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Ledum groenlandicum, Labrador tea, is an ericaceous evergreen shrub of acidic, wet areas common to northern regions of North America. The range has historically been reported as far south as northern New Jersey (Britton and Brown 1897; Gleason and Cronquist 1991). Reports and herbarium vouchers intimated that this species was restricted to Morris and Sussex Counties. However, the latest New Jersey Natural Heritage ranking for L. groenlandicum in Morris County is SX. -species that have been determined or are presumed to be extirpated, documented from a single location (NJ Natural Heritage Program 1999). Hough (1983) stated "verified Morris County site 1977, recently reported destroyed." The Morris County's occurrences are well documented for the single location between Dover and Mount Hope. This area was a larch swamp discovered by Mr. M. E. Palmer, a Budd Lake resident who with Kenneth Mackenzie visited and first collected specimens from this site in 1918, the earliest record: Mackenzie 8390, (CHRB, NY). This area was given the appellation of "Palmer's Bog" by Mackenzie (1918) in his follow-up article. Other vouchers were gathered from approximately the same site: "Dover," 1932, J. L. Edwards 774, (CU); "0.75 miles SSW of Mt. Hope," 1948, J. L. Edwards s.n., (CHRB); "North of Mt. Pleasant Avenue between Mt. Hope and Dover," 1958, Frank Hirst 43, (PH). No vouchers were found for Morris County at BKL, GH, NYS, SIM, or YU (herbaria abbreviations based on Holmgren, et al., 1990). Unfortunately, this Morris County location experienced vast disturbance, including housing, construction of Interstate 80, and shopping malls that obliterated all trace of the larch swamp and

Alpine populations of Ledum groenlandicum Oeder have higher photosynthetic rates and appear to achieve maximum photosynthesis at lower temperatures than bog populations. These photosynthetic differences presumably adapt alpine populations to the shorter seasons, lower carbon dioxide concentrations, and lower temperatures experienced in alpine environments, and they agree with similar patterns observed in other species which grow at a range of elevations. Reciprocal transplant experiments show that the differences in photosynthetic characters are correlated with differences in the relative fitnesses of bog and alpine plants in bog and alpine environments. See full-text article at JSTOR

Temperature-related photosynthetic and respiratory acclimation responses were examined in alpine, subarctic, and bog populations of Ledum groenlandicum Oeder, a widespread ericaceous shrub species. Acclimation responses to temperature were measured both after 12- to 16-week exposures to either cool (15? C light - 10?C dark) or warm (30?C light - 25?C dark) thermal regimes and again after each of a series of 2-week exposures to new thermal regimes. Dark respiratory rates were decreased by warm acclimation and increased by cool acclimation. These shifts in rates were frequently completed within 2 weeks in a new thermal regime. Maximal net photosynthetic rates generally did not differ significantly among either populations or thermal regimes; however, the temperature for maximal net photosynthesis in each population was increased to 25?C by warm acclimation and decreased to 20?C by cool acclimation. Net photosynthetic rates were increased at cool temperatures by cool acclimation and increased at warm temperatures by warm acclimation. In contrast to respiratory responses, these photosynthetic acclimation shifts were not completed within 2 weeks in a new thermal regime. Ledum groenlandicum populations differed markedly in their potentials for net photosynthetic and dark respiratory acclimation. Alpine and subarctic populations acclimated to greater degrees than their continental and maritime bog counterparts.

Lodgepole pine/Labrador tea (Pinus contorta Dougl. ex Loud. var. latifolia/Ledum groenlandicum Oeder) relevés were classified and characterized based on data from archival sources (n = 428). Eleven forest communities were recognized and were distinguished by the relative dominance of Sphagnum, Cladina and Cladonia, Lycopodium, Vaccinium species, or feathermosses. Picea mariana (Mill.) BSP was the common secondary successional species. Most paired-community comparisons were nonoverlapping in ordination space, although intermingling sometimes occurred along interfaces. Lodgepole pine/Labrador tea stands occurred on upland sites within the boreal–cordilleran ecoclimatic transition zone along the eastern slopes of the Rocky Mountains from southwestern Alberta to the southern Yukon Territory. Nine communities had mesic to subhygric moisture and submesotrophic to mesotrophic nutrient regimes. The exceptions were a Pinus contorta/Ledum groenlandicum/Sphagnum (wetter sites) and a Pinus contorta/Ledum groenlandicum/Cladina mitis (drier sites) community. An inverse correlation occurred between latitudinal location and elevation of occurrence (r = –0.56, P < 0.001, n = 403) with a northward decline of 65 m/100 km. The concept of a "type community" is proposed for formally documenting the composition of plant communities and optimizing the comparability of different types. Eight of the recognized communities fulfilled the proposed criteria for a type community and two were considered provisional types.Key words: vegetation classification, Pinus contorta, Ledum groenlandicum, type community.

Few guidelines exist for the effective revegetation of peatlands following the removal of in-situ oil and gas infrastructure. We conducted a manipulative field study in northeast Alberta, Canada, on a well pad undergoing removal and revegetation to test different management practices for facilitating vegetation establishment and recovery of a sphagnum-dominated peatland. A randomized block design was used to evaluate the effect of various revegetation practices, including augmenting natural recovery with the use of native transplants, acrotelm transfer from a similar intact donor peatland, and the use of variable surface microtopography. Although overall survival of transplants was similar between areas smoothed and left rough, areas that were rough had greater species richness under natural recovery, including trees, shrubs, and other perennial herbs. Moreover, survival and growth of woody transplants (Picea mariana—black spruce and Ledum groenlandicum—Labrador tea) were greater when planted within the top and middle microtopographic positions rather than micro-depressions. Survival of transplanted sedges (Carex spp.) was high at all topographic positions, but benefited the most in growth from planting in depressions. Contrary to expectations, no benefits of acrotelm application were found on vegetation recovery during the first two seasons, and even reduced the presence of some native vegetation. Although transplants directly contributed to revegetation, the recovering peatland remained highly dissimilar ( 90%) in composition relative to the neighboring peatland after two years.

