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EXPERIMENTS AND OBSERVATIONS ON EPIPHYTIC LICHENS AS EARLY WARNING SENTINELS OF FOREST DECLINE Martha G. Scott Thomas C. Hutchinson Department of Botany and Institute for Environmental Studies University of Toronto Toronto, Ontario, Canada. MSS IA1. ABSTRACT Forest declines are now widely reported in Europe and eastern North America, especially in high elevation areas where fogs, oxidants and SO2 frequently co-occur. Analyses of cloudwater indicate that high-altitude fogs are more acidic (x#pH of 3.8) than ambient precipitation at the same sites and may be present for up to 50% of the year. A combination of high humidity and nutrient enrichment normally allows for a prolific, species-rich epiphytic lichen flora on coniferous trees in the transition zones. In previous field studies, we have shown that boreal forest-floor lichens such as Cladina rangiferina respond to seasonal sprays of simulated, acidic rain of less than pH 3.5 by producing abnormal morphological and cytological structures. We have, therefore, selected a number of high-altitude sites showing varying degrees of forest dieback in Quebec, Vermont and New York (North America) and in the Black Forest and Hartz Mountains (Germany) to determine whether similar abnormalities occur in lichen populations exposed to ambient levels of acidity. We shall discuss the suitability of two, widely-distributed epiphytic lichens, Hypogymnia physodles and Pseudevernia sp., as early warning indicators of forest dieback, based on a combination of morphological, cytoplasmic and chemical data. INTRODUCTION The nature of the forest decline, which is currently affecting tree species in Europe, Scandinavia and eastern North America, is complicated both by the plethora of hypotheses which have been advanced to explain the diebacks and by the complexity of the forest ecosystem itself. A delicate balance exists between above-ground foliar processes such as gas exchange, cuticular integrity and stomata! mechanisms and less visible below-ground factors such as soil chemistry, decomposer organisms, mycorrhizal associations and nutrient availability. Superimposed upon these interrelationships are disease vectors, climatic variables, community and stand dynamics and anthropogenically-derived pollutants, all of which may play a vital role in determining the health of trees within narrowly-defined geographical limits. In order to understand the dynamics of specific dieback scenarios and the possible involvement of atmospheric pollutants such as acid rain, acid fogs and oxidants, it is necessary to document links between known levels of inputs (eg., SO4 and NO3) and regional declines of specific species. Unfortunately, the long-term monitoring of ambient 205

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206 precipitation chemistry is time-consuming and expensive and, to date, only a handful of such programmer exist. The CHEF project (Chemistry of High Elevation Fog- Schemenauer 1986), currently being implemented at two sites in Quebec, and a similar study at Whiteface Mountain in New York, are two such programmes which provide accurate information about atmospheric chemistry in high-elevation forests where significant declines of balsam fir and red spruce are occurring. This report presents the results of studies conducted both in Germany and at the high-elevation locations noted above, on two widely-distributed species of lichens, Hypogymnia physodes and Pseudevernia sp. which show good potential as sentinels of forest dieback. 2. Historically, there are distinct advantages in predicting the severity of atmospheric pollution on the basis of changes in 'simple' organisms such as lichens and mosses, which have neither roots nor the waxy cuticle which protects higher plants. Traditionally, the presence or absence of key indicator species has been used as a kind of 'litmus paper' to map levels of SO2 emitted from point-source industrial processes (Leblanc and Rao 1966. Seaward 1987~. The disadvantages of this technique lie in the fact that expertise in lichen taxonomy is required to interpret the data and that the response of a particular lichen to a gaseous pollutant may be an "all-or-nothing phenomenon," open to a number of alternative explanations. However, the acidophilic nature of lichen thalli, in particular of the fungal partner in the symbiosis, suggests that these organisms may be much more tolerant of acid rain and fogs than they are of gaseous pollutants (Scott and Hutchinson, 1987~. In fact, lichen populations epiphytic on declining Norway spruce in Germany are actually flourishing. Tolerant lichen species which gradually change in some aspect of their biology over a long period have potential value as bioindicators of tree dieback in impacted areas. Accordingly, the objectives of this current study are two-fold: 1. To assess the effect on lichen tissue chemistry of elevated levels of sulphate, nitrate, ozone and possibly metals. In 1986, the mean fog pH at high elevation sites in eastern Quebec was 3.S, whereas the mean pH of precipitation at the same sites was 4.3 (Schemenauer 1986~. Modelling techniques suggest that fogs and clouds blanket these mountaintops for up to 50% of the year. To determine whether specific morphological or cellular aberrations exist in species of Hypogymnia and Pseudevernia epiphytic on declining balsam fir and red spruce at these sites. Our previous research in a boreal forest ecosystem showed that branching pattern abnormalities and changes in starch and lipid content of algal cells could be induced in Claciina species by seasonal sprays of simulated rain of pH less than 3.5. METHODOLOGY Only a brief summary of our experimental design and methodology will be presented here. Data are preliminary and have not yet been statistically analysed. Our study sites are listed in the following table. To date, all of the high elevation locations have been sampled. However, low elevation sites experiencing acidic fogs near the Bay of Fundy, Nova Scotia and a northern boreal forest site with low pollutant inputs will be visited in 1988. A range of altitudes is included for each mountain.

