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Deadwood-associated insects and saprotrophic fungi are principal agents of wood decomposition in boreal forest. Silvicultural treatments that alter microclimate and availability of deadwood likely affect composition and growth rates of both insect and fungal communities, leading to changes in wood decomposition rates. Here, we relate both saproxylic beetle and dominant polypore assemblages with woody decomposition rates and environmental variables in experimental partial cuts, clearcuts, and uncut controls using a series of causal models to determine the relationship between stand structure, biodiversity, and ecosystem function in black spruce ( Picea mariana (Mill.) BSP) forests. Overall beetle and fungal composition differed between uncut stands and harvested stands. Main effects of harvesting included large increases in wood-feeding beetles and the fungus Gloeophyllum sepiarium (Wul.:Fr.) Karst. We suggest that these species were promoted by specific alterations in microhabitat conditions of deadwood. Within clearcuts specifically, changes in species composition and significantly more fungal degree-days resulted in significantly higher decomposition rates. We concluded that levels of partial cutting in the range of 15%–20% retention were not sufficient to maintain predisturbance communities but were sufficient to maintain wood decomposition rates similar to uncut stands.

Modification of forest attributes and structural components like downed wood (DW) during forest harvest can lead to local species loss. Epixylic bryophytes have been proposed as good indicators of such changes. Unharvested control, variable canopy retention, and single pass harvest represent a gradient in forest harvest impact and can be used to test the response of epixylic bryophytes to different levels of environmental change. The objective of this study was to see if variable canopy retention attenuates environmental change associated with harvesting, consequently maintaining an epixylic community more similar to unharvested stands than single pass harvesting. Environmental conditions and DW characteristics were sampled on 225 DW pieces distributed in 45 permanent plots. Results showed that treatment affected epixylic richness through its impact on canopy openness and DW diameter and decomposition class. Fewer species were found in more open habitats and more species were found on bigger and more decomposed DW. Most epixylic species were more commonly found on the forest floor than on the DW. In conclusion, variable canopy retention harvest offered microclimatic conditions and DW availability and quality more suitable for epixylic species than single pass harvest, which was less suitable for epixylic species.

Observed modifications of ectomycorrhizal (ECM) communities have been connected to the increased N depositions of the 20th century. Because of their narrow niche width, small disturbances of soil conditions can produce greater effects on the fungal species than on their host trees. This study investigated the ECM community in a black spruce ( Picea mariana (Mill.) BSP) stand subjected to long-term additions of 9 and 30 kg N·ha–1·year–1 of ammonium nitrate, representing 3 and 10 times the atmospheric N deposition at the site, respectively. Root tip vitality and ECM presence were detected on samples collected from the organic horizon and ECM were classified into morphotypes according to their morphological and anatomical characters. In the control, 80.6% of the root tips were vital, 76.5% of them showing ECM colonization. Higher root tip vitality and mycorrhization were observed in the treated plots. Forty-one morphotypes were identified, most of them detected at the higher N inputs. Results diverging from the expectations of a reduction in ECM presence and diversity could be related to a higher growth rate of the trees following fertilization. The repeated application of small N doses could have been a better imitation of natural inputs from atmospheric deposition and could have provided more reliable responses of ECM to treatment.

The predicted climate warming and more frequent and longer droughts are expected to produce potentially severe water stresses in the boreal forest. The aim of this experiment was to study the effect of a summer drought on xylem phenology and anatomy of mature black spruce ( Picea mariana (Mill.) BSP) trees in their natural environment. The trees were excluded from rain during June–September 2010 by the installation of under-canopy roofs in four sites of the boreal forest of Quebec. Xylem phenology, stem radius variations, and physiological traits of treated and control trees were monitored at short time resolution. At the end of the growth season, cell characteristics were measured. The rain exclusion reduced the cell area of the xylem, but no significant change was observed in cell wall thickness, cell production, or phenology. Stem radius variations of the treated trees were lower but followed the same pattern as the control. After removal of the exclusion, trees and soil quickly recovered their normal water status. One summer of drought led to the formation of smaller tracheids but showed that black spruce is resistant to this rain exclusion treatment. This is likely due to the ability to collect water from sources other than the superficial soil horizon.

Spruce budworm ( Choristoneura fumiferana (Clemens)) defoliation is known to regularly produce radial growth decrease in black spruce ( Picea mariana (Mill.) Britton, Sterns & Poggenb.) in the boreal forest of Quebec. Some studies have already shown that the first year of defoliation does not induce growth losses in the stem but could occur in other tree parts. We therefore examined the timing and duration of the growth reduction caused by the last outbreak in black spruce by also considering the branches. More than 79% of branches and 65% of stems exhibited a >40% growth decrease.The reduction was first registered in the upper part of the stem before being detected lower in the stem in 87% of the trees. Probabilities of growth reduction in the upper part of the stem were highest in 1976 and 1977. In the lower stem, the probabilities were highest in 1978. An interesting finding was that in 69% of the studied stands, the probability of growth reduction started earlier (1–2 years) in the branches than in the stem at 1.3 m. Branch analysis should be considered whenever questions arise in regard to the evolution of spruce budworm defoliation as well as the timing of observed growth reduction in black spruce.

