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ABSTRACTClimate warming in the North could lead to lichen decline within critical woodland caribou habitat. We used repeat measurements of sixty-nine plots over ten years (2007–2008 and 2017–2018) to assess lichen biomass changes under a warming climate along a latitudinal/climatic gradient in northwestern Canada. We compared lichen biomass on sensitive landscape features, including peat plateaux (permafrost-containing bogs), areas of permafrost thaw within the peat plateaux (collapse scars), and low-productivity upland forests occurring on mineral soils. Field-based measures of lichen cover and height were coupled with samples of lichen biomass to develop biomass prediction equations. The optimal model incorporated both cover and height, with landscape feature as a covariate. Although height significantly improved the equation fit, models were successfully developed with cover alone. Modeled lichen biomass differed significantly between landscape features, declining from peat plateau (502 g m−2) to upland forest (54.0 g m−2) and collapse scar (0.690 g m−2) environments. In the absence of permafrost collapse at any monitoring location, lichen biomass declined significantly over the ten years for peat plateaux (−75.6 g m−2) and upland forests (−17.5 g m−2). These results will be important for quantifying landscape-level lichen biomass changes under climate warming in boreal and subarctic environments.

ABSTRACTKnowledge of regeneration processes of the endangered whitebark pine (Pinus albicaulisEngelm.) is critical for developing approaches for recovery and restoration of the species. We investigated biophysical associates of whitebark pine seedling occurrence and density in different mesohabitats (defined by community type and elevation) within the northern Rocky Mountains of Alberta. We developed candidate linear models to examine factors influencing occurrence and abundance. Occurrence was positively related to bare mineral soil and species richness in forest mesohabitats, while in both open and alpine-treeline environments it was positively related to prostrate shrub cover. Negative associates included tree cover, rocky substrates, and seedling cover of other conifers. Model validation showed a strong correlation between observed and predicted occurrence (correlations of 0.60, 0.56, and 0.56 for forest, open, and alpine-treeline mesohabitats, respectively). Climate models best predicted seedling density; abundance was highest on south-facing slopes in all mesohabitats. Correlations between observed and predicted density were 0.83, 0.92, and 0.72 for forest, open, and alpine-treeline mesohabitats, respectively. Our study identifies biophysical parameters to consider when planting blister rust—resistant seedlings and suggests that open mesohabitats along south-facing slopes may be best for regeneration of whitebark pine, particularly near the northern limits of its range.

AbstractForests dominated by the endangered tree species whitebark pine (Pinus albicaulis) are threatened by multiple stresses (fire suppression, climate change) and disturbances (white pine blister rust [Cronartium ribicola], mountain pine beetle [Dendroctonus ponderosae]). To gain insight into how these ecosystems respond, we quantified vegetation change over 2 decades (21–29 y) in xeric and submesic P. albicaulisecosystems near the northern edge of the species' range on the leeward side of the Coast Mountains of British Columbia, Canada. We compared changes in overstory and understory vegetation composition of these stands to changes in mesic, non-whitebark pine ecosystems in the same region. Multi-response permutation procedure (MRPP) analysis showed that the overstory of xeric whitebark pine ecosystems became compositionally similar to mesic ecosystems, i.e., there was increased dominance by Abies lasiocarpaor Tsuga mertensiana.Yet understory composition in xeric whitebark pine stands changed little and there was continued regeneration of P. albicaulis.Submesic whitebark pine stands developed a dense canopy dominated by T. mertensiana, and although their understories did not become compositionally similar to mesic ecosystems, there was minimal P. albicaulisregeneration. Understory stability in xeric and submesic whitebark pine ecosystems over 21–29 y suggests compositional resilience in these ecosystems to multiple stresses and disturbances. However, ongoing disturbance affecting both overstory and understory P. albicaulismight still result in the loss of this keystone species.

