Jack Pine Stands Research Articles

Survey of Shoot Damage Caused by the Exotic Pine Shoot Beetle in Michigan Pine Stands

Abstract The exotic pine shoot beetle, Tomicus piniperda [L.] (Coleoptera: Scolytidae) is a Eurasian pest of pines that was first discovered in North America in 1992 near Cleveland, Ohio. It has since been found in at least 72 counties in Michigan, 285 additional counties in 11 other north central and eastern states, and the provinces of Ontario and Quebec. We counted injured shoots along linear transects in ten stands of Scotch (Pinus sylvestris L.), red (Pinus resinosa Aiton), and jack pine (Pinus banksiana Lambert) in lower Michigan (30 stands total) to estimate the frequency of shoot damage attributable to pine shoot beetle, other shoot-feeding insects, weather, and other damaging agents from 1997 to 1999. Fifteen of the stands were located in southwestern counties where pine shoot beetle has been established for at least 8 to 10 yr. The other 15 stands were in northern counties where pine shoot beetle establishment is more recent. In the southwestern stands, pine shoot beetle killed significantly more shoots in Scotch pine stands than in red or jack pine stands, and injured more shoots in Scotch pine stands than all other insects combined. Two of these Scotch pine stands were near an area with an abundance of Scotch pine brood material available to parent beetles. Damage in these two stands averaged roughly 10 to 12 shoots per m2 in 1998 and 1999, compared with 0.6 to 1.6 shoots per m2 in other Scotch pine stands, and less than 0.2 shoots per m2 in nearby red or jack pine stands. Pine shoot beetle was at very low or undetectable levels in northern stands in all years. Shoots injured by three other shoot-feeding insects were occasionally encountered, most often in red pine stands, but caused an insignificant amount of damage. With the exception of the southwestern Scotch pine stands, most of the shoot damage, particularly in northern jack pine stands, was attributable to squirrels or abiotic factors such as wind, ice or snow. North. J. Appl. For. 18(4):101–109.

The 3/4 power law in forest management: how to grow dead trees

Structural complexity of managed forests is proving to be vitally important for the conservation of wildlife and ecological processes. We test for the factors most important in determining the availability of snags (dead standing trees) in fire-origin boreal forests of northwestern Ontario. The strongest correlate of snag basal area (m 2/ha) was the amount of live tree basal area, which accounted for 68% of variation in the production of snags. The relationship between live and dead tree basal area followed a 3/4 power law with a slope of 0.74 for the forest community and differing slopes for forest stands and forest age. A relationship between tree mortality and metabolic rate is consistent with rate of self-thinning theory. This invariance indicates that total community biomass is likely to be insensitive to species diversity. Mixed hardwood forest types produced the greatest basal area of snags, followed by poplar, mixed conifer, jack pine and spruce stands. The percentage of stems that were dead was greatest in young forests (18% of stems in 0–60-year-old forests), decreased to a low percentage of 12% in 61–80-year-old forests, and thereafter increased with age of forests from 15 to 16% in 81–100, >100-year-old forests, respectively. In contrast, the number of small diameter (10–22 cm dbh) snags (stems/ha) was greatest in 61–100-year-old forests, whereas medium diameter (22–30 cm dbh) snags and large diameter (>30 cm dbh) snags were greatest in old-growth (>100 years) forests. The management implications are that increased live tree density due to environmental conditions, or possibly intensive forest management practices following clear cutting, may secondarily result in greater snag production and the structural complexity that favors wildlife biodiversity. Forest management guidelines that incorporate allometric relationships are needed to ensure maintenance of biodiversity and habitat heterogeneity following timber harvesting.