Variants of partial harvesting are gaining favour as means to balance ecosystem management and timber production objectives on managed boreal forest landscapes. Understanding how residual trees respond to these alternative silvicultural treatments is a critical step towards evaluating their potential from either a conservation or a wood supply perspective. We used dendroecological techniques combined with a chronosequence approach to quantify the temporal radial growth response pattern of residual black spruce ( Picea mariana (Mill.) BSP) trees to partial harvest in northeastern Ontario. At its peak, 8–9 years after harvest, radial growth of residual trees had doubled. The growth pattern was characterized by a 2-year phase of no response, a subsequent period of increase 3–9 years after harvest, and a stage of declining rates 10–12 years after harvest. The magnitude of tree growth response depended strongly on tree age: peak postharvest growth was substantially higher for young trees, while old trees displayed only modest growth increases. Both the large magnitude and the time delay in postharvest growth responses have important implications for the development of more accurate quantitative tools to project future yields and, more generally, for determining whether partial harvesting is a viable management option for the boreal forest.

Yield tables are used to identify trends in growing space efficiency (GSE) and to relate GSE to self-tolerance and intraspecific competition. The method is useful when data specifically collected for this purpose are not available. Plonski’s normal yield tables for jack pine (Pinus banksiana Lamb.), paper birch (Betula papyrifera Marshall), trembling aspen (Populus tremuloides Michx.), and black spruce (Picea mariana (Mill.) B.S.P.) are used. An exponential volume–age function was partitioned into volume–area and area–age functions. The exponents of these two components form the B/D ratio, which is used to determine the mode of the stand at a given time, e.g., if B/D is 3/2, then the stand is in area exploitation mode. The dominant mode is the one most responsive to availability of growth resources, showing greater acceleration when resources are plentiful and more rapid deceleration when resources are scarce. Jack pine and paper birch are identified as area occupiers, whereas trembling aspen and black spruce are area exploiters and are therfore self-tolerant. Asymmetric competition was deemed to be present for paper birch throughout the life of the stand on site class I and for trembling aspen on all sites prior to senescence.

Forest biomass, rates of production, and carbon dynamics are a function of climate, plant species present, and the structure of the soil organic and mineral layers. Inventory data from the U.S. Forest Service (USFS) Inventory Analysis Unit was used to develop estimates of the land area represented by the major overstory species at various age-classes. The CENTURY model was then used to develop an estimate of carbon dynamics throughout the age sequence of forest development for the major ecosystem types. The estimated boreal forest area in Alaska, based on USFS inventory data is 17 244 098 ha. The total aboveground biomass within the Alaska boreal forest was estimated to be 815 330 000 Mg. The CENTURY model estimated maximum net ecosystem production (NEP) at 137, 88, 152, 99, and 65 g·m–2·year–1 for quaking aspen (Populus tremuloides Michx.), paper birch (Betula papyrifera Marsh.), balsam poplar (Populus balsamifera L.), white spruce (Picea glauca (Moench) Voss), and black spruce (Picea mariana (Mill.) BSP) forest stands, respectively. These values were predicted at stand ages of 80, 60, 41, 68, and 100 years, respectively. The minimum values of NEP for aspen, paper birch, balsam poplar, white spruce, and black spruce were –171, –166, –240, –300, and –61 g·m–2·year–1 at the ages of 1, 1, 1, 1, and 12, respectively. NEP became positive at the ages of 14, 19, 16, 13, and 34 for aspen, birch, balsam poplar, white spruce, and black spruce ecosystems, respectively. A 5°C increase in mean annual temperature resulted in a higher amount of predicted production and decomposition in all ecosystems, resulting in an increase of NEP. We estimate that the current vegetation absorbs approximately 9.65 Tg of carbon per year within the boreal forest of the state. If there is a 5°C increase in the mean annual temperature with no change in precipitation we estimated that NEP for the boreal forest in Alaska would increase to 16.95 Tg of carbon per year.

In this paper, the biochemical changes associated with a 20 μM abscisic acid (ABA) and desiccation treatment on mature black spruce somatic embryos (SEs) were examined. It was previously shown that this ABA treatment of black spruce SEs resulted in an earlier, more uniform germination (i.e., root and shoot growth synchrony) and increased SE tolerance to slow and fast desiccation. In this paper, mature SEs (control SEs) were either placed on maturation media containing 20 μM ABA for 7 days (ABA-treated SEs) or placed on maturation media for 7 days without ABA (control–ABA SEs). Only the ABA treatment resulted in an increased SE protein content, dry mass, and SE ABA content compared with the control SEs. The ABA treatment was the only treatment that maintained a high percent germination following slow desiccation. Seven proteins with molecular mass of 42-, 33-, 32-, 28-, 27-, 21-, and 20-kDa were identified as storage proteins. An examination of in vivo protein synthesis showed that storage protein synthesis occurred in control SEs, ABA-treated SEs, and control –ABA SEs. There were minor changes, such as a cessation or decline in storage protein synthesis, in the ABA-treated and control –ABA SEs. Protein isolated from the treated and control SEs was probed with an antibody raised to the maize dehydrin. This antibody reacted strongly to a 23-kDa protein and reacted slightly to three other proteins in mature zygotic and somatic embryos and in all treated SEs. The ABA-treated SEs appeared to have a slightly elevated quantity of the 23-kDa dehydrin-like protein (based on intensity of the band in the Western blot). Desiccation of these SEs resulted in a decline in this protein to a level similar to that found in the controls. The ABA treatment induced the synthesis of two low molecular mass proteins (12- and 8-kDa) and their synthesis continued after these somatic embryos were desiccated. The synthesis of the 8-kDa protein was induced when control SEs were desiccated. These results suggest that the ABA treatment extended the maturation stage of development of the black spruce SEs and resulted in an increase in a dehydrin-like protein.

