Boreal Forest Of Saskatchewan Research Articles

Comparison of tree-ring and eddy-covariance derived annual ecosystem production estimates for jack pine and trembling aspen forests in Saskatchewan, Canada

Reliable projections of future carbon (C) dynamics are essential to resource management decision making under a changing climate. Additional corroborative data may reduce uncertainty in C flux estimates. Here we use a tree-ring based hybrid biometric modelling approach to estimate annual ecosystem production at jack pine (Pinus banksiana) and aspen (Populus tremuloides and Populus balsamifera) plots co-located with eddy-covariance installations in the boreal forest of Saskatchewan, Canada for a 28 year (1985 to 2012) period. Correspondence between tree-ring and eddy-covariance derived estimates was better for jack pine (14-year overlap, 1999 to 2012) than aspen (16-year overlap, 1997 to 2012), and better for some C fluxes than others. In particular, tree-ring estimates of annual and cumulative net ecosystem production were larger than eddy-covariance derived estimates for the overlapping period. Allometric equations, belowground production, and biomass turnover could neither be confirmed nor ruled out as causes of discrepancy, but a lower stand density and higher carbon use efficiency would together reduce observed differences for aspen. Tree-ring based estimates of biomass increment or net primary production showed good temporal correspondences with both current and previous year eddy-covariance analogues, and net and gross primary production. Similar comparisons for net ecosystem production and heterotrophic respiration had mixed results. This study improves on previous work by comparing independent estimates of the same fluxes quantities and demonstrates the value of tree-ring data for evaluating C flux estimates.

Controls on evapotranspiration from jack pine forests in the Boreal Plains Ecozone

AbstractThe exchanges of water, energy and carbon between the land surface and the atmosphere are tightly coupled, so that errors in simulating evapotranspiration lead to errors in simulating both the water and carbon balances. Areas with seasonally frozen soils present a particular challenge due to the snowmelt‐dominated hydrology and the impact of soil freezing on the soil hydraulic properties and plant root water uptake. Land surface schemes that have been applied in high latitudes often have reported problems with simulating the snowpack and runoff. Models applied at the Boreal Ecosystem Research and Monitoring Sites in central Saskatchewan have consistently over‐predicted evapotranspiration as compared with flux tower estimates. We assessed the performance of two Canadian land surface schemes (CLASS and CLASS‐CTEM) for simulating point‐scale evapotranspiration at an instrumented jack pine sandy upland site in the southern edge of the boreal forest in Saskatchewan, Canada. Consistent with past reported results, these models over‐predicted evapotranspiration, as compared with flux tower observations, but only in the spring period. Looking systematically at soil properties and vegetation characteristics, we found that the dominant control on evapotranspiration within these models was the canopy conductance. However, the problem of excessive spring ET could not be solved satisfactorily by changing the soil or vegetation parameters. The model overestimation of spring ET coincided with the overestimation of spring soil liquid water content. Improved algorithms for the infiltration of snowmelt into frozen soils and plant‐water uptake during the snowmelt and soil thaw periods may be key to addressing the biases in spring ET.

Using experimentation to understand the 10-year snowshoe hare cycle in the boreal forest of North America.

Population cycles have long fascinated ecologists from the time of Charles Elton in the 1920s. The discovery of large population fluctuations in undisturbed ecosystems challenged the idea that pristine nature was in a state of balance. The 10-year cycle of snowshoe hares (Lepus americanus Erxleben) across the boreal forests of Canada and Alaska is a classic cycle, recognized by fur traders for more than 300years. Since the 1930s, ecologists have investigated the mechanisms that might cause these cycles. Proposed causal mechanisms have varied from sunspots to food supplies, parasites, diseases, predation and social behaviour. Both the birth rate and the death rate change dramatically over the cycle. Social behaviour was eliminated as a possible cause because snowshoe hares are not territorial and do not commit infanticide. Since the 1960s, large-scale manipulative experiments have been used to discover the major limiting factors. Food supply and predation quickly became recognized as potential key factors causing the cycle. Experiments adding food and restricting predator access to field populations have been decisive in pinpointing predation as the key mechanism causing these fluctuations. The immediate cause of death of most snowshoe hares is predation by a variety of predators, including the Canada lynx (Lynx canadensis Kerr). The collapse in the reproductive rate is not due to food shortage as was originally thought, but is a result of chronic stress from predator chases. Five major issues remain unresolved. First, what is the nature of the predator-induced memory that results in the prolonged low phase of the cycle? Second, why do hare cycles form a travelling wave, starting in the centre of the boreal forest in Saskatchewan and travelling across western Canada and Alaska? Third, why does the amplitude of the cycle vary greatly from one cycle to the next in the same area? Fourth, do the same mechanisms of population limitation apply to snowshoe hares in eastern North American or in similar ecosystems across Siberia? Finally, what effect will climatic warming have on all the above issues? The answers to these questions remain for future generations of biologists to determine.