INFLUENCE OF LOGGING, FIRE, AND FOREST TYPE ON BIODIVERSITY AND PRODUCTIVITY IN SOUTHERN BOREAL FORESTS

The effects of logging on ecosystem sustainability are controversial. Surprisingly, existing data are inadequate to allow a comprehensive evaluation of logging effects on biodiversity, composition, and productivity since appropriate comparisons of stands of similar ages and differing disturbance histories are rare. We addressed this issue using a study of 2000 plots in 80 southern boreal forest stands in northern Minnesota, USA, wherein we contrasted naturally regenerated aspen (Populus tremuloides), jack pine (Pinus banksiana), and black spruce (Picea mariana) stands established following logging or the dominant natural disturbance, wildfire, for stands of two age classes (25–40 and 70–100 yr old). For young stands, those established postlogging had higher vascular plant diversity than those postwildfire. Otherwise, we found no evidence of differing species diversity (including canopy tree, shrub, herbaceous, and bryophyte species), composition, productivity, or nitrogen cycling, in forest stands of comparable age and forest type that originated after logging compared to after wildfire. These variables, however, differed significantly among forest types, with aboveground net primary productivity and plant species diversity generally higher in aspen than jack pine stands, even when growing on comparable soils, and lowest in black spruce. Although there is evidence that logging has increased the proportional landscape dominance by aspen, a forest type with higher diversity, nutrient cycling, and productivity than other types, our evidence refutes the idea that disturbance by logging has diminished stand-scale productivity or plant diversity in comparison to the common natural disturbance, wildfire.

Effects of edges on plant communities in a managed landscape in northern Wisconsin

The effects of edges on plant communities following clearing of coniferous forests in the Great Lakes region had not been previously examined. This study quantified plant responses to six recent (8–12 years old) clearcut edges adjacent to jack pine (Pinus banksiana) and red pine (Pinus resinosa) plantations. Percent cover of each understory plant species was estimated within 10 randomly placed plots at 19 distances along a 240 m transect extending from the clearcut, across the edge, and into the forest interior. Species richness was significantly higher in the jack pine stands (n=10.2–12.2) than in the red pine stands (n=6.1–9.1, p<0.05). Among the 67 species detected, 18 and two species were unique to the jack and red pine stands, respectively. Detrended correspondence analysis (DCA) and abundance band ratios were used to divide species into functional groups according to their distributions along the transect. A depth-of-edge influence was determined for species that showed a clear preference for the clearcut, interior, or edge habitat. Compositional gradients were also reflected in a DCA of distance sampled based on species abundance. Finally, regression models were developed to predict diversity from topographic, structural, and stand composition variables. A synthesis model is presented to describe plant species distributions across forest/clearcut edges. In this model, edge species patterns can show stronger effects on one side of the forest/clearcut edge than the other side.

Bird–habitat relationships in jack pine boreal forests

We made counts of 42 bird species at 217 points in 44 jack pine Pinus banksiana stands in the boreal region of north-central Saskatchewan, Canada because of concerns about the impact of forestry on avian biodiversity. Using multivariate analyses we describe the main patterns of bird species abundance and composition in relation to local habitat variables. According to canonical correspondence analysis (CCA), 17 of 43 explanatory variables accounted for significant variation in the bird species matrix: stand age, tamarack Larix laricina canopy cover, percentage shrub Alnus glutinosa, canopy closure (6–30%), percentage herbs, maximum canopy height, percentage shrub Alnus viridis, percentage moss, percentage shrub Betula nana, minimum and mean shrub height, percentage litter, white birch Betula papyrifera canopy cover, white spruce Picea glauca canopy cover, mean canopy height, canopy closure (71–100%), and zero shrub canopy closure. Habitat and stand identity (clustering of sites within stands) explained 55.5% of the total variation; 16.3% was unique to habitat alone (29.4% of the total variance explained — TVE) and 17.2% (31.0% TVE) was shared with stand identity. Stand identity accounted for 22.0% (39.6% TVE) of the variation. Neotropical migrants associated with “overmature” mixed-wood stands included Cape May Dendroica tigrina, bay-breasted D. castanea and Tennessee Vermivora peregrina warblers. Conversely, orange-crowned V. celata, palm D. palmarum, and Nashville V. ruficapilla warblers were found in young stands. The presence of several Neotropical migrants was associated with mixed-wood attributes (ovenbird Seiurus aurocapillus with aspen, red-eyed vireo Vireo olivaceus with shrub alder, and Swainson’s thrush Catharus ustulatus with canopy white birch). Jack pine stands older than commercial rotation age must be maintained in a managed landscape because their bird communities differ from younger stands. Because of the limited avian diversity in pure jack pine stands, sufficient mixed-wood stands must be regenerated to sustain populations of characteristic bird species. We recommend that jack pine mixed-woods be managed using shelterwood or selective cuts, and that rotation age of some stands be increased. Without the extensive fires necessary for regeneration, cutting patterns at the landscape level should approximate natural disturbance patches both in size and frequency of disturbance.