Pollen, spore, macrofossil and carbon data from a peatland near Cordova, Alaska, reveal insights into the climate–vegetation–carbon interactions from the initiation of the Holocene, c. the last 11.5 ka, to the present (1 ka = 1000 calibrated years before present where 0 = 1950 CE). The Holocene period is characterized by early deposition of gyttja in a pond environment with aquatics such as Nuphar polysepalum and Potamogeton, and a significant regional presence of Alnus crispa subsp. sinuata. Carbon accumulation (50 g/m2/a) was high for a short interval in the early Holocene when Sphagnum peat accumulated, but was followed by a major decline to 13 g/m2/a from 7 to 3.7 ka when Cyperaceae and ericads such as Rhododendron (formerly Ledum) groenlandicum expanded. This shift to sedge growth is representative of many peatlands throughout the south-central region of Alaska, and indicates a drier, more evaporative environment with a large decline in carbon storage. The subsequent return to Sphagnum peat after 4 ka in the Neoglacial represents a widespread shift to moister, cooler conditions, which favored a resurgence of ericads, such as Andromeda polifolia, and increased carbon accumulation rate. The sustained Alnus expansion visible in the top 10 cm of the peat profile is correlative with glacial retreat and warming of the region in the last century, and suggests this colonization will continue as temperature increases and ice melts.

Plant uranium concentrations generally reflect soil or rock substrate concentrations in upland areas, but they may not in lowland areas where the rhizoids of Sphagnum spp. and the rocks of Ledum groenlandicum may be in direct contact either continuously or on a seasonal basis with the groundwater. This study points out the importance of selecting plant species and collection sites where the true substrate can be well defined and sampled. Sphagnum spp. and Ledum groenlandicum best reflect the substrate uranium concentrations in lowland areas, Umbilicaria spp. and Cladonia spp. in rock outcrop, and Picea mariana and Betula papyrifera in upland locations. The study shows the best plant part to sample is the older tissue such as the stems, twigs, and wood. Since no systematic changes in plant tissue concentrations were found throughout the season, sampling can be carried out anytime. Expression of soil concentrations on an ash weight basis gave a considerably different result than those on a dry weight basis, particularly when comparisons were made between litter-enriched mineral soil and true organic soils. The amount of ash varied among plant organs, species, and taxonomic divisions, and a constant value cannot be used to convert plant ash concentrations to concentrations on a dry weight basis.

Despite covering vast areas of boreal North America, the ecological factors structuring mycorrhizal fungal communities in peatland forests are relatively poorly understood. To assess how these communities vary by age (younger vs. mature), habitat (fen vs. bog), and host (conifer trees vs. ericaceous shrub), we sampled the roots of two canopy trees (Larix laricina and Picea mariana) and an ericaceous shrub (Ledum groenlandicum) at four sites in northern Minnesota, USA. To characterize the specific influence of host co-occurrence on mycorrhizal fungal community structure, we also conducted a greenhouse bioassay using the same three hosts. Root samples were assessed using Illumina-based high-throughput sequencing (HTS) of the ITS1 rRNA gene region. As expected, we found that the relative abundance of ectomycorrhizal fungi was high on both Larix and Picea, whereas ericoid mycorrhizal fungi had high relative abundance only on Ledum. Ericoid mycorrhizal fungal richness was significantly higher in mature forests, in bogs, and on Ledum hosts, while ectomycorrhizal fungal richness did not differ significantly across any of these three variables. In terms of community composition, ericoid mycorrhizal fungi were more strongly influenced by host while ectomycorrhizal fungi were more influenced by habitat. In the greenhouse bioassay, the presence of Ledum had consistently stronger effects on the composition of ectomycorrhizal, ericoid, and ericoid-ectomycorrhizal fungal communities than either Larix or Picea. Collectively, these results suggest that partitioning HTS-based datasets by mycorrhizal type in boreal peatland forests is important, as their responses to rapidly changing environmental conditions are not likely to be uniform.

The reproduction of lowbush blueberry (Vaccinium angustifolium Aiton) is closely tied to insect pollination, owing to self-incompatibility. Many species are known to have greater pollination efficiency than the introduced Apis mellifera L., commonly used for commercial purposes. In this study, we measured the pollen loads of several antophilous insect species, mostly Apoidea and Syrphidae, present in four lowbush blueberry fields in Lac-St-Jean, Québec. To measure pollen loads and species specificity toward V. angustifolium, we net-collected 627 specimens of pollinators, retrieved their pollen loads, identified pollen taxa, and counted pollen grains. We found that the sizes of pollen loads were highly variable among species, ranging from a few hundred to more than 118,000 pollen grains per individual. Bombus and Andrena species in particular carried large amounts of Vaccinium pollen and thus may have greater pollination efficiency. Also, two species (Andrena bradleyi Viereck and Andrena carolina Viereck) showed nearly monolectic behavior toward lowbush blueberry. Finally, we identified alternative forage plants visited by native pollinators, notably species of Acer, Rubus, Ilex mucronata, Ledum groenlandicum, and Taraxacum. Protecting these flowering plants should be part of management practices to maintain healthy pollinator communities in a lowbush blueberry agroecosystem.

Plants in nutrient-poor environments typically have low foliar nitrogen (N) concentrations, long-lived tissues with leaf traits designed to use nutrients efficiently, and low rates of photosynthesis. We postulated that increasing N availability due to atmospheric deposition would increase photosynthetic capacity, foliar N, and specific leaf area (SLA) of bog shrubs. We measured photosynthesis, foliar chemistry and leaf morphology in three ericaceous shrubs (Vaccinium myrtilloides, Ledum groenlandicum and Chamaedaphne calyculata) in a long-term fertilization experiment at Mer Bleue bog, Ontario, Canada, with a background deposition of 0.8 g N m−2 a−1. While biomass and chlorophyll concentrations increased in the highest nutrient treatment for C. calyculata, we found no change in the rates of light-saturated photosynthesis (A max), carboxylation (V cmax), or SLA with nutrient (N with and without PK) addition, with the exception of a weak positive correlation between foliar N and A max for C. calyculata, and higher V cmax in L. groenlandicum with low nutrient addition. We found negative correlations between photosynthetic N use efficiency (PNUE) and foliar N, accompanied by a species-specific increase in one or more amino acids, which may be a sign of excess N availability and/or a mechanism to reduce ammonium (NH4) toxicity. We also observed a decrease in foliar soluble Ca and Mg concentrations, essential minerals for plant growth, but no change in polyamines, indicators of physiological stress under conditions of high N accumulation. These results suggest that plants adapted to low-nutrient environments do not shift their resource allocation to photosynthetic processes, even after reaching N sufficiency, but instead store the excess N in organic compounds for future use. In the long term, bog species may not be able to take advantage of elevated nutrients, resulting in them being replaced by species that are better adapted to a higher nutrient environment.