There have been a recent series of papers that have documented underestimation of the age of boreal forest conifers. DesRochers and Gagnon (1997) demonstrated that excavation, serial sectioning to locate the root collar, and detailed dendrochronological analysis of aboveand below-ground sections (cross-dating) of the lower stem of black spruce (Picea mariana (Mill.) BSP) is necessary for exact age estimates. This has been further demonstrated on balsam fir (Abies balsamea (L.) Mill.) by Parent et al. (2000, 2002) and Parent and Morin (2002), and for a variety of boreal mixedwood species by Gutsell and Johnson (2002). Peters et al. (2002) have demonstrated the same difficulties in aging white spruce (Picea glauca (Moench) Voss). We have two objectives in writing this comment on the Peters et al. (2002) paper: (1) To clarify and discuss the issue of the timing of white spruce recruitment in boreal forests. We are concerned that Peters et al. (2002) will lead readers to believe that recruitment of white spruce in boreal mixedwood forests occurs only for a short period immediately after disturbance. (2) We also wish to discuss the place of very accurate but expensive techniques versus less accurate and inexpensive techniques in stand dynamics research. Peters et al. (2002) report the age structure and aging error for white spruce from nine 7-year-old and three older boreal mixedwood stands. They found a 2.4-year mean underestimate of time of establishment in a 20-year-old stand and a 6.4-year underestimate in two 38-year-old stands if tree sections were cut at ground level and rings counted, compared with ages determined by excavation to the root collar and careful cross-dating. Their conclusions were that “previous assumptions that age of white spruce can be accurately determined by ring counts at ground level (Youngblood 1995; Lieffers et al. 1996; Galipeau et al. 1997) are not valid in mixedwood stands in Alberta”, and “the mean number of missing rings found for trees in 38-year-old stands (6.4) nearly accounts for the regeneration lags and extended regeneration duration typically observed in non-cross-dated older stands (Youngblood 1995; Lieffers et al. 1996)”, and “aging errors have led to inaccurate depiction of regeneration patterns during early mixedwood stand development”. We are concerned that readers of Peters et al. (2002) will conclude that recruitment of spruce occurs almost exclusively in a short period after disturbance and that previous studies indicating that recruitment is sometimes delayed or extended were in error. From our reading of these three older papers cited in Peters et al. (2002), we believe that the authors would still have come to the same conclusions that they state in their papers even if they had aged their stands by excavation and cross-dating (assuming similar errors in aging). These papers’ general conclusions were that white spruce recruitment often begins immediately or shortly after disturbance, but in some stands or conditions the recruitment is delayed or extended over a long time period. The data from 46to 86-year-old Alberta stands in Lieffers et al. (1996) show two of nine stands with at least a 20-year delay before spruce recruitment began, and all sites with continuing spruce recruitment for 15–65 years. Youngblood (1995) found white spruce recruitment periods extending for more than 100 years based on ground-level age, although he did not sample all the spruce in his stands. Galipeau et al. (1997) found an initial 20-year white spruce recruitment pulse was followed by a second pulse beginning 40 years after fire in their 70-year-old stand. Even if the ground-level aging error increases with stand age, as Peters et al. (2002) suggest, the magnitude of the errors they found is certainly not large enough to eliminate these recruitment lags and prolonged recruitment periods. Peters et al. (2002) reported data on only three older stands with a narrow range of conditions; in all of their stands the stand-replacing fire was synchronous with a mast year, and there were ample mature spruce seed trees at time of disturbance. In boreal mixedwoods, however, there is considerable spatial and temporal variation in the availability of a seed source, substrates for seed germination, and in the light resource available for seedling growth and survival (Lieffers and Stadt 1994; Wright et al. 1998; Canham et al. 1999). Thus, the older stands studied by Peters et al. (2002) represented a small fraction of the conditions for white

