce-tamarack (Larix laricina) sites in interior Newfoundland. Cladonia arbuscula and C. rangiferina occurred with high frequency but low cover by the 10th postfire year. Cover was still less than 20% on sites burned 35 to 36 years earlier. Cladonia stellaris occurred on 14-year-old burned sites, but increases in cover and frequency were negligible as time since fire increased to 36 years. On another site, cover of C. mitis, C. rangiferina, and C. stellaris in a 35-year-old burned stand was about half that in an adjacent unburned site. Cladonia mitis and C. rangiferina cover increased rapidly between 30 and 60 years after fire. At about 80 years after fire, C. stellaris began to dominate. Caribou grazing may delay or inhibit the development of this later successional stage of C. stellaris dominance .
|Average percent frequency/percent cover of reindeer lichens in 7- to 36-year-old black spruce-tamarack stands |
|Years since fire||7||10||14||22||32||36|
In late-seral black spruce forests in southeastern Labrador, low site productivity may allow C. stellaris to persist indefinitely. On 10- to 12-year-old burned sites, C. mitis and C. rangiferina may occur. Of these early postfire species, C. mitis expands more rapidly, reaching maximum cover 40 to 60 years after fire, and C. rangiferina reaches a lower peak cover 75 to 85 years after fire. Cladonia stellaris may establish on 35-year-old stands, but maximum cover is not reached until 80 to 90 years after stand establishment. On productive sites where closed canopies develop, C. stellaris abundance declines rapidly in shady, mesic conditions that provide prime Schreber's moss habitat. On drier, less productive sites, C. stellaris may persist as the dominant ground cover until the next fire .
Jack pine-spruce: Cladonia mitis and C. stellaris were found on burned jack pine-spruce before C. rangiferina. In a chronosequence study in the southeastern Northwest Territories and northern Saskatchewan, C. mitis and C. stellaris biomass and cover peaked in 80 to 100-year-old stands. Cladonia rangiferina cover never equaled that of C. mitis and C. stellaris .
|Average cover of reindeer lichens with increasing time since fire in boreal jack pine-spruce forests from the Northwest Territories and Saskatchewan |
|Years since fire||1-20||21-40||41-60||61-80||81-100||101-150||151-200||201-250||251-300|
|C. mitis and
In central Quebec's black spruce and jack pine boreal forests, C. mitis and C. rangiferina were present with greater abundance and sooner after fire than C. stellaris. Ground layers in stands about 50 years old were dominated by C. mitis and C. rangiferina, while C. stellaris dominated the ground layer in 71- and 110-year-old stands .
Relative frequency of reindeer lichens along a boreal forest postfire successional gradient in central Quebec (adapted from )
|Years since fire||<10 years||24 and 28 years||50 and 51 years||71 and 110 years|
In jack pine-black spruce forests of northern Quebec, C. mitis was the ground layer dominant in postfire stands less than 67 years old, while in stands over 132 years old, C. stellaris dominated . Severity of a crown fire affected reindeer lichen abundance on 57-year-old jack pine-black spruce forests in northwestern Quebec through its effect on seed sources and tree regeneration. Sites were sampled within areas of closed-canopy regeneration and in more open forests. Surface fire severity was considered comparatively uniform, as humus thickness was similar in open- and closed-canopy areas. Differences in reindeer lichen cover were likely most affected by canopy regeneration. Cladonia mitis was significantly more abundant in open- than closed-canopy plots, while C. rangiferina and C. stellaris were significantly more abundant in closed-canopy than open plots (P<0.001) . Citing work by Lechowicz and Adams , Arseneault  suggested that differences in abundance may have been due to C. mitis's greater tolerance of high evaporation rates in full sunlight.
Average percent cover of reindeer lichens 57 years after severe and reduced severity crown fire in jack pine-black spruce forests in northwestern Quebec 
|Severe crown fire, open canopy||Reduced severity crown fire, closed canopy|
Large numbers of caribou, causing heavy grazing and trampling, can impact reindeer lichen habitats by exposing mineral soil, altering successional trajectories, and potentially setting succession back many decades . Cladonia stellaris does not withstand heavy grazing and trampling . See Successional Status for further information.
Small mammals: In a review, Sharnoff reported that reindeer lichens are eaten by southern red-backed voles . It is possible that other small mammals feed on reindeer lichens.
Palatability/nutritional value: While reports suggest that reindeer lichens are nutritionally inferior to arboreal lichens and vascular plants, they are still preferred by caribou over other forage, at least in winter. A review by Ahti and Hepburn  suggests that reindeer lichens alone probably cannot sustain caribou, although there was no time frame provided for this assertion. A study of the chemical composition of caribou forage plants near Inuvik, Northwest Territories, showed that the protein content of reindeer lichens was significantly lower than that of vascular plants . It is possible that energy conservation during winter foraging may compensate for the lower nutritional content.VALUE FOR REHABILITATION OF DISTURBED SITES:
OTHER MANAGEMENT CONSIDERATIONS:
Pollution: Reindeer lichens are sensitive to pollution and have been used as pollution load indicators . Cladonia mitis, C. rangiferina, and C. arbuscula are rated sensitive to heavy metals and acid rain in the USDA Forest Service's Pacific Northwest region . Reindeer lichen tissues contained heavy metals and sulfur oxides as far as 15 miles (24 km) downwind from pulp and paper mills in International Falls, Minnesota. The concentration of pollutants, however, was lower in terrestrial reindeer lichens than in arboreal lichen species .
Mountain pine beetle: Preliminary results from a study in west-central British Columbia suggest that lodgepole pine death due to a mountain pine beetle epidemic may negatively impact terrestrial reindeer lichens. Decreased abundance of reindeer lichens corresponded to increases in kinnikinnick and, to a lesser extent, Schreber's moss. Researchers speculated that increased abundance of these species in areas of reduced lodgepole pine canopy cover may be due to increased light and nutrient availability and/or increased forest floor and soil moisture. Although supporting evidence is needed, there is some concern that more mountain pine beetle outbreaks, possibly exacerbated by climate change, may have deleterious impacts on forage lichens utilized by caribou populations in the region .
Tree regeneration: Some evidence suggests that reindeer lichens may inhibit tree seedling establishment but facilitate growth of those seedlings that do establish. Houle and Filion  found that lichen removal in white spruce/C. stellaris forests in northwestern Quebec resulted in greater white spruce seedling establishment but reduced seedling growth, particularly in juveniles less than 8 inches (20 cm) tall. They also observed that nearly all seedlings emerged from the edges of the lichen-removal quadrats or close to the lichen mat. Based on these results and a review of the literature, researchers speculated that reindeer lichens inhibited white spruce seedling establishment through allelopathy, physical impediment, altered soil temperature, and/or light capture. They suggested that small openings in the lichen mat may provide favorable recruitment microsites through increased seed retention, protection from predators, and/or increased soil moisture. Growth of juveniles may be increased by the water-holding capacity or nutrient leaching of the lichen mat . In contrast to these results, jack pine and white spruce seedlings watered for 17 weeks through mulches of C. rangiferina or C. stellaris had significantly reduced growth compared with controls mulched with peat moss (P<0.05). The researcher suggested that reindeer lichens may interfere with jack pine and white spruce seedling development, although the mechanism was not determined .
Vascular plant development: In a long-abandoned (≥50 years) agricultural field in west-central Wisconsin, brittle prickly-pear (Opuntia fragilis) flowered more when cooccurring with C. mitis and C. rangiferina. The reindeer lichen presence lowered summer surface soil temperatures by up to 7 °F (4 ºC), which may have improved soil moisture conditions .
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