Changes in population size and genetic diversity of a raptor species occurring in the boreal forest of Saskatchewan

The American Kestrel (Falco sparverius) is one of North America’s most common raptors. However, recent data reveals a decrease in the number of individuals at both migration and nesting sites, sparking concern that the North American subspecies (F. s. sparverius) may be in decline. In this study we used long-term monitoring data to examine whether a decrease observed in a study population of breeding F. s. sparverius in the boreal forests of Saskatchewan over the past two decades coincided with a loss in genetic diversity. While count data collected showed a significant decline in occupancy of nest boxes, genetic summary statistics and Bayesian modeling methods revealed evidence for a population expansion occurring in the decades directly before the start of the nest box program. The initial contradictory nature of the count and genetic data was resolved when the results examined together revealed that the detected changes in population size coincided with changes in land-use around the study site, suggesting that the shifts in numbers of F. s. sparverius may represent the subspecies’ ability to respond rapidly to changes in suitable habitat. This study highlights the importance of integrating both genetic and population data into studies that examine changes in population size, especially for a migratory species where the connections between breeding sites and landscape changes may be fluid and rapid.

Quantifying the effects of climate change and harvesting on carbon dynamics of boreal aspen and jack pine forests using the TRIPLEX-Management model

A model that accurately evaluates changes in forest productivity and carbon (C) stocks in response to climate change and forest management will permit us to assess the impact of global changes. The goal of this study is to forecast potential effects of climate change and clearcuts on C dynamics of boreal trembling aspen (Populus tremuloides Michx.) and jack pine (Pinus banksiana Lamb.) forests near the southern edge of the boreal forest in Saskatchewan, Canada. We validated the TRIPLEX-Management model against eddy covariance measurements, C stocks, and growth data. Constant climate (repeated measurements) and four climate change scenarios (IPCC SRES A2 and B1) generated from Coupled Global Climate Model (CGCM3.1) and the Model for Interdisciplinary Research on Climate (MIROC3.2), respectively, were used in scenario simulations. Clearcuts were assumed to occur in 2010 and 2055 for each forest type. Normalized root mean square error (NRMSE) between simulated and observed variables including C fluxes, C stocks (e.g., aboveground biomass C and soil organic C), and stand characteristics such as mean DBH (diameter at breast height) and stand density ranged from 11% to 22%. The Willmott index of agreement (d) between simulated and observed variables ranged from 0.95 to 1.00 with the exception of net ecosystem productivity (NEP, d=0.88). The model tended to project higher NEP and C stocks under warm but wet climate (CGCM3.1 A2 and B1) vs. warm and dry climate (MIROC3.2 A2 and B1), and slightly higher NEP under IPCC SERS B1 vs. A2, for both forest types. When clearcuts occurred, the model projected negative NEP (C losses) during the seven to 11years following clearcuts for both forest types under the five climate scenarios. Regrowth of the forest generally led to greater C accumulation when clearcuts occurred in 2010 than in 2055. Overall, the TRIPLEX-Management model is capable of simulating C dynamics for aspen and jack pine forests as well as their responses to drought and harvesting disturbances. Climate change at the southern edge of the boreal forest in North America may enhance the C sequestration rate if there are no severe drought events. A longer rotation age (>90years), may therefore, not be necessary in southern boreal forests in order to increase C sequestration.

Gastrointestinal Helminth Parasites of Double-Crested Cormorants (Phalacrocorax auritus) at Four Sites in Saskatchewan, Canada

Abstract We examined the gastrointestinal parasite fauna of adult double-crested cormorants from breeding colonies on 4 very different lakes spanning a major ecotone from prairie to boreal forest in Saskatchewan, Canada. Our objectives were to document regional parasite fauna and identify potential differences based on breeding colony location. Eight species of helminths were identified from the stomach and small intestinal contents of 92 cormorants collected during the summers of 2006 and 2007: 2 nematodes—Syncuaria squamata and Contracaecum cf. rudolphii; 2 trematodes—Ribeiroia ondatrae and Drepanocephalus spathans; and 4 cestodes—Ligula colymbi, Schistocephalus solidus, Paradilepis caballeroi, and Paradilepis sp. Our results include an apparently undescribed species of Paradilepis, new host records for L. colymbi, S. solidus, and R. ondatrae, and new geographic records for S. squamata, D. spathans, and P. caballeroi in cormorants of western Canada. Anisakids, C. cf. rudolphii, were present in total sto...