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207 Site Elevation Germany: Black Forest Region - 4 sites 500 - 1300 m Hartz Mountains - 2 sites 800 - 1000 m Czechoslovakian Border - 1 site up to 1200 m North America: Mt. Tremblant (Quebec) 100m, 590 m, 860m Mt. Sutton (Quebec) 845m, 970 m Whiteface Mountain (N.Y.) SS4m, 1 1 60m Camelts Hump (Vermont) 884m, 1067m Low Elevation Sites: Sudbury, Ontario (near smelting operations) - Ciadina sp. Burt Lake, Ontario - boreal forest ecosystem Bay of Fundy, Nova Scotia - low elevation with acidic fog monitoring station Two species of lichen were present at most of the study locations. Hypogymnia physod~es, a foliose epiphyte of conifers, has a ubiquitous distribution and is semi-tolerant of gaseous pollutants such as SO2. Two species of the subfruticose Pseudevernia (P. consocians in NA and P. furfuraceae in Europe) were chosen also because of irregular morphological features noted during preliminary site visits in 1987. Because of the wide geographical disparities between the study sites, appropriate control sites were difficult to establish. Although the boreal forest location in northern Ontario is unaffected by air currents from the southwest, it is a low-elevation site. However, boreal and high-altitude transitional forests are quite similar in structure and contain many of the same understory species. Low-elevation sites at the base of the mountains are inappropriate because the mixed hardwood forests do not support the same lichen flora and microhabitat factors are completely different. At two elevations on Mount Tremblant and Mount Sutton, therefore, we selected paired sites of different exposures to prevailing winds, in order to test the hypothesis that atmospheric inputs from the SW were more damaging to lichens than inputs from an eastern or northern source. At each site, 10 balsam fir and red spruce trees, with a DBH of approximately 50 cm, were selected at random from within a defined area. Crown dieback was rated subjectively using a scale of 1 to 5, with 1 being healthy (less than 20% dead branches and chlorotic needles) and 5 being dead. The percentage cover of all lichen species present on a one-metre segment of the bole of the trees (measured upwards from DBH) was also recorded. From within this 1 metre zone, even-aged samples of H. physodes and Pseudevernia were then harvested for laboratory analyses. The following tests were performed for each collection: ( 1 ) Lichen thalli were examined and photographed using a dissecting microscope. Unusual branching or lobation patterns were noted, along with abnormal production of sexual and asexual reproductive structures (Sigal and Nash 1983~. This information will be quantified.