Twelve Alaska native plants were propagated from softwood and semi-hardwood stem cuttings collected from late June through August. Cuttings of new growth were treated with 0.3% indole-3-butyric acid powder and propagated in horticultural grade perlite and vermiculite (1:1 by vol) under intermittent mist with bottom heat [26C (79F)] in a greenhouse with a minimum night temperature of 15C (59F). After 6 weeks, cuttings were harvested and evaluated for rooting percentage and root quantity. Four species rooted poorly (< 25%) regardless of collection date: Siberian alder (Alnus viridis ssp. fruticosa), silverberry (Elaeagnus commutata), Bebb willow (Salix bebbiana) and shrub birch (Betula glandulosa). Best rooting (> 80%) occurred June 20 for: Beauverd spiraea (Spiraea stevenii), sweetgale (Myrica gale), and thinleaf alder (Alnus incana ssp. tenuifolia). Peak rooting for dwarf birch (Betula nana), feltleaf willow (Salix alaxensis), balsam poplar (Populus balsamifera), Labrador tea (Ledum groenlandicum) and littletree willow (Salix arbusculoides) was early to mid July. During peak rooting times, all successful species developed adequate root quantities for survival following transplanting.

A combination of light microscopy (including differential interference contrast) and laser scanning confocal microscopy was used to document the colonization patterns of epidermal cells and details of intracellular hyphal complexes of five native ericaceous hosts: Vaccinium oxycoccos L. (bog cranberry), Ledum groenlandicum Oeder. (Labrador tea), Vaccinium myrtilloides L. (velvet-leaf blueberry), Kalmia angustifolia L. (sheep laurel), and Gaultheria procumbens L. (wintergreen). Colonization patterns, hyphal complex morphology, and the structure of thick-walled epidermal cells varied considerably among hosts. Multiple hyphal connections were observed between adjacent epidermal cells, indicating that one fungal entry point may result in the colonization of more than one epidermal cell. Further field observations combined with fungal isolations from field-collected plants, identification, and reinoculation studies of other species in the large Ericaceae family are required to determine the full range of structural details in ericoid mycorrhizas.Key words: ericoid mycorrhizas, hair roots, intracellular hyphal complexes, confocal microscopy.

Northern peatlands are substantial sinks of carbon (C), yet the sources of carbon dioxide (CO2) emitted from peatlands are largely unknown. Since the relationship between roots and peat in C cycling is important, vascular plants growing on the surface of peat deposits should influence CO2 efflux from the peat surface and the overall C balance in peatlands. In our study, 30-cm peat cores were removed from an ombrotrophic bog in boreal, continental western Canada. Surface vegetation in the cores remained intact and included a continuous bryophyte cover dominated by Sphagnum fuscum. In addition, some cores were collected such that either ericaceous shrubs (Ledum groenlandicum) or sedges (Eriophorum vaginatum) were present. We investigated how the presence of each vegetation type influenced soil respiration and the microbial mineralization of root exudates using a pulse 14C labeling of vegetation in the intact peat cores. The role of root biomass and root respiration in CO2 emission and C allocation was quantified for each type of vegetation and compared through both measurement and modeling. Our results show that vascular plants contributed 35-57% of total CO2 efflux from the peat surface, primarily derived from rhizosphere processes, including root respiration as well as microbial mineralization of root exudates. The mineralization of root exudates contributed 14-53 pmol C-CO2.m-2-d-' (17- 24% of total) to CO2 efflux, depending on vegetation type and moisture conditions. The type of vegetation present did not influence the total amount of photosynthetic fixation over the course of the study, but did affect how C was allocated within and between both the aboveground and belowground components of the peat column.

A total of 27 extracts from non-cultivated and weedy vegetables traditionally consumed by ethnic Albanians (Arbereshe) in the Vulture area (southern Italy) were tested for their free radical scavenging activity (FRSA) in the DPPH (1,1-diphenyl-2-picrylhydrazil radical) screening assay, for their in vitro non-enzymatic inhibition of bovine brain lipid peroxidation and for their inhibition of xanthine oxidase (XO). In both antioxidant assays strong activity was shown for Leopoldia comosa (bulbs, syn.: Muscari comosum) and Centaurea calcitrapa (young whorls). In the lipid peroxidation assay, extracts from leaves of Origanum heracleoticum, Urtica dioica and Tordylium apulum showed a remarkable inhibitory activity (> 50%), too. In the case of Leopoldia comosa and Origanum heracleoticum this activity was comparable to quercetin (at a concentration of 50 microM) and Rhodiola rosea extract. Extracts from non-cultivated Cichorium intybus, Chondrilla juncea and Stellaria media showed strong in vitro inhibition of xanthine oxidase, with an activity higher than that of a reference extract from Ledum groenlandicum. These findings suggest that weedy vegetables may be useful antioxidants of interest in the prevention of ageing related diseases, CNS disorders and as potential sources of phytomedicines against hyperuricaemia and gout.

Rust fungi in the genus Chrysomyxa Unger occur in boreal forests of the northern hemisphere on Pinaceae (mostly Picea A. Dietr.), and most species alternate to angiosperm hosts in the Ericaceae. About 30 species are known worldwide. Although several species are economically important pathogens of spruce and rhododendrons, knowledge about species delineations, relationships among species on different continents, and life cycles is lacking. A group of species with similar spore size, including the Chrysomyxa ledi de Bary complex, was re-examined using field observations, inoculation experiments, and light and scanning electron microscopy. In addition to host specificity, characters found useful in species delineation were urediniospore and aeciospore size and shape, and ornamentation of spores and the aecial peridium. Detailed descriptions are given for eight Chrysomyxa species, including synonyms, types, distribution, relationship to other species, and disease impact. The members of the C. ledi complex are considered separate species: Chrysomyxa ledi on Ledum palustre, Chrysomyxa nagodhii sp.nov. on Ledum groenlandicum and Ledum decumbens, Chrysomyxa neoglandulosi sp.nov. on Ledum glandulosum, Chrysomyxa cassandrae on Chamaedaphne calyculata, Chrysomyxa rhododendri on Rhododendron spp., and Chrysomyxa vaccinii comb.nov. on Vaccinium parvifolium. Chrysomyxa chiogenis, with similar spore size, is included for comparison. A previously unrecognized small-spored species, Chrysomyxa reticulata sp.nov., is described on Ledum spp. and Rhododendron spp. Evidence is presented that C. reticulata spreads from native Ledum spp. in North America to cultivated rhododendrons. A new anamorphic species, Peridermium zilleri, likely belonging in Chrysomyxa, is described on Picea sitchensis from coastal British Columbia.Key words: Uredinales, Rhododendron, needle rust, Ledum, systematics.