Can a satellite-derived estimate of the fraction of PAR absorbed by chlorophyll (FAPAR chl) improve predictions of light-use efficiency and ecosystem photosynthesis for a boreal aspen forest?

We used daily MODerate resolution Imaging Spectroradiometer (MODIS) imagery obtained over a five-year period to analyze the seasonal and inter-annual variability of the fraction of absorbed photosynthetically active radiation (FAPAR) and photosynthetic light use efficiency (LUE) for the Southern Old Aspen (SOA) flux tower site located near the southern limit of the boreal forest in Saskatchewan, Canada. To obtain the spectral characteristics of a standardized land area to compare with tower measurements, we scaled up the nominal 500 m MODIS products to a 2.5 km × 2.5 km area (5 × 5 MODIS 500 m grid cells). We then used the scaled-up MODIS products in a coupled canopy-leaf radiative transfer model, PROSAIL-2, to estimate the fraction of absorbed photosynthetically active radiation (APAR) by the part of the canopy dominated by chlorophyll (FAPAR chl) versus that by the whole canopy (FAPAR canopy). Using the additional information provided by flux tower-based measurements of gross ecosystem production (GEP) and incident PAR, we determined 90-minute averages for APAR and LUE (slope of GEP:APAR) for both the physiologically active foliage (APAR chl, LUE chl) and for the entire canopy (APAR canopy, LUE canopy). The flux tower measurements of GEP were strongly related to the MODIS-derived estimates of APAR chl ( r 2 = 0.78) but only weakly related to APAR canopy ( r 2 = 0.33). Gross LUE between 2001 and 2005 for LUE chl was 0.0241 µmol C µmol − 1 PPFD whereas LUE canopy was 36% lower. Time series of the 5-year normalized difference vegetation index (NDVI) were used to estimate the average length of the core growing season as days of year 152–259. Inter-annual variability in the core growing season LUE chl (µmol C µmol − 1 PPFD) ranged from 0.0225 in 2003 to 0.0310 in 2004. The five-year time series of LUE chl corresponded well with both the seasonal phase and amplitude of LUE from the tower measurements but this was not the case for LUE canopy. We conclude that LUE chl derived from MODIS observations could provide a more physiologically realistic parameter than the more commonly used LUE canopy as an input to large-scale photosynthesis models.

Regional mapping of gross light-use efficiency using MODIS spectral indices

Direct estimation of photosynthetic light-use efficiency (LUE) from space would be of significant benefit to LUE-based models which use inputs from remote sensing to estimate terrestrial productivity. The Photochemical Reflectance Index (PRI) has shown promise in tracking LUE at the leaf- to small canopy levels, but its use at regional to global scales still remains a challenge. In this study, we used different formulations of PRI calculated from the MODIS ocean band centered at 531 nm and a set of alternative reference bands at 488, 551, and 678 nm to explore the relationship between PRI and LUE where LUE was measured at eight eddy covariance flux towers located in the boreal forest of Saskatchewan, Canada. The magnitude and variability of LUE was significantly lower at the times when useful MODIS ocean band images were available (i.e. around midday under clear-sky conditions) relative to the rest of the growing season. PRI 678 (reference band at 678 nm) showed the strongest relationship ( r 2 = 0.70) with LUE 90a (i.e. 90-minute mean LUE calculated using Absorbed Photosynthetically Active Radiation, APAR), but only when all sites were combined. Overall, the relationships between the MODIS PRIs and LUE 90a were always stronger for observations closer to the backscatter direction and there were no significant differences in the strength of the correlations whether LUE was calculated based on incident PAR or on APAR. Predictions of ecosystem photosynthesis at the time of the MODIS overpasses were significantly improved by multiplying either PAR or APAR by MODIS PRI ( r 2 improved from 0.09 to 0.44 and 0.54 depending on the PRI formulation). We used our PRI-LUE model to create a regional LUE 90a map for the three cover types covering 47,500 km 2 around the flux sites. The MODIS PRI-derived LUE 90a map appeared to capture more realistic spatial heterogeneity of LUE across the landscape compared to a daily LUE map derived using the look-up table in the MODIS GPP (MOD17) algorithm. While our LUE map is only a snapshot of minimum regional LUE 90a values, with appropriate gap-filling methods it could be used to improve regional-scale monitoring of GPP. Moreover, the strong relationship between midday and daily LUE on clear days ( r 2 = 0.93) indicates that instantaneous MODIS observations of LUE 90a could be used to estimate daily LUE. Finally, pixel shadow fraction from the 5-Scale geometric-optical model was closely related to both MODIS PRI and tower-derived LUE suggesting that differences in stand leaf area and in diffuse illumination among flux sites play a role in the relationship we observed between LUE and MODIS PRI.

