The ASTIS database cites the following 16 publication(s) by Wayne Strong. Publications are listed from newest to oldest. Please tell us about publications that are not yet cited in ASTIS.
High-latitude Yukon boreal-cordilleran grassland plant communities / Strong, W.L.
(Arctic, v. 68, no. 1, Mar. 2015, p. 69-78, ill., maps)
ASTIS record 80615.
High-latitude (61.9 - 62.8 N) graminoid plant communities located near the northern limit of boreal forest occurrence in the Carmacks - Pelly Crossing area of Yukon were sampled and classified, and four sociations were recognized: Calamagrostis purpurascens (purple reedgrass), Hesperostipa comata (needle-and-thread grass), Poa glauca - Artemisia frigida (glaucous bluegrass - pasture sagewort), and Pseudoroegneria spicata - Artemisia frigida (bluebunch wheatgrass - pasture sagewort). These plant communities occurred primarily on south-southwest slopes (180 - 230) with 45% - 75% gradients. Relative to southern Canada mixedgrass prairie, Yukon grasslands were likely species poor, had less total canopy cover, and produced less than half as much aboveground herb biomass (typically 200 - 300 kg/ha). The distribution of the sociations appeared limited to ~60 - 65 N latitude in the Yukon-Alaska region. Calamagrostis was the most abundant and widespread grassland sociation in the study area. The four sociations occupied less than 4% of the Carmacks - Pelly Crossing landscape, although they represented the most extensive high-latitude boreal grassland vegetation in Canada ( 2600 ha) and they were among the most northerly in North America. (Au)
Artemisia; Biological sampling; Biomass; Classification; Grasses; Meadows; Palaeobotany; Plant distribution; Plant ecology; Slopes; Taiga ecology; Temporal variations
Aishihik region, Yukon; Braeburn Lake region, Yukon; Carmacks region, Yukon; Pelly Crossing region, Yukon; Stewart Crossing region, Yukon
Northernmost North American Pinus contorta var. latifolia (lodgepole pine) sociations and vegetation diversity relative to its central range east of the Rocky Mountains / Strong, W.L.
(Nordic journal of botany, v. 32, no. 2, Apr. 2014, p. 222-232, ill., maps)
Supplementary material: Appendix I: Primary Pinus contorta var. latifolia central range relevés sources, available with the online version of this paper.
ASTIS record 80264.
Lodgepole pine (Pinus contorta var. latifolia) stands were sampled in central Yukon, Canada (61.5-64°N latitude), which represented the northernmost 9% of the tree's North American range. Within this area, lodgepole pine occupied only ˜ 2% of the landscape. This study determined: 1) what forest sociations occurred (i.e. structural dominance-types); 2) how plant growth form composition and richness differed from the central portion of the species' geographical range; and 3) if stands were biased towards occurring on more thermally favorable south-facing slopes. Five lodgepole pine sociations were recognized among 100 relevés: Rhododendron groenlandicum (Labrador tea); Cladonia arbuscula (green reindeer lichen); Calamagrostis purpurascens (purple reedgrass); Hylocomium splendens (stairstep moss) and Alnus viridis (green alder, n = 4 relevés). Rhododendron stands were proportionally more common on low gradient sites and had more total plant cover than the other sociations. Cladonia and Calamagrostis stands were typically associated with dry coarse-textured soils and warm dry sites, respectively; whereas the composition of the Hylocomium sociation reflected the detrimental influences of atypically dense forest canopies on understory vascular plants. Only the Calamagrostis sociation was unique to the study region. Species richness among common northern lodgepole pine sociations averaged 16-19 taxa per relevé (p > 0.05). Northern compared to central range (n = 1394) relevés were compositionally different based on little overlap of their datasets in the ordination space. Northern vegetation had less (p < 0.001) total plant (129% vs 184%), deciduous shrub (9% vs 26%), broad-leaved herb (5% vs 25%), and bryophyte (27% vs 54%) cover; had greater macro-lichen cover (13% vs 5%) and lower floristic richness (11 vs 24 taxa) and was less than half as phytosociological diverse. Lodgepole pine stands in the northernmost portion of their range were not biased towards occurring on south-facing slopes, which suggested an ecological potential for range expansion. (Au)
H, J, A, E
Alders; Aspect; Bioclimatology; Biological sampling; Bryophytes; Lichens; Lodgepole pines; Microclimatology; Mosses; Plant cover; Plant distribution; Plant ecology; Plant growth; Rhododendrons; Shrubs; Taiga ecology
Dawson region, Yukon; Kluane National Park and Reserve, Yukon; Yukon
Leonard Vincent Hills (1933-2013) / Strong, W.L. Kooyman, B.P.