COMMUNITY-WIDE IMPACTS OF A GENERALIST BROOD PARASITE, THE BROWN-HEADED COWBIRD (MOLOTHRUS ATER)

Many ecologists have searched for species that contribute strongly to the structure and composition of communities of organisms. It has been speculated that the Brown-headed Cowbird (Molothrus ater), a generalist brood parasite, is capable of changing songbird communities. Cowbird parasitism may reduce numbers of suitable hosts, i.e., songbirds that accept cowbird eggs and raise cowbird young. In contrast, songbird species that eject cowbird eggs, nest in cavities, feed their nestlings mainly seeds or fruits, or are too big to parasitize, should escape the effects of cowbird parasitism. Thus, cowbirds may change the composition of songbird communities by selectively depressing numbers of suitable host individuals and species. We tested this hypothesis using an existing cowbird removal program in the state of Michigan, USA. This program was designed to protect the endangered Kirtland's Warbler (Dendroica kirtlandii) from cowbird parasitism throughout its 19 200-km2 breeding range. We compared songbird community composition in stands of young jack pine (Pinus banksiana) where cowbirds had been removed for 5–11 yr to communities in Control sites 5–10 km from cowbird traps and >10 km from cowbird traps. We predicted that cowbird Removal sites would support greater songbird richness and evenness and a greater proportion of suitable host vs. unsuitable host individuals relative to Control sites. Results from songbird point counts revealed that species richness and evenness were very similar at cowbird Removal and Control sites and that Removal sites contained only 4.0–8.7% more suitable host individuals than Control sites. Our results suggest that cowbirds do not strongly influence the composition of songbird communities in jack pine forests of Michigan. Several factors may explain a lack of community-wide response to long-term cowbird removal, including the population dynamics of songbirds on a broader scale. We conclude that there is little support for adding cowbirds to the short list of species that can regulate entire communities. Our results have implications for the increasingly widespread use of cowbird removal as a management tool.

Late Holocene Climate of the James Bay Area, Quebec, Canada, Reconstructed Using Fossil Beetles

We used fossil beetles recovered from three peatlands of the James Bay area (Radisson, northern Quebec, Canada), and the mutual climatic range (MCR) method, to produce a quantitative reconstruction of summer temperatures during the last 5000 yr. Our main objective was to test the hypothesis that a significant climatic cooling episode occurred during the late Holocene epoch, leading to the opening up of the boreal forest, and to the progressive replacement of black spruce (Picea mariana) forests by jack pine (Pinus banksiana) stands. Beetle assemblages in the Radisson area were very stable during the late Holocene epoch. We used a total of 22 beetle species to conduct the MCR analyses. Reconstructed mean July temperatures ranged from 14.5 to 17.5°C, which is close to the present-day (A.D. 1977–1996) temperature range found in the Radisson area. The general stability of beetle assemblages, and the MCR analyses, suggest that there was no major change in July temperatures during the last 5000 yr in the Radisson area. This study provides no evidence that the progressive replacement of black spruce forests by jack pine stands in the Radisson area during the last 2700 yr can be explained by a longterm climatic cooling episode affecting the postfire regeneration potential of trees. Consequently, an alternative hypothesis (more frequent fires favoring jack pine) should be seriously considered to explain the late Holocene changes in the forest environment of the Radisson area.

Late Holocene Climate of the James Bay Area, Quebec, Canada, Reconstructed Using Fossil Beetles

We used fossil beetles recovered from three peatlands of the James Bay area (Radisson, northern Quebec, Canada), and the mutual climatic range (MCR) method, to produce a quantitative reconstruction of summer temperatures during the last 5000 yr. Our main objective was to test the hypothesis that a significant climatic cooling episode occurred during the late Holocene epoch, leading to the opening up of the boreal forest, and to the progressive replacement of black spruce (Picea mariana) forests by jack pine (Pinus banksiana) stands. Beetle assemblages in the Radisson area were very stable during the late Holocene epoch. We used a total of 22 beetle species to conduct the MCR analyses. Reconstructed mean July temperatures ranged from 14.5 to 17.5°C, which is close to the present-day (A.D. 1977–1996) temperature range found in the Radisson area. The general stability of beetle assemblages, and the MCR analyses, suggest that there was no major change in July temperatures during the last 5000 yr in the Radisson area. This study provides no evidence that the progressive replacement of black spruce forests by jack pine stands in the Radisson area during the last 2700 yr can be explained by a longterm climatic cooling episode affecting the postfire regeneration potential of trees. Consequently, an alternative hypothesis (more frequent fires favoring jack pine) should be seriously considered to explain the late Holocene changes in the forest environment of the Radisson area.

