Darwyn S. Coxson

Microsite Displacement of Terrestrial Lichens by Feather Moss Mats in Late Seral Pine-Lichen Woodlands of North-central British Columbia

Abstract Pine-lichen woodlands in north-central British Columbia show a long period of successional development where reindeer lichens (Cladina spp.) dominate plant cover at the forest floor surface. However, in mid- to late-successional stands lichen cover is replaced in a mosiac of surface microsites by feather moss mats (largely Pleurozium schreberi), with moss mats often burying lichen mats that previously had occupied these microsites. We have compared moss and lichen dominated microsites at this stage of stand development, looking at the influence of canopy structural variables and development of forest floor plant communities on microsite expression. Microsites with high feather moss mat cover had greater canopy leaf area index values, compared to microsites where lichen cover predominated. Leaf area index values were highly correlated with stand level structural variables, including basal area, total volume, and biomass of the dominant canopy tree species Pinus contorta. Changes in stand architecture were further associated with the accumulation of litter and organic matter at the forest floor surface. These factors suggest that the manipulation of stand structure in managed forests, for instance through partial-cut harvesting, may delay successional changes and promote continued lichen growth in these forest types. This is an important consideration in the management of pine-stands in northern B.C., where lichen mats provide significant forage values for caribou populations.

Lichen Colonization and Gap Structure in Wet-temperate Rainforests of Northern Interior British Columbia

Abstract Abundant canopy lichen communities characterize wet-temperate rainforests on the windward slopes of interior mountain ranges in north-central British Columbia, Canada. Historically, these forests have regenerated through gap-dynamics; however, our knowledge of lichen colonization within gaps is limited. We have now compared lichen biomass on regenerating trees in naturally occurring 1–3 ha gap-disturbances (these gaps presumed to have originated from insect out-breaks in the late 1800s) with those on regenerating trees of similar age growing in the understory of the surrounding old growth forest. Only small differences were seen in total lichen biomass on regenerating trees between the two settings, however, analysis of the individual lichen groups (Alectoria, Bryoria, Foliose, and Cyanolichen) revealed striking differences. The Bryoria group was 35% more abundant on gap trees (632 g/tree) and was distributed vertically through a larger proportion of the tree crown. The Cyanolichen functional group was largely absent from gap trees, despite high levels of biomass loading (1,332 kg/ha) in the surrounding old-growth stand. Alectoria and Foliose functional groups did not differ significantly in biomass or distribution between regenerating trees of the two types. Tree size positively affected lichen loading. Total lichen biomass was 38% greater on the larger size class (31–44 cm dbh) regenerating trees, with the Alectoria functional group alone having 45% greater biomass on larger trees. Presence or absence of leaves on branch substrate had no effect on lichen loading. Stand-level projections indicate that the old growth forest had 19% more arboreal lichen biomass (2,684 kg/ha) and contained greater lichen species diversity than did the “second-growth” regenerating forest patches. The low cyanolichen biomass in naturally occurring gap openings poses concern for the proposed utility of “new-forestry” type harvesting practices to retain canopy biodiversity using current harvest rotation intervals.

Nitrogen Inputs by Associative Cyanobacteria across a Low Arctic Tundra Landscape

Abstract Available soil N is a key factor limiting plant productivity in most low arctic terrestrial ecosystems. Atmospheric N2-fixation by cyanobacteria is often the primary source of newly fixed N in these nutrient-poor environments. We examined temporal and spatial variation in N2-fixation by the principal cyanobacterial associations (biological soil crusts, Sphagnum spp. associations, and Stereocaulon paschale) in a wide range of ecosystems within a Canadian low arctic tundra landscape, and estimated N input via N2-fixation over the growing season using a microclimatically driven model. Moisture and temperature were the main environmental factors influencing N2-fixation. In general, N2-fixation rates were largest at the height of the growing season, although each N2-fixing association had distinct seasonal patterns due to ecosystem differences in microclimatic conditions. Ecosystem types differed strongly in N2-fixation rates with the highest N input (10.89 kg ha−1 yr−1) occurring in low-lying Wet Sedge Meadow and the lowest N input (0.73 kg ha−1 yr−1) in Xerophytic Herb Tundra on upper esker slopes. Total growing season (3 June–13 September) N2-fixation input from measured components across a carefully mapped landscape study area (26.7 km2) was estimated at 0.68 kg ha−1 yr−1, which is approximately twice the estimated average N input via wet deposition. Although biological N2-fixation input rates were small compared to internal soil N cycling rates, our data suggest that cyanobacterial associations may play an important role in determining patterns of plant productivity across low arctic tundra landscapes.

