Davis, M. B. (ed.) 1996. Eastern Old-Growth Forests: prospects for rediscovery and recovery. Island Press, Washington, DC.
For further information and additional resources, contact www.islandpress.org
The intimate physiological relationship between lichen thalli and the environment, the perennial nature of lichens and their sensitivity to disturbance, means that lichens act as continuous monitors of the environment. An appreciation of their qualities as biological monitors, and the study of the parameters limiting the occurrence of particular species, has led to their use as indicators of a variety of environmental factors.
--Hawksworth and Hill (1984)
My interest in lichens and their microhabitat requirements began in northern California when I took a special topics course in Lichenology while an undergraduate at Humboldt State University. It was the first time the course had been offered, and the requirement that each student submit a collection of 50 named specimens came with the incentive that extra credit would be awarded for any species new to the herbarium. Well, didn't we search the nooks and crannies of the Pacific Northwest for the most obscure lichens we could find in hopes of earning a few extra credit points! Among the specimens I submitted--and which earned me extra credit--were two species belonging to the Order Caliciales, a group commonly known as the "stubble lichens". Only one to two millimeters tall and looking like beard stubble, the lichens in this group are frequently overlooked by collectors and as a result go unreported.
I went on to pursue other interests in graduate school, but the ecology of lichens--particularly the "stubble lichens"--recaptured my attention when I came to northern Maine in 1976. As I gained a better understanding of the microhabitat requirements of the Caliciales, I became adept at finding them and soon realized that older forests were yielding a greater diversity of species than younger ones.
Several years earlier, Francis Rose (1974, 1976) had drawn similar conclusions
after comparative studies of the lichens present in 102 oak and beech woodlands
in the British Isles. Rose found a definite positive correlation between lichen
diversity and stand age. Woodlands known to be very old usually contained 120
to 150 lichen species per square kilometer, and often many more, while woodlands
known to be of recent origin typically had totals of 40 or fewer species. Moreover,
Rose showed that some lichens were found only at sites that had contained mature
trees for many centuries, and he wondered if the presence or absence of these
species could be used to assess environmental continuity (or disturbance) in
these environments. By concentrating on those taxa that appear to be almost
(or entirely) "faithful" to ancient woodland sites, Rose constructed an Index
of Ecological Continuity (IEC) that could be used to assess the relative age
of a particular woodland:
The term "ancient" forest is used here to describe those old-growth forests that have been around long enough to acquire the types of microhabitats that enable the rarer Caliciales and other indicator species to become established. Once established--and because dispersal is limited--these ancient forest indicators require ecological continuity of mature trees and a constant supply of substrate in various stages of decomposition to persist. Goward (1994) prefers the word " "antique" to describe these old old-growth forests, which he defines as a fourth category of forest succession following pioneer, seral, and young old-growth forests. An understanding of lichens and their colonization patterns will help put these observations into perspective.
Lichens can be described as a stable, self-supporting association of a fungus and an alga, or cyanobacterium, in which the resulting life form and behavior differ markedly from those of either of the partners growing alone (Hawksworth and Hill 1984). The lichen association is recognized as a "lifestyle"--equivalent to saprophytism or parasitism--by which a fungus can satisfy its need for carbohydrates required for respiration and growth. By thus relying on a photosynthetic symbiont, the lichenized fungus can even colonize bare rock or hitch a ride on the back of a tortoise. For, unlike its saprophytic or parasitic counterparts, the lichenized fungus takes nothing from the substrate upon which it grows; once established, it survives on nutrients that wash over it or are deposited daily upon it from the atmosphere.
The effectiveness of lichenization as a nutritional option is evidenced by the fact that approximately 13,500, or one in five, species of ascomycetous fungi are lichenized (Hawksworth and Hill 1984). Under the rules of the International Code of Botanical nomenclature, the names given to lichens refer to the fungal partner while the identity of the algal partner is irrelevant for nomenclatural purposes. In the British Soldier lichen, for example, the scientific name Cladonia cristatella refers to a particular fungus known only in the lichenized state. The algal partner in this species (Trebouxia erici) may also exist in the free-living state or even be found in other lichens--thereby expanding even further its distribution into habitats not generally colonized by aquatic organisms.
