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COSEWIC assessment and status report on the Boreal Felt Lichen in Canada

Limiting Factors and Threats

The major threats to the survival of the suboceanic boreal lichen forest habitats of Atlantic Canada and hence to the survival of the cyanophilic lichen communities contained are outlined in the following sub-sections:

A) Clear Cuts and Tree Plantations

Commercial tree harvesting on the Avalon Peninsula and elsewhere in Southern Newfoundland has exceeded the annual quotas set by about 20% and has led to a shortage in forest resources [Data compiled by the senior author for the years 1992-1999: harvested roundwood data taken from Compendium of Forest Statistics for the Council of Forest Ministers (http://nfdp.ccfm.org) and Annual Allowable Cut for insular Newfoundland taken from the Twenty Year Development Plans (1990-2009 and 1996-2015), Department of Forest Resources and Agrifoods].

In many parts of Newfoundland, clear-cutting has led in recent years, since about 1970, to the replacement of many natural to semi-natural forest communities by black spruce and balsam fir plantations. Any of the epiphyte-bearing phorophytes would have been lost during the establishment of clearcuts. The Lobarion community as a whole would not have the capability to regenerate. Even if sufficiently high number of spores of E. pedicellatum were to arrive from distant places, no new thalli could be formed due to the lack of Frullania in tree plantations.

The colonization within established spruce plantations by the above mentioned lichen species and by Frullania is also made difficult by the following factors:

  • Under the present environmental conditions, the low buffering capacity and rather strong acidity of black spruce barks make it difficult for E. pedicellatum to become established on the trunks of these trees and even on the branches. Even balsam fir plantations are not colonized by E. pedicellatum or Frullania. The reason for this may have something to do with the death of the original mycorrhizal fungi in clear-cut areas. In contrast, black spruce in natural, more or less well-lit but highly humid Sphagnum-rich forests, is occasionally colonized, although considerable decreases in their populations have been observed in recent years. Trunk occurrences have become virtually non-existent and even on the branches the health of the thalli has deteriorated and their numbers have dwindled along with the regenerative capacity to form juvenile thalli. Two exceptional thalli of E. pedicellatum on the trunks of black spruce next to the Ripple Pond Ridge logging road have remained in healthy condition due to the fact that a steady stream of clear humid air keeps rising from the low-lying wetland immediately to the south during the milder parts of the year. The reasons for these losses lie in the increasing threats from acid fog and acid rain, which seem to affect the chemistry of black spruce bark even under low level impact conditions to such an extent that the barks become unsuitable for colonization by Erioderma. This postulated scenario is supported by the complete absence of E. pedicellatum from otherwise ecologically suitable stands of black spruce in Nova Scotia. Such low level impact of air pollutants seems to have sealed also the fate of this lichen on Norway spruce in Europe.

  • The dark shade that exists in recently established tree plantations during the first 10-15 years prior to pre-commercial thinning is not conducive to the reintroduction of viable colonies of Scytonema - enriched Frullania, or to the re-synthesis and development of thalli of E. pedicellatum. Not even traces of Frullania had been found on the barks of black spruce in the plantations to the North of Fundy National Park (Veinotte, 1998 and Maass, personal observations), even though this hepatic commonly occurs in natural woodlands of New Brunswick on both coniferous and deciduous trees.

An added problem is that clear-cuts hardly ever get fertilized leading to the loss of symbiotic mycorrhizal fungi. This could lead to a gradual depletion of nutrients in the thin acidic glacial soils in Newfoundland, Nova Scotia and New Brunswick.