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208 (2) Tissue, containing both the algal and fungal symbionts, was fixed for TEM using a previously-published protocol (Scott and Larson 1984~. (3) Following digestion with nitric acid, the tissue chemistry of unwashed lichens was analysed using either ICP (inductively-coupled plasma emission spectroscopy) or atomic absorption spectroscopy. Data were obtained for a number of elements and expressed on a ug/g dry weight basis (n=5-~. (4) Pieces of lichen thalli similar in dry weight and exposed surface area were soaked in double-distilled water for one hour. Aqueous extracts were then filtered and analysed for cations (Na+, NH4+, K+) and anions (C1-, F-, N03, P04, SOT) using DIONEX (n=6 reps/study site). RESULTS AND DISCUSSION Our results clearly demonstrate that both morphological and chemical indicators of air pollution effects can be seen in lichen epiphytes of declining trees. As seen in Table 1, the percentage cover of the dominant epiphyte H. physodes decreases with increasing altitude at all but the most northern location (Mt. Tremblant). Ideally, lichen growth should be extremely vigorous in such a cool, moist habitat. The lowest percentage cover of dominant lichen species on boles of balsam fir was recorded near the summit of Whiteface Mountain, where the average crown dieback rating was 4.1, or extremely severe. On-site observations also indicated that many lichens were white or pinkish in appearance, a symptom which may be the result of membrane damage resulting in destruction of chlorophyll. Table 1. Percentage Cover of llchene on boles (DBH) of Baleam Fir growing at high elevation sitea in eastern North America. Site ~ H`fpogy~nnla physotes Total Dominant Total Lichen Crown Dleback species Cover Ratlug - x S.E. x S.E. Mt. Tremblant: 590 m 26 8 S5 66 27 2 .8 860 m 36 S 77 84 7 2.6 Mt. Sutton: 865 m 29 5 83 103 11 3.3 970 m 26 5 65 94 25 3.1 Whlteface (MY. ): 884 m 35 5 66 90 8 3.3 1160 m 21 5 44 72 15 4.1 Camel'n Hump: 884 m 35 6 71 97 12 3.4 1067 m 29 3 49 89 12 3.2

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209 Micrographs of Cladina rar~giferina (boreal), H. physodes and P. furfuraceae are presented in Plates 1 and 2. Figures 1-3 show podetia of C. rangiferina which received periodic sprays of acidic rain (a field simulation experiment) (Hutchinson et al., 1987~. As compared to the normal situation in which branching occurs close to the tip (Fig. 1), affecter! lichens produced numerous stunted branches on fully-elongated portions of the thallus which usually do not initiate new growth (Fig. 2~. These short branches dichotomize repeatedly and rapidly produce sexual structures (Fig. 3~. In addition, there is an increase in the number of algal clusters as compared to the volume of the thallus comprised of fungus. At high elevation sites, thalli of a number of species showed either branching pattern abnormalities (Figs. 4,5,7) or they produced enormous numbers of asexual structures. German populations of Pseudevernia furfuraceae from both the Schwarzwald regions and the Hartz Mountains (acid fog, ozone and S02) produced club-shaped structures which failed to dichotomize at the growing tips (Fig. 4 arrow). Asexual structures known as isidia, which contain both the algal and the fungal symbiont (Fig. 5,6) are the normal reproductive propagule of this genus. However, thalli harvested from severely declining sites in both Europe and North America produced large numbers of these highly branched structures with little subsequent elongation of the 'internodal' regions (Fig. 5~. This phenomenon occurred on both large and small diameter thalli in the populations. Lobes of Hypogymnia physodes (not shown) were also convoluted and had prolific marginal soralia (another form of asexual structure). Morphological changes in lichen thalli exposed to air pollution have been reported in the literature for Parmelia species exposed to high dosages of SO2 near Sudbury, Ontario (LeBlanc and Rao 1966) and for H. enteromorpha from the heavily-impacted San Bernardino Mountains in California (Sigal and Nash 1983~. These authors also observed an abnormally high production per mm2 Of asexual pycnidia. Factors which control branching patterns in healthy lichenized fungi are very poorly understood. In non-lichenized Ascomycetes, sources of carbon, nutrients and especially nitrogen (Griffin, 1981) have been reported to control the degree of 6hyperbranching' of hyphae. Since the stemflow of declining trees may be both acidic and enriched with canopy leachates, altered nutritional factors may, indeed, play a role in stimulating branch production in lichens at high elevation sites. A fertilization effect from the nitrate component of the acidic fogs may also be related to the vigorous lichen growth. At the cellular level (Plate 2), Figures ~ and 9 show transmission electron micrographs of C. rangiferina exposed to simulated rains in a boreal forest ecosystem (Hutchinson et al., 1987). Compared to the normal appearance of the cytoplasm (Fig. 8, pH 5.6), thalli sprayed with rain of pH 2.5 or 3.0 contained algal cells with huge peripheral lipid bodies (Fig. 9) and large deposits of intrathylakoidal starch. This phenomenon has been reported in lichens exposed to high levels of industrial pollution, including S02 near urban centres in Madrid (Silva-Pando and Ascaso 1982) and in higher plants exposed to salt stress (Winter 1982~. In high elevation populations of Hypogymnia and Pseudevernia, starch and lipid are also accumulated by algal cells (Figs. 10, 13~. This apparent sequestering of photosynthetic pro~iucts may represent a failure to translocate sugar alcohols to the fungal partner and might ultimately result in decreased growth of the hyphae and possibly saprophytism. Within the population of algal cells in an affected lichen, healthy and senescent algal cells co-occur. However, the most severely declining sites had the highest percentage of algae with cytoplasmic damage. Deterioration of the chloroplast and cellular membranes was commonly found, along with extensive cell wall degradation. The degree of cellular damage to the lichens appeared to be correlated with the tree dieback rating for the site.