Most of what one sees and calls a lichen is fungal. The algal partner is found just under the upper surface of the lichen thallus, surrounded by the filamentous hyphal strands of the fungus. While the fungus often reproduces by sexual means, the lichen per se does not. New lichens arise from old only when a germinating fungal spore "captures" a compatible alga or, more typically, when an asexual propagule containing a few fungal strands and algal cells detaches from the thallus surface and is washed or blown to another location.
Plant communities dominated by lichens and mosses have been less well studied than those consisting mainly of seed plants. According to Canters et al (1991), the distribution of lichens "is governed by microclimatic factors that influence higher plants in different ways or not at all." As discussed by Armstrong (1988), newly dispersed lichen propagules must attach themselves to an appropriate substrate, survive to maturity, and be able to reproduce successfully. In addition to competition, the development of lichen assemblages on bark and wood substrates is determined by such factors as age, corrugation, pH, moisture-holding capacity and nutrient status of the substrate, as well as degree of illumination and humidity of the microenvironment, inclination of surfaces, aspect, air pollution and stand continuity (e.g., Barkman 1958, Brodo 1973, James, Hawksworth and Rose 1977).
According to Goward (1994)--describing his work with epiphytic macrolichens in British Columbia's intermontane old-growth forests, the most ubiquitous species tend to become established early on in forest succession, while most of the less common species do not begin to appear until the forest has attained old-growth status, usually at about 150 to 200 years. By then the forest, as a result of increasing structural heterogeneity, has presumably acquired a full complement of potential microsites suitable for colonization by lichens and has thereby become available for sporadic and random inoculation by lichen propagules originating from old-growth forests elsewhere. This suggests that the diversity of lichens on any given tree can be expected to increase over time (with certain limitations: See Goward 1994), with a disproportionate number of rare species being restricted to very old (i.e., ancient or "antique") stands. In Europe, much has been written about successional relationships between epiphytic lichen communities, for example that between the Lobarion pulmonariae and Calicion hyperelli alliances (e.g., James, Hawksworth and Rose 1977, Rose and Wolseley 1984). Species of the Lobarion pulmonariae behave as old forest indicators and, indeed, are represented among the old-growth forest indicators selected by Rose (1974, 1976). But Rose's index also includes elements of the Calicion hyperelli--the alliance that succeeds the Lobarion pulmonariae with increasing stand age and drying of substrate--and it is the presence or absence of these species that provides the evidence as to whether a forest that looks old really is old and has been little disturbed over a long period of time.
While the method developed by Rose (1974, 1976) has, until now, been used
only for oak and beech woodlands in Britain, Hawksworth and Hill (1984) had
little doubt that the approach would apply equally to other forest types in
other regions of the world. The aim of this investigation is to formulate a
set of indices for assessing ecological continuity in the northern hardwoods
and spruce-fir forests of northern New England and western New Brunswick.
According to National Weather Service summaries (e.g., NOAA 1985), regional climate might best be classified as "severe typical continental". Winters are particularly severe and windy, with seasonal snowfalls averaging over 100 inches and temperatures of zero (F) or lower normally occurring more than 40 times per year. Summers are cool and have abundant rainfall, with practically no dry periods of more than three or four days, and during the autumn mostly sunny warm days and crisp cool nights predominate.