(Arctic, v. 66, no. 4, Dec. 2013, p. 509-511, ill.)
ASTIS record 78909.
Leonard (Len) V. Hills was a palynologist and palaeontologist who enthusiastically pursued research, especially those studies that involved palaeoenvironmental interpretation. He was born in a log cabin at Judah, about 28 km south of Peace River, and raised in the rural Peace River district of west-central Alberta during the 1930s and 1940s. His formal education began in a one-room country school, but he finished high school in Peace River. After working several years for Mobil Oil Canada on a geophysical crew in southern Alberta, Len decided to further his education. At the University of British Columbia, he earned a BSc with honors (1960) in geology and archaeology, although early in his program he had seriously considered majoring in forest science rather than geology. His baccalaureate degree was quickly followed by a MSc (1962) from the University of British Columbia and a PhD (1965) from the University of Alberta, both in geology, with specialization in palynology. After working briefly for Shell Oil in Edmonton, Len obtained an assistant professorship at the University of Calgary in 1966 and rose to the rank of full professor within eight years. Much of his university research involved compiling and interpreting ancient microfossil (and to a lesser extent, Holocene) pollen stratigraphic sequences, which seemed his favorite, but his work also included macro-fossil and archaeological analyses. Although Len retired from his university position in 1996, he continued to conduct research, publish in peer-reviewed journals, and edit scientific documents. He also consulted for many years on numerous palaeontological impact assessment surveys for petroleum sites, pipelines, bridges, and road construction projects, which sometimes resulted in the recognition of archaeological resources. Len continued to supervise and mentor students in several faculties at the University of Calgary until a few weeks before his death in early August 2013, finally stopping not for lackof interest, but because of physical inability. Len's professional career as a geologist began during his undergraduate program, when he did field work for the British Columbia Department of Mines (1957-58) and later for the Geological Survey of Canada in British Columbia and Quebec. In 1964, Len made his first trip to the Arctic, accompanying Geological Survey of Canada Arctic geologist Hans P. Trettin (Frisch, 2013) to study the Melville Island "tar sands" (Trettin and Hills, 1966), which included a trip to Bathurst Island. Despite what was likely a harsh environment and physically demanding circumstances during the excursion, this first Arctic experience must have been professionally rewarding, because Len returned at least five times from 1968 to 1975 and again in the early 1990s to conduct additional research. These trips included work on Banks, Queen Elizabeth, Meighan, Axel Heiberg, Ellesmere, and Prince Patrick Islands, where he described Devonian to Cretaceous stratigraphic sections within the Sverdrup basin (an important hydrocarbon source area) and collected samples for microfossil analysis. During the early years, microfossil sequences in Arctic bedrock formations were not well known. In addition to stratigraphic work, Len and his students differentiated new microfossil taxa within recognized entities, identifying and naming ~50 new genera, species, and varieties of palynomorph. Not all of Len's research was restricted to microfossils. He, in association with other researchers, also recognized and named several previously unrecognized extinct macroflora: a spruce (Picea banksii Hills & Ogilvie), a walnut (Juglans eocinerea Hills & Sweet), an alder (Paraalnipollenites confusus Hills & Wallace), and a water fern (Azolla geneseana Hills & Weiner) that occurred in the present-day Arctic during a much warmer geological period. Over time, Len's primary attention gradually shifted from the Arctic southward to Yukon and the adjacent mainland portions of the Northwest Territories, into northern British Columbia, and eventually to southern Alberta, although he spent a great deal of time supervising students who conducted their thesis research in the Arctic and contributed to palaeontological studies conducted by others in the region. (Au)
V, B, H, I
Animal migration; Biographies; Geology; Hills, Leonard Vincent, 1933-2013; Palaeoecology; Palaeontology; Palynology; Palynomorphs; Plant succession; Plant taxonomy; Recent epoch; Trumpeter Swans
G0813, G0822, G0821
Alberta; British Columbia; Canadian Arctic
Range constraints for introduced elk in southwest Yukon, Canada / Strong, W.L. Chambers, J.H.S. Jung, T.S.
(Arctic, v. 66, no. 4, Dec. 2013, p. 470-482, ill., maps)
ASTIS record 78907.