Polymorphic site index curves for jack pine in Northern Ontario

Stem-analysis data from dominant and codominant trees were collected from 383 plots located in fully stocked, even-aged, undisturbed mature jack pine stands. Separate site index curves were independently formulated for four regions of northern Ontario using the Newnham constrained nonlinear regression model; these formulations were used for comparing regional site index curves at three levels of site index (10 m, 15 m and 20 m).Comparisons showed that no significant differences existed between the four regional curves as well as with previously published site index curves for the North Central Region. Each of the four regions had similar polymorphic height-growth patterns; therefore, data for the four regions were combined and a single formulation was used to develop a polymorphic set of site index curves for all of northern Ontario. We found that poor sites in each region had almost linear height growth up to 100 years breast-height age, but for each region height growth became more curvilinear with increasing site index. The recommended site index curves for northern Ontario are based on a formulation using only data from plots 100 years and less but this formulation was not significantly different from a formulation using only data from plots 80 years and less, or a formulation that included all data from plots older than 100 years breast-height age.Comparisons were made between our northern Ontario curves and other jack pine site index curves for Ontario as well as curves for other areas of Canada and the United States. These comparisons generally showed considerable older age differences. Reasons for these differences are uncertain but could be due to differences in the amount and kind of data used for these other curves, could be due to differences in analytical methods, or could be due to regional differences in climate, soil and topography. Key words: site quality evaluation, polymorphic height growth, regional site index curves, site index prediction equations, comparisons among site index curves.

A review of factors affecting the population dynamics of jack pine budworm (Choristoneura pinus pinus Freeman)

AbstractJack pine budworm (Choristoneura pinus pinus Free.) (Lepidoptera: Tortricidae) is a native insect that periodically defoliates areas of jack pine (Pinus banksiana Lamb.) in the subboreal forests of North America east of the Rocky Mountains. Outbreaks of jack pine budworm generally occur at 6‐ to 12‐year intervals and collapse after 2–4 years. Periodicity of outbreaks varies and is associated with site‐related factors. Survival of early‐instar larvae during spring dispersal is tied to the abundance of pollen cones (microsporangiate strobili), which provide a refuge for larvae until current‐year needles expand. Jack pine trees that have been heavily defoliated produce few pollen cones in the following year, often resulting in high mortality of early‐stage larvae. A diverse guild of generalist parasitoids attack jack pine budworm, but only a few species account for most mortality in any area. Collapsing jack pine budworm populations are characterized by sharp declines in early instar survival, coupled with an increased rate of parasitism in the late larval and pupal stages. The reciprocal interaction between heavy defoliation and low pollen cone production, and increased parasitism of late‐stage larvae or pupae, are consistent with second‐order density dependence factors identified in analysis of a long‐term population data set. Since the 1950s, several jack pine budworm outbreaks have been roughly synchronous over a large geographic area, suggesting that Moran effect processes, as well as moth dispersal or other factors, may be involved in jack pine budworm dynamics. Although the short duration of outbreaks enables most trees to recover, over time dead trees and top‐killed trees accumulate in jack pine stands. Jack pine is well adapted to fire and when fires ignite, the accumulation of dead trees and woody debris often leads to intense wildfires followed by prolific regeneration. The three‐way interaction of jack pine, jack pine budworm, and fire ultimately serves to maintain vigorous stands and ensures continued hosts for jack pine budworm.

Impacts of wild fire severity and salvage harvesting on the nutrient balance of jack pine and black spruce boreal stands

In August of 1995, wildfires burnt over 50 000 ha of boreal forest in northwestern Quebec. A balance sheet approach was used in order to assess the long term effects of fire and subsequent salvage harvesting operations on nutrient site capital. Following a validation of burn severity indices and maps, we conducted an evaluation of soil nutrient pools in (1) lightly to moderately, (2) severely burned, and (3) unburned stands with similar biophysical characteristics. Above-ground biomass values for unburned stands, precipitation and N biological fixation inputs were drawn from the literature. Weathering rates were drawn from previous work and estimated with the PROFILE model. Fire significantly reduced forest floor dry weight by 41% in the light/moderate class and by 60% in the severe class while forest floor total Ca concentrations increased following both types of burn. Forest floor exchangeable Ca and total Mg concentrations increased following a light/moderate burn. Fire increased exchangeable K concentrations in the 0–10 cm mineral layer but had no other effects on mineral soil concentrations or characteristics. Forest floor nutrient content was significantly reduced on severely burned areas only. Kjeldahl N content was reduced by 44%, exchangeable Mg by 53% and exchangeable K and total K by 60 and 51%, respectively. Reduction of K soil content was important enough that inputs through weathering and precipitation would take 278 years to compensate for soil losses following a severe fire. The projected effects of salvage harvesting on severely burned sites indicated that Ca, Mg and K would not return to their pre-burn level in the course of a 110-year rotation.

