Spruce Mortality Research Articles

Recent Permafrost Dynamics in a Subarctic Floodplain Associated with Changing Water Levels, Quebec, Canada

We have reconstructed from tree-rings the dynamics of mineral frost mounds on the floodplain of a subarctic river (Riviere Boniface, northern Quebec) likely associated with snow precipitation and temperature changes during the past centuries. Due to their peculiar location in the river bed, we have postulated that the inception and decay of frost mounds (thermokarst ponds) were associated with snow-controlled water levels of the river. The periods of establishment, growth, and mortality of spruce around and in two thermokarst ponds on the shore zone were identified. The oldest tree-ring dates show that permafrost mounds formed during a period of water lowering in the 17th century, likely in a long-enduring sequence of low waters initiated around cal AD 1150 (910 yr BP), which persisted for at least 200 yr until the beginning of the 20th century. Two main periods of spruce mortality were identified, in the late 19th century and early 20th century and in the 1950s-1960s, which corresponded to a rising river level probably due to greater snow precipitation. The patterns of spruce establishment and mortality were strikingly similar in the studied sites. The first spruce to establish were all located along the pond's edges and they were also the first ones to die; most of the youngest spruce established later in the central part of each feature, i.e., in the early to mid-1850s to 1910, and died during the 1950s-1960s. The sequence of events reported here suggests an important lowering of the Riviere Boniface during the first part of the Little Ice Age (end of the 16th century-17th century) which was drier and cold. During the second part of the Little Ice Age (mainly 19th century), greater precipitation occurred and climaxed in the 20th century when climate warmed and the river stage reached its maximum level. Changes in snow precipitation were probably more instrumental than temperature changes in the rise and fall of permafrost landforms because of the snowpack's direct influence on the soil thermal regime and river level during snowmelt.

Use of forest inventory and monitoring data in the spruce budworm decision support system

Spruce budworm ( Choristoneura fumiferana Clem.) outbreaks cause severe mortality and growth loss of spruce and fir forest over much of eastern North America. The spruce budworm decision support system (DSS) links prediction and interpretation models to the ARC/INFO GIS, under an ArcView graphical user interface. It assists forest managers to predict budworm outbreak effects on forest structure and productivity, forecast forest growing stock and sustainable harvest levels, optimize protection (biological insecticide use) programs, and use silviculture and harvest scheduling to restructure forests to reduce future damage. The spruce budworm DSS has been operationally implemented on 8 million ha of susceptible forest in the province of New Brunswick, and is being implemented on test landbases in Quebec, Ontario, and Alberta. The use of inventory and monitoring data in the DSS will be described in four areas, stand growth model calibration; model validation; pest monitoring; and forest stratification for calculating marginal timber supply benefits.

Density-dependent effects of northern hardwood competition on selected environmental resources and young white spruce ( Picea glauca) plantation growth, mineral nutrition, and stand structural development – a 5-year study