Forage availability, snow depths, and winter temperatures were assessed to determine if they might impose range constraints on introduced elk (Cervus elaphus) that voluntarily colonized a 95 km² area of southwest Yukon (Canada) in 1959. Parkland-like vegetation of stunted aspen (Populus tremuloides) and nonforest upland plant communities, which is atypical vegetation for a boreal forest environment, composed 30% of the colonized area. About 95% of the area produced less than 300 kg/ha of forage, which represents poor productivity compared to more southern elk ranges. In the remaining 5%, indigenous graminoid communities produced (average ± SD) 408 ± 131 kg/ha of forage, exceeded only by nonindigenous roadside vegetation with 652 ± 115 kg/ha. Data from radio-collared animals indicated that most elk occurrences (38% year-round) were associated with parkland-like vegetation, and fecal pellet groups were six times as frequent in indigenous graminoid vegetation as in forest vegetation. Late February 2011 snow depths of 41 ± 7 cm, during a year with a below-normal snowfall, suggested a potential for reduced winter access to forage. Meteorological data from 1981 – 2010 indicate that one-third of winter daily minima in the study area were likely lower than -20°C, a threshold below which the metabolism of an elk calf must increase to maintain its body temperature. Each assessed habitat variable was unfavorable to elk compared with other western North American winter ranges, which may have limited the development of a more robust population in the southwestern Yukon. (Au)
I, F, H, E, J
Animal distribution; Animal ecology; Animal food; Animal population; Animal waste products; Atmospheric temperature; Bioclimatology; Biomass; Elk; Forests; Grasses; Plant distribution; Plant-soil relationships; Radio tracking of animals; Salinity; Snow; Soil chemistry; Taiga ecology; Telemetry; Wildlife habitat; Winter ecology
Takhini River region, Yukon
Holocene migration of lodgepole pine (Pinus contorta var. latifolia) in southern Yukon, Canada / Strong, W.L. Hills, L.V.
(Holocene, v. 23, no. 9, Sept. 2013, p.1340-1349, ill., maps)
ASTIS record 77736.
A palynological reconstruction (n = 25 profiles) suggests that the northern extent of lodgepole pine (Pinus contorta var. latifolia Engelmann ex S. Watson) occurred between 59° and 60°N latitude in northwest North America from 10,000 to 7000 calendar years before present (cal. yr BP) prior to entering Yukon. Although specific migration pathways could not be resolved with the available palynological data, mountains along the southern edge of Yukon appear to have diverted lodgepole pine migration through the Carcross and Frances Lake areas in southwest and southeast Yukon, respectively. Migration in the southwest (70 m/yr) was likely confined to lower elevations of the Yukon and Teslin river valleys, with lodgepole pine reaching 61°N ~2000 cal. yr BP. Along the eastern route, migration was channeled through a 15–20 km wide pass in a 200 km mountainous front. After breaching the Liard drainage divide north of Frances Lake ~4000 cal. yr BP, migration progressed northwest (160–220 m/yr) along the Tintina Trench. Lodgepole pine was estimated to have reached its near present-day northern limit (~63°N) ~1790 cal. yr BP, which is ~1290 years earlier than previously thought. This difference in arrival dates is due the use of a >5% rather than a >15% pine pollen content threshold, which appears to correspond with >1% pine tree cover in the landscape. Climatic cooling after 1000 cal. yr BP that caused a population decline at higher elevations is hypothesized to explain the present-day sparse and disjunct distribution of pine across Yukon north of 61°N. (Au)
B, H, J, A, E
Biomass; Databases; Deglaciation; Effects of climate on plants; Forests; Glacial epoch; Laurentide Ice Sheet; Lodgepole pines; Mountains; Palaeobotany; Palaeoecology; Palynology; Plant distribution; Plant ecology; Plant succession; Plants (Biology); Pollen; Radiocarbon dating; Recent epoch; Sedimentation; Spruces; Stratigraphy; Taiga ecology; Temporal variations; Trees
G0811, G0822, G0821, G0812
Alberta; British Columbia; N.W.T.; Yukon
Ecoclimatic zonation of Yukon (Canada) and ecoclinal variation in vegetation / Strong, W.L.
(Arctic, v. 66, no. 1, Mar. 2013, p. 52-67, ill., map)
ASTIS record 77499.