Bryophyte-cyanobacterial associations as a key factor in N2-fixation across the Canadian Arctic

Nitrogen inputs via biological N2-fixation are important in arctic environments where N often limits plant productivity. An understanding of the direct and indirect theoretical causal relationships between key intercorrelated variables that drive the process of N2-fixation is essential to understanding N input. An exploratory multi-group Structural Equation Modeling (SEM) approach was used to examine the direct and indirect effects of soil moisture, plant community functional composition, and bryophyte and lichen abundance on rates of nitrogen fixation at a low arctic ecosystem, two high arctic oases and a high arctic polar desert in the Canadian Arctic. Increasing soil moisture was strongly associated with an increasing presence of bryophytes and increasing bryophyte abundance was a major factor determining higher N2-fixation rates at all sites. Shrubs had a negative effect on bryophyte abundance at all sites with the exception of the polar desert site at Alexandra Fjord highland. The importance of competition from vascular plants appears to be greater in more productive sites and may increase at lower latitudes. Moisture availability may have an indirect effect on ecosystem development by affecting N input into the system with bryophyte-cyanobacterial associations playing an important intermediary role in the process.

Macrolichen colonization on 120-140 year old Tsuga heterophylla in wet temperate rainforests of central-interior British Columbia: a comparison of lichen response to even-aged versus old-growth stand structures

Canopy lichen abundance was assessed by size class on regenerating hemlocks, comparing trees of similar size and age (c. 120-140 yrs) growing in the understorey of old-growth cedar-hemlock stands with those growing in adjacent even-aged hemlock stands (natural origin patches c. 1-3 ha in size). Five chlorolichen taxa were associated with old-growth understorey trees: Cavernularia hultenii, Hypogymnia vitatta, Parmelia hygrophila, Platismatia norvegica ,a ndUsnea spp. Lobaria pulmonaria was the most abundant cyanolichen on regenerating hemlock in the old-growth forest stands, particularly in lower canopy (under 12 m) exposures. However, other cyanolichen taxa such as Nephroma helveticum, Sticta fulginosa ,a ndPseudocyphellaria anomala, reached their greatest abundance at mid-canopy (12-24 m) positions. Smaller cyanolichen thalli (<9 cm 2 ) were abundant on regenerat- ing hemlocks across all canopy positions in the old-growth forest, raising the question as to whether or not cyanolichen thalli in mid- to upper-canopy environments represented long-established individuals facing severe growth constraints, or were simply thalli that had experienced higher rates of fragmentation, and thus did not achieve larger sizes. In comparison, cyanolichens of all taxa were essentially absent from the small-patch even-aged forest stands. Given that dispersal of propagules was not likely a major limiting factor, these 120-140 year old even-age stands may not yet have attained sufficient old-growth characteristics (especially canopy microclimate and canopy through- flow enrichment) to support cyanolichen growth. These findings have major conservation biology implications for wet interior cedar-hemlock forests in British Columbia, where forest harvesting is creating a mosaic of even-aged stands, whose projected age at the time of next harvest (rotation age) will be 120 years or less.