The rust fungus Chrysomyxa woroninii causes perennial witches’ brooms on several species of Ledum in northern and subalpine regions of Europe, North America and Asia. Spruce bud rust has been assumed to be the aecial state of C. woroninii because of the close proximity of infected Ledum plants and systemically infected buds on Picea. The lack of experimental evidence for this connection, however, and the presence of other species of Chrysomyxa on the same hosts has led to confusion about the life-cycle of C. woroninii. In this study, infections on both spruce and Ledum were studied in the field and in a greenhouse. The link between the two states was proven by inoculating spruce with basidiospores from Ledum groenlandicum. After infection of spruce in spring, probably through the needles, the fungus overwinters in the unopened buds until the next spring, when the infected shoots are distinguished by stunting and yellow or red discolouration. Microscopic examination of dormant Ledum shoots showed that C. woroninii overwinters in this host in the bracts and outer leaves of the vegetative buds, and in the pith and cortex of the stem. The telia of C. woroninii , on systemically infected Ledum leaves of the current season, are easily distinguished from the telia of other Chrysomyxa species on the same hosts. The latter produce localized telia and uredinia only on overwintered leaves, produce aecia on spruce needles in the same year as infection occurs, and are not systemic in spruce. The restricted habitat distribution of C. woroninii and the need for overwintering outdoors suggest that this rust fungus has specific environmental requirements for survival.

The teleomorphic state of the ericoid mycorrhizal Hymenoscyphus ericae is known only from the type deposition. The production of both the teleomorph and anamorph by an isolate recovered from Ledum groenlandicum collected in an acidic peatland in Alberta, Canada, provided an opportunity to describe and illustrate the holomorph for a North American collection as a new record and as a supplement to the original diagnosis. It also provided further evidence that Hymenoscyphus ericae and Scytalidium vaccinii represent states of a single species, a hypothesis that previously had been tested using nuclear ribosomal DNA analysis. Appropriate cultural conditions and the use of molecular markers are advocated in order to facilitate the identification of mycorrhizal isolates which often remain sterile in pure culture.

This study was undertaken to estimate the aboveground biomass and carbon pool of plant communities in two bogs: one to be experimentally flooded to simulate a hydroelectric reservoir and the other left unflooded as a reference. The biomass of trees, saplings, and tall shrubs was estimated using allometric regression equations, while that of tree and tall shrub seedlings, low shrubs, herbs, bryophytes, and litter was harvested from 0.25-m2 plots. The eight communities were open or treed in low to high densities with Picea mariana (Mill.) BSP. and sparse Larix laricina (Du Roi) K. Koch. Aboveground community biomass (excluding litter) ranged from 7189 ± 924 (mean ± SE) to 72 909 ± 20 627 kg·ha-1, and litter ranged from 1181 ± 548 to 7664 ± 2848 kg·ha-1. Mean carbon concentration in the plant material analyzed ranged from 430 to 540 mg C·g-1. Carbon concentration of leaves in woody species was higher than in branches and stems. Carbon pool estimates (excluding litter) for the communities ranged from 3140 ± 480 to 35 010 ± 8890 kg C·ha-1. Community carbon per unit area as a percentage of biomass per unit area ranged from 44 to 48%. The available carbon pool (including litter and excluding tree branches and stems) of communities in the experimental bog ranged from 6386 to 9907 kg C·ha-1. Low shrubs, dominated by Chamaedaphne calyculata (L.) Moench in wetter, more open communities and Ledum groenlandicum Oeder in drier, more densely treed communities, composed 34-53% of the available carbon pool. Litter was the largest contributor (33%) to the available carbon pool in the most densely treed community, and bryophytes (mostly Sphagnum angustifolium (C. Jens. ex Russ.) C. Jens. in Tolf and Sphagnum fallax (Klinggr.) Klinggr., 46%) in the sedge community. The available carbon pool in aboveground vegetation of the experimental bog was estimated to be 1.17 × 105 kg C, approximately 12% of the estimated carbon pool in the peat.Key words: biomass, bog, carbon, experimental reservoir.

This study documents changes in community and functional group across environmental gradients sensitive to climate warming in boreal permafrost peatlands and describes how future changes in temperature and precipitation may lead to changes in species composition and ecosystem properties. At the landscape scale, the presence of permafrost strongly influenced species composition. The position of permafrost thaw affected surface water pH and species composition. At local scales, a combination of water table depth and vegetation structure strongly controlled community composition. Permafrost plateau plots with high Picea mariana basal area were characterized by darker and drier understorey conditions, low cover of Sphagnum fuscum, Ledum groenlandicum, and lichen, and high cover of feather mosses. Aquatic collapse scar plots were dominated by aquatic Sphagnum and Carex, whereas more xeric plots were dominated by hummock Sphagnum and ericaceous shrubs. Functional group responses indicated that changing environmental conditions with climate warming may have significant impacts on community composition and ecosystem processes. A decomposition example is presented to show how changes in species and functional group composition could have important implications for ecosystem-level processes like peat accumulation during climate warming.Key words: bogs, fens, boreal, permafrost, vegetation, ordination

The effects of leaves and litter of the boreal forest understory shrub, Ledum groenlandicum, on soil characteristics and black spruce (Picea mariana) seedling growth were investigated. Organic and mineral soils, not previously associated with L. groenlandicum, were amended with leaves and litter of this species. The objectives of the present study were: (i) to determine the changes in soil characteristics after amending with L. groenlandicum, (ii) to determine the quantitative variation in the concentration of water-soluble phenolic allelochemicals in mineral and organic soil layers modified by L. groenlandicum and (iii) to study the growth response of black spruce in soils treated with different L. groenlandicum amendments. The amended organic and mineral soils were analyzed for pH, organic matter, PO4, N, Ba, Cu, Zn, Fe, Mn, Ca, Na, K, Mg, Al and total phenolics equivalence. Results indicate that organic soils amended with L. groenlandicum leaves and litter were significantly different from unamended control soil for most of the chemical characteristics, while amended mineral soil was different from that of unmodified mineral soil for PO4, organic matter, K and total phenolics equivalence. Water-soluble phenolics from L. groenlandicum and changes in nutrient availability are plausible causes of L. groenlandicum interference with black spruce seedling growth.