An ecological climatic zonation of Canada’s Yukon Territory (1:1 000 000 scale) was developed from field observations, aerial photographs, ecological literature, forest cover maps, and regression models. The 11 recognized ecoclimatic regions include Arctic (1), Subarctic (1), Alpine (4), Subalpine (1), and Boreal (4) entities. Region differentiation was based on vegetation thought to reflect climate more strongly than soil or topographic conditions. Sites with such vegetation are referred to as “reference sites.” The concept of a reference site was used because conventional zonal site criteria are difficult to apply in mountainous terrain and at high latitudes, where permafrost is an integral environmental component. Alpine regions were differentiated from other ecoclimatic regions through regression analysis of tree line elevations (n = 188, >= 76% explained variance). An ecocline of vegetation types for each region was developed on the basis of ecological moisture regimes. The climatic distinctiveness of regions was tested by statistical comparison and ordination of monthly temperature and precipitation data (1984 – 2007) from 26 and 24 meteorological recording locations, respectively. Significant differences (p < 0.001) between regions were found in temperature and most precipitation variables. A latitudinal gradient was evident among ordinated meteorological recording locations. Non-forest vegetation represents at least 70 – 75% of Yukon. Forests with closed and semi-closed canopies occurred primarily south of 64° N latitude at low elevations. (Au)
H, E, J, A, S
Alpine treeline; Alpine tundra ecology; Atmospheric temperature; Bioclimatology; Effects of climate on plants; Forest ecology; Land classification; Mapping; Maps; Meteorology; Plant cover; Plant distribution; Plant succession; Plant-soil relationships; Plant-water relationships; Plants (Biology); Precipitation (Meteorology); Seasonal variations; Taiga ecology; Temporal variations; Trees; Tundra ecology; Weather stations
Stand-level attributes of snowshoe hare (Lepus americanus) habitat in a post-fire trembling aspen (Populus tremuloides) chronosequence in central Yukon / Strong, W.L. Jung, T.S.
(Canadian field-naturalist, v.126, no. 4, 2012, p. 295-305, ill.)
Issue includes a video supplement.
ASTIS record 78012.
Large-scale fires are anticipated to increase in frequency in the boreal forest under global climate warming scenarios. To understand concomitant responses by wildlife to fire-induced habitat changes, fecal pellet counts were used to assess Snowshoe Hare (Lepus americanus) use of four age-classes of boreal forest after fire in central Yukon, Canada. Use of stands across a chronosequence of 8-177 years was bimodal. Post-fire Trembling Aspen (Populus tremuloides) stands <=20 years old had greater densities of Snowshoe Hare pellets (median 156 pellets/dam²) than Trembling Aspen stands 21-70 years old, mixedwood stands 71-120 years old (<17 pellets/dam²), or Western White Spruce (Picea albertiana)-dominated stands 121-170 years old (71 pellets/dam²). Forty stand-level compositional and structural variables were assessed as possible predictors of Snowshoe Hare pellet densities. Multidimensional scaling was used to identify variables (n = 10) that were most strongly related to pellet densities and was followed by multiple regression. Canopy cover of Trembling Aspen <50 cm tall and Western White Spruce <=1 m tall, and deadfall depth, in combination, were the best estimators of Snowshoe Hare pellet densities among stands in the chronosequence (P<0.001, 64.5% variance explained). Although Trembling Aspen <50 cm tall explained the most variance, its canopy cover did not exceed 10%. More Trembling Aspen cover <50 cm tall and greater deadfall depths within the chronosequence were associated with stands <=20 years old. Peak Snowshoe Hare use occurred in early (<=20 years old) rather than mid-successional (21-120 years old) stands, contrary to use patterns reported elsewhere. The lack of tall understory shrubs likely limited the use of mid-successional stands. (Au)
I, H, J
Age; Animal distribution; Animal ecology; Animal population; Animal waste products; Fire ecology; Forest fires; Hares; Measurement; Plant cover; Plant distribution; Plant growth; Plant succession; Poplars; Shrubs; White spruces; Wildlife habitat
Little Fox Lakes region, Yukon; Pelly Crossing region, Yukon
Tree canopy effects on understory species abundance in high-latitude Populus tremuloides stands, Yukon, Canada / Strong, W.L.
(Community ecology : CE, v. 12, no. 1, June 2011, p. 89-98, ill.)
ASTIS record 75916.
To determine the effect of tree canopy composition on understory species abundance, three-hundred 2 m × 2-m quadrats from 30 high-latitude boreal forest stands were sampled. In addition, all trees within a 3 m radius of each quadrat center and >=1 m tall were also measured for height, basal diameter, and canopy width (n = 3130). Stands were 33-178 years old, with canopies of Populus tremuloides (trembling aspen) and Picea spp. (spruce) in varying proportions. Arctostaphylos uva-ursi, Calamagrostis purpurascens, Chamerion angustifolium, Shepherdia canadensis, and Hylocomium splendens were the most frequent understory species among quadrats. Scatterplots of P. tremuloides and individual vascular understory species cover values lacked bivariate trends, but the understory species had distinct maxima that ranged from 20 to 90%. A moderately strong correlation (r = 0.52, P <0.001) occurred between P. tremuloides canopy and total vascular understory plant covers, but weak individual species correlations (r = 0.22-0.35, P <0.001), suggested understory species variation was primarily determined by factors other than the amount of immediately overhead canopy cover. Canonical correlation analysis (R = 0.82, P <0.001) indicated that greater vascular understory plant cover occurred when forest stands consisted of P. tremuloides with large canopies and large basal diameters, and lacked Picea. Maximum cover for vascular understory species declined when Picea cover exceeded 7-10%. In combination, P. tremuloides stem densities or a metric based on summed canopy areas converted to a diameter value (canopy-area diameter), and the vertical silhouette area of Picea canopies (canopy profile area), as independent linear regression variables, explained ~79% of the variance in total vascular understory plant cover. Several Picea basal area-derived metrics were strongly and positively associated with increasing H. splendens cover, but canopy profile area was more informative. Populus tremuloides canopy area and Picea canopy profile area, as indicators of shading, may be important determinants of vascular understory vegetation abundance in stands where solar radiation enters at angles of up to 52° during the summer. (Au)
H, E, J
Light; Measurement; Mosses; Plant anatomy; Plant cover; Plant distribution; Plant succession; Poplars; Shrubs; Solar radiation; Spruces; Taiga ecology
Braeburn Lake region, Yukon; Pelly Crossing region, Yukon
Lateral Picea shadow effects on Populus tremuloides understory vegetation in central Yukon, Canada / Strong, W.L.