Variation in epiphytic lichen and bryophyte composition and diversity along a gradient of productivity in Populus tremuloides stands of northeastern British Columbia, Canada

Abstract The influence of site productivity on epiphyte diversity on aspen (Populus tremuloides) trunks was examined in 19 stands from northeastern British Columbia, whose site indices (dominant tree height at 50 y) ranged from 6.7 to 27.9 m. Canopy epiphyte communities responded strongly to gradients in site productivity. Correlations between plot scores along the axes of non-metric multidimensional scaling ordinations and environmental variables indicated that site index, diameter at breast height, tree age, bark cation concentrations (K, Ca, Mg, and Mn), canopy cover, and bark roughness were significant explanatory variables for epiphyte community composition at trunk base and at breast height. Less productive sites (site indices below 17.25) were dominated by crustose lichens. Indicator species in these sites included Caloplaca cerina, C. holocarpa, and Catillaria glauconigrans. Closed-canopy environments in the more productive stands were dominated by mosses. Associated indicator species included Brachythecium spp., Pylaisiella polyantha, and Eurhynchium pulchellum. Cover of epiphytic species at breast height was higher in stands with low site indices, whereas cover of epiphytic species at trunk base was higher in stands with high site indices. These findings would suggest that management for epiphyte community diversity in aspen dominated landscapes will necessitate the retention of mature aspen stands from across a range of site productivities.

Arboreal forage lichens in partial cuts – a synthesis of research results from British Columbia, Canada

The mountain ecotype of the woodland caribou (Rangifer tarandus caribou) is highly dependent on the arboreal hair lichens Bryoria spp. and Alectoria sarmentosa during winter. In parts of British Columbia, partial-cutting silvicultural systems have been used in an effort to provide continuously usable winter habitat for mountain caribou, while allowing some timber removal. We reviewed available information about the changes in hair lichens after partial cutting in Engelmann spruce (Picea engelmannii) – subalpine fir (Abies lasiocarpa) forests of British Columbian and Idaho. Generally, abundance of Bryoria spp. in the lower canopy of individual residual trees increases with increased exposure after partial cutting, until the new regeneration begins to shelter the lower canopy of the residuals. Heavy basal area removal, however, results in low lichen availability at the stand level for many years. Abundance of Bryoria on the regeneration is low, and appears to be limited largely by the structure of the young trees, not by lichen dispersal, although dispersal capability may be limiting in Alectoria. Both distributional and physiological data suggest that Bryoria is intolerant of prolonged wetting, and that increased ventilation, rather than increased light, accounts for enhanced Bryoria abundance in the partial cuts. Alectoria sarmentosa reaches its physiological optimum in the lower canopy of unharvested stands; its growth rates are somewhat reduced in the more exposed environment of partial cuts. Both genera are capable of rapid growth: over a 7-year period, individual thalli of A. sarmentosa and Bryoria spp. (excluding those with a net biomass loss due to fragmentation) in an unlogged stand more than tripled their biomass. Calculated growth rates, as well as dispersal potential, are influenced by fragmentation. Bryoria produces more abundant, but smaller, fragments than Alectoria, and fragmentation in both genera increases in partial cuts. In subalpine mountain caribou habitat, partial-cutting prescriptions that enhance exposure of residual trees while keeping basal area removal low will maintain forage best. Regeneration management should focus on maintaining ventilation in the lower canopy of the residual stand.

Phylogenetic position of a Pacific Northwest North American endemic cyanolichen, Nephroma occultum (Ascomycota, Peltigerales )

Nephroma occultum is a COSEWIC listed cyanolichen of “Special Concern”. It is endemic to old-growth cedar-hemlock forests in western North America. This is the first study to place N. occultum into a phylogenetic framework using nucleotide sequence and secondary structure data. It also addresses the phylogenetic relationship between N. occultum and N. arcticum . Analysis of fungal Internal Transcribed Spacer (ITS) ribosomal DNA (rDNA) produced four major clades. The cyanobacterial transfer RNA Leu intron (tRNA Leu ) from N. occultum was separated from that of N. isidiosum and fell between the Eurasian and North American epiphytic taxa. Examination of length and complexity of the folded secondary structures revealed different trends in the ITS1 and ITS2 rRNA regions. Even though N. occultum is endemic to North America, it seems more closely related to South American temperate rainforest species than to the sympatric N. arcticum . Nephroma occultum is alone among the studied species of Peltigerales in having an exceptionally long ITS1 region, and a different tRNA Leu intron DNA sequence of the photobiont suggesting association with a unique genotype of Nostoc . It may be argued that the fitness of N. occultum may be influenced by the complex ITS1 RNA structure, a unique photobiont genotype undergoing a genetic bottleneck, no sexual reproduction to generate variation, and the inability to associate with different photobionts to adapt to changing habitats.