Trace element analysis of conifer tissues demonstrates the application of biogeochemistry to mineral exploration for gold and other metals hosted by lower Paleozoic metasediments in eastern Nova Scotia. At the regional scale, enrichment of up to 170 ppb Au and 72 ppm As in the ash of twigs from balsam fir (Abies balsamea) coincides with known gold districts and major shear zones. These concentrations are approximately 30 times background level. The twig trace element chemistry indicates previously unsuspected Au potential in Carboniferous Horton Group sedimentary rocks, and around the contact aureoles of Devonian granitoids where the twigs are also enriched in Cs (×30), Sb (×3), Rb (×3) and W (×10). Along the Minas Fault, separating the Avalon and Meguma terranes, anomalous groupings of Ba and Cr in twigs suggest exploration potential for base metal (Cu-Pb-Zn) and mafic or ultramafic (Co-Ni-Pt group element) associations. Detailed biogeochemical studies at five till- and/or bog-covered localities near the Beaver Dam gold deposit outline mineralization buried beneath up to 25 m of surficial sediment. An association of Au, As and Cs in the vegetation provides consistent patterns equal to or better than the more erratic geochemical response in soil and till surveys over the same areas. Concentrations of up to 170 ppb Au in the ash of twigs indicate locations suitable for further exploration. The low shrubs Labrador tea (Ledum groenlandicum), leather leaf (Chamaedaphne calyculata) and bog laurel (Kalmia polifolia) were collected from two small boggy areas suspected to overlie gold-bearing bedrock. Typically, these species contain

International audience; This study examines the recovery of the microbial compartment following active restoration of a North American ombrotrophic peatland extracted for horticultural peat-based substrates and restored by the Sphagnum moss transfer method. We used phospholipid fatty acids (PLFAs) to portrait the microbial community structure and Community Level Physiological Profiles (CLPP) to describe the functional diversity of the microbial communities. Our results indicate that the PLFA profiles were different between the beginning and the end of the growing season, but that it was impossible to distinguish five different vegetation classes found along the disturbance-recovery gradient on the basis of the microbial community structure. The pH, the cover of mosses, Ledum groenlandicum and Eriophorum vaginatum var. spissum were the best environmental predictors for the PLFA composition. The newly formed peat found in aerobic conditions beneath restored Sphagnum carpets had the highest decomposition capacity, whereas the lowest rates were found in the surface samples of non-restored conditions or in the deepest horizons of the natural samples. A large proportion of the variation in the physiological profiles was explained with variables related to the vegetation cover, the physicochemical environment and the microbial structure of the community, which is very promising for future monitoring studies. Overall, this study demonstrates that the recovery of particular plant groups, namely mosses and shrubs in restored peatlands might be the driver of changes occurring in the structure of the microbial communities in restored peatlands.

Labrador tea (Ledum groenlandicum), a slow-growing late successional evergreen, is highly unpalatable to snowshoe hares (Lepus americanus). Germacrone, a sesquiterpene that is the major component of the essential oil ofL. groenlandicum, was shown by bioassay to be a potent antifeedant to hares. Its concentrations in leaves and intemodes of the plant are high enough to defendL. groenlandicum from hares. This chemical defense of Labrador tea from herbivory is consistent with the resource availability theory of antiherbivore defense.

Through their diet, herbivores inhabiting contaminated sites may be chronically exposed to a variety of aryl hydrocarbons (e.g., dioxins and polycyclic aromatic hydrocarbons [PAHs]). However, little is known about how differences in morphology and physiology among plant species alter the environmental accumulation of aryl hydrocarbons or their release and subsequent activity in the gastrointestinal tract of herbivores after ingestion. In the present study, the activity of aryl hydrocarbons during digestion was examined using six Arctic plant species growing in impacted and reference sites near Inuvik, Northwest Territories, Canada. The plant species studied were black spruce (Picea mariana), labrador tea (Ledum groenlandicum), bog birch (Betula glandulosa), green alder (Alnus crispa), water sedge (Carex aquatilis), and little-tree willow (Salix arbusculoides). Plants were digested using a simulator of the upper digestive tract, and aryl hydrocarbon release was evaluated using an aryl hydrocarbon-receptor assay. Bioaccessible aryl hydrocarbon activity varied among the plant species tested. The species with the greatest activity was green alder, and the species with the least activity was black spruce. Further investigation revealed that digested plant extracts may antagonize the aryl hydrocarbon receptor and prevent bioactivation of the aryl compound benzo[a]pyrene. Thus, PAH risk from the ingestion of vegetation varies among plant species and may depend on antagonists present in the vegetation.

Mining and processing of lead (Pb)/zinc (Zn) ore at the Anvil Range mine occurred near the town of Faro in the Yukon Territory, Canada, for approximately 30 years, beginning in 1968. A study was undertaken to examine whether the mining activities had left a detectable "footprint" on the environment in the way of heavy metal phytoaccumulation. Foliage of three native plant species was sampled: bog blueberry (Vaccinium uliginosum), Labrador tea (Ledum groenlandicum), and willow (Salix sp.), at approximately 0.25, 2.5, 12, 30, and 200 (control) km distant from the mill (ore-processing facility at the mine). Foliage samples were oven-dried, wet- or dry-ashed, and analyzed for metal content using ICP-AES. In addition to Pb and Zn, the primary ore constituents, copper (Cu), iron (Fe), and cadmium (Cd), were also assayed. As expected, foliar Pb and Zn concentrations were elevated in plants at the sites closest to the mill, i.e., 0.25 and 2.5 km from the mine facility. Copper and Fe, both essential nutrients for plants, were also elevated in foliage at the sites closest to the mill, but not to a level that would be of concern. Foliar Cd levels were highest in Salix relative to the other species but were not affected by proximity to the mill. Results suggest that Ledum may be the best indicator of high environmental concentrations of Pb, while Salix may be the best indicator of elevated Zn and Cd.

Forty‐two plant foods known to have been used in the past by native people of the Nuxalk Nation, Bella Coola, British Columbia, Canada, were studied. To estimate the availability of the most prominent plant food resources, field estimates were made using modifications of standard techniques for quantifying plant species. Assessments of accessibility, abundance and frequency of food species were made. In addition, harvesting efficiency of 24 species was determined. Twenty species were selected as being the most readily available food resources, and therefore good candidates for nutritional research and promotion. These included the trees: Populus trichocarpa, Pyrus fusca, Tsuga heterophylla; the shrubs: Amelanchier alnifolia, Ledum groenlandicum, Ribes divaricatum, Rosa nutkana, Rubus idaeus, R. parviflorus, R. spectabilis, Sambucus racemosa, Vaccinium ovalifolium, V. parvifolium, Viburnum edule, and the herbs: Cornus canadensis, Epilobium angustifolium, Heracleum lanatwn, Maianthemum dilatatum, Potentilla...