The effects of competition from red raspberry ( Rubus idaeus L.) and northern hardwood tree species on white spruce ( Picea glauca (Moench) Voss) seedlings were examined on a clearcut site of the boreal mixedwood forest of the Bas-Saint-Laurent region of Quebec, Canada. A controlled experiment involving a gradient of five vegetation densities on the basis of the leaf area index (LAI) was established in a completely randomized plot design with six replications. Each of the five levels of vegetation cover (including vegetation-free plots) were examined to evaluate how they affected environmental factors (quantity and quality of light reaching the spruce seedlings, and soil temperature), spruce growth (height, basal diameter, volume index, and above-ground biomass), spruce mortality, browsing damage, spruce foliar mineral nutrition, as well as the stand structural development, during the first 5 years after seedling planting. Each spruce growth variable analyzed in this study, according to a RMANOVA procedure, followed a negative hyperbolic form of density dependence of competitive effects. Loss of growth in young white spruce plantations in competition with northern hardwoods is likely to occur with the first few competitors. In cases where higher levels of competing vegetation were maintained over time, loss of spruce growth was extremely severe, to an extent where the exponential growth character of the young trees has been lost. At the end of the fifth year, spruce growing with no interference were larger in mean total above-ground biomass by a factor of 9.7 than those growing with the highest level of vegetation cover. Spruce did not develop a strategy of shade avoidance by increasing tree height, on the contrary. Spruce mortality differed among treatments only in the fifth year, indicating that early evaluation of spruce survival is not a strong indicator of competitive effects, when compared to diameter growth. Spruce foliar N and Ca contents were significantly reduced by the first level of competing vegetation cover, while K increased with the density of the vegetation cover, and P and Mg were not affected. Nitrogen nutrition of young white spruce planted on recently disturbed sites is discussed in relation to the potential root discrimination of this species against soil nitrate, a reaction observed by Kronzucker et al. [Kronzucker, H.J., Siddiqi, M.Y., Glass, A.D.M., 1997. Conifer root discrimination against soil nitrate and the ecology of forest succession. Nature London 385, 59–61]. The effects of hardwood competition indicate a prevalence of competition for light over a competition for nutrients, as revealed by the substantial increase in the h/ d ratio of white spruce. Two indicators, h/ d ratio and the quantity of light received at the tree seedling level, are suggested as a basis for the management of hardwood competition in a white spruce plantation. Analysis of the stand structural development indicates that spruce height distribution was affected only by moderate or dense cover of vegetation, while diameter distribution, when compared to competing vegetation-free plots, was affected by the lowest level of vegetation cover. This study shows that competition influenced the stand structural development in the same way as genetic and micro-site factors by aggravating the amplitude of size inequality. The impact of hardwood competition is discussed in view of reaching an equilibrium between optimal spruce plantation growth and benefits from further silvicultural treatments, and maintaining hardwood species known to improve long term site quality, within a white spruce plantation.

Fate of Hydrocarbon Contaminants In Natural Wetlands

Abstract Conventional clean-up approaches to contaminated wetlands are aggressive and expensive, and may harm the wetland ecosystem. Current findings suggest that wetlands may be capable of attenuating contamination through natural processes including sorption, biodegradation, and volatilization. The objective of the study was to conduct a field evaluation of the role of these attenuation mechanisms at four contaminated natural wetlands in Alberta. A second focus of the study was to evaluate contaminant impact on the wetlands vegetation. The results indicate that contaminant attenuation in wetlands are influenced by several parameters, including depth of impact, contaminant composition, presence of peat, flow rates, and seasonal effects. Overall, natural processes appear to be completely attenuating hydrocarbon contamination at two of the four wetlands study sites. At the other two sites, minor concentrations were reaching downgradient receptors. Impact on vegetation was observed at three of the four sites, primarily through mortality of black spruce. The impact on shallow vegetation was generally negligible. Introduction Wetland contamination by hydrocarbons as a result of upstream oil and gas activity is well known, both in Alberta and worldwide. Conventional clean-up approaches (e.g., excavation, trenching, and burning) are aggressive and expensive, and may harm the wetland ecosystem. A more passive, longer term solution may be to focus on containing or removing the source and allow natural processes to remediate the remaining contamination. This approach, known as intrinsic remediation or natural attenuation, has been shown to be effective in various scenarios, from fuel-contaminated groundwater at Air Force Bases to oil spill-impacted shorelines. There has been little investigative work on the subject of intrinsic remediation in hydrocarbon-impacted wetlands. Current findings suggest that wetlands may be capable of retarding and potentially depleting contaminant plumes through natural remediation processes including: sorption, biodegradation, and volatilization. Wetlands are typically water-saturated environments with a high percentage of peat. Peat is an organic-rich material containing partially to highly decomposed plant fibres, roots, and mosses(1). Wetlands containing peat have several unique attributes, which enhance contaminant attenuation in the following ways:Sorption: Sorption may be described as the partitioning of contaminants from the liquid phase to the soil matrix. The peat matrix is highly porous (up to 70%) and has been found to be capable of absorbing up to eight times its weight in oil(2). Peat contains approximately 40% organic carbon by weight. Laboratory testing completed by Tinh et al.(3) indicates that peat's adsorptive capacity is between 30 to 50% of granular activated carbon. Peat is therefore an excellent filter for organic contaminants.Biodegradation: Microorganisms indigenous to the environment are capable of biodegrading most organic contaminants found in petroleum fuels, both aerobically and under anerobic conditions. Due to their high organic content and biodiversity, wetlands exhibit microbial activity exceeding most natural environments(4). The enhanced microbial activity results in greater potential for biodegradation, whereby microbes stimulate the breakdown of organics such as hydrocarbons to form CO2, water, and biomass.Volatilization: Volatilization describes the partitioning of hydrocarbons from the soil phase, dissolved phase, and/or liquid phase into the vapour phase.