Hierarchical habitat selection by woodland caribou: its relationship to limiting factors

Habitat selection is a hierarchical process that may yield various patterns depending on the scales of investigation. We employed satellite radio‐telemetry to examine patterns of habitat selection by female woodland caribou in central Saskatchewan at both coarse (seasonal range) and fine (daily area) scales. At each scale, we converted spatial data describing compositions of available and used habitat to standardised resource selection indices and examined them with multivariate analyses of variance. Seasonal ranges generally showed preferential inclusion of peatlands and black spruce dominated stands relative to recently disturbed stands and early seral stage forests. In all populations, caribou preferred peatlands and black spruce forests to all other habitat types at the daily area scale, in general, these patterns may reveal the effective avoidance of wolves, the primary factor limiting caribou throughout the boreal forest. In three populations where seasonal ranges showed the selective inclusion of either young jack pine stands or clearcuts along with peatlands and black spruce forests, we found a relative avoidance of the clearcuts and young jack pine stands at the daily area scale. As all caribou populations in the area are thought to be relics of a once more continuous distribution, the seasonal range selection by animals in disturbed areas may better describe historic rather than current habitat selection. We found inter‐annual variation in selection at the coarser spatial scale in one population, and inter‐seasonal variation in selection at the finer spatial scale in three populations, indicating that the relative grains of the spatial and temporal scales coincide. We were better able to explain the seasonal variations in finer scale selection by considering available forage, a factor less likely than predation to limit woodland caribou populations. The data agree with the theory that the spatial and temporal hierarchy of habitat selection reflects the hierarchy of factors potentially limiting individual fitness.

Performance of the Canadian land surface scheme at temperate aspen‐birch and mixed forests, and a boreal young jack pine forest: Tests involving canopy conductance parametrizations

The Canadian Land Surface Scheme (CLASS) was evaluated using off‐line tests, with data collected at temperate aspen‐birch and mixed forests located near Chalk River, Ontario, and at a young jack pine forest located near Thompson, Manitoba. Measurements of stomatal conductance and leaf area index were used to develop canopy conductance parametrizations for the aspen‐birch and the jack pine stands, and these were incorporated into CLASS in a modified run. The behaviour of the residuals from the unmodified run with respect to environmental variables at the mixed stand were used as a guide to producing a modified ad‐hoc canopy conductance parametrization for use at that site. It was found that CLASS exaggerates the diurnal range in soil heat flux. This leads to an underestimation of the diurnal range in available energy, and it is argued that this has implications for its partitioning into the turbulent fluxes of sensible and latent heat. Over time, systematic errors will accumulate which, in the case of the latent heat flux, can affect the long‐term water balance. Errors in the size of the turbulent fluxes over short time periods can limit the usefulness of CLASS for resolving mesoscale circulations in a regional model. These problems are believed to be related to CLASS's assumption of zero wind speed under the canopy, and the lack of an insulating litter layer at the soil surface. An unmodified CLASS produced estimates of sensible and latent heat fluxes that broadly agreed with measured values at the temperate stands but not at the jack pine stand, where the latent heat flux was significantly overestimated. The modified canopy conductance parametri‐zations improved the representation of the latent heat flux at all of the sites, particularly at the jack pine stand. Overestimation at the aspen‐birch stand may be related to site heterogeneity not being adequately represented in the measurement of stomatal conductance, or to difficulties in defining the vertical distribution of leaf area index for scaling stomatal conductance to the canopy level. As expected, a positive or negative bias in the modelled latent heat flux is associated with an opposite bias in the modelled sensible heat flux. The tendency towards positive intercepts and slopes less than unity in linear regressions relating modelled and measured fluxes is a symptom of the underestimation of the diurnal range in available energy. Recommendations are made to allow for vertical discontinuities in texture within a soil layer and a variable permeable depth, and to allow transpiration when the soil water suction exceeds –1.5 MPa. This is particularly important when soil moisture or texture is heterogeneous. Finally, it is suggested that volumetric soil moistures should be allowed to fall below the originally prescribed limiting value of 0.04. This is necessary for evaporation to continue in very sandy, dry soils.