The litter bag technique was used to examine the decomposition of six litter types (representing Picea mariana, Cladina stellaris, Betula glandulosa, and Ledum groenlandicum) and standard cellulose. The decomposition was measured over a 2-yr period, with tissue samples placed on a recently burnt site and on top of and beneath a lichen mat in a mature spruce-lichen woodland in northern Quebec. Mass losses after 2 yr were between 10 and 60%, with the largest losses occurring in B. glandulosa and L. groenlandicum leaves and the smallest in C. stellaris; 60-90% of the Ist-yr mass loss occurs during the winter (September to June). The exponential decay constant k ranged from -0.05 to -0.53. There were few statistically significant differences in decomposition rate among the three sites. Of the chemical constituents analyzed, original concentrations of Ca, carbohydrate, P, K, and N were closely correlated either with the decomposition parameter k or with mass remaining after I or 2 yr. Ca, Mg, and K are rapidly lost from the decomposing tissues, except for C. stellaris. All the tissues, except B. glandulosa, showed an accumulation of N, associated with high C:N ratios. The results emphasize the importance of N to this ecosystem, in that it tends to remain immobilized in the litter, at least over the first 2 yr.

A study was carried out on the Influence of 15.2 "mol m-1 (0.34 ppm) (Canadian maximum acceptable Umlt) of SO. on net CO. as­ 'slmilation rate (NAR) and visible symptom development of several boreal forest woody species. Fumigation with SO, slgnlOcantly re­ duced NAR In all species and produced visible symptoms of Injul")' In 2 to 20 d •. The decrease In NAR of deciduous species {aspen (Populus tremuloides Mlchx.), willow (Salix sp.), green alder (Alnus crlspa (Alt.) Parsb), and paper birch (Betula papyri/era Marsh)} was slg­ nlOcandy more rapid than of conifers { jack pine (Pinus banksiona Lamb.), white spruce (PIcea glauca (Moench) Voss), and black spruce (P. mariana (Mill.) BSP)} or an evergreen angiosperm (Labrador tea (Ledum groenlandicum Oeder» wben grown on a fertilized Brunlsol. cases did not appear until NAR bad decreased considerably. Tbe re­ sponse of tbese metaboUc and visible responses appeared to be related to differences In S uptake owing In part to higher gas exchange rates for deciduous species than for conifers. Conifers growing In on sands tailings responded to SO. with a slg­ nlOcantly more rapid decrease In NAR as compared with those grow­ Ing In tbe Brunlsol. Because botb soils were fertilized, nutrient status was ruled out as a cause. It Is suggested that the conifers obtained from tbe taiUngs dike were predisposed to SO. fumigation by eitber tbe presence of toxic material in tbe tailings sand or tbelr history of ex­ posure to moderate levels of SO •. Sulfur uptake and visible symptom development were not different on tailings as compared witb tbe Brunlsol.

Twigs of shrub alders (Alnus crispa and Alnus rugosa) tend to contain more gold than other common species in the northern forests of Saskatchewan. Alders are not cyanogenic, hence samples can be ashed to preconcentrate gold without loss of the metal as the volatile gold cyanide. Samples from mineralized zones commonly have over 50 ppb Au in the ash of the outermost 50 cm of alder twig. Background values are about 10 ppb Au. In the absence of alder from a given locality, other species may provide useful information on gold in the substrate. Examples are given of surveys using balsam fir (Abies balsamea), white spruce (Picea glauca) and black spruce (Picea mariana). A reconnaissance scale survey in which alder twigs were collected at 2-km intervals has outlined an area, coincident with a major lithostructural domain, within which ashed twigs contained from 20 to 130 ppb Au ( x = 45 ppb Au ). In sharp contrast, alders in a neighbouring area contained less than 10 ppb Au. It appears that this regional approach to biogeochemical sampling in glaciated terrains may provide a quick appraisal of the gold potential of underlying bedrock. Platinum and palladium show a tendency to concentrate in twigs and trunk of black spruce (Picea mariana) and jack pine (Pinus banksiana), and in stems of labrador tea (Ledum groenlandicum). Spruce was sampled close to a worked out nickel-copper deposit that contained 3000 ppb Pt and 6000 ppb Pd. The ashed twigs yielded up to 880 ppb Pt and 1350 ppb Pd, compared to background levels of below 10 ppb Pt and 2 ppb Pd.

The pattern of geographic variation in the annual shoot production of the three bog shrubs (leatherleaf (Chamaedaphne calyculata), bog laurel (Kalmia polifolia), and Labrador tea (Ledum groenlandicum) was examined using data collected at eight peatland sites along an 800-km latitudinal transect. Productivity varied significantly among sites, with L. groenlandicum exhibiting the greatest range of values (114–505 mg/shoot), followed by K. polifolia (83–341) and C. calyculata (73–241). This variation could be best interpreted by including both climatic and substrate variables in a multiple regression equation. The combination of three site variables (heat sum, depth to standing water, and water conductivity) accounted for between 63 and 86% of the observed variation in shoot productivity. Adding four other variables increased the percentage of variation explained to between 95 and 99%.

Buffering capacity to acidity was defined as the microequivalents of H+ required to produce a 5 μeqiv. change of H+ concentration in a homogenate prepared from leaf tissue. The results for six species collected from the southern boreal forest of Saskatchewan, Canada, showed that trembling aspen (Populus trenudoides Michx.) and Labrador tea (Ledum groenlandicum Oeder.), had the highest buffering capacities (379 and 189 μeuiv. H+ ∙ g−1, respectively), while jack pine (Pinus banksiana Lamb.) had the lowest (33 μequiv. H+ ∙ g−1). Tamarack (Larix laricina (Du Roi) K. Koch), white spruce (Picea glauca (Moench) Voss), and black spruce (Picea mariana (Mill.) BSP) had intermediate values. Buffering capacity and pH of homogenates for all species showed seasonal fluctuations, with the lowest values occurring in the middle of the growing season. The results suggest that foliage of evergreen conifers, particularly jack pine, is less well buffered against acidic pollution than that of broad-leaved species such as trembling aspen.