This paper reports on the behaviour of 1 0 experimental crown fires conducted between 1 997 and 2000 dur­ ing the International Crown F ire Model l ing Experiment ( lCFME) in Canada's Northwest Terri tories. The primary goal of I C F M E was a replicated series of high-intensity crown fires designed to val idate and improve existing theoretical and empirical models of crown fire behaviour. Fire behaviour characteristics were typical for fully developed boreal forest crown fires, with fires advancing at 1 5-70 m/min, consuming significant quantities of fuel ( 2 .8-5 .5 kg/m2) and releasing vast amounts of thermal heat energy. The resulting flame fronts commonly extended 25-40 m above the ground with head fire intensities up to 90 000 kW/m. Depth of bum ranged from 1 .4-3.6 cm, representing a 25%-65% reduction in the thickness of the forest floor layer. Most of the smaller diameter «3.0 cm) woody surface fuels were consumed, along with a significant proportion of the larger downed woody material . A high degree of fuel consump­ tion occurred in the understory and overstory canopy with very l ittle material less than 1 .0 cm in diameter remaining. The documentation of fire behaviour, fire danger, and fire weather conditions carried out during I C F M E permitted the evaluation of several empirically based N orth American fire behaviour prediction systems and models. Resume: Cet article traite du comportement de 1 0 feux de cime experimentaux provoques entre 1 997 et 2000 dans Ie cadre de l'Experience internationale de modelisation des feux de cimes ( E I MFC) dans les Territoires du Nord-Ouest au Canada. Le principal objectif de cette experience consistait a reproduire une serie de feux de cime de forte intensite con9us pour valider et ameliorer les modeles theoriques et empiriques existants de comportement des feux de cime. Les caracteristiques du comportement des feux de cime etaient typiques des feux de cime en foret boreale mature, OU les feux progressent a 1 5 a 70 m/min, en consumant d'importantes quantites de combustibles ( 2 ,8 a 5,5 kg/m2) et generent de fortes quantites d'energie thermique sous forme de chaleur. Les fronts de flamme qui en resultent s'elevaient gene­ ralement a 25 a 40 m au-dessus du sol avec des intensites a la tete du feu al l ant jusqu'a 90 000 kW/m. La profondeur de brGlage variait de 1 ,4 a 3,6 cm, ce qui representait une reduction de 25 % a 65 % de I'epaisseur de la couverture morte. La plupart des combustibles de surface de plus petit diametre «3,0 cm) ont ete consumes de meme qu'une im­ portante proportion du plus gros materiel l igneux au sol. II y a eu une forte consommation de combustibles dans Ie couvert des etages inferieur et superieur ou il restait tres peu de materiaux d'un diametre inferieur a 1 ,0 cm. La docu­ mentation du comportement du feu, Ie danger de feu et les conditions meteorologiques propices aux incendies fores­ tiers ont permis d'evaluer plusieurs systemes et modeles empiriques nord-americains de prediction du comportement des feux. [Traduit par la Redaction] Received 26 September 2003. Accepted 10 February 2004. Published on the N RC Research Press Web site at http: //cjfr.nrc.ca on 1 2 August 2004. B.J. Stocks,2 B.M. Wotton, M.D. Flannigan, J.A. Mason, C.R. Hartley, and T. W. Blake. N atural Resources Canada, Canadian Forest Service, Great Lakes Forestry Centre, 1 2 1 9 Queen Street East, Sault Ste. Marie, ON P6A 2E5, Canada. M.E. Alexander, CN. Stefner, and M.E. Maffey. N atural Resources Canada, Canadian Forest Service, Northern Forestry Centre, 53201 22 Street, Edmonton, AB T6H 3S5. Canada. S.W. Taylor and C.N. Dalrymple. Natural Resources Canada. Canadian Forest Service, Pacific Forestry Centre. 506 West Burnside Road, Victoria, BC V8Z I M5, Canada. N. Lavoie. University of Alberta, Faculty of Agriculture, Forestry, and Home Economics, Department of Renewable Resources, Edmonton, AB T6G 2 1 -1 I, Canada. M.C. Cruz. University of Montana, College of Forestry and Conservation, Missoula, MT 598 1 2, U SA. R.A. Lanoville. Government of Northwest Territories, Department of Resources, Wildlife and Economic Development, Forest Management Division, P.O. Box 7, Fort Smith, NT XOE OPO, Canada. IThis article is one of a selection of papers published in this Special Issue on The International Crown Fire Modelling Experiment ( I C F M E) in Canada's Northwest Territories: Advancing the Science of Fire Behaviour. "Corresponding author (e-mai l : bstocks@nrcan.gc.ca). Can. J. For. Res. 34: 1548-1560 (2004) doi: 10.1 1 39/X04-054 © 2004 N RC Canada

Black spruce (Picea mariana (Mill.) Britton, Sterns & Poggenb.) and white spruce (Picea glauca (Moench) Voss) are phylogenetically proximal species that differ in productivity. Crown characteristics of these two species have not been extensively studied, in spite of the importance of these two species to the Canadian boreal forest and the importance of tree crowns for understanding and modelling tree growth. In this paper, we characterize and compare the crown lengths, crown profiles (i.e., radii), shapes, and surface areas of these two species using 65 white spruce and 57 black spruce trees destructively sampled in the provinces of Alberta, Ontario, and Quebec, Canada. Crown length was measured on every sam- ple tree, while crown profile was obtained by reconstructing crowns from branch measurements. Our results showed that crown lengths did not differ between these two species given the same tree size and growth conditions. However, these two species establish under different growth conditions resulting in crown length differences. Further, differences in crown radii and profiles were found even under the same growth conditions. White spruce trees had wider crown radii and profiles changed from a parabola to a cone shape under increased density. As a result, differences in crown surface areas were found. Abstract: Les epinettes noires (Picea mariana (Mill.) Britton, Sterns & Poggenb.) et blanches (Picea glauca (Moench) Voss) sont des especes phylogenetiquement proximales dont la productivite differe. Les caracteristiques de la cime de ces