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210 1 _ - ~.. Figure 1. Light micrograph of growing tips of C. rangiferina from a boreal forest ecosystem. Podetia sprayed with 'rain' of pH 5.6 had numerous terminal apothecia (Ap). (Hutchinson et al., 1987~. Figure 2. Initialtion of numerous small branches on a mature lower portion of C. rangiferina sprayed periodically for five years with artificial rain of pH 2.5. Figure 3. High magnification of a newly- initiated branch with a developing sexual structure (Ap - apothecium). The dark coloration is a result of numerous, large algal cell clusters. Figure 4. Pseudevernia furfuraceae from the Schwarzwald region (greater than 1 OOOm), West Germany. Note the heavily isidiate regions (large black arrow), which failed to dichotomize.

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211 e Figure 5. Higher magnification of a portion of the thallus shown in Figure 4. Isidia (Is) are highly branched. :~4 Figure 6. A portion of the same species (P. furfuraceae) from a lower elevation collection (SOOm) in the Schwarzwald. The thallus is relatively smooth, with fewer numbers of isidia Figure 7. P. furfuraceae from the Hartz mountains. Branched isidia are short and thickened. Algal cells (A) are darkened and necrotic-looking, as is much of the upper surface of the thallus. :i~ ::~ Figure 8. Cytoplasm of the unicellular alga, Trebouxia, in C. ran~iferina from the boreal forest simulation experiment. this micrograph is representative of either unsprayed podetia or podetia sprayed with rain of pH 4.0-5.6. A- algal layer. PB-pyrenoid body (starch organizing centre). Ch-Chloroplast. Hy- Hyphae. (Hutchinson et al., 1987~.

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212 . ..~ Ida . ~ it, ff< .:. ~ by. _ L_ P. ~ by: ~ C`_ _ hi. I. 3. {,_ Figure 9. Algal cell from the same species sprayed with simulated rain of pH 2.5. Note the large deposits of peripheral lipid (Li). Figure 10. Algal cells of P. consocians from a high elevation site on Camels Hump, Vermont. Cells are relatively normal in appearance, except that they contain numerous starch grains (St) and poly-phosphate type bodies (Pp). Figure 11. Epiphytes (Ep), with well- preserved cytoplasm are commonly found on the surface of lichens harvested from the Hartz mountains in Germany. Although many of the lichenized "algae were senescent, there were an abundance of micro-organisms on the upper cortex. Figure 12. High magnification of the thylakoid membranes (Th) in the chloroplast (Ch) of an alga from H. ohvsodes (Schwarzwald region). Note the interthylakoidal starch grains (St) and the disruption of membrane structure.