Ecosystem development on terraces along the Kugururok River, northwest Alaska

:Riverside terraces along the Kugururok River in the Noatak National Preserve provided an opportunity to study primary succession, considering general trends that apply across all terraces, and unique events that influence individual terraces. The 30-year-old willow/poplar (Salix spp., Populus balsamifera L.) terrace had no trees taller than 1.5 m; the abundant spruce trees were not tall enough to emerge from the canopy height of the willows and poplars, and moose (Alces alces [Clinton]) browsing limited the canopy height of these plants. The 75-year-old poplar/spruce (Picea glauca [Moench] Voss) terrace had a high density of poplars (> 1000/ha) and low density of spruce (125/ha); heavy browsing by moose reduced the density of poplar by about one-half. The removal of the poplar by moose in this stand resulted in sustained increases in growth of individual spruce trees. The 100-year-old younger spruce/poplar terrace had about twice as many spruce trees (1250/ha) as poplar trees (500/ha), and the spruce trees were larger on average than the poplar trees. In the 220+ year-old older spruce/poplar type, only a few poplars remained (about 25/ha), and the number of spruce trees (600/ha) was only half that of the younger stage, either from lower initial spruce density on this terrace, or increased mortality of spruce. The 240+ year-old spruce type was a second-generation forest, characterized by a high density (1950/ha) of small spruce trees, some of which were tilted, indicating discontinuous permafrost. Plant litterfall mass showed no strong trend with terrace age, although N content of litterfall appeared to decline by about 1/3 in the spruce-dominated stages. Fungal biomass increased with ecosystem age, whereas bacterial biomass and microfauna declined. We found no evidence of declining soil N supply in older stages, but fertilization experiments would be needed to determine if N limitation of productivity changed with ecosystem development. We conclude that the general successional trend of increased spruce dominance is robust for this location, but that unique events play important roles in determining tree densities and the timing of the shift in dominance from poplar to spruce. The arrival of moose in the 1970s accelerated dominance by spruce on young terraces.

Foliar phytochelatin levels as indicators of forest decline

Evidence in favour £hytochelatins (PC) are produced by many higher and lower plant species in response to exposure to heavy metals 2. PC production is constitutive and is presumed to play a protective role in reducing potential physiological stress by binding the metals in a less physiologically active state s. This recent study 1 looked for consistency in the patterns of foliar PC concentrations in the context of both elevational and regional gradients in the mortality of red spruce in the northeastern USA. This is a region within which decreases in radial growth and increases in canopy deterioration and mortality of red spruce in recent decades are strongly linked to acidic deposition 4. Gawel

Nitrogen saturation in a high elevation New England spruce-fir stand

High rates of nitrogen (N) deposition were first postulated as a cause of N saturation (i.e. the availability of NH4-N and NO3-N in excess of total combined plant and microbial nutritional demand) and spruce mortality during the 1980s. To test this hypothesis, N addition plots were established in 1988, in a high elevation spruce-fir forest in southeastern Vermont, an area of relatively low N deposition (5.4 kg N bulk deposition ha−1 year−1). To test how the form of applied N may influence forest growth and N-cycling, four replicated treatment plots received either NH4Cl-N, NaNO3-N, or a combination of both N forms at rates ranging from 15.7 to 31.4 kg N ha−1 year−1. The N additions were applied in three equal doses each year between June and August from 1988 to 1994. In addition to N treatments, two control plots were also established. Between 1988 and 1990, annual in situ net N mineralization and net nitrification in the forest floor, litterfall and forest floor mass and elemental concentration, foliar elemental concentration, and basal area growth by species were measured on each plot. In July 1994, basal area growth by species, net N mineralization potential and net nitrification potential in the forest floor, and foliar and forest floor elemental concentration were again measured on all plots. Inter-treatment and intra-treatment basal area growth changed substantially between 1988 and 1994. Spruce, fir, and birch trees on the N addition plots receiving <20 kg N ha−1 year−1 had the highest rate of growth between 1988 and 1990 and then had the highest rate of decline between 1991 and 1994. Spruce, fir, and birch trees on the N addition plots receiving >25 kg N ha−1 year−1 showed moderate rates of decline from 1988 to 1994. Numerous birch and maple sprouts were noted on the sites with the highest rates of decline, but no spruce or fir seedlings were observed. In July 1994, net N mineralization potential was highest on the control plots and net nitrification potential of the forest floor was highest on the plots receiving 15.7 kg N ha−1 year−1. A strong positive correlation existed between forest floor %N and net nitrification potential. Foliar %N was positively correlated with added N and negatively correlated with the change in net basal area growth. Foliar Ca:Al concentrations may also be negatively related to changes in net basal area growth. Our results suggest that N saturation has caused foliar nutrient imbalances on the N addition plots, and that the stands may be changing in species composition and structure. No long-term effects of N-form additions on N saturation and forest health were observed. Continued N additions may change the stands from a slow growing and slow N-cycling coniferous forest, to a fast N-cycling and fast growing deciduous forest.