This paper presents soil fluxes of methane (CH4), nitrous oxide (N2O), and carbon dioxide (CO2) from 12 sites located in four major forest types, black spruce ( Picea mariana (Mill.) BSP), jack pine ( Pinus banksiana Lamb.), aspen ( Populus spp.), and alder ( Alnus spp.) stands, in the Eastmain and Chibougamau regions of Quebec. Fluxes were determined with closed chambers during the snow-free period from May to October 2007. Well-drained black spruce, jack pine, and aspen forest soils were net sinks of atmospheric CH4 (–0.33 ± 0.11 mg·m–2·day–1), while alder-dominated wetland soils were sources of CH4 (0.45 ± 0.12 mg·m–2·day–1). The cut-over alder wetland soil produced 131 times more CH4 than the undisturbed wetland soil. Soil moisture and temperature mainly regulated CH4 fluxes. N2O fluxes from these forest soils were highly variable and smaller (1.6 ± 0.33 µg N·m–2·h–1) than those from deciduous forest soils. N2O emission from the cut-over black spruce forest soil was 2.7 times greater than that from the mature black spruce forest soil. Large C/N ratios (27 to 78) and slow soil N mineralization and nitrification rates in these forest soils may have led to small N2O fluxes. CO2 emissions from these forest soils, ranging from 0.20 to 2.7 g·m–2·day–1, were mainly controlled by soil temperature.

This paper reports on the behaviour of 10 experimental crown fires conducted between 1997 and 2000 during the International Crown Fire Modelling Experiment (ICFME) in Canada's Northwest Territories. The primary goal of ICFME was a replicated series of high-intensity crown fires designed to validate and improve existing theoretical and empirical models of crown fire behaviour. Fire behaviour characteristics were typical for fully developed boreal forest crown fires, with fires advancing at 15–70 m/min, consuming significant quantities of fuel (2.8–5.5 kg/m2) and releasing vast amounts of thermal heat energy. The resulting flame fronts commonly extended 25–40 m above the ground with head fire intensities up to 90 000 kW/m. Depth of burn ranged from 1.4–3.6 cm, representing a 25%–65% reduction in the thickness of the forest floor layer. Most of the smaller diameter (

A current trend in the development of forest stand models is to use spatially explicit, individual-tree infor- mation to simulate forest dynamics with increased accuracy. By adding spatial information, such as tree coordinates, crown shape, and size, it is hypothesized that the computation of the model's driving function is improved over tradi- tional competition indices, especially when simulating multistoried stands. In this paper, we want to test whether computationally demanding competition indices outperform traditional indices in predicting mean basal area increment. The study was undertaken in old, uneven-aged black spruce (Picea mariana (Mill.) BSP) stands in northeastern Que- bec, Canada. The predictability of individual tree growth rates was related to crown dimensions and other stand and tree variables measured in the field. Data were collected from 90 trees coming from stands of varying site quality (range 9.6-16.5 m height at 50 years, age taken at 1 m) and age (range 66-257 years). Hegyis's distance-dependent competition index was found to be the most strongly correlated competition measure (r = 0.57) with mean basal area growth of the last 20 years. This value, 12% higher than the value obtained from the best distance-independent compe- tition index (r = 0.45), clearly shows that precision gains can be achieved when estimating basal area increment with spatial indices in black spruce stands. Using indices computed from virtual hemispherical images did not prove supe- rior to simpler distance-dependent indices based on their individual correlations with basal area increment. When in- cluded in a basal area increment model for the last 20 years of growth, however, the gains in precision were comparable to Hegyi's competition index. This indicates that indices derived from a hemispherical approach have some value in spatially explicit forest simulations models but that further tests using younger stands are needed to confirm this result in black spruce stands. Resume : La tendance actuelle dans la mise au point de modeles a l'echelle du peuplement forestier consiste a em- ployer de l'information spatialement explicite a partir d'arbres pris individuellement afin de simuler la dynamique des forets avec une precision accrue. En ajoutant de l'information spatiale telle que la localisation des arbres, la forme et la dimension des houppiers, on presume que le calcul de la fonction motrice du modele est amelioree par rapport aux in- dices de competitions traditionnels, particulierement pour la simulation de peuplements pluri-etages. Dans cet article, nous voulons tester si les indices de competition qui sont particulierement couteux en temps de calcul informatique surpassent les indices traditionnels en precision pour predire l'accroissement moyen en surface terriere. L'etude a ete entreprise dans de vieux peuplements d'epinette noire de structure inequienne (Picea mariana (Mill.) BSP) localises dans le Nord-Est du Quebec, au Canada. La previsibilite des differents taux de croissance des arbres a ete reliee a la dimension des houppiers et a d'autres variables du peuplement et a des mesures d'arbres prises sur le terrain. Des don- nees ont ete recueillies sur 90 arbres provenant de peuplements de diverses qualites de station (ecart allant de 9,6 a 16,5 m de haut a 50 ans, âge pri sa1m ) et differents âges (ecart allant de 66 a 257 ans). L'indice de competition de- pendant des distances de Hegyi s'est avere la mesure de competition la mieux correlee (r = 0,57) avec l'accroissement moyen en surface terriere des 20 dernieres annees. Cette valeur, 12 % plus haute que la valeur obtenue a partir du meilleur indice de competition independant des distances (r = 0,45), demontre clairement que des gains de precision peuvent etre realises en estimant l'accroissement moyen en surface terriere avec des indices de type spatial dans des peuplements d'epinette noire. L'emploi d'indices de competition calcules a partir d'images hemispheriques virtuelles ne s'est pas avere meilleur que l'utilisation d'indices de competition dependants des distances, plus simples, si on se base sur leurs correlations avec l'accroissement moyen en surface terriere. Lorsqu'inclus dans un modele d'accroissement moyen en surface terriere au cours des 20 dernieres annees, cependant, les gains en precision pour le modele etaient comparables a ceux obtenus avec l'indice de competition de Hegyi. Ceci indique que les indices derives d'une ap- proche hemispherique ont une certaine valeur dans les modeles de simulation forestiere spatialement explicites, mais egalement que d'autres essais avec de plus jeunes peuplements sont necessaires pour confirmer ce resultat pour les peuplements d'epinette noire. Mailly et al. 443