(Forest ecology and management, v.261, no. 11, 1 June 2011, p.1866-1875, ill.)
ASTIS record 73749.
Laterally cast Picea albertiana ssp. albertiana (western white spruce) shadows were analyzed to determine their effect on understory plant abundance in two high-latitude (62.7 N) boreal Populus tremuloides (trembling aspen) forest stands. Each stand had a uniform and continuous overstory, and occurred on level to gently sloping terrain with a submesic moisture regime. Picea >1 m tall had <20% cover in each stand. with few trees equaling or exceeding the height of the P. tremuloides canopy. Understory vegetation composition was sampled in 30-m x 30-m plots that were subdivided into 1.5-m x 1.5-m cells (200 sampled per plot). Picea shadow locations and their areal extent were determined on an hourly basis (7:00-19:00 h Pacific Standard Time on the summer solstice) for individual plot cells using silhouette diagrams constructed from tree height and canopy-related data (n = 140 trees). Shadow data were analyzed using the lower- (QL, minimum to first-quartile values) and upper-most (Qu, third-quartile values to maximum) portions of each species' abundance distribution. Kruskal-Wallis tests (P <0.001) indicated that greater Arctostaphylos uva-ursi (bearberry) abundance occurred where shadow cover was the least (daytime average ~24%); Whereas Geocaulon Iividum (toadflax), Hylocomium splendens (stairstep moss), and Shepherdia canadensis (buffaloberry) incurred the most shadows (>34% cover) and had the shortest periods of continuous (<6 h) sunlight exposure with <30% Picea shadow cover. Hylocomium and Shepherdia also occurred nearer Picea than Arctostaphylos. Rosa acicularis (wild rose), Linnaea borealis (twinflower), Vaccinium vitis-idaea (bog cranberry), Chamerion angustifolium (fireweed), and Calamagrostis purpurascens (purple reedgrass) incurred intermediate amounts of shadow. Differences in hourly shadow abundance values (QU minus QL plot cells) were greatest for Arcfostaphylos (-14.7%) and Rosa (-10.8%), but H. splendens (+3.8%) and Geocaulon had the least (+1.7%). Greater Hylocomium and Shepherdia abundance occurred in plot cells with more shadow indicating a tolerance for shade, which was contrary to the other species. These differences may represent examples of niche partitioning based on relative light availability. Individual understory species based on percent cover and species richness were more strongly correlated with Picea shadow cover than canopy cover. As a direct representation of impeded light transmittance, assessment of lateral tree shadows may represent a viable approach for investigating within stand compositional variation and temporal change among forest understory species, when a distinct physiognomic difference occurs between seral and climax overstory species. (Au)
H, J, E, N, C
Diurnal variations; Effects of climate on plants; Forestry; Growing season; Light; Measurement; Photosynthesis; Plant cover; Plant distribution; Plant growth; Plant succession; Plants (Biology); Poplars; Shrubs; Solar radiation; Stems; Taiga ecology; White spruces; Willows
Pelly Crossing region, Yukon; Von Wilczek Lakes region, Yukon
Habitat use and ecologically sustainable carrying capacity for elk (Cervus elaphus) in the Takhini Valley, Yukon / Chambers, J.H.S. Strong, W.L. [Supervisor]
Calgary, Alta. : University of Calgary, 2010.
xii, 122 p. : ill., maps ; 28 cm.
Thesis (M.E.Des.) - University of Calgary, Faculty of Environmental Design, Calgary, Alta., 2010.
ASTIS record 75935.