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213 - Figure 13. The alga of H. physodes from a high elevation collection on Whiteface Mountain, N.Y. Note the large, peripheral lipid bodies (Li) and the accumulation of starch bodies (arrow). Two strong patterns emerge from examination of the tissue chemistry data in Table 2. First, at heavily impacted sites such as Whiteface Mountain, there is a general pattern of loss of important plant nutrients, such as P. Mg and Mn, with increasing elevation. At sites with intermediate dieback, some of these nutrients, especially Ca, may be substantially elevated, possibly because of foliar leaching or mobilization of cations from bark substrates exposed to acidified stemflow. In the case of calcium, two values are presented for each site, one with all trees included in the sample, and a separate mean from which values for dead trees were removed. It is apparent that a tremendous flush of Ca is released from senescent trees, thus substantially elevating the lichen tissue content of elemental Ca. Even with the dead trees removed, however, Ca levels are elevated at sites with a SW exposure, compared to sheltered sites at an equivalent altitude on the same mountain. Calcium content of epiphytic lichens may, therefore, be a useful marker of tree senescence. As far as the metals are concerned, lichens from heavily-impacted high- elevation sites contain high levels of Al, Fe, Pb and Cu (not shown). All of these metals may, in some way, be related to by-products of industrial processes. Aluminum has been reported by Scherbatskoy ( 1982) and Scherbatskoy and Klein ( 1983) to occur in cores taken from declining red spruce at high elevation sites. It is interesting to note the pattern for Pb which is positively correlated with increasing elevation, with the exception of sheltered sites which contain only background levels of Pb. Although the data for anions and cations in aqueous extracts of lichen tissues are incomplete, the pattern for ammonia is similar to that observed for the metals. Nitrate and sulfate are also substantially elevated, especially in lichens from the collection near the Czechoslovakian border. In conclusion, epiphytic lichens appear to have potential as bioindicators of forest decline. To be useful as early warning indicators, however, it is important to identify morphological and chemical markers in advance of severe tree dieback. Both the growth pattern abnormalities and the accumulation of Ca and metals

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Table 2. Tissue che~atr' (ug/g) of Hypo~nla ohysodes from high elevation sites. Site (Elevation) P Ca Al Fe Pb S N . . Genuine: S18CL Forest 2248 8~ 1038 71 ~23 17,4 558 2348 1032 60 Czechoslovakia (1000- 1200~) 1390 2322 1147 1606 56 2856 1786 16, 300 Mt. ~re~laDt: 100 metros 1323 87,12~) 604 750 26 2630 S90 metrca 884 6409 591 807 67 1947 13,200 (2110)* 860 metros 1285 56SO S07 548 92 1702 14,100 (2347) * 860 m(sheltered) 686 2069 173 184 28 1237 11,300 Mt. Sutton: 845 metros 1422 6597 649 928 138 1996 16,900 (2012)* 845 Sheltered) 1938 3346 715 1025 65 1600 12,300 970 met res 754 10,406 690 818 99 1237 12,100 (3935)*- Whiteface (N.~. ): 884 metres 1765 6471 608 779 48 1393 9,300 (3468) 1160 metres 8S0 9568 870 1382 87 1720 13,800 (1016) Camel's Bump (VA): 884 metros 1341 14 ,657 (2409) 1067 Petrel 1836 14,836 ( 2665) 890 629 92 1896 11, 100 548 650 78 1478 8,100 occur in species of Hypogymnia and Pseudevernia epiphytic on apparently healthy conifers. If, in fact, we can demonstrate that good correlations exist between atmospheric inputs and changes in lichen flora, then these studies may provide a faster, more economical way to assess ambient air quality in the absence of permanent atmospheric monitoring stations. ACKNOWLEDGMENTS Our thanks are due to Dr. R. Schemenauer of the Atmospheric Environment Service of Environment Canada for his considerable help and encouragement in initiating this project. We also thank field workers on the Chemistry of High Elevation Fog (CHEF) project. Marilyn Feth and Catriona Gordon provided invaluable technical assistance. The project was funded by the Wildlife Toxicology Fund to whom we are most grateful. Travel funds were supplemented by the Canadian Forestry Service.