Allometric equations were developed relating aboveground biomass, coarse root biomass, and sapwood area to stem diameter at 17 study sites located in the boreal forests near Thompson, Man. The six species studied were trembling aspen (Populus tremuloides Michx.), paper birch (Betula papyrifera Marsh.), black spruce (Picea mariana (Mill.) BSP), jack pine (Pinus banksiana Lamb.), tamarack (Larix laricina (Du Roi) Koch.), and willow (Salix spp.). Stands ranged in age from 4 to 130 years and were categorized as well or poorly drained. Stem diameter ranged from 0.1 to 23.7 cm. Stem diameter was measured at both the soil surface (D0) and breast height (DBH). The relationship between biomass and diameter, fitted on a log–log scale, changed significantly at ~3 cm DBH, suggesting that allometry differed between saplings and older trees. To eliminate this nonlinearity, a model of form log10 Y = a + b(log10 D) + c(AGE) + d(log10 D × AGE) was used, where D is stem diameter, AGE is stand age, and the cross product is the interaction between diameter and age. Most aboveground biomass equations (N = 326) exhibited excellent fits (R2 > 0.95). Coarse root biomass equations (N = 205) exhibited good fits (R2 > 0.90). Both D0 and DBH were excellent (R2 > 0.95) sapwood area predictors (N = 413). Faster growing species had significantly higher ratios of sapwood area to stem area than did slower growing species. Nonlinear aspects of some of the pooled biomass equations serve as a caution against extrapolating allometric equations beyond the original sample diameter range.

Quantification of the effects of stand age on its net primary productivity (NPP) is critical for estimating forest NPP and carbon budget at regional to global scales. This paper reports a practical method for quantifying age–NPP relationships using existing normal yield tables, biomass equations, and measurements of fine-root turnover and litterfall. Applying this method, we developed mean age–NPP relationships for black spruce (Picea mariana (Mill.) BSP) stands in Ontario. We define "mean age–NPP relationship", as the changes in NPP that occur with age under long-term mean environmental conditions. These relationships indicate that NPP at more productive sites culminates to a higher value and at an earlier age and also declines more rapidly thereafter. A further component analysis indicates that the decrease in biomass growth of woody tissues is the main contributor to the decline with age. Finally, error assessment suggests that the uncertainty in NPP estimates can be substantially reduced with a better quantification of fine-root turnover and litterfall, which are the two dominant NPP components, particularly in the later stages of stand development. With new techniques now available, more accurate measurement of these components is possible, and thus strongly recommended.

The influence of spruce budworrn (Choristoneurafumiferana (Clem.)) defoliation was analysed at different stem heights by counting the number of latewood tracheids and measuring tree-ring width. The total height of the tree was divided into three different equal parts: the lower, the middle, and the upper sections of the total stem length. However, only the results of the lower and the upper sections will be presented in this paper. The reduction of ring widths started in the upper part for the living crown and continued downwards to the stem base (0 m) with a delay of 1–2 years. The number of latewood tracheids generally showed a reduction 1 year earlier than the ring widths, particularly in the crown, but also in the other parts of the stem. Considering this, we think that the reduction of the number of latewood tracheids may date the beginning of spruce budworm defoliation more accurately and present a better characterization of the first impact of spruce budworm than the measuring of the ring widths. This parameter will be particularly helpful (when expensive equipment, such as a densitometer or an image analysis system cannot be used) in detecting past outbreaks in the tree-ring records, especially when defoliation records are missing and when the reduction of the ring widths is not very pronounced.

This paper reviews the geographic extent, distribution, plant communities, forage productivity and animal production of Crown range in British Columbia. Over 10 million ha of Crown range is distributed among 11 biogeoclimatic zones. Forestland comprises nearly 80% of the landbase grazed. In the southern interior, the most important zones include the Bunchgrass, Ponderosa Pine, Interior Douglas-Fir and Montane Spruce zones. Forage yields vary from as much as 2700 kg ha−1 on grassland to −1 under dense forest canopy. On seeded clearcuts, however, production may exceed 1500 kg ha−1. Average daily gains for steers and calves on forest range vary from 0.8 to 1.1 kg d−1. In the central interior and Peace River areas, the Sub-Boreal Pine–Spruce, Sub-Boreal Spruce and Boreal White and Black Spruce zones provide most of the forage for beef cattle. Seventeen community pastures, comprising nearly 170 000 ha, produce almost 50 000 animal-unit months (AUMs) of forage for cattle in this region. Forage production potential is high, especially on community pastures, but the grazing period is generally only 4–5 mo. Management of livestock and forage on Crown range in British Columbia may be more complex than in other regions of Canada because of the diversity of vegetation and climate and the extensive overlap of range use with other resource interests. Consequently, livestock and forage management needs to be modified to produce optimal returns to the livestock industry within an integrated-use framework. Keywords: Animal production, beef cattle, British Columbia, forage production