EFFECTS OF INTERACTING DISTURBANCES ON LANDSCAPE PATTERNS: BUDWORM DEFOLIATION AND SALVAGE LOGGING

Prior to European settlement, the 450000-ha Pine Barrens region in northwestern Wisconsin, USA, was characterized by a landscape mosaic of large, open patches, savannas, and closed forest stands of jack pine (Pinus banksiana). Crown-fires created large open patches that persisted on the droughty soils, providing important habitat for a number of area-sensitive, open-habitat species. Insect outbreaks may have contributed to periodic fires by increasing the fuel load. Today, fires are suppressed in the managed landscape, but insect defoliation remains a major disturbance. Salvage logging commonly follows insect outbreaks. Our objective was to evaluate landscape pattern changes caused by this interaction of natural disturbances and forest management. We examined changes in landscape pattern during the most recent (1990–1995) outbreak of jack pine budworm (Choristoneura pinus pinus) in northwestern Wisconsin using four Landsat TM satellite images (1987, 1991, 1993, and 1995). The 1987 image provided the basis for a species-level forest classification identifying mature jack pine and open habitat prior to the budworm outbreak. Each subsequent image was used to identify clearcuts in mature jack pine. The 1995 image was also used to classify stand development in the open habitat of the 1987 image so that the overall availability of open habitat in 1995 could be assessed. GIS data layers were used to analyze logging rates and clearcut sizes separately for different classes of land ownership and soils. Approximately 12500 ha were salvage logged during the 1990–1995 outbreak. Logging rates were highest on the most infertile soils, and on private, industrial forest land. Annual logging rates of different landowners were 3–6 times higher during the outbreak than previous to it. Salvage cut sizes were larger than clearcuts prior to the outbreak. New cuts were mostly located next to previous cuts, thus increasing the size of openings on the landscape. Initial survey results by N. Niemuth show that populations of one area-sensitive open-habitat species (Sharp-tailed Grouse, Tympanuchus phasianellus) thrive on the salvage cuts. Insect defoliation and subsequent salvage logging did create new habitat for open-habitat species that were declining. Landscape pattern changes due to multiple interacting disturbances have rarely been studied. The interaction of jack pine budworm defoliation and salvage logging substantially changed landscape pattern in the Pine Barrens. We speculate that interaction between insect defoliation and fire may have significantly shaped the presettlement landscape.

Nutrient dynamics of the southern and northern BOREAS boreal forests

The objective of this study was to compare nutrient concentration, distribution, and select components of nutrient budgets for aspen (Populus tremuloides), jack pine (Pinus banksiana), and black spruce (Picea mariana) forest ecosystems at the BOReal Ecosystem Atmosphere Study (BOREAS), southern and northern study areas near Candle Lake, Saskatchewan and Thompson, Manitoba, Canada, respectively. The vegetation (excluding fine roots and understory) in the aspen, black spruce, and jack pine stands contained 70-79%, 53-54%, and 58-67% of total ecosystem carbon content, respectively. Soil (forest floor and mineral soil) nitrogen (N), calcium (Ca), and magnesium (Mg) content comprised over 90% of the total ecosystem nutrient content, except for Ca and Mg content of the southern black spruce stand and Ca content of the southern aspen stand which were less than 90%. Annual litterfall N content was significantly greater (p < 0.05) for trembling aspen (30-41 kg N ha-1 yr-1) than for jack pine (5-10 kg N ha-1 yr-1) or black spruce (6-7 kg N ha-1 yr-1), and was generally greater, but not significantly, for the southern than for the northern study area. Aboveground net primary production was positively correlated (R2 = 0.91) to annual litterfall N content for the BOREAS forests, and for all boreal forests (R2 = 0.57). Annual aboveground nutrient (N, Ca, Mg, and K) requirements (sum of the annual increment of nutrient in foliage, branches, and stems) were significantly greater (p < 0.05) for trembling aspen than for jack pine or black spruce forests. Annual aboveground N requirements ranged from 37-53, 6-14, and 6-7 kg N ha-1 yr-1 for trembling aspen, jack pine, and black spruce forests, respectively. The greater nutrient requirements of deciduous than evergreen boreal forests was explained by a greater annual production of biomass and lower use efficiency of nutrients. Nutrient cycling characteristics of boreal forests were influenced by climate and forest type, with the latter having a greater influence on litterfall N, annual nutrient requirements, nutrient mean residence time, and nutrient distribution.