Study sites were selected on the basis of their characterization as spruce-fir or northern hardwoods forest types, as defined by the Society of American Foresters (Eyre 1980). Seven of these sites, two of which are at Big Reed Preserve, were considered old-growth forests by the Maine Critical Areas Program (Grena et al 1983):
Six sites, selected on the basis of their suspected old-growth forest status, have been designated or are currently being evaluated as Research Natural Areas (RNA) by the U.S. Forest Service:
Two Natural Heritage Program natural areas have also been selected on the basis of their suspected status as old-growth forest sites:
The remaining 18 sites had not been previously investigated. These include
northern hardwoods stands at Mount Bailey, Big Brook, Hedgehog Mountain, Morrison
Mountain, Township 19 Range 11, Township 4 Range 7, Pennington Pond, Smith Road,
and Charette Hill and spruce-fir stands at Sagamook Mountain, Mount Carleton,
Township 8 Range 9, Cross Lake, Bartlett Stream, Township D Range 2, Yankeetuladi
Softwoods, Timoney Mountain and Nixon Siding. The stands at Mount Bailey, Big
Brook, Sagamook Mountain, and Mount Carleton are in the Mount Carleton Provincial
Park in western New Brunswick; all others are in northern Maine. The northern
hardwoods stands at Township 4 Range 7 and Township 19 Range 11 and the spruce-fir
stands at Township D Range 2 are logged sites adjacent to the previously-investigated
old-growth forests at Lunksoos Mountain, Yankeetuladi Hardwoods, and Number
Nine Mountain, respectively.
Any analysis of ecological continuity based on the percentage occurrence of selected indicator species is only as valid as the representative species assemblages are complete. Since many of the potential indicator species are rare even at ancient forest sites, every attempt was made to create as complete an inventory as possible. The Relevee Analysis for Classification approach to sampling (Mueller-Dombois & Ellenberg 1974) allowed the highest sampling intensity with reduced likelihood of missing localized areas of high species diversity. Numerous replicates increased the probability that potential indicator species--many of which are not visible with the naked eye, let alone identifiable in the field--would be captured.
Each site was visited twice. Accompanied by a field assistant, I spent six to eight hours per visit sampling the lichens in environmentally uniform habitats. The vertical structure, percent canopy closure, estimate of deadfall and topography were evaluated for each site, as was the apparent condition of the trees and their lichen epiphytes. Lists were made of vascular plant species from the canopy, subcanopy, shrub, and herb layers.
Epiphytes growing on the bark or wood of standing as well as fallen trees
were collected as they were encountered, without bias as to their condition,
and every effort was made to collect specimens from each tree species represented
at the site. Specimens on standing trees were collected from as high on the
trunk as could be reached, downward to soil level, and from accessible branches.
As a student of the Caliciales accustomed to "thinking small" and looking for
specimens in obscure places, I left few nooks and crannies unexplored. All surfaces
and edges of substrate fragments were thoroughly examined in the laboratory
where specimens were identified using standard techniques and following nomenclature
according to Brodo (1991) and Egan (1987, 1989, 1990, 1991).
While each lichen species is distributed according to its own microhabitat requirements, there is a tendency for gymnosperms (softwoods) and angiosperms (hardwoods) to host quite dissimilar epiphyte communities. This has lead me to propose two indices of ecological continuity (IEC): One for sites dominated by gymnosperms (i.e., spruce-fir forest types); and the other for sites dominated by angiosperms (i.e., northern hardwoods forest types) (Table 3-1)
The criteria for selecting old-growth forest indicator lichen species and the methods for calculating indices of ecological continuity follow Rose (1974, 1976), but the formulation of such indices has been modified slightly. With the inclusion of all but the most common Caliciales species, the list of species selected as indicators rises above 30.
Selection of indicator species is based on the multiple, exclusive (and near exclusive) occurrence of the species in forests with a documented long continuity. These include the northern hardwoods stands at Big Reed Preserve, Musquacook and Yankeetuladi in Maine and The Bowl in New Hampshire and the spruce-fir stands at Big Reed Preserve and Dry Town in Maine and Nancy Brook and Gibbs Brook in New Hampshire. The lichen species selected appear to be faithful to the ancient forest conditions present at these sites and, while widely distributed in the northeast, are not generally collected outside of undisturbed habitats (e.g., Gowan and Brodo 1988, Hale 1979, Harris 1977, Selva unpubl.). In calculating the IEC value at angiosperm-dominated sites, only the indicators collected on angiosperms are considered. Similarly, only the indicators collected on gymnosperms are considered in calculating the IEC value at gymnosperm-dominated sites. By basing these calculations on old-growth indicator lichen species found on the dominant trees only, IEC values are readily comparable among the sites of a particular forest type.