Mature boreal forest ecosystems in interior Alaska are large annual carbon sinks. Annual tree production is the largest carbon flux. A model of that combined energy, heat, and moisture exchange, tree photosynthesis and respiration, decomposition, and nitrogen mineralization was used to examine the physiological controls of the carbon balance of boreal forests. Simulated annual tree production, forest floor decomposition, nitrogen mineralization, and soil respiration were not significantly different from observed data for nine black spruce (Piceamariana (Mill.) B.S.P.), five white spruce (Piceaglauca (Moench) Voss), two quaking aspen (Populustremuloides Michx.), two paper birch (Betulapapyrifera Marsh.), and three balsam poplar (Populusbalsamifera L.) forests near Fairbanks, Alaska. The model also reproduced features of observed fertilization, soil warming, and litter transplant experiments. Net carbon uptake during tree growth was the largest simulated carbon flux, and these analyses suggest that differences in the carbon balance of these forests can be explained, in part, through key physiological parameters that link photosynthesis, carbon allocation, nitrogen requirements, litter quality, and foliage longevity. The simulations suggest that the greatest source of variation in these parameters occurs between coniferous and deciduous life-forms not among species. Simulation experiments showed that the coniferous and deciduous physiological parameters maximized annual tree production for coniferous and deciduous forests, respectively, thereby providing a physiological basis for the evolution of the different life history characteristics of deciduous and coniferous species. The strong coherency among physiological parameters allows them to be estimated from easily obtained data and may provide a basis to examine carbon fluxes over large regions.

Boreal forests contain large quantities of soil carbon, prompting concern that climatic warming may stimulate decomposition and accentuate increasing atmospheric CO2 concentrations. While soil warming increases decomposition rates, the accompanying increase in nutrient mineralization may promote tree growth in these nutrient-poor soils and thereby compensate for the increased carbon loss during decomposition. We used a model of production and decomposition to test this hypothesis. In black spruce (Piceamariana (Mill.) B.S.P.), white spruce (Piceaglauca (Moench) Voss), and paper birch (Betulapapyrifera Marsh.) forests, decomposition increased with the soil warming caused by a 5 °C increase in air temperature. However, increased nitrogen mineralization promoted tree growth, offsetting the increased carbon loss during decomposition. In the black spruce forest, increased tree production was maintained for the 25 years of simulation. Whether this can be maintained indefinitely is unknown. In the birch forest, tree production decreased to prewarming levels after about 10 years. Our analyses examined only the consequences of belowground feedbacks that affect ecosystem carbon uptake with climatic warming. These analyses highlight the importance of interactions among net primary production, decomposition, and nitrogen mineralization in determining the response of forest ecosystems to climatic change.

This paper reports results of a study designed to examine the control that soil temperature exerts on soil processes associated with nutrient flux, and in turn, on tree nutrition in interior Alaska black spruce ecosystems. Approximately 50 m2 of forest floor in a 140-year-old black spruce ecosystem, which had developed on permafrost, was heated to 8–10 °C above ambient temperature. This perturbation amounted to approximately a 1589 degree-day seasonal heat sum (above 0 °C), 1026 degree-days above the control total of 563 degree-days. The forest floor, surface 5 cm of mineral soil, and soil solution were compared with those of an adjacent control plot to evaluate the change in nutrient content and decomposition rate of the forest floor. The nutritional response to soil heating of current black spruce foliage also was evaluated. Soil heating significantly increased decomposition of the forest floor, principally because of an increase in biomass loss of the O21 layer. The increased decomposition resulted in greater extractable N and P concentrations in the forest floor, higher N concentrations in the soil solution, and elevated spruce needle N, P, and K concentrations for the experimental period. These results are discussed in light of the importance of soil temperature and other state factors that mediate ecosystem function.

This paper considers the extent to which phosphorus (P) supply for plant use is controlled by the chemical quality of forest floor organic matter, independent of climate. Using plant bioassays, forest floor materials from representative examples of each of the major forest types in interior Alaska were examined for nutrient supplying power. The work supports conclusions reached in earlier studies which indicated that black spruce forest floors were highly nutrient limited compared with those of other interior Alaska forest types. In addition, floodplain white spruce forests may experience marked P deficiency because of dilution of the element by periodic siltation. Potential phosphorus supply for seedling growth was best described by P concentration of the rooting medium. The supply also was related to the concentrations of lignin and tannin which control forest floor decomposition and recycling of P within the microbial population.