Bionomics of the four‐eyed spruce bark beetle, Polygraphus rufipennis (Kirby) (Col., Scolytidae) in Newfoundland II. Host colonization sequence

Abstract: The four‐eyed spruce bark beetle, P. rufipennis, is a phloeophagous bark beetle restricted to Abietineae hosts in northern and mountainous area of North America. Projected wood shortages in Newfoundland have focused attention on the bark beetle and its role in contributing to black spruce mortality. Our findings disclosed that colonization on felled and standing trees by P. rufipennis followed the typical host selection sequence of scolytids, notably, emergence, dispersal, selection and establishment. All brood stages except eggs overwintered in black spruce, however, the majority of overwintering stadia consisted of larvae and callow adults. Adult mortality was significant during winter, especially in standing severed and felled trees. In Newfoundland, P. rufipennis had 1 generation and produced a spring and summer brood. Four weeks after establishing a first brood, parent adults re‐emerged to establish a second brood. Development from egg to adult took ≅2 months. P. rufipennis of either sex initiated attack at mean densities per 100 cm2 of 8.1 and 9.3 on felled and standing‐severed trees, respectively. Densities were significantly lower at 4.7 per 100 cm2 on standing unsevered trees. Following copulation, males stayed with the females and exhibit guarding behaviour by occupying the entrance hole. Significantly higher numbers of galleries were established on trees felled in shade than in full sunlight. Black spruce attacked by P. ruipennis were often secondarily attacked by Dryocoetes affaber and Crypturgus borealis. Other associates included Medetera sp. and the cylindrical bark beetle, L. intricatus.

Recent White Spruce Dynamics at the Subarctic Alpine Treeline of North-Western Canada

1 Dendroecological techniques are used to reconstruct the recent population dynamics of white spruce (Picea glauca) at the alpine treeline of north-western Canada in order to test the following hypotheses: (i) the recruitment/survival and mortality patterns of white spruce at treeline are episodic, controlled by climatic variations; and (ii) the response of treeline position to climate change has been limited by a degree of inertia inherent in marginal white spruce populations. 2 The oldest white spruce at all sites, including those at treeline, established at or before AD1800. Rates of successful establishment were low in the early to mid19th century, but have since increased substantially. Mathematical modelling of age distributions and comparison with proxy climate data suggest that summer temperatures both at time of germination and for up to 50 years after germination are important in determining recruitment and survival. 3 Dendrochronological dating of dead spruce remains indicates that a mass mortality of white spruce occurred at a hilltop site during the culmination of the Little Ice Age in the mid-19th century. Subsequent re-establishment at this site has not taken place despite a long-term warming trend. 4 The correlation of recruitment/survival records and mortality events with proxy climate data support the first hypothesis. The second hypothesis is supported by (i) the lack of any substantial increases in treeline altitude during the past 150 years; and (ii) the survival of white spruce throughout a long period of fluctuating climatic conditions at a site currently unsuitable for establishment of spruce. During the past 100-150 years the general trend within these forest-tundra stands has therefore been one of increasing population density, accompanied by only very minor changes in the upper limit of trees.