The retardation in the development of the lichen epiphyte floras in tree plantations has been observed and studied in areas to the north of Fundy National Park, as a contribution to an understanding of the Greater Fundy Ecosystem in New Brunswick (Veinotte 1998). Whereas almost all of the four Reference Stands, which were representative of the mature mixed forests in the northern half of Fundy National Park, contained species of Nephroma and Lobaria (almost exclusively on deciduous trees but very exceptionally also on trunks of red spruce (Picea rubens), these cyanophilic species had been absent from all of the black spruces in the 6, 10, 15, 18 and 23 year old plantations studied. Only exceptional thalli of Leptogium cyanescens had been found on an occasional deciduous shrub encountered in the 10 and 15 years old plantations. The latter species is only marginally a component of the Lobarion.

Finally it has been shown that large-scale logging greatly reduces internal stand moisture levels by altering the stand’s ability to buffer periods of desiccation. This is believed to have contributed to the demise of Erioderma pedicellatum in Sweden. As mentioned earlier, one of the original localities in Värmland, Sweden, was designated as a nature reserve in 1952 shortly after a mass occurrence of the species was discovered there by Ahlner in 1941 and 1946 (Ahlner 1948). The presence of logging immediately adjacent to the park boundary and the subsequent desiccation of habitat was one of the suspected causes for the eventual extirpation of the species in this locality (http://www.nhm.uio.no/botanisk/bot-mus/lav/factshts/eriopedi.htm).

B) Atmospheric Pollution

It has long been suspected that acid rain eliminates sensitive lichens from suitable ecosystems for two reasons (Hawksworth and Rose, 1976; Richardson, 1992). First the already naturally acidic substrates are further acidified, thereby reducing the buffering capacity of the bark (Nieboer et al., 1984). Second the lichen thallus is immediately affected by the uptake of air pollutants (Farmer et al., 1992). Cyanolichens, in particular, are more vulnerable to the effects of air pollution. All of the cyanophilic lichens are capable of trapping and utilizing molecular nitrogen from the air for the generation of nutrients containing nitrogen. A common characteristic of theirs is that the nitrogen-fixing enzyme, nitrogenase, has a remarkable intolerance for the presence of SO2 (James, 1973).

The presence of acid rain appears to contribute to the loss of Erioderma pedicellatum from its spruce substrates. Even on the slightly less acidic bark of balsam fir, a partial die-back of Erioderma thalli has been observed. The eventual loss of thalli begins with a necrotic zone around the holdfast area and eventually spreads in all directions (Moberg and Holmasen, 1982). Damage to these holdfast zones is pronounced on thalli found on the highly acidic barks of black spruce. The damage to the holdfast areas of Erioderma pedicellatum has been exceptional among the cyanophilic lichens, and therefore is ranked highest on the list for sensitive species of Nova Scotia. In addition, community lichens associated with E. pedicellatum habitats such as the Lobarion are also given a relatively high ranking and have been shown to be sensitive to air pollution (Gauslaa, 1995), including Coccocarpia palmicola, Erioderma mollissimum, Parmeliella parvula and Fuscopannaria ahlneri.

Acid fog is more dangerous than acid rain because sensitive plants remain enveloped in stagnant acid fog for extended periods of time. This could be one of the two determining factors in the gradual disappearance of sensitive cyanophilic lichens from southern Nova Scotia. Acid deposition studies by Cox et al. (1989) in the Bay of Fundy region have shown that the average fog pH was 3.6, i.e., one pH unit lower than the average rain pH in the same area. Although no direct evidence has been shown for the effects of acid fog on lichens, evidence gathered in recent years (Cox et al.1996; Cox et al. 1998; Kouterick et al.1998) indicates that foliar browning in many of the natural stands of heartleaf birch (Betula cordifolia) and white birch in the outskirts of the Bay of Fundy is, either directly or indirectly, caused by acidic fog. Nova Scotia is prone to acid fog since it is closer to the influx of air pollution from the industrial centers of the northeastern U.S.A. and southern Ontario (Maass, 2001). This is in contrast to Newfoundland where the contribution of long range transported air pollution is far less significant than pollution from local sources, including the Come-by-Chance Refinery and the Holyrood Generating Station on the Avalon Peninsula as well as the Pulp and Paper Mills on the West Coast (Wadleigh et al., 1999).