Population growth of a (re)introduced elk (Cervus elaphus) herd (n = 144) in the Takhini Valley, southwest Yukon, has increased the need to determine an ecologically sustainable carrying capacity for the primary range. Elk telemetry data, aerial photographs, and contour maps were used to define the study area (95 km²), which represented 56% of the total local range used in 2007 and 2008. Plot sampling, plant community classification, and air-photo mapping were used to determine the composition and areal extent of vegetation types, each of which was used to evaluate forage availability. Seven treed and five nontreed types were recognized, with treed forest types representing 68% of the area. Nontreed vegetation produced more forage (279-652 kg/ha) than all treed types, except Populus tremuloides/Rosa acicularis-Arctostaphylos uva-ursi vegetation (438 kg/ha), which was the second-most common type in study area (15% of area). No significant differences (P <0.05) were found between crude protein amounts among vegetation types, though graminoids were lower in crude protein than either forbs or shrubs (P <0.001). Different carrying capacity scenarios were developed based on cumulative assumptions. These included considerations of forage quantity, availability and preference, horse (Equus ferus caballus) and mule deer (Odocoileus hemionus) requirements, and diet similarities with elk. Winter was the most limiting season because forage was senesced. The most conservative scenario included ecologically sustainable safe-use factors, and resulted in an estimated winter carrying capacity of 72-144 elk for the study area. The assessment of carrying capacity was most sensitive to browse consumption and competition with horses. These factors require further investigation to refine the estimated ecologically sustainable carrying capacity. (Au)
H, I, J, L
Aerial photography; Animal behaviour; Animal deterrents; Animal distribution; Animal food; Animal health; Animal population; Animal waste products; Biomass; Deer; Effects monitoring; Elk; Grazing; Growing season; Horses; Mapping; Mathematical models; Plant cover; Plant taxonomy; Plants (Biology); Proteins; Radio tracking of animals; Roads; Safety; Seasonal variations; Taiga ecology; Telemetry; Theses; Trees; Wildlife habitat; Wildlife management
Alaska Highway region, Yukon; Takhini River region, Yukon
Pinus contorta var. yukonensis var. nov. (Pinaceae) from south-central Yukon, Canada / Strong, W.L.
(Nordic journal of botany, v. 28, no. 4, Aug. 2010, p. 448-452, ill.)
ASTIS record 71262.
Pinus contorta Douglas ex Loudon var. yukonensis W. L. Strong (Yukon pine), a new variety, is described from south-central Yukon, Canada. It is a stout tree with long lower branches, often with paired lower and forked upper stems, and weakly platy to smooth gray bark on the lower stem, when < 70 years old; with bark on the lower stem becoming furrowed and platy on older trees. This contrasts with the narrow columnar habit, simple stem, and scaly bark associated with the more common inland var. latifolia. In several respects, var. yukonensis is more similar to var. contorta (a coastal variant), although occupying a different ecological regime and spatially disjunct (i.e., a high latitude and high elevation variant). Variety yukonensis may represent the taxon alluded to in previous leaf oil terpene and genetic studies, and a possible Beringian survivor. (Au)
Biochemistry; Conifers; Deglaciation; Evolution (Biology); Genetics; Glacial epoch; Lodgepole pines; Plant anatomy; Plant collections; Plant distribution; Plant growth; Plant physiology; Plant taxonomy; Refugia; Revegetation; Seeds; Taiga ecology
British Columbia, Northern; Whitehorse region, Yukon
Populus tremuloides Michx. postfire stand dynamics in the northern boreal-cordilleran ecoclimatic region of central Yukon Territory, Canada / Strong, W.L.
(Forest ecology and management, v.258, no. 7, 15 Sept. 2009, p.1110-1120, ill., maps)
ASTIS record 68433.