Four small oligotrophic basin mires on the Precambrian Shield were quantitatively analyzed for vegetation patterns and surface water and groundwater chemistry. Mean concentrations of ions in the surface waters of all vegetation stands indicate these mires to be characterized by low calcium content (0.6–1.9 mg Ca L−1), low corrected conductivity (12–31 μmho cm−1 (1 mho = 1 S)), and relatively high pH (4.0–5.7). Mire 224 is dominated by Chamaedaphne calyculata, Scheuchzeria palustris, and Carex oligosperma. The surface water mean determinations are Ca, 1.10 ± 0.51 mg L−1; Mg, 0.57 ± 0.2 mg L−1; corrected conductivity, 16.7 ± 4.2 μmho cm−1; and pH 4.37. Abundance patterns of the dominant Carex species can be correlated with pH of the surface water of the mire. Mire 239 is characterized by Smilacina trifolia, Ledum groenlandicum, and Carex trisperma. The mean surface water determinations are Ca, 1.53 ± 0.36 mg L−1; Mg, 0.59 mg L−1; corrected conductivity, 21.2 ± 2.0 μmho cm−1; and pH 4.0. Significant differences in pH, Ca, and Mg occur between the interior and edge portions of this bog. Water chemistry from portions burned in 1974 showed no difference from unburned portions. The vegetation of mire 661 contains a sequence of communities positioned relative to the inflow streams, with a Myrica gale – Alnus rugosa community followed by a zone dominated by Picea mariana then a Larix laricina zone and then by an open Sphagnum papillosum – Menyanthes trifoliata lake edge zone. More ombrotrophic areas are dominated by Sphagnum fuscum. Ca, Mg, and Fe concentrations, pH, and corrected conductivity were reduced through this sequence. Comparison of weekly samples of water entering and leaving this mire in 1981 showed a reduction of Ca, Mg, SO4, NO3 N, alkalinity, and pH.

Individual leaves of three bog ericads, leatherleaf (Chamaedaphne calyculata), bog laurel (Kalmia polifolia), and Labrador tea (Ledum groenlandicum), were retained for a maximum of two growing seasons in a peat bog in southern Ontario. The premature loss of mature leaves, resulting from artificial defoliation, significantly reduced the growth of new shoots of L. groenlandicum and K. polifolia but not of C. calyculata. Defoliation effects were directly proportional to the normal retention time for overwintering leaves. Mature leaves probably translocate photosynthate, nitrogen, and phosphorus to other plant parts. This would explain why leaf dry weights were greatest at the start, rather than at the end, of the leaves' second growing season. Net photosynthetic rates decreased with leafage, but in terms of leaf nitrogen content, new and old leaves fixed equal amounts of carbon.

Open woodland forests dominated by Pinus banksiana occur on sandy soils in northeastern Alberta and northwestern Saskatchewan and are generally even-aged and uniform in height. Ordination techniques were used to divide the stands (n = 38) into the following communities: Pinus banksiana/Vaccinium myrtilloides seral community; Pinus banksiana/Cladina mitis, Pinus banksiana/Vaccinium myrtilloides/Cladina mitis in uplands; and Pinus banksiana–Picea mariana/Ledum groenlandicum/Cladina spp. in lowlands. Fires occur with a mean return interval of 38 years (range at six locations, 28–54 years). Pinus banksiana recolonizes rapidly after fire, and average thickness of lichen cover is reached in 45 years. This is a shorter time interval for recovery than is reported for the Northwest Territories. Stands that escape fire 90+ years become more open in upland sites, but in lowlands Picea mariana becomes codominant with associated shift in lichen species and an increase in bryophytes.

Dunn, C.E., 1981. The biogeochemical expression of deeply buried uranium mineralization in Saskatchewan, Canada. In: A.W. Rose and H. Gundlach (Editors), Geochemical Exploration 1980. J. Geochem. Explor., 15: 437–452. Ten kilometres from the eastern edge of the Athabasca Sandstone, near McClean Lake, uranium mineralization (locally up to 27% U3O8) lies 150 m beneath the surface at the unconformity between the Athabasca and crystalline basement. A biogeochemical survey of the area sampled AH and BF soil horizons, peat moss, and plant organs from the dominant species, viz. black spruce (Picea mariana), jack pine (Pinus banksiana), labrador tea (Ledum groenlandicum), and leather leaf (Chamaedaphne calyculata). Uranium concentrations in the ash of various media are surprisingly high: spruce twigs up to 154 ppm U; labrador tea and leather leaf stems around 100 ppm U. Conversely, labrador tea roots yield < 5 ppm U and spruce trunk wood usually < 1 ppm U. Soils give values of 1—3 ppm U. Contoured U values reveal that highest concentrations occur in plants growing above, but laterally displaced from the mineralization. Track-Etch data show a similar pattern. Upward migration of ions along steeply inclined fractures is invoked to explain the phenomenon. Other elements are presents in varying concentrations, depending upon the plant species and the plant organ. High concentrations of several elements are recorded, most notably Cd and Ag in the conifers.

For 21 study sites in the Acadia Forest Experiment Station, near Fredericton, New Brunswick, 34 commonly occurring understory species were studied to determine the depth of underground plant organs capable of growing shoots. Depth of these plant parts tended to be species specific. These depth data, together with a knowledge of the sprouting ability of the underground organs, were used to postulate which species would survive fires of varying intensities. Most species found in the litter layer or in the F and H layer of the forested study sites would be susceptible to fires of low intensity. Rubus canadensis, Kalmia angnstifolia, Vaccinium myrtilloides, Pteridium aquilinum, and Viburnum cassinoides would probably survive severe fires because the subterranean plant organs capable of reproduction were found in the mineral soil. In the bog study sites, Vaccinium oxycoccos, Andromeda glaucopliylla, Kalmia angustifolia, Chamaedaphne calyculata, Ledum groenlandicum, and Rhododendron canadense would likely survive severe fires because the plant organs capable of vegetative reproduction were found 25 cm below the surface of the bog.