Does exogenous carbon extend the realized niche of canopy lichens? Evidence from sub-boreal forests in British Columbia

Foliose lichens with cyanobacterial bionts (bipartite and tripartite) form a distinct assemblage of epiphytes strongly associated with humid microclimatic conditions in inland British Columbia. Previous research showed that these cyano- and cephalolichen communities are disproportionately abundant and species-rich on conifer saplings beneath Populus compared to beneath other tree species. More revealing, lichens with cyanobacterial bionts were observed beneath Populus even in stands that did not otherwise support them. We experimentally test the hypothesis that this association is due to the interception of glucose-rich nectar that is exuded from Populus extra-floral nectaries (EFN). Using CO2 flux measurements and phospholipid fatty acid (PLFA) analysis with experimental applications of 13C6-labeled glucose, we demonstrate that cyano- and cephalolichens have a strong respiratory response to glucose. Lichens treated with glucose had lower net photosynthesis and higher establishment rates than control thalli. Furthermore, lichens with cyanobacterial bionts rapidly incorporate exogenous 13C into lichen fatty acid tissues. A large proportion of the 13C taken up by the lichens was incorporated into fungal biomarkers, suggesting that the mycobiont absorbed and assimilated the majority of applied 13C6 glucose. Our observations suggest that both cyanolichens and cephalolichens may utilize an exogenous source of glucose, made available by poplar EFNs. The exogenous C may enable these lichens to become established by providing a source of C for fungal respiration despite drought-induced inactivity of the cyanobacterial partner. As such, the mycobiont may adopt an alternative nutritional strategy, using available exogenous carbon to extend its realized niche.

Diel Periodicity of Photosynthetic Response in the Subalpine Moss Pohlia wahlenbergii

Net photosynthetic (NP) response in the subalpine moss Pohlia wahlenbergii (Web. & Mohr) Andr. showed pronounced patterns of diel periodicity under midsummer conditions. Rates of light-saturated NP uptake were highest in the early morning hours, at 8 mg CO2 g-1 hr.-., declining to near 5 mg CO2 g-1 hr.-1 by late afternoon. Concurrent changes in light-limited NP uptake saw quantum efficiency decline from 0.018 to 0.009. Both light-limited and light-saturated NP uptake showed full recovery during the late evening and nighttime periods. One interpretation of these diel oscillations may be that of reoccurring photodestruction (and repair) of pigment com- plexes, although this degree of photosensitivity is unusual for a plant which has grown in a high light environment. Alternatively, these changes may reflect endogenous photosynthetic rhythms, similar to thosepreviously documented in phytoplankton and diatom populations. This interpretation is supported by the absence ofbleaching or chlorophyll destructionfollowingperiods ofhigh insolation exposure. The occurrence of diel oscillations in P. wahlenbergii has important implications for the calculation of net primary productivity, with increased quantum efficiency during the early morning and late evening periods resulting in a homeostasis of NP uptake under conditions of a changing, but predictable, light environment. For photosynthesis and growth to occur, photo- trophs must live in an environment with a tolerable range of photon flux densities. If light quantity is below this range, not enough energy may be cap- tured to maintain sufficient rates of photosynthesis. If photon irradiance is increased above the level that saturates the rate of photosynthesis, then photo- destruction of pigment protein complexes may fol- low, as received energy exceeds that which can be dissipated by photochemical processes (Powles &