Most of the northern hardwood forests in the Northeast include some gymnosperm associates. Likewise, most of the spruce-fir forests in the region include some angiosperms. Because the gymnosperm and angiosperm associates might also harbor potential indicator species, they too must be considered in the assessment of stand continuity. In an attempt to quantify the "enrichment" that associate gymnosperm indicators bring to an angiosperm-dominated site and that associate angiosperm indicators bring to a gymnosperm-dominated site, a second IEC value was calculated for each site which includes indicator lichen species found exclusively on these associates. Through an index calculated in this way is a truer reflection of the character of a site, it is not as readily comparable among the sites of a particular forest type. Given the extensive enrichment found at some sites, it is conceivable (though improbable) that a gymnosperm-dominated stand, for example, could be assigned ancient forest status as a northern hardwoods forest on the basis of indicators found on its angiosperm associates.
The evidence presented in Table 3-2 suggests that many of the previously-investigated old-growth stands included in this study have not yet reached an ancient stage of succession or else have experienced recent disturbance. Based on the assumption that the presence of 20 lichen indicator species is evidence that a forest is ancient, 8 of the study's 15 previously-documented old-growth forests can be classified as ancient forest sites (IEC = 100). These are the northern hardwoods stands at Big Reed Preserve, Musquacook, Yankeetuladi, The Bowl and Mountain Pond and the spruce-fir stands at Big Reed Preserve, Norton Pool, and Nancy Brook. The previously-investigated old-growth northern hardwoods stands at The Cape (IEC =90), Lunksoos Mountain (IEC = 90), Gifford Woods (IEC = 80), and Chandler Ridge (IEC = 35) and the previously-investigated old-growth spruce-fir stands at Gibbs Brook (IEC = 95), Dry Town (IEC = 90), and Number Nine Mountain (IEC = 40) would not be considered ancient forest sites according to this definition, although it could be argued that those sites with IEC values of 90 and 95 could lay claim to such status.
With regard to the northern hardwoods stand at Gifford Woods, the data here only confirm what has been written in unpublished Vermont Natural Heritage Program reports, namely that "its small size, multiple uses, and its roadside location are all deterrents to the continued health of this forest and to its continued credibility as a natural area".
The lack of evidence of a previous generation of trees may help explain the low IEC values assigned to the northern hardwoods stand at Chandler Ridge and the spruce-fir stand at Number Nine Mountain: These stands simply aren't very old. According to Grena et al (1983), the present stand at Number Nine Mountain, for example, had come in after a disturbance some 138 years ago.
Finally, with regard to the 18 previously-uninvestigated sites included in this study, the northern hardwoods stands at Hedgehog Mountain (IEC = 120), Mount Bailey (IEC = 115), and Big Brook (IEC = 110) are confirmed as ancient forest sites, and the IEC = 75 assessed the spruce-fir stand at Township 8 Range 9 is enriched to IEC = 100 with the addition of associate angiosperms ancient forest indicators. The remainder of the stands received IEC scores ranging from 5-75. The presence of a few index lichen species at a site may have little indicator value-- except perhaps to suggest that such a stand is probably older than other nearby stands with fewer indicator species. For those stands assigned scores of 50 or less here, these values are considered to be accurate reflections of the much modified or secondary nature of these communities as recorded in site descriptions.
Data recorded at each of the study sites (Table 3-2) seem to confirm the observation of Rose (1976) that lichen diversity becomes richer over time--as reflected in increasing IEC values. Particularly interesting in this regard is the increasing number of species in the Order Caliciales. The suggestion that Caliciales species might themselves be used to assess forest continuity grew out of earlier, and ongoing, work in Maine and New Brunswick (Selva 1988, 1990), and appears to be confirmed in the present study. Preliminary data suggest that certain species assemblages can be used to recognize particular stages of succession on both wood and bark substrates, an observation supported by the work of Soderstrom (1988) who recognized early and late species sequences on decaying coniferous wood in northern Sweden.