Biomass and net primary productivity of three forested perched and three forested raised ombrotrophic bogs were determined and compared. The tree stratum was dominated by Picea mariana (Mill.) B.S.P. and the low shrub stratum by Ledum groenlandicum Oeder and Chamaedaphne calyculata (L.) Moench. Based on a modified forest growth and yield model (STEMS), aboveground living biomass of the tree stratum on the perched bogs was declining by about 0.5 t ha−1 year−1 from a base of 100.7 t ha−1, and on the raised bogs it was increasing by 0.2 t ha−1 year−1 on a base of 31.0 t ha−1. Net primary productivity of that stratum was 3.1 and l.0 t ha−1 year−1 on the perched and raised bogs, respectively. Low shrub aboveground productivity, equal to mortality, was 0.4 and 2.0 t ha−1 year−1 on the perched and raised bogs, respectively. This was about 40% of the standing biomass of shrubs in both bog types. Aboveground net primary productivity of woody strata was 3.5 and 3.0 t ha−1 year−1 on the perched and raised bogs, respectively. These data are comparable to earlier estimates of Sphagnum production on the same bogs: 3.8 t ha−1 year−1 on perched bogs and 3.2 t ha−1 year−1 on raised bogs. Vascular herbs contributed an additional 0.2 t ha−1 year−1 to aboveground production on the perched bogs and 0.1 t ha−1 year−1 on the raised bogs. The higher productivity of perched bogs is probably related to slightly higher nutrient status related to their landscape position. The total productivity of all strata of these ombrotrophic sites approaches that of upland sites in the same region.

In 1978, polyphagous larvae of the chain-dotted measuring worm (Cingilia catenaria (Drury)) (Lepidoptera: Geometridae) completely defoliated three species of ericad at the Luther Marsh bog in southern Ontario, but consumed less than 1% of the ericad leaf area each year between 1974 and 1977. The three ericads, bog laurel (Kalmia polifolia Wang.), leatherleaf (Chamaedaphne calyculata (L.) Moench.), and Labrador tea (Ledum groenlandicum Oeder.), were equally effective in defending leaves against all herbivores except larvae of C. catenaria, to which all were equally susceptible at high larval density. During the study period the frequency of intense herbivory was not great enough to seriously diminish the advantage of nutrient conservation associated with the 2-year leaf-retention period exhibited by these ericads.In laboratory feeding trials involving an unlimited food supply, C. catenaria larvae preferred leaves of K. polifolia and C. calyculata over L. groenlandicum leaves. Chemical feeding deterrents such as condensed tannins, although present in relatively large concentrations in the leaves, appeared to be less important than nutrients, such as nitrogen and carbohydrates. Pubescence on the undersides of L. groenlandicum leaves probably acted as a physical deterrent to larval feeding. The possession of antiherbivore leaf characteristics (e.g., thick cuticle, condensed tannins, terpenes, pubescence) by these three ericads may reflect selective pressure by herbivores in the past and (or) current edaphic constraints (i.e., limited water availability in winter and lack of nitrogen and phosphorus during the growing season).

During powerline construction, a portion of a wooded (Picea mariana) peat plateau in northern Manitoba was stripped of surface vegetation. Seven years later, aerial biomass of plants recolonizing the surface of the disturbed area was estimated to be 2098 kg ha−1, only 26.4% of the undisturbed portion's aerial biomass of 7939 kg ha−1.Tree biomass represented 28.7% of the aboveground biomass of the wooded plateau. The relative proportions of photosynthetic phytomass increased from 17% in the wooded to 53% in the disturbed area. Major ericaceous species (Ledum groenlandicum, Chamaedaphne calyculata, and Kalmia polifolia) responded after disturbance by increasing reproductive effort and the ratio of photosynthetic to woody tissue.Permafrost subsidence in the disturbed portion was not evident in the period since vegetation removal, although surface erosion of peat was visible and could be expected to increase in the next several years.

The seasonal timing of shoot extension by three ericaceous shrubs (Ledum groenlandicum, Chamaedaphne calyculata, and Kalmia polifolia) was monitored at eight peat bogs along an 800-km latitudinal transect through Ontario, Canada, and at a transplant garden containing plants from four of the peat bogs. The timing of shoot extension varied among plants from different locations, both in the transplant garden and in the field. A regression model containing two independent variables (heat units (i.e., degree-days) and either the average annual degree-day total for a plant's geographic origin or the average frost-free period) could account for 95 to 99% of the seasonal plus intersite variation in shoot extension recorded in the transplant garden. The seasonal pattern of shoot extension predicted for each of the eight peat bogs with the regression model was close to the observed pattern in most cases. The average difference between predicted and observed percentages of shoot extension ranged from 4% for L. groenlandicum to 7% for K. polifolia.

Two commonly occurring, perennially frozen, organic soils were studied, one from the south-west part of the Discontinuous Permafrost Zone and the other from the Continuous Permafrost Zone of the Hudson Bay Lowland in northern Manitoba. These soils had a characteristic domed or slightly elevated topography with a dense cover of black spruce (Picea mariana (Mill.) BSP.), Ledum groenlandicum Oeder, feathermoss, and sphagnum moss. The water content of the active layer was found to be much lower than the water (ice) content of the frozen layer. The exchangeable calcium and hydrogen and pH were higher in the frozen layer than in the active layer but no significant difference was found in the exchangeable magnesium, potassium, and sodium of the two layers. The high concentration of Ca in the frozen layer is likely due both to the transfer of soil moisture and nutrients along the thermal gradient and, as has been found previously, to the high selectivity of organic soils for calcium over magnesium and monovalent cations.

Peat mounds with frozen permafrost cores, or palsas, occur in areas with sporadic permafrost in subarctic and boreal parts of Canada. In northern Ontario, the surface vegetation of palsas is characterized by the presence of Cladonia alpestris, C. rangiferina, and C. sylvatica with occasional stunted Picea mariana which are surrounded by Ledum groenlandicum and Vaccinium vitis-idaea. From vegetational analysis, hummock and palsa morphology, and radiocarbon dating, evidence is given for a recent origin under climatic conditions similar to the present. The largest palsas appear to be about 200 years old. Details of energy exchange during July are given for mature, partially eroded, and collapsed palsas. The formation of palsas may be dependent on changes in surface albedo associated with vegetational change from Sphagnum fuscum to Cladonia spp. dominated communities where the albedo was found to increase from 13.8% to 21.3%. However, evidence is presented that decreased penetration of heat during summer associated with the drying of surface peat may be important in palsa formation. Lower thermal conductivity of the peat at this time would insulate the ice core from insolation. Collapse of palsas was attributed to surface and marginal erosion and higher heat penetration to the core associated with wetter peat conditions on the palsa.

Seimatosporium ledi sp. nov. causing leaf spot of Ledum groenlandicum Oeder. in Canada is described and its relationship with allied fungi including S. lichenicola (Corda) Shoemaker & Müller (= Coryneum vaccinii Fuckel; = C. rhododendri Schw. var. fusoideum Dearness nom. nud.) and S. rhododendri (Schw.) comb. nov. (≡ C. rhododendri Schw.; = C. triseptatum Peck) is discussed.