AbstractRecreational activities in alpine areas have been increasing in recent decades, creating the need to improve our understanding of the impacts of these activities and how they are best managed. We explored impacts of recreational trail use on dry alpine meadows in the northern Canadian Rockies of Alberta. Data collected in 142 plots (0.5 m × 1 m) were used to compare plant community metrics among (1) a recreational trail, (2) intact tundra meadows (undisturbed), and (3) sparsely vegetated gravel steps formed by frost disturbance (naturally disturbed). As compared to undisturbed tundra, trails had substantially lower cover of vascular plants (4% vs. 35%), lichen (0% vs. 10%), and cryptogamic crust (0% vs. 4%); trails also had lower species richness (7 vs. 11 species per plot), but greater soil compaction (2.75 vs. 1.25 kg cm-2). Trails differed from natural gravel steps, which had three times more biotic cover and different composition. This highlights the difference in effects of human and natural disturbance. Positive feedback effects of trampling in tundra ecosystems may lead to altered environmental conditions, including decreased infiltration capacity and nutrient cycles in soils, and more extreme temperatures at the soil surface. These feedbacks could inhibit regeneration of abandoned trails.

AbstractWe studied effects of oil and gas exploration, using the most recent seismic exploration technologies, on tundra plant communities and soils in four vegetation types in the Low Arctic of western Canada, two to three years post-disturbance. For all four vegetation types, seismic lines had less vascular plant cover and more bare ground than adjacent “reference” tundra. For the two upland tundra vegetation types, mosses and lichens were less abundant on seismic lines than in reference plots. There were no apparent differences in organic layer thickness between seismic lines and reference areas, but active layer depth (at the time of sampling) was significantly greater on seismic lines for the upland tundra and one of the wetland vegetation types. Diversity and richness were lower, and community composition was different, on seismic lines (as compared to reference plots) in upland tundra vegetation types but not in wetland types. The results suggest that (1) upland vegetation types are less resistant to seismic disturbance, (2) active layer depth increases following seismic disturbance, and (3) impacts from modern seismic techniques in upland tundra are similar to, or somewhat greater than, the initial impacts observed from the earliest phases of winter exploration ∼30 years ago.

This study evaluated the contribution of different ages of foliage to the nutrient and carbon balance of black spruce (Picea mariana (Mill.) B.S.P.) from a nutrient-poor peatland in Alberta. Seasonal patterns of foliar nitrogen and phosphorus concentration and content were examined in six needle cohorts up to 10 years old. Trees were treated to simulate excess nutrient deficiency (removal of all one-year-old foliage), nutrient excess (fertilized with 250, 50, 100 kg ha-1 NPK split application in June and July), or left as controls. Gas exchange (net assimilation-Na, stomatal conductance-gs, mesophyll conductance-gm, water-use efficiency-WUE, dark respiration-RS) was measured on six different needle cohorts in several control trees in 1989 and 1990. Nitrogen and phosphorus concentration decreased with needle age. Foliar nutrient concentration fell from April to June and then was stable until September except for the fertilized trees where it increased. There was no evidence of greater than normal retranslocation of nutrients from older needles for defoliated trees or greater than normal nutrient loading in older needles of fertilized trees. NA, gs, gm, WUE, and RS were similar for all needles up to six or eight years old, these older needles having NA of 65% of current needles and similar RS. The results do not support to conclusion that older needles of black spruce are retained as an adaptation to nutrient stress. It does not appear that older needles serve as a nutrient storage site in conditions of excess nutrient availability or a greater than normal nutrient source during times of excess nutrient deficiency. It appears that the maintenance of long-livedfoliage in black spruce does not provide for greater flexibility in tree nutrient allocation. Their contribution to the carbon balance of the tree seems to be sufficient to explain their retention.