Quantifying Harvesting Impacts using Soil Compaction and Disturbance Regimes at a Landscape Scale

Several indicators have been identified for the conservation and maintenance of soil criterion in the Montreal Protocol. The objective of this study was to use soil compaction and disturbance measures to determine harvesting impacts at a landscape scale in the boreal forest of Saskatchewan. Forest harvesting impacts were studied pre and postharvest for five harvested sites by (i) sampling soil bulk density (Db) at prescribed grid‐points, and (ii) measuring soil disturbance regimes on two 30‐m transects at each grid‐point. Mean soil Db in the harvested area increased significantly (8–11%) from pre to postharvest conditions for the two winter‐harvested sites at both the 10‐ and 20‐cm depths, while two of the three summer harvested sites also showed significant Db increases (7–15%) at the 10‐cm depth. Combining all five sites, showed that after harvest 32% of all the grid‐points had an increased Db of >15%. Mean soil Db at a 10‐cm depth for roadways and landings was significantly higher (8–14%) than postharvest Db for postharvest levels at four of the five harvested sites. Surface soil disturbance regimes were higher for the summer‐harvested sites than that for the winter‐harvested sites. Landscape position showed no significant differences in Db between the shoulder, backslope, and footslope positions; however, within each landscape position, significant differences in Db were found between pre and postharvest conditions. Soil Db and soil disturbance regimes measured on a grid basis provided a simple, but reliable method for monitoring soil compaction and disturbance effects from harvesting at a landscape scale.

Accurately ageing trees and examining their height‐growth rates: implications for interpreting forest dynamics

Summary We examined the validity of classifying tree species as early, mid‐, or late‐successional based on age and height‐growth rates, by comparing the age and height‐growth rates of trees in the boreal forest. Age was first examined using the traditional method of coring 30 cm above the root collar; then dendrochronology was used to locate the root collar and missing annual growth rings. Traditional ageing differentially underestimates tree age; species classified as early successional (Populus tremuloides, Betula papyrifera, and Pinus banksiana) are less severely underestimated than those classified as mid‐ and late‐successional (Picea glauca, Picea mariana, and Abies balsamea) (0–11 vs. 0–43 years), and also have relatively fewer locally missing growth rings. Ageing at the root collar shows that all tree species recruit within 5–10 years after fire and age cannot therefore be used to determine successional status. Mean time taken to grow to each 1‐m increment from the root collar was estimated for each species. Species classified as early successional have relatively higher growth rates between the root collar and the first metre; they are therefore less severely underestimated when aged above the root collar, explaining why they often appear older than species classified as mid‐ and late‐successional. The lack of species differences above 1 m means that height‐growth rates cannot be used to classify these tree species as early, mid‐, or late‐successional. In the boreal forest of Saskatchewan, the rapid recruitment of all tree species after fire, and the short fire cycle mean that the forest dynamics between catastrophic wildfires are driven primarily by the mortality rates of each species.

Range use and movement rates of woodland caribou in Saskatchewan

We employed satellite-telemetry data to examine seasonal movement rates, annual- and seasonal-range sizes, and season-to-season range fidelity of female woodland caribou (Rangifer tarandus caribou) from five populations in the boreal forest of Saskatchewan. The populations studied are limited by predation, and we investigated whether female caribou exhibited movement and range use consistent with predator avoidance. Additionally, we document an animal-centred technique for assessing site fidelity on the basis of individual range use throughout a year. Females accompanied by calves had lower movement rates and smaller seasonal ranges than females without calves. Movement rates among female caribou tended to decline between the rut and the postcalving and summer seasons. Trends indicated that seasonal ranges were larger prior to calving than during the postcalving and summer seasons. We interpreted the range sizes and movement rates observed as being consistent with predator avoidance in nonmigratory caribou populations. Despite these results and high rates of calf mortality in the area, we did not find interannual fidelity to calving sites.