The collapse of the Erioderma pedicellatum - phorophyte connection has probably resulted from the gradual lowering of the buffering capacity of the spruce bark over a period of time, during acid rain or acid fog episodes that would of course simultaneously inhibit the activity of the nitrogenase system. The undernourished hyphae of the holdfast area, after having been deprived of the supply of essential nitrogenous substances (including vitamins), may then become highly susceptible to the presence of SO2 and NOx or to the strong acids derived from them in the stemflow.

In general, it is clear that Erioderma and other lichens possessing the cyanobacterium symbiont Scytonema are highly sensitive to atmospheric pollution. The impact on Erioderma pedicellatum, of the proposed development of a hydrometallurgical plant by INCO at Argentia, using new technology, warrants close monitoring.

C) Pest Control and the Use of Harmful Aerial Sprays

The recent threats to the coniferous woodlands and black spruce plantations in the Bay D'Espoir areas around Jipujijkuei Kuespem Park by the Yellow-headed Spruce Sawfly (Pikonema alaskanensis) have been of great concern. As an interim measure, because of BT having been shown to be ineffective in the elimination of the larval stages of this pest, the use of TRICHLORFON (which is known under the trade name "DYLOX") had been approved by the Pest Management Regulatory Agency of Health Canada in 1998 as a spray reagent.

Since the upper cortex of E. pedicellatum does not appear to have significant water repelling properties, its cyanobacterial layer would be readily accessible to aqueous droplets containing this chemical, which could then do damage to the cellular membranes and to the nitrogenase of Scytonema under dry weather conditions. Such a mode of action could seriously decimate the E. pedicellatum populations in the Bay D'Espoir area.

Fortunately, the use of trichlorfon as a spray reagent against the sawflies in Newfoundland has been abandoned for the time being. A far less harmful agent, azadirachtin, an extract from the Indian Neme tree (Azadirachta indica), is currently being used.

Likewise, trichlorfon sprays have not been approved for the Nova Scotia or New Brunswick regions. Instead, efforts are currently underway, in cooperation with the Federal Forestry Service in Fredericton, N.B., to investigate the suitability of specific BT strains (such as BT-i).

It is sometimes difficult to judge whether a particular insect infestation is more harmful to the lichens growing on a tree or the spray reagent that is to be used to reduce the spread of that insect. It probably depends on the extent of the defoliation of the tree and on the annual fluctuations in the population numbers of the insect.

D) Forest Fires

Many areas of Newfoundland have been strongly affected by forest fires. A particularly extensive fire had raged through large tracts of land behind the base of the Burin Peninsula in 1960. This fire may account for the absence of viable E. pedicellatum communities from this general area.

In addition to the obvious impacts of fire, the presence of SO2 in the smoke from burning woodlands is well known and is able to destroy the nitrogen-fixing lichens that happen to be downwind from the burn (see Denison et al. 1976).

E) Droughts and Hurricanes

Extreme weather induced events, such as drought or windstorms, can affect populations of E. pedicellatum. Prolonged periods of drought may lead to the death of thalli through exposure to heat-induced desiccation. The susceptibility of Erioderma to desiccation may be the result of an upper cortex that appears to lack a vapour barrier in the form of a lipophilic layer of alkanes (see Piervittori et al. 1997). The absence of such a “boundary layer” would promote losses in thallus moisture during dry weather periods (Fos at al. 1999). E. pedicellatum and other lichen populations can also be severely decimated through tree windfalls along the edges of the forests (Boyce, 1988). One such storm had blown across the Avalon Peninsula from a northeasterly direction in November of 1994 and caused considerable wind-fall, in Salmonier Nature Park (SNP), the Lockyer’s Waters Area and on the Ripple Pond Ridge (see NF-62b).