Mortality of balsam fir and black spruce advance growth 3 years after clear-cutting

The effects of balsam fir (Abiesbalsamea (L.) Mill.) and black spruce (Piceamariana (Mill.) B.S.P.) seedling attributes on survival were measured on four cutovers regenerated to black spruce and three regenerated to balsam fir. In each of these, about 240 stems were permanently identified shortly after logging and their main characteristics were noted. Survival was assessed after 1 and 3 years. First-year mortality reached 24% for balsam fir and and 21% for black spruce. It varied with height and seedling quality. Mortality during the second and third year after harvesting was less important and was more evenly distributed between the different height classes. When all height classes were combined, the logistic regression calculated for total balsam fir mortality was able to correctly classify the observations in 74% of the cases by using three variables: prerelease height growth, lean angle, and a wound index. For black spruce, seven variables were needed to correctly classify 78% of the observations. These were: height, prerelease height growth, live crown ratio, lean angle, distance to the straightening point, and two wound indices. Separate logistic regressions were calculated for stems smaller or taller than 30 cm. These regressions performed considerably better for the taller height class for both species. For balsam fir, lean angle and one or another wound index still remained in relation with survival. For black spruce, prerelease height growth and lean angle remained in relation with survival. Distance to the straightening point was only retained for stems below 30 cm while live crown ratio and the two wound indices were retained for stems over 30 cm. These results suggest that an evaluation of seedling quality using measures of previous suppression and logging damage should be introduced in regeneration surveys to better predict the evolution of a cutover after harvesting.

Long-term recovery of vegetation on two experimental crude oil spills in interior Alaska black spruce taiga

Vegetation was sampled on two black spruce taiga sites in interior Alaska, 15 and 20 years after crude oil was experimentally applied as low-volume sprays or high-volume point spills. Low volume spray spills that uniformly covered the ground caused initial damage to vegetation, but after 20 years recovery of the understory vegetation was almost complete, with dramatic recovery and expansion of fruticose lichens. High-volume point spills created small areas of surface oil saturation with dead vegetation and little sign of recovery but spread out mostly belowground with little or no apparent effect on the shallowly rooted vegetation above even after 15–20 years. Because winter point spills created a much greater area of surface oil, their effects were more damaging. After 15 years on the saturated surface oiled areas, only Eriophorum vaginatum tussocks survive and grow. At both sites with surface oil, black spruce mortality was high, with no evidence of long-term recovery and with continuing chronic effects after 15 years. However, from a long-term perspective the black spruce taiga ecosystem appears to be able to recover from low volume spray spills and to retain large amounts of crude oil from high-volume point spills belowground with minimal damage to the vegetation. Because of the permafrost, removal of crude oil from this ecosystem by soil excavation is undesirable. In situ acceleration of oil breakdown using fertilizers and bacteria is a possible option; seeding or planting of E. vaginatum on surface-oiled areas may also provide some cover and belowground biomass. Key words: oil spills, taiga, black spruce, interior Alaska, vegetation recovery.

Acid rain and soils of the Adirondacks. II. Evaluation of calcium and aluminum as causes of red spruce decline at Whiteface Mountain, New York

Several recent publications suggest that acid deposition produces high anion concentrations in the soil solution of high-elevation forests, causing Al-induced Ca deficiency in red spruce (Picearubens Sarg.) root tips. Some authors suggest that this results in decreased growth below and above ground, decline, and ultimately in death. Accordingly, we examined soil solution Al and Ca, soil and foliar chemistry, and their relationship to red spruce decline on Whiteface Mountain, New York, where severe red spruce mortality occurred between the mid-1960s and late 1980s. Spruce mortality and crown condition are strongly related to elevation, but there is no evidence that the occurrence or degree of spruce decline is related to exchangeable Al, Mg, Ca, or their ratios in mineral or organic horizons. Foliar Ca and Mg concentrations that we measured were in the range judged to be sufficient based on field fertilization studies. Soil solution ratios of Ca:Al in mineral and organic horizons were above the threshold (1:1 molar ratio) proposed as detrimental to Ca uptake in all samples collected during three of four growing seasons, and soil-solution Al concentrations were well below levels thought to inhibit spruce root growth. If Al toxicity is a factor in red spruce decline on this mountain, it is acting in a way that is not detectable using soil and foliar analyses.