Postfire vegetation development among 8-185-year-old stand was assessed based on 100 relevés from the northern boreal-cordilleran ecoclimatic region (61-63°N) in the central Yukon Territory, Canada. Vegetation sampling included only stands thought to have originated from postfire Populus tremuloides Michx. regeneration that occurred on well drained and low gradient sites. Seven vegetation types were recognized based on cluster analysis and Kruskal-Wallis testing. Relevé ordination using Detrended Correspondence Analysis (70% explained variance) indicated six of the vegetation types represented a secondary successional chronosequence, based on their juxtaposition and a strong correlation of the primary axis with stand age (r = 0.89, P < 0.001). No correlation (P > 0.05) occurred between stand location and age. The youngest vegetation (8-11 years) had a moderate cover of P. tremuloides and Salix spp. up to 5 m tall, with a ground cover of Ceratodon purpureus (Hedw.) Brid. and Bryum caespiticium Hedw. This vegetation was expected to result in P. tremuloides, mixed P. tremuloides and Picea glauca (Moench) Voss, and P. glauca/Hylocomium splendens forest stands with increasing age, respectively. P. tremuloides//Calamagrostis purpurascens - Arctostaphylos uva-ursi stands formed the mid-seral vegetation. Along the chronosequence, total tree, P. tremuloides, shrub, and herb cover peaked 50-70 years after stand initiation; P. glauca cover, total and nonvascular species richness, and dominance concentration gradually increased (P < 0.001); vascular plant richness decreased; bryophytes had a U-shaped abundance pattern; and total plant cover was constant through time (125%). Richness totalled 113 species with averages of 13-18 per relevé. Coarse woody debris was most abundant (maxima 100-223 m³/ha) during the first 20 years of stand development then declined to <50 m³/ha. Successionally, a stem exclusion stage occurred (years 8-18), but with a delayed peak of 2-4 years and reduced densities (1.47 stems/m²) relative to southern boreal stands. No understory suppression, and therefore, no reinitiation stage occurred. Following stem exclusion, an accelerated canopy transition stage occurred relative to southern boreal forests due to early establishment rather than better height-growth rate of P. glauca relative to P. tremuloides. P. glauca tended to equal the cover of P. tremuloides 95-100 years after stand initiation. The oldest vegetation type in the chronosequence more closely resembled old-growth than a gap dynamic stage of development, possibly because of its youthful average age of 125 years. A modification was proposed for the canopy transition stage (Chen-Popadiouk stand development model) to account for the “forced” replacement of P. tremuloides by P. glauca. Differences in stand development were attributed to the cold northern climate. (Au)
H, J, E, N, C
Dendrochronology; Effects of climate on plants; Fire ecology; Forest fires; Forestry; Plant cover; Plant distribution; Plant growth; Plant succession; Plant-soil relationships; Plants (Biology); Poplars; Shrubs; Stems; Taiga ecology; White spruces; Willows
Yukon Plateau, Yukon
Taxonomy and origin of present-day morphometric variation in Picea glauca (×engelmannii) seed-cone scales in North America / Strong, W.L. Hills, L.V.
(Canadian journal of botany, v. 84, no. 7, July 2006, p.1129-1141)
ASTIS record 66079.
White spruce (Picea glauca (Moench) Voss) and Engelmann spruce (Picea engelmannii Parry ex Engelm.) seed-cones from 676 sites in Canada and the northern United States were analyzed to determine the degree and spatial extent of interspecific hybridization. Fifteen cone-scale variables were analyzed, with percent free-scale and scale shape considered best for differentiating these taxa. The results show that putative Engelmann spruce and their hybrids occur mostly in the vicinity of the Rocky Mountains. Putative white spruce occurs across Canada east of the Rocky Mountains, whereas white × Engelmann hybrids occur eastward to Manitoba and northward to 68° latitude in northwest Canada. To explain the occurrence of the latter taxon hundreds of kilometres from an Engelmann spruce pollen source, it is hypothesized that palaeohybridization occurred during the Wisconsinan glacial period, probably in the southern Montana - Wyoming - Black Hills (South Dakota) region, with the resulting hybrids spreading north and northeastward into interior Canada following the retreat of the Laurentide glacier. White and Engelmann spruce have morphologically distinct cone-scales, whereas their hybrids have intermediate characteristics. An emended species (Picea albertiana) and two subspecies (P. albertiana subsp. albertiana and P. albertiana subsp. ogilviei) are proposed to account for morphological intermediates between the parent species. (Au)
H, B, A
Evolution (Biology); Glaciation; Palaeobotany; Palaeoecology; Palynology; Plant anatomy; Plant distribution; Plant taxonomy; Pleistocene epoch; Refugia; Revegetation; Seeds; Spruces
G0811, G06, G0821, G0822
Alaska; Alberta; British Columbia; Canada; Montana; Wyoming; Yukon
Late-glacial and Holocene palaeovegetation zonal reconstruction for central and north-central North America / Strong, W.L. Hills, L.V.
(Journal of biogeography, v. 32, no. 6, June 2005, p.1043-1062, ill., maps)
Appendix: List of pollen stratigraphy sites and their literature citation, and associated data.
ASTIS record 75933.