Variation in the amount and pattern of plasticity was studied in three cytotypes (4x,6x,and 8x) of Stellaria longipesand diploids of its suspected progenitor S. longifolia.All 13 traits considered showed plasticity. There were significant differences among cytotypes and habitats in plasticity for many traits. Overall, the diploids, S. longifolia,were most plastic, and the three cytotypes of S. longipesdid not differ in amount of plasticity. Stellaria longifoliashowed divergence from S. longipesin the pattern of plasticity as well. In general, cytotypes with more similar chromosome numbers had the same pattern of plasticity for more traits. Individuals from tundra populations differed in their pattern of plasticity from those of montane, boreal, and prairie origin, which were more similar to one another. Differences in plasticity among cytotypes were due primarily to divergence in amount, while differences among habitats were most often accounted for by divergent patterns of plasticity. We conclude that both polyploidy and natural selection have affected the evolution of plastic responses in this species complex. Analysis of the correlation between pairs of traits provided evidence that the pattern and amount of plasticity operate independently of one another and may be evolving separately.

Calamagrostis canadensis(a rhizomatous grass) exists in temperate forest sites of different successional age. It can rapidly colonize disturbed sites to form dense swards. We examined allozyme variation in: four populations (mature forest, intermediate aged forest, forest cutblock, wetland); nine small plots (2 m × 4 m) within the cutblock; and progeny of several families from three populations; in order to assess the mode of colonization of disturbed areas and the effect of successional changes on population genetic structure. All four populations showed equal and extensive genetic variation (1.5 to 1.7 alleles per locus [K], 41.7% to 50% polymorphic loci [PPL], Hst= 0.155 to 0.208) and were not genetically differentiated (Gst= 0.0193, 1= 0.986 to 0.997). The cutblock subpopulations also showed considerable genetic variation (K = 1.6 to 1.8, PPL = 50% to 58.3%, Hst= 0.151 to 0.278) and no microdifferentiation (Gst= 0.034, I =0.967 to 0.997). We found 14 different genotypes among the 30 individuals sampled from the cutblock as a whole (based on five polymorphic loci). The cutblock subpopulations had from nine to 14 different genotypes each (same five loci, 18 individuals per subpopulation). Seed produced was primarily outcrossed (multilocus estimate 0.888 to 0.900). We concluded that disturbed sites are colonized primarily by sexually produced seedlings. Potential genetic drift and natural selection, which occur during subsequent successional changes, do not result in reduced genetic variation or population differentiation.

Patterns of morphological variation were studied in herbarium specimens of Stellaria longipes, an herbaceous perennial and subsequently in a growth chamber experiment using three cytotypes (4x, 6x, 8x) of S. longipesand diploids of its proposed progenitor S. longifolia.Despite extensive phenotypic plasticity in many traits, patterns of variation resulting from ecotypic differentiation within S. longipescould be detected in the field. A distinct form of S. longipes, which is restricted primarily to arctic and alpine tundra locations, shows genetic differentiation for the following traits: few flowers per ramet, a low proportion of flowering ramets, and ovate leaves. The three cytotypes of S. longipescould be distinguished by their mean genotypic value for leaf length and number of flowers per ramet. The extent of phenotypic plasticity in these traits makes it unlikely that the cytotypes could be distinguished in the field. The direction and extent of morphological divergence between S. longifoliaand S. longipessuggest an alloploid origin for S. longipes.Variational trends (among‐habitat types and cytotypes) in trait means are similar to those reported previously for the pattern of plasticity. This supports the argument that similar forces guide evolution of the mean and pattern of plasticity of a trait.

Population differentiation for phenotypic plasticity of 12 morphological and reproductive traits was investigated in five populations of the Stellaria longipescomplex including a population of the sand dune endemic S. arenicola.Population differentiation was detected for the mean (genotypic) value, amount of plasticity, and pattern of plasticity of traits. Average amount of plasticity was not related to degree of isozyme variability in the populations. Differentiation for pattern of plasticity was much more common than for amount. The direction and extent of divergence among populations was dependent on which of the three trait aspects was under consideration (mean, amount of plasticity, pattern of plasticity) and did not reflect their similarity as revealed by enzyme electrophoretic data. It was concluded that trait means, amounts of plasticity, and patterns of plasticity are independent of one another during evolutionary divergence and may be influenced by mosaic selection.