Compact Airborne Spectrographic Imager (CASI) used for mapping biophysical parameters of boreal forests

During the Boreal Ecosystem‐Atmosphere Study (BOREAS), which took place in Saskatchewan and Manitoba in 1994, the Compact Airborne Spectrographic Imager (CASI) acquired images of boreal forests. In this paper we present results of radiometric and geometric analysis of the CASI data for developing algorithms for retrieving leaf area index (LAI) and crown closure of the boreal forest. The images of over 30 sites, composed of black spruce, jack pine, and aspen stands, were acquired on different days and locations with various solar illumination and view geometries. The geometrical‐optical model, named “4‐Scale” [Chen and Leblanc, 1997, 1316–1337], was used to correct the images to a common solar zenith angle (35°) and a common view angle (nadir). The 4‐Scale model is also used for radiometric analysis based on spectral signatures of leaves and the background (moss, grass, and soil) acquired using various field and laboratory techniques. The red reflectance of all three cover types decreased with increasing LAI as expected. Similar but weaker decreasing trends were found in the near‐infrared (NIR) band for conifer stands in contrast to previous findings for cropland and grassland. No significant NIR response to LAI was found for aspen stands. It is shown from 4‐Scale that as LAI increases, the crown and ground shadow fractions of conifer forests increase, while the sunlit background fraction decreases and the sunlit crown fraction increases. The large change in the shadow fractions is the major factor controlling the behavior of red and NIR signals. Since boreal forests have abundant green moss and understory as the background, there is only a small difference in optical properties between the overstory and the background. The increases in the shadow fractions with LAI help strengthen the response of optical measurements to changes in LAI, providing a key mechanism for remote information retrieval. The implications of these findings on formulating/selecting vegetation indices and inversion models are discussed in this paper. Relationships of crown closure with CASI measurements are also included in the analysis.

Validité de la carte forestière pour décrire les habitats fauniques à l'échelle locale : une étude de cas en Abitibi-Témiscamingue

Wildlife habitats may be described at low cost using forest maps. Because the main objective of forest maps is to estimate the wood volume over large areas whereas wildlife applications often require accurate data at the stand level, their accuracy may not be acceptable. During a study of marten (Martes americana) habitat, we ground-checked 1:20 000 forest maps in two areas (70 and 123 km2) in the Abitibi-Témiscamingue region. Surveys involved 72 stands : 44 black spruce (Picea mariana), 18 jackpine (Pinus banksiana), 5 mixed deciduous, and 5 deciduous stands. The dominant tree species group was accurate in most black spruce (43 over 44) and jackpine stands (16 over 18). For mixed and deciduous stands, gross errors were noted in the cover type and the dominant tree species group. The cover density on the map was poorly related to the crown closure measured on the ground. There was a closer agreement between height classes on the map and actual height. In black spruce stands, the age class enabled discriminating between young (30- and 50-years classes) and old stands (90- and 120-years). We conclude that caution is needed when using forest maps to describe wildlife habitats, and that the accuracy of the mapped attributes should be checked before using such data at local scales. Key words: forest maps, forest survey, GIS, ground check, wildlife habitat

Detecting Jack Pine Budworm Defoliation Using Spectral Mixture Analysis: Separating Effects from Determinants

Insect defoliation is a major disturbance force in forested ecosystems. Monitoring outbreaks, and estimating the areas affected, is therefore important for both forest managers and forest ecologists. The objective of our study was to classify jack pine budworm defoliation levels in Landsat TM imagery recorded previous to and during the 1990–1995 outbreak in our 450,000 ha study area in northwestern Wisconsin (USA). Many previous studies correlated insect defoliation and remotely sensed imagery with moderate to good success, but it often remained unclear if actual defoliation effects or other forest attributes correlated with defoliation were detected. For example, a larger deciduous component in mixed jack pine stands will limit budworm populations and thereby defoliation. The deciduous component in stands is a determining factor for insect defoliation, whereas needle discoloration and tree mortality are their effect. We used pre-outbreak Landsat TM data (1987) to identify determining factors for jack pine budworm population levels and peak-outbreak imagery (1993) for detecting actual defoliation. Our satellite data were atmospherically corrected using a radiative transfer model (5S). Spectral mixture analysis was performed using spectrometer measurements of jack pine needles and bark as representations of surface materials (“endmembers”). The explanatory power of the resulting fraction images was evaluated using jack pine budworm population data collected at 33 sampling points. Near-infrared reflectance (NIR) increased in defoliated stands between 1987 and 1993, but single date NIR in each year was negatively correlated with budworm levels in 1993 ( r=−0.69 and −0.47). This was because hardwood trees within jack pine stands caused higher NIR reflectance but limited jack pine budworm populations. The 10% NIR difference between pure and mixed jack pine stands outweighed the 3–5% increase in NIR due to defoliation and necessitated stratification of the satellite data by tree species. Spectral mixture analysis performed on pure jack pine stands resulted in a strong negative correlation between the 1993 green needle fraction and the 1993 budworm population data ( r=−0.94). This study was, to our knowledge, the first that applied spectral mixture analysis for forest damage detection, and also the first to use insect population measurements as independent field data. These methods, and the separation of determinants and effects of jack pine budworm defoliation, enabled us to detect actual defoliation with high accuracy.