Mortality trends in a southern Appalachian red spruce population

Mortality of red spruce ( Picea rubens Sarg.) was assessed in an old-growth spruce-fir forest before and after adelgid-induced mortality of canopy fir at about 1985. Mortality rates of red spruce canopy trees remained low (less than 2% year −1) following the loss of fir from the canopy. However, the proportion of mortality attributable to wind increased from less than 60 to 90%. Transects placed in areas of concentrated wind damage revealed that uprooting or snapping accounted for 94% of the mortality of spruce canopy trees in the winter of 1987–1988. The transect data were biased toward wind-damaged areas and revealed the potential impact of wind-related mortality on spruce. There was no evidence of atypically high wind velocities in the general area, or of a decline in the radial growth of spruce trees prior to death. It was concluded that the loss of Fraser fir ( Abies fraseri (Pursh) Poir.) from adelgid infestation has increased wind exposure to the remaining canopy trees. The increased exposure of southern Appalachian red spruce to wind must be considered in studies of its health.

The Physical, Chemical, and Biological Effects of Crude Oil Spills after 15 Years on a Black Spruce Forest, Interior Alaska

The effects of two large experimental crude oil spills conducted in the winter and summer of 1976 in a permafrost-underlain black spruce forest of interior Alaska were assessed 15 years after the spills. Effects on permafrost, as determined from measurements of active layer thaw depths and of the total amount of ground subsidence, were far more pronounced on the winter spill due to a larger surface-oiled area. The winter spill also had a more drastic effect on the vegetation. Where the black, asphalt-like surface oil was present, black spruce mortality was 100% and there was very little live plant cover except for cotton grass tussocks. Changes in oil chemistry varied with depth; surface samples had signs of microbiological degradation, whereas some subsurface samples taken just above the permafrost had no evidence of degradation and still contained volatile fractions.Key words: crude oil, spill, terrestrial, taiga, permafrost, black spruce forest, interior Alaska

Susceptibility of Western Conifers to Laminated Root Rot (Phellinus weirii) in Oregon and British Columbia Field Tests

Abstract Several species of conifers were outplanted around infected stumps in Oregon and British Columbia to measure their susceptibility to laminated root rot caused by Phellinus weirii. Grand fir (Abies grandis) experienced nearly 30% mortality caused by P. weirii. Douglas-fir (Pseudotsuga menziesii) mortality exceeded 20%. Noble fir (A. procera), Sitka spruce (Picea sitchensis), giant sequoia (Sequoiadendron giganteum), western hemlock (Tsuga heterophylla), and ponderosa pine (Pinus ponderosa) mortality averaged less than 10%. Western white pine (P. monticola) and lodgepole pine (P. contorta) mortality was less than 1%. Phellinus weirii did not cause mortality of western redcedar (Thuja plicata) or redwood (Sequoia sempervirens). Apparent susceptibility, based on mortality over 17-20 growing seasons, was similar to that recorded in past field observations. West. J. Appl. For. 8(2):67-70.

The Role of Abiotic Stresses in the Decline of Red Spruce in High Elevation Forests of the Eastern United States

In the early 1980s heavy mortality of red spruce (Picea rubens Sarg. on mountains in the northeastern USA was recognized as a region-wide phenom­ enon (36). At about the same time, reports of forest decline in the Federal Republic of Germany were common in the scientific literature and popular press. Aluminum toxicity to roots resulting from acid deposition and ozone­ induced carbon budget alterations were the most prominent of the early German hypotheses. Mountain top forests of the eastern U.S. are frequently immersed in highly acidic cloudwater (47), elevated ozone (54), and other pollutants: since there were no consistent, obvious biological causes, hypoth­ eses were advanced that included airborne chemicals as possible causes of red spruce mortality. Those claims were regarded with skepticism by many, since outside southern California, no regional-scale forest health problems had been demonstrated to be the result of air pollution. The scientific debate that ensued brought together forest pathologists, atmospheric scientists, tree physiolo­ gists, soil scientists, forest mensurationists, dendroclimatologists, and forest

White spruce (Picea glauca [Moench] Voss): stagnating boreal old-field plantations unresponsive to fertilization and weed control