Acclimation to light in planted and naturally regenerated populations of white spruce seedlings

Physiological responses to sun and shade were examined in white spruce (Picea glauca (Moench) Voss) seedlings collected from three naturally regenerated (N1-N3) and three planted (P1-P3) stands in the boreal forest of Saskatchewan. Seedling survival was greater in the sun than in the shade pretreatment periods. Dark respiration declined by 70% in shade- compared with sun-acclimated seedlings; however, the decline was not statistically significant because of the large within-population variation. Quantum yield, total chlorophyll content, specific leaf area, and absolute water content of needles increased by 45, 33, 32, and 50%, respectively, in response to shade. At low light levels, shade-acclimated populations showed greater photosynthetic rates and steeper light-response curves than seedlings growing in full sun. Seedlings of P3, N2. and N3 saturated at about 200 µmol·m-2·s-1 PAR in the shade, with no increase in photosynthesis at higher light intensities. At light saturation, populations P1 and N3 showed similar photosynthetic rates to both light acclimation regimes; populations P2, P3, and N2 had lower light-saturated photosynthesis in sun, compared with shade pretreatment. Only in N1 was photosynthetic rate greater after sun than shade pretreatment; this population behaved like a "sun" and "shade" population depending on pretreatment. Differences in physiological responses to light among populations suggest the presence of more than one ecotype. N1 showed the greatest plasticity in response to light pretreatment. The remaining populations behaved more like shade-adapted populations, with little adjustment to light conditions. Intrapopulation variation was large for both regeneration types. It appears that selection pressure during reforestation was not great enough to cause a decline in intrapopulation variation in planted compared with naturally regenerated white spruce seedlings.Key words: Picea glauca, white spruce, light acclimation, photosynthesis.

Bird blow flies, Protocalliphora (Diptera: Calliphoridae), in cavity nests of birds in the boreal forest of Saskatchewan

Bird blow flies, Protocalliphora (Diptera: Calliphoridae), in cavity nests of birds in the boreal forest of Saskatchewan

Clearcut Harvesting and Structural Dynamics of a Boreal Forest in Saskatchewan

The conversion of natural forests into managed forests raises concerns about sustained timber production and nature conservation. This study combined long-term inventory projections for some 84,000 ha of productive boreal mixedwood in Saskatchewan with fragmentation analysis. A spatially unrestricted clearcut harvesting regime was simulated for a I 00-year period (1984-2084). The current harvest rates of 1.5 m3 ha−1 per year could be sustained, but the age class distribution of the forest would markedly shift towards younger stands. Maximizing timber yields could raise harvest rates by 10%. These harvest rates would make it increasingly difficult to set aside permanently productive forest for ecosystem protection and alternative forest uses. A reduction of current harvest rates by at least 30% would support forest conservation. Spatial restrictions of the harvesting regime would be required to prevent forest fragmentation.

Boreal forest ecosystem characterization with SIR-C/XSAR

Discusses early results obtained from Spaceborne Imaging Radar-C (SIR-C) and X-band synthetic aperture radar (XSAR) data over a boreal forest in Saskatchewan, Canada. Multifrequency and multipolarization image data were made available during the SRL-1 (Apr. 10, 1994) and SRL-2 (Oct. 1, 1994) missions. These image data sets were analyzed and maps of forest cover type and above ground woody dry biomass were generated. A portion of the Southern Study Area of the Boreal Ecosystem-Atmosphere Study (BOREAS) was mapped for forest cover type with classification accuracies on the order of 80%. Maps of estimated biomass were also produced that match observed patterns and preliminary ground data. The upper limit of sensitivity of the radar to boreal forest biomass in the study area was about 20 kg/m/sup 2/ or 200 tons/ha. The highest average observed biomass in the ground measurements was about 25 kg/m/sup 2/. The highest sensitivity of the radar to biomass was attained using April backscatter data and a ratio of L-band HV to C-band HV. Results show that radar estimates of biomass were within /spl plusmn/2 kg/m/sup 2/ at the 95% confidence level. A comparison of the April and October data sets was conducted to understand the effects of seasons on the analysis. It appears that the frozen trees and wetter background contributes to increased backscattering observed in the April data. These early results indicate that multiple polarization and multiple frequency SAR data can be used to monitor and map northern forest biomes.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Derivation of Snow Water Equivalent in Boreal Forests Using Microwave Radiometry