Bat Activity in the Boreal Forest: Importance of Stand Type and Vertical Strata

We examined habitat use by bats in the boreal forest of central Saskatchewan during summer 1995 by monitoring echolocation calls across forest types and through the canopy of mature forest. We sampled bat activity in mature aspen ( Populus tremuloides )-white spruce ( Picea glauca ) mixedwood, aspen, and jack pine ( Pinus banksiana ) stands and recorded passes from little brown ( Myotis lucifugus ), northern long-eared ( M. septentrionalis ), big brown ( Eptesicus fuscus ) or silver-haired bats ( Lasionycteris noctivagans ), and hoary ( Lasiurus cinereus ) bats. There were significantly more bat passes per night in the aspen-white spruce mixedwood forest than in aspen or jack pine forest. There was no difference in the proportion of feeding buzzes recorded from aspen-white spruce mixedwood and aspen forest. In aspen forest, mean number of hoary bat calls per night was higher above than below the canopy, whereas number of Myotis calls was higher within and above the canopy than below the canopy. There was no difference in the number of feeding buzzes recorded among the three canopy heights. Bat activity peaked toward sunset below the canopy but was more uniform within and above the canopy. Our results highlight the importance of mature aspen-white spruce mixedwood and aspen forest as habitat for boreal forest-dwelling bats and demonstrate for the first time that insectivorous bats are active both within and above canopy levels of the boreal forest.

Characterization of the Reflectance Anisotropy of Three Boreal Forest Canopies in Spring–Summer

As a part of the Boreal Ecosystem-Atmosphere Study (BOREAS), measurements of the spectral reflectance anisotropy of three boreal forest canopies were studied for cloudless sky conditions at the phenological growth stages which were at or near maximum leaf area index at each site. The three sites were relatively homogeneous mature stands of black spruce, jack pine, and aspen located in the southern boreal zone of central Saskatchewan. Measurements of the spectal bidirectional reflectance factors with a 15° instrument field of view in three spectral bands centered at 662 nm, 826 nm, and 1658 nm were made with the PARABOLA instrument over a range of solar zenith angles typically varying from 35° (near solar noon) to 70°. The measured reflectance factors showed large anisotropy at all three sites and for all three wavelengths, with prominant backscatter peak reflectances, and strong retro solar view angle (hot spot) maximum reflectances in the visible (662 nm) and shortwave infrared (1658 nm) for the jack pine and black spruce sites, with a less pronounced hot spot at the aspen site. Pronounced effects of canopy and understory shadowing in the visible, as a function of solar zenith angle (SZA), were observed for the black spruce and jack pine sites, with resultant large linear increases in computed normalized difference and simple ratio vegetation indices as SZA increased for near-nadir view angles. Hemispheric spectral reflectances or spectral albedos were computed from angular integration of PARABOLA measured bidirectional reflectances. Visible (662 nm) hemispheric reflectances for the jack pine and black spruce canopies showed very little variation with solar zenith angle, while near-infrared hemispheric reflectances increased strongly with increasing SZA. Estimates were made of the total shortwave albedo for the aspen and jack pine sites from irradiance and reflectance weighting of the spectral hemispheric reflectances in the three measured wavelengths. Comparison of estimated to pyranometer measured total albedo showed all estimates to be biased high, but only by about 0.007–0.018, depending on which of two sets of pyranometer measured albedos were utilized for the comparison. The measured bidirectional reflectance factor (BRF) data sets reported in this study coupled with ancillary data of biophysical parameters collected at the same sites by BOREAS researchers provide a unique data set for the development and characterization of canopy bidirectional reflectance modeling and for the interpretation of remotely sensed data for boreal forest canopies.