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215 REFERENCES GRIFFIN, D.H. 1981. "Growth and Development of the Thallus" in Fungal Physiology. John Wiley and Sons, New York. Pp. 117-130. HUTCHINSON, T.C., M. SCOTT, C. SOTO, and M. DIXON. 1987. The effect of simulated acid rain on boreal forest floor feather moss and lichen species. Pp. 411- 426 in Effects of Atmospheric Pollutants on Forests, Wetlands and Agricultural Ecosystems, T.C. Hutchinson and K.M. Meema teds.), Springer-Verlag Berlin Heidelberg. LEBLANC, F., and D.N. RAO. 1966. Reaction de quelques lichens and mousses epiphytiques a l~anhydride sulfureux dans la region de Sudbury, Ontario. The Bryologist 69:338-346. SCHEMENAUER, R.S. 1986. Acidic Deposition to Forests: The 1985 Chemistry of high elevation fog (CHEF) project. Atmosphere-Ocean (24~4:303-328. SCHERBATSKOY, T. 1982. Changes in Aluminum and heavy metal concentrations in Picea rubens wood in Northern Vermont. Cambial Activities Increment 7:2-3. SCHERBATSKOY, T., and R.M. KLEIN. 1983. Response of spruce and birch foliage to leaching by acidic mists. J. Environ. Qual. 12:189-195. SCOW, M.G., and D.W. LARSON. 1984. A correlated light and electron microscope study of Umbilicaria lichens. Can. J. Bot. 62~9~:1947-1964. SCOTT, M.G., and T.C. HUTCHINSON. 1987. Effects of a simulated acid rain episode on photosynthesis and recovery in the caribou-forage lichens, Cladina Stellaris (Opiz.) Brodo and Cladina rangiferina (L.) Wigg. New Phytologist 107:567-575. SEAWARD, M.D. 1987. Effects of quantitative and qualitative changes in air pollution on the ecological and geographical performance of lichens. Pp. 439-448 in The Response of Forests, Crops and Wetlands to Atmospheric Pollution, T.C. Hutchinson and K. Meema (eds.) Springer-Verlag. Berlin, Heidelberg. SIGAL, L.L., and T.H. NASH III. 1983. Lichen communities on conifers in southern California mountains: an ecological survey relative to oxidant air pollution. Ecology 64~6~: 1343- 1354. SILVA - PANDO, F.J., and C. ASCASO. 1982. ~ ~. Modificaciones ultraestructurales de t~quenes ep~~~tos transplantados a zones urbanas de Madrid. Collectanea Botanica 13(1):351 -374. WINTER, E. 1982. Salt tolerance of Trifolium alexandrinum L. III. Effects of salt on ultrastructure of phloem and xylem transfer cells in petioles and leaves. Australian J. Plant Physiol. 9:239-250.

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Table 2. Tissue che~atry (ug/g) of Hypo~nla Physodes from high elevation sites. Site (Elevation) P Ca Al Fe Pb S N . . Gerund: S18CL Forest 2248 8 ~1038 71 ~23 17,4 558 2348 1032 60 Czechosloval~la (1000- 1200~) 1390 2322 1147 1606 56 2856 1786 16, 300 Mt. ~re~laDt: 100 metros 132387,12~) 604 750 26 2630 S90 metros 8846409 591 807 67 1947 13,200 (2110)* 860 metros 128556SO S07 548 92 1702 14,100 (2347) * 860 m(sheltered) 6862069 173 184 28 1237 11,300 Mt. Sutton: 845 metros 14226597 649 928 138 1996 16,900 (2012)* 845 Sheltered) 19383346 715 1025 65 1600 12,300 970 met res 75410,406 690 818 99 1237 12,100 (3935)* Whiteface (N.~. ): 884 metres 1765 6471 608 779 48 1393 9,300 (3468) 1160 metres 8S0 9568 870 1382 87 1720 13,800 (1016) Camel's Bump (VA): 884 metros 1341 14 ,657 (2409) 1067 eetree 183614,836 ( 2665) 890 629 92 1896 11, 100 548 650 78 1478 8,100 occur in species of Hypogymnia and Pseudevernia epiphytic on apparently healthy conifers. If, in fact, we can demonstrate that good correlations exist between atmospheric inputs and changes in lichen flora, then these studies may provide a faster, more economical way to assess ambient air quality in the absence of permanent atmospheric monitoring stations. ACKNOWLEDGMENTS Our thanks are due to Dr. R. Schemenauer of the Atmospheric Environment Service of Environment Canada for his considerable help and encouragement in initiating this project. We also thank field workers on the Chemistry of High Elevation Fog (CHEF) project. Marilyn Feth and Catriona Gordon provided invaluable technical assistance. The project was funded by the Wildlife Toxicology Fund to whom we are most grateful. Travel funds were supplemented by the Canadian Forestry Service.