Efforts have been made by several investigators to produce a reliable global microwave snow algorithm to estimate snow depth or snow water equivalent (snow volume) and snow extent. Complications arise when trying to apply a global algorithm to specific regions where the climate, snowpack structure and vegetation vary. In forest regions, the microwave emission from dense coniferous forests may overwhelm the emission from the underlying snow-covered ground. As a result, algorithms employing microwave data tend to underestimate snow depths. Preliminary results indicate that the amount of underestimation can be minimized when the fraction of forest cover can be accounted for and used as an additional input in microwave algorithms. In the boreal forest of Saskatchewan, the standard error between the measured and the estimated snow water equivalent was reduced from 2.7 to 2.1 cm by using a generalized snow retrieval algorithm that includes the percentage of forest cover. However, perhaps as much as 25% of the boreal forest of North America and Eurasia is too dense to enable satisfactory snow water equivalent determination to be made using passive microwave techniques alone. Key words: brightness temperature, boreal forest, microwaves, radiometer, snowpack

Acid-buffering capacity of foliage from boreal forest species

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.

An Aerial Census of Bald Eagles in Saskatchewan

An aerial census was conducted to determine the numbers and productivity, and to delineate distribution of bald eagles (Haliaeetus leucocephalus) in a 270,000-km2 area of northern Saskatchewan. Randomly located sample units were designed to contain uniform amounts of primary nesting habitat. An estimated 3,900 breeding areas, 6,900 adults, 4,700 immatures, and 2,500 nestlings were present in the summer of 1974. In southwestern regions 0.95 young per breeding area were produced, indicating reproduction above the estimated minimum required for maintenance. There was a positive correlation between breeding area density and April mean temperature. Two models for eagle distribution in the province are discussed. As a monitoring tool, the census technique could detect a population change of 27%. J. WILDL. MANAGE. 43(1):61-69 In 1969 Whitfield et al. (1974) censused the bald eagle population in approximately 20% of the boreal forest of central Saskatchewan and Manitoba. They estimated 460 to 697 breeding areas and a fall population of 1,600 to 8,000 eagles in the most densely inhabited part of their study area. Their results showed that these provinces are major inland bald eagle breeding grounds in North America. The study reported here was undertaken to estimate the size, reproductive success, and pattern of distribution of the bald eagle population in Saskatchewan in the summer of 1974, and to develop an aerial census technique suitable for monitoring the population. We are grateful to 3 agencies for financial support: Canadian Wildlife Service; Churchill River Study, Wildlife Sector (CRSWS); and Parks Canada. The CRSWS also made data available to us. We acknowledge the criticism and advice of R. W. Longley on meterological interpretations, E. Nordbrock on statistical procedures, and J. B. Gollop who reviewed the manuscript. MATERIALS AND METHODS Census Area and Sample Units The 270,000-km2 census area includes most of the boreal forest of Saskatchewan from approximately Lat. 54'N to the province's northern boundary at Lat. 60'N (Fig. 1). The area's southern boundary was chosen to eliminate from the census that portion of the province which we believed from previous work to have few breeding bald eagles (Whitfield et al. 1974). All of the census area except a strip of varying width along the southern edge is on the Precambrian Shield. The shield is covered with numerous lakes and ponds and its boundary with the more southerly sedimentary rock is marked by a series of large lakes which straddles the zone of contact. Relief is generally low and drainage is into Hudson Bay and the Arctic Ocean. The major physiographic regions are the Precambrian Shield, including the Athabasca Plains and Rock Knob Complex, and the Central Lowlands south of the shield (Richards and Fung 1969). J. Wildl. Manage. 43(1):1979 61 This content downloaded from 207.46.13.73 on Sat, 14 May 2016 06:08:52 UTC All use subject to http://about.jstor.org/terms 62 BALD EAGLES IN SASKATCHEWAN* Leighton et al.

A quantitative study and multivariate analysis of corticolous lichen communities in the southern boreal forest of Saskatchewan

Quantitative data on the occurrence of corticolous lichens in 40 forest stands involving a total of 8000 randomly selected quadrats have been gathered and subjected to both ordination by principal-components analysis and agglomerative classification in an attempt to define community relations. The results of these two methods of analysis are in agreement and indicate that variation between communities is essentially discontinuous and related to the host substrate. Effects of a more continuous nature related to moisture levels and age of the trees within each stand are also strongly suggested by the ordinations. The distribution of the different growth forms is related to environmental variables and discussed.

The Savannah Concept and Its Use

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