At least one of the original habitats of Erioderma pedicellatum in Nova Scotia was completely destroyed by a windfall when a severe storm traveled from a southwesterly direction and hit the eastern shores of Guysborough County near Wine Harbour (NS-40).

F) Global Warming

On a macro-scale, the birch die-back in Eastern Canada and in the adjacent parts of the U.S.A. can be viewed as being the immediate result of global warming, according to the work by Auclair (1987) and Auclair et al. (1992). See the explicit review by Braathe (1995). Even though the effects of global warming upon lichens are not as easy to measure as the extent of the birch die-back in Eastern North America (through aerial reconnaissance), they may manifest themselves in having given rise to partial losses of earlier established distributional ranges. In particular, those respective lichens that largely depend on a particular tree species (such as birch) as its main phorophyte, or lichens that are extremely dependent upon high humidity habitats, such as Erioderma pedicellatum, may be sensitive to climate change.

G) Effects of Herbivory on the Growth of Balsam Fir Seedlings

The effects of moose browsing in central Newfoundland have been discussed and evaluated over a period of time by Bergerud and Manuel (1968) and Thompson and Curran (1993). Due to the density of browsing on balsam fir seedlings by moose the mixed coniferous woodlands are gradually being converted into forests in which spruces are the dominant species. The suppression of balsam fir regrowth, based on the current hypothesized life cycle of Erioderma, places limitations on the regeneration of viable E. pedicellatum habitats. There is little doubt that black spruce had once played an important role in providing alternative phorophytes for E. pedicellatum thalli. However, the high acidity of the spruce bark can become in itself a limiting factor to the distribution of E. pedicellatum in Newfoundland, accelerated in the presence of long range transported or locally generated pollutants.

The effect of severe moose browsing on balsam fir is quite evident in Lockyer’s Waters. This could have detrimental effects on the regeneration of young balsam fir stands adjacent to sites containing Erioderma and could therefore inhibit the ability of the formerly large population of more than 953 documented thalli to renew itself through the initiation of new life cycles on nearby trees of suitable age, illumination and environmental health. [According to careful recounts of thallus numbers by Mr. Eugene Conway during the fall of 2002, considerable losses have occurred, leaving only about 20% of the originally counted thalli in place.]

H) Effects of the Microfauna Herbivory on Erioderma

Mites often feed on mosses and on the decaying parts of bark. The effects of browsing by mites on Erioderma thalli are also quite evident in certain field sites although, in general, they do not impose a threat to existing populations of the lichen. Yetman (unpublished data from Masters thesis) has identified at least one species of mite from the Lockyer’s Waters locality that was collected from the surface of a moist Erioderma thallus.

Browsing by snails has also been observed but is a minor threat that occasionally leads to partial removal of the upper cortex and the photobiont layer beneath.

Large-scale mono-cultures also raise the question whether the fungal endo-symbionts in the needles of conifers are naturally introduced. These micro-fungi appear to play an important role in the life of the tree by increasing the resistance of the foliage to attacks by foraging insect larvae (Calhoun et al. 1992, Clark et al. 1989, Todd 1988). The presence of such natural insect feeding deterrents in the needles may not only provide a certain amount of protection against defoliation of the conifers but may also moderate the activities of the micro-fauna on the barks on which the lichens grow.

I) Land Development

Road building and the spread of both tourism and industrial activities, such as the harvesting of forests that had not been accessible previously, often go hand in hand. A good example of this had been the building of the Burgeo Road where forest harvesting began soon after the opening of the road. It also opened up the possibilities for conducting a survey of the rare lichens in the area. Unfortunately, what had been gained would soon be lost, which had included the northernmost occurrence of Erioderma pedicellatum on black spruce.

The spread of the cottage industry is similarly taking its toll, mostly in making the more remote parts of the forests more accessible to their utilization. This would include domestic cutting, recreational activities and increased vehicle traffic (Brawn and Ogden, 1977). This is no doubt a legitimate threat in Lockyer’s Waters.