Many epiphytic Caliciales species prefer microhabitats of high humidity and rather low light intensity (Tibell 1980), often sharing such niches with few other species. Though they may be found on all sides of older trees, they are more likely to be Encountered near the base of the trunk on angiosperms--typically on the side opposite the more conspicuous lichen vegetation--and at breast height, rarely lower, on most gymnosperms. Interestingly, a close inspection of the trunks of many trees that appear to be without lichens at old-growth sites reveals that they are, in fact, colonized by one to several Caliciales species. That many of these species are able to tolerate the increasing acidity of bark during stand succession may be a decisive factor in competition with macrolichens for space (Hyvarinen, Halonen, and Kauppi 1992). Finally, except for the presence of Sphinctrina species, neither the upper trunk nor the branches of angiosperms or gymnosperms support a well developed Caliciales flora.
In both the present study and that by Tibell (1992) lichens in the Order Caliciales
have been shown to be ideal biomonitors of forest microhabitats. They and their
macrolichen counterparts can serve as valuable evidence of great age, or lack
of it--particularly for forests where other documentary evidence of antiquity
is not available--and demand the attention of all who wish to understand forest
I thank the editor and Trevor Goward for their patient, critical review of
the manuscript and The Maine Chapter of the Nature Conservancy, the Appalachian
Mountain Club, the New Brunswick Museum, the National Geographic Society, the
Northeastern Forest Experiment Station and The University of Maine at Fort Kent
for their generous financial support. Also gratefully acknowledged is the assistance
of Peter Garrett and his staff at the Northeastern Forest Experiment Station
and M. Paul Edberg, my field assistant, and the support of my wife, Marcy, daughter,
Katheryn, and son, Matthew.
Armstrong, R. A. 1988. "Substrate Colonization, Growth, and Competition." In CRC Handbook of Lichenology, Volume II, edited by M. Galun, 3-16. CRC Press, Boca Raton, FL.
Barkman, J. J. 1958. Phytosociology and Ecology of Cryptogamic Epiphytes, Van Gorcum & Company, Assen. Netherlands.
Brodo, I. M. 1973. "Substrate Ecology." In The Lichens, edited by V. Ahmadjian and M. E. Hale, 401-41. Academic Press, New York, NY
Brodo, I. M. 1991. "Studies in the Lichen Genus Ochrolechia. 2. Corticolous Species of North America." Canadian Journal of Botany 69: 733-72.
Canters, K. J., H. Scholler, S. Ott, and H. M. Jahns. 1991. "Microclimatic Influences on Lichen Distribution and Community Development." Lichenologist 23: 237-52.
Egan, R. S. 1987. "A Fifth Checklist of the Lichen-forming, Lichenicolous and Allied Fungi of the Continental United States and Canada." The Bryologist 90: 77-173.
Egan, R. S. 1989, 1990, 1991. "Changes to the 'Fifth Checklist of the Lichen-forming, Lichenicolous and Allied Fungi of the Continental United States and Canada." The Bryologist 92: 68-72, 93: 211-19, 94: 396-400.
Eyre, F. H., ed. 1980. Forest Cover Types of the United States and Canada, Society of American Foresters, Washington, D.C.
Gowan, S. P. and I. M. Brodo. 1988. "The Lichens of Fundy National Park, New Brunswick, Canada." The Bryologist 91: 255-325.
Goward, T. 1994. "Notes on Oldgrowth-dependent Epiphytic Macrolichens in Inland British Columbia, Canada." Acta Botanica Fennica 150: 31-8.
Grena, J., C. Cogbill, L. Widoff, H. Tyler, and A. Giffen. 1983. Natural Old-growth Forest Stands in Maine, Maine State Planning Office, Augusta, ME.