Two stagnant teenaged but pre-thicket plantations of white spruce (Picea glauca [Moench] Voss) on old-field sites in the Ontario Clay Belt were studied near Cochrane (49°04′N 81°02′W). Three herbicide × four fertilization treatments were applied, with four independently randomized replications at each site. Weed control (heavy, moderate and none) was with glyphosate, pronamide or nothing, respectively. Ammonium nitrate was broadcast in the first year at 0.0, 55.9, 112.0 and 167.9 kg/ha. Plots were 15 m × 15 m, surrounded by 2-m buffer zones. Performance data on individually identified trees were gathered over a 6-year period in the second decade after planting. Mortality of spruce continued throughout the study and was influenced significantly (P = 0.01) by tree size and by treatment. Mortality increased significantly in treatments that included glyphosate. However, treatments did not significantly (P = 0.05) affect any measured growth parameter. No treatment was silviculturally consequential. Stressed spruce were able to respond only sluggishly to weed control and/or fertilization.

Effect of cover crops on Cylindrocladium sp. in an Ontario bare-root nursery

Four species were grown as cover crops and incorporated into soil of field plots at Midhurst Nursery, Midhurst, Ontario, two times per growing season for 2 successive years. After two seasons, microsclerotial populations of Cylindrocladium sp. were higher in soils planted with alfalfa (Medicagosativa L., cv. Vernal) (p = 0.03) and Sudan grass (Sorghumbicolor (L.) Moench, cv. Green Leaf) (p = 0.10), and not different in soils with spring wheat (Triticumaestivum L., cv. Glen Lea), than populations in noncropped, fallow plots. Lower populations of the fungus were detected in soils planted with flax (Linumusitatissimum L.) (p &lt; 0.08) than in the fallow ones. Highest disease incidence in black spruce (Piceamariana (Mill.) B.S.P.) transplants occurred when grown in plots treated with alfalfa, Sudan grass, and wheat. Disease incidence was lower in transplants grown in the flax plots than in those grown in the other plots (p &lt; 0.001), including the fallow ones (p = 0.055). Spruce mortality was also less in the flax plots compared with all other treatment plots (p &lt; 0.001).

Influence du drainage et de la texture du dépôt sur la vulnérabilité du Sapin baumier et de l'Épinette blanche aux attaques de la Tordeuse des bourgeons de l'épinette

Balsam fir (Abiesbalsamea (L.) Mill.) and white spruce (Piceaglauca (Moench) Voss) mortality was measured in five areas of the province of Quebec severely affected by spruce budworm (Choristoneurafumiferana (Clem.)) defoliation. Mortality was compared for different combinations of soil texture and drainage. For balsam fir, two vulnerability classes, based on combinations of soil texture and drainage, were defined. In the first class, mortality reached 74% of the preoutbreak volume, as compared with 86% in the second class. For white spruce, three vulnerability classes were defined based on soil texture and drainage combinations. In the low, moderate, and high vulnerability classes, white spruce mortality reached 10, 26, and 52%, respectively. Soil moisture regime is an important factor in determining vulnerability. From these results, we propose an ecosystem classification based on vulnerability to spruce budworm. Particular reference is made to what significance the findings may have for forest integrated pest management.

Size-specific mortality, growth, and structure of a Great Smoky Mountains red spruce population

Old-growth population dynamics of Picearubens Sarg. were studied in a montane spruce–fir forest in North Carolina and Tennessee. Size-class structure fit a semilogarithmic rotated sigmoid curve typical of a stable population. Although the population contained trees of all ages, a large proportion of the population was less than 100 years old; few trees were greater than 350 years old. Mortality rates were estimated from a 2-decade census and from population structure data. For trees above breast height, annual mortality was approximately 1% of the population. Small trees (&lt;30 cm dbh) and large trees (&gt;60 cm dbh) had mortality rates exceeding 0.7% per year. Intermediate-sized trees tended to have low mortality rates (&lt;0.5% per year) and high radial growth rates. Growth in the 10-year interval preceding death tended to be slow for standing dead trees. Standing death of canopy trees was more prevalent than death by windfall. These findings emphasized the influence of stand dynamics on spruce growth and mortality.