Aim: The purpose of this study is to develop palaeovegetation zonation models for central and north-central North America, based on late-Quaternary and Holocene pollen stratigraphic data (n = 246 sites). A secondary purpose was to evaluate an hypothesis (Strong & Hills, 2003) to explain the disjunct distribution of species in western Alberta. Location: Hudson Bay-Lake Michigan to the Rocky Mountains region, north of 36° N to the Arctic Ocean (c. 70° N). Methods: Pollen profiles spanning 40 years of palaeoecological research in North America were extracted from published and unpublished archival sources. Individual profiles were subdivided into 1000-year increments based on the assumption of a constant sedimentation rate between stratigraphic dates (e.g. surface sediments, radiocarbon 14C dates, tephra layers). The pollen composition among profiles was standardized to 54 commonly recognized taxa, with percentage composition within each stratigraphic sample prorated to 100% prior to analysis. Near-surface sediments from these profiles were included as analogues of modern vegetation. Cluster analysis was used as a guide to the classification of 2356 temporal stratigraphic samples, which resulted in the recognition of 16 pollen groups. These groups were summarized in terms of their pollen composition, mapped, and used in combination with terrain information and an ecological knowledge of the study area to construct six physiognomically-based palaeovegetation zonation models at 2000-year intervals from 14,000 to 4000 yr bp (radiocarbon years before present). Results: The 14,000 yr bp model placed Boreal and Cordilleran Forests proximal to the southern glacial front, whereas Arctic tundra dominated the Yukon Territory-Alaska ice-free zone. Pollen and macrofossil evidence suggests that this Boreal Forest zone contained a mixture of coniferous and deciduous tree species. Grassland was postulated immediately south of the forest zone, with its northern extreme near 49° Nlatitude in the Alberta-Montana border area. Separation of the Laurentide and Cordilleran glacial fronts about 12,000 yr bp initiated the northward advance of Boreal Forests into western Canada. By the end of the Hypsithermal at about 6000 yr bp, Boreal Forests occurred near the Arctic Ocean, and Grassland and Aspen Parkland zones may have extended to 54° N and 59° N latitude in Alberta, respectively. Between 6000 and 4000 yr bp, a 5° and 1° latitudinal southward shift of the northern Boreal Forest and Grassland/Aspen Parkland boundaries occurred, respectively, near their contemporary positions with corresponding expansions of the Subarctic and Arctic zones. Modern Canadian Cordilleran Forests along the eastern slopes of the Rocky Mountains were interpreted as originating from the north-central Montana-south-western Alberta area. Jack pine (Pinus banksiana Lamb.), a common Boreal Forest species, appears to have entered central Canada via the north side of Lake Superior after 11,000 yr bp. Main conclusions: Modern vegetation in central Canada evolved from biomes located in the northern USA during the late-Quaternary. The Boreal Forest biome contained the same arboreal taxa as the modern vegetation, except it lacked jack pine. The proposed regional palaeovegetation models support the hypothesis of Strong & Hills (2003), but new independent palaeoecological data will be needed for a proper evaluation. (Au)
B, H, J, A
Biomass; Conifers; Databases; Deglaciation; Forests; Glacial epoch; Grasses; Laurentide Ice Sheet; Palaeobotany; Palaeoecology; Palynology; Plant distribution; Plant succession; Plants (Biology); Pollen; Poplars; Radiocarbon dating; Recent epoch; Sedimentation; Stratigraphy; Taiga ecology; Temporal variations; Trees; Tundra ecology
G0811, G081, G0822, G0823, G0824, G0825, G06
Alaska; Alberta; Canada; N.W.T.; North America; Ontario; Prairie Provinces; Rocky Mountains, Alberta; Yukon
Lodgepole pine/Labrador tea type communities of western Canada / Strong, W.L.
(Canadian journal of botany, v. 80, no. 2, Feb. 2002, p. 151-165, ill., 1 map)
ASTIS record 51817.
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. (Au)
Black spruces; Forest ecology; Ledum; Lodgepole pines; Mosses; Plant distribution; Plant succession; Plant taxonomy; Plant-water relationships; Plants (Biology); Wildlife management
G0811, G0822, G0821
Alberta; British Columbia, Northern; Rocky Mountains, Alberta; Rocky Mountains, British Columbia; Yukon
Rooting depths and successional development of selected boreal forest communities / Strong, W.L. La Roi, G.H.
(Canadian journal of forest research, v. 13, no. 4, Aug. 1983, p. 577-588, figures, tables)
(Contribution - Boreal Institute for Northern Studies, no. 121)
ASTIS record 13703.
The root density and depth patterns of four boreal forest age sequences were analyzed for successional trends. Rooting depths increased with age on sandy substrates which supported aspen (Populus tremuloides Michx.) and jack pine (Pinus banksiana Lamb.) communities. Rooting depth did not change in an aspen series on fine-textured substrates or in a black spruce (Picea mariana (Mill.) BSP) series growing on organic substrates. Plant communities growing on mineral soils showed a decrease in near-surface root densities and understory vascular plant cover with increasing age. Maximum rooting was deepest on sandy substrates and shallowest on organic deposits. Roots in all stands were concentrated near the ground surface. ... (Au)
Forest ecology; Plant cover; Roots
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