Hale, M. E. 1979. How to Know the Lichens, 2d ed. Wm.C. Brown Publishers, Dubuque, IA.
Harris, R. C. 1977. Lichens of the Straits Counties, Michigan. Published by the author AnnArbor, MI.
Hawksworth, D. L. and D. J. Hill. 1984. The Lichen-forming Fungi. Glasgow: Blackie & Son, Ltd, Glasgow, Scotland
Hyvarinen, M., P. Halonen, and M. Kauppi. 1992. "Influence of Stand Age and Structure on the Epiphytic Lichen Vegetation in the Middle-boreal Forests of Finland." Lichenologist 24: 165-80.
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Kasmer, J. M. 1985. "A Biogeophysical Inventory of the Big Reed Pond Preserve T8 R10 WELS, Maine." A report prepared for the graduate program in Field Naturalism at the University of Vermont, Burlington and for the Maine Chapter of the Nature Conservancy, Topsham.
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Rose, F. 1974. "The Epiphytes of Oak." In The British Oak: Its History and Natural History, edited by M. G. Morris and F. H. Perring, 250-73. Classey Faringdon, United Kingdom.
Rose, F. 1976. "Lichenological Indicators of Age and Environmenal Continuity in Woodlands," Lichenology: Progress and Problems edited by D. H. Brown, D. L. Hawksworth, and R. H. Bailey, 279-307. Academic Press, New York, NY.
Rose, F. 1992. "Temperate Forest Management: Its Effects on Bryophyte and Lichen Floras and Habitats." In Bryophytes and Lichens in a Changing Environment, edited by J. W. Bates and A. M. Farmer, 211-33. Clarendon Press, Oxford, England.
Rose, F. and P. Wolseley. 1984. "Nettlecombe Park--Its History and its Epiphytic Lichens: An Attempt at Correlation," Field Studies 6:117-48.
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Coniferous Forests," Nordic Journal of Botany 12: 427-50.
|Anaptychia palmulata||Leptogium saturninum|
|Arthonia byssacea||Lobaria pulmonaria|
|Arthonia didyma||Lobaria quercizans|
|Bacidia rubella||Loxospora elatina|
|Buellia schaereri||Myelochroa aurulenta|
|Catinaria atropurpurea||Normandina pulchella|
|Catinaria laureri||Pertusaria waghornei|
|Cetrelia chicitae||Pyrenula laevigata|
|Collema nigrescens||Ramalina intermedia|
|Collema subflaccidum||Ramalina pollinaria|
|Dimerella pineti||Rinodina ascociscana|
|Lecanactis chloroconia||trangospora microhaema|
|1. Big Reed Preserve*||136(21)||103(12)||155||190|
|2. Musquacook*||105(11)||94 (9)||150||155|
|3. Yankeetuladi Hardwoods*||97(10)||89 (9)||120||125|
|4. Hedgehog Mountain||79(11)||77 (9)||120||125|
|5. The Bowl*||101(15)||91(13)||115||125|
|6. Mount Bailey||106(11)||101(10)||115||115|
|7. Big Brook||89(14)||85(11)||110||130|
|8. Mountain Pond*||82 (9)||77 (9)||100||100|
|9. The Cape*||83(11)||80 (8)||90||95|
|10. Lunksoos Mountain*||78 (5)||78 (4)||90||90|
|11. Gifford Woods*||80(10)||76 (6)||80||90|
|12. Morrison Mountain||60 (7)||60 (7)||75||75|
|13. Township 19 Range 11||58 (5)||52 (2)||45||50|
|14. Township 4 Range 7||46 (2)||46 (2)||40||40|
|15. Chandler Ridge*||53 (6)||49 (3)||35||45|
|16. Pennington Pond||48 (2)||48 (2)||5||5|
|17. Smith Road||41 (0)||38 (0)||5||5|
|18. Charette Hill||40 (4)||36 (3)||5||5|
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