Soil chemical properties were studied after a wildfire in stands of white spruce (Piceaglauca (Moench) Voss), black spruce (Piceamariana (Mill.) B.S.P.), paper birch (Betulapapyrifera Marsh.), and quaking aspen (Populustremuloides Michx.). Samples of the forest floor and surface 5 cm of mineral soil were collected from burned sites and unburned controls and analyzed soon after the fire. With the exception of soil pH, effects of the fire on soil chemistry differed among the four forest types. Generally, amounts of exchangeable K, Ca, and Mg did not appreciably increase in the forest floor and surface mineral soil except in heavily burned areas in white spruce and black spruce. Fire reduced amounts of N by about 50% in white spruce, aspen, and birch forest floors. In black spruce, quantities of N were slightly higher in heavily burned locations. Forest floor C:N ratios were substantially lower in heavily burned locations in white spruce and black spruce than in unburned controls. Burning did not have a marked influence on supplies of available P in the forest floor, except in heavily burned black spruce, where average amounts were 12.50 g/m2 versus only 0.46 g/m2 in the control. Burning caused more moderate gains in available P in surface mineral soils under aspen and white spruce. We concluded that fire caused marked short-term changes in soil chemistry in the four forest types. How long these changes will persist is unknown.

Arthropod composition was similar in six vegetation types in a taiga ecosystem of Alaska. Four taxonomic classes representing 94 arthropod families were found at the herb, shrub, and tree levels of aspen (Populustremuloides Michx.), paper birch (Betulapapyrifera Marsh.), balsam poplar (Populusbalsamifera L.), white spruce (Piceaglauca (Moench) Voss), and black spruce (Piceamariana (Mill.) B.S.P.) vegetation types. Of all vegetation types, ground herbs contained the highest density of arthropods. Black spruce types had the highest arthropod densities at the tree level but the lowest diversity of species. Populations of arthropods were highest during June and July in hardwood types and during July and August in spruce types. Concentrations of sodium and magnesium increased as trophic levels increased; highest concentrations were in arthropod predators. Concentrations of potassium and calcium increased from the herbivore to the saprovore level. Annual element budgets for sodium, magnesium, potassium, and calcium are discussed.

To date, methods of deriving site index (S) equations assume that stochastic error is only present in the regressor. This paper develops a method, termed the "structural method," which recognizes that both dominant stand height (H) and S measurements contain stochastic error. To achieve this, the structural method utilizes the structural relationship that exists between H and S to derive an S equation. S equations are derived for black spruce, Piceamariana (Mill.) B.S.P., using the structural method and various other methods, with linear and nonlinear models that are currently in use. Data used in the study consist of 56 black spruce permanent sample plots, containing a total of 382 observations, from north central Ontario and the Clay Belt Region of northern Ontario. This data set is split into 36 plots (260 observations) for deriving S equations and 20 plots (122 observations) for testing the equations for accuracy in predicting H, S, and future H. The equations are also examined for bias over stand age. Results show that height development of black spruce is not asymptotic and is best described by a linear model. Overall, the structural method provides the most accurate S equation within the range of the data. It predicted 90% of the H test observations with an error of 0.4 m or less, 89% of the S test observations with an error of 0.4 m or less, and 90% of the future H test observations with an error of 0.7 m or less. The structural method also has the advantage of producing only one equation for predicting both H and S. This enables estimates of both H and S to be made from one graph of H over age by S classes.

A soda lime technique was used to measure CO2 evolution at the soil surface in four mature forest types (aspen (Populustremuloides Michx.), paper birch (Betulapapyrifera Marsh.), black spruce (Piceamariana (Mill.) B.S.P.), and white spruce (Piceaglauca (Moeneh) Voss)) in interior Alaska. Surface temperature, 15-cm depth temperature, and soil moisture were measured concurrently with CO2 evolution. Accumulated CO2 evolution ranged from 1315 to 1654 g CO2•m−2 for the period May 1 – September 30 in 1981 and 1982 in the four stands. Data were used to develop three-dimensional response surfaces and test mathematical models of respiration in relation to substrate temperature and moisture. GRESP, a biologically based model, provided a fairly accurate simulation of the seasonal course of respiration as a function of substrate temperature and moisture. In an attempt to better define the observed response surface trends, a best-fit equation model, BRESP, was formulated. BRESP includes the moisture portion of the GRESP equation, and an altered temperature equation which more adequately defines the upper and lower thresholds of respiration in relation to substrate temperature. GRESP and BRESP each produced similar r2 values; however, higher order polynomial equations gave a better-fit model. The weakest area of all models for simulating seasonal trends was during the periods of peak respiration in June.

Forest-floor decomposition is compared among 16 Alaskan taiga forest stands. These include black spruce (Piceamariana (Mill.) B.S.P.), white spruce (Piceaglauca (Moench) Voss), and birch (Betulapapyrifera Marsh.), aspen {Populustremuloides Michx.), and balsam poplar (Populusbalsamifera L.) types, spanning a wide range in decomposition rates, forest-floor microclimates, and litter quality. Jenny's index of decomposition rate, k, is reasonably well correlated with annual cellulose (filter-paper) decomposition differences among stands. Both estimates of decomposition rate are correlated with forest-floor heat sum and forest-floor nitrogen concentration. These between-site correlations support inferences based upon experimental work claiming that temperature and forest-floor chemical quality have a major influence upon the level of decomposition in a particular stand. Inferences about the factors regulating decomposition rate around an average level within one stand cannot legitimately be made from the same correlations. Moisture has not been considered in this analysis, but could also be important to between-stand differences in decomposition rate.