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In many northern forests, the preferred time of harvesting is when the ground is frozen. Logging activities on frozen ground reduce the cost of forest operations by allowing heavier loads on temporary roads and makes crossing wetlands feasible. Increased winter temperature and more frequent winter thaws decrease the period of frozen ground conditions. In order to adapt to shorter periods of frozen logging season, forest companies might have to access frozen harvesting sites in the non-frozen season. In this study, we examined the cost of temporary forest road construction in terms of switching logging activities from frozen to non-frozen conditions. The objectives were to estimate the costs of non-frozen temporary roads for four harvesting units with different difficulty of access. We also analyzed construction costs for both frozen and non-frozen access under possible different wetter and drier scenarios. The results show that the average cost of temporary road construction increased from $1,200 km−1 or $0.30 m−3 in frozen conditions to $5,962 km−1 or $2.14 m−3 in non-frozen conditions. Under the extreme wet scenarios, the cost of non-frozen roading ($ m−3) of the unit with the most difficult access was up to 14.6 times more than frozen road construction. If the soil dried faster than the base case scenario, cost increases of non-frozen road construction ($ km−1) were expected to be between 2.3 times and 8.6 times more than the frozen road construction cost, depending upon the difficulty of accessing the unit. [ABSTRACT FROM AUTHOR]

Copyright of Forestry Chronicle is the property of Canadian Institute of Forestry and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Journal of Forest Research is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In some boreal forests sites, there are considerable amounts of natural regeneration of white spruce (Picea glauca (Moench) Voss) after logging, even without silvicultural treatments to encourage establishment. We assessed the factors controlling the amount of this regeneration 8–15 years postharvest on previously aspen-dominated (Populus tremuloides Michx.) boreal mixedwood sites. We surveyed 162 transects across 81 cutovers, exploring the effects of mast years, season of harvest, distribution of seed trees, weather conditions around the time of harvest, and abundance of grass or woody vegetation on white spruce regeneration. Substantial amounts of naturally regenerated white spruce were found; however, sites with no seed trees had virtually no spruce regeneration. Average stocking was 7% (percentage of 9 m2 plots along a transect across a cutover that had at least one seedling), ranging from 0% to 62%. Stocking levels were higher in cutblocks that had been harvested in the summer, prior to seedfall of a mast year, and where there was a seed source within 60 m. Stocking was lower when conditions were cool and wet the year before and 2 years after harvest and when the site contained extensive cover of grass or woody vegetation. [ABSTRACT FROM AUTHOR]

This study tests the hypothesis that ring growth in the upper stem portion of trees is affected by climatic conditions differently than rings formed at breast height (1.3 m). A total of 389 trees from a network of 65 lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) sites in Alberta were examined using detailed stem analysis in order to examine interannual patterns of basal area increment and volume increment at different positions along the stem. Growth at lower sections of the bole was mainly driven by temperature and moisture conditions in the seasons prior to the growing season in the year of ring formation, while upper stem growth was more related to conditions during the year of growth, i.e., temperature in the early summer, or moisture in late winter to early spring. This translates into increased allocation of wood to the lower stem when prior late summer conditions are cool and wet, prior winters are mild (warm with little snow) and early summer conditions in the year of ring formation are hot and dry. [ABSTRACT FROM PUBLISHER]

Copyright of Forestry Chronicle is the property of Canadian Institute of Forestry and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Permanent sample plots (PSPs), measured at 5- to 10-year intervals, are presently used to monitor stand development in boreal forests in Canada. These data cannot easily be used to study inter-annual variability in stand development processes nor can they monitor the effects of transient factors affecting stands annually because of their coarse temporal resolution. It also takes a considerable period of time to obtain time series of data for regions without PSPs. Long re-measurement intervals are necessary because instruments like diameter tapes, calipers and clinometers cannot discern annual growth in these slow-growing forests. Dendrochronological stand reconstruction techniques are a method that can be used to obtain annual data on forest growth and stand development. We show that these techniques can provide annual information on stand development patterns while periodic measurements of PSPs cannot, and that these data can be obtained in a short period of time, relative to waiting to obtain data from PSPs established today. Detailed, annual data will become more important in the future, as climate change will affect both forest growth and stand dynamics. Annual resolution data on these processes will be required to describe and account for these effects. [ABSTRACT FROM AUTHOR]

The dynamics of aspen (Populus tremuloides Michx.) species composition (SC, defined as the ratio of aspen basal area to total stand basal area) in boreal mixedwoods were modelled in this study using the difference equation method, based on datasets collected from repeatedly measured permanent sample plots (PSPs) across Alberta. The aspen SC measured at time 1 was taken as a key predictor variable to project SC values at future ages. Since site quality was found to impact the aspen SC, site index (SI) was incorporated into the model. To correct the autocorrelation and heteroskedasticity problems associated with PSPs data, the non-linear mixed-model technique was applied to accommodate the variance-covariance structure of the error terms and to estimate model parameters. The final model was evaluated on an independent dataset collected from a different region in Alberta, based on a number of statistical measures including a goodness of prediction index (GOPI) from forward and backward projections, and examinations of residual and studentized residual plots. The low prediction bias and high GOPI value obtained from forward and backward projections on the validation data suggest that the model fitted the data well and can be reliably applied to predict changes in aspen SC in boreal mixedwoods across Alberta. The model showed a decline in the SC after year 30, but the decline was steeper in sites of low SI. The model can be used for modelling the transitions of forest compositions in boreal mixedwood forests. [ABSTRACT FROM AUTHOR]

Copyright of Botany is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Forestry Chronicle is the property of Canadian Institute of Forestry and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Forestry Chronicle is the property of Canadian Institute of Forestry and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Crown shyness is the empty space between crowns in fully stocked stands that is not related to tree-fall gaps. The objectives of this study were to determine the stand and site factors that control crown shyness in lodgepole pine (Pinus contorta Dougl. ex Loud.) stands and to evaluate whether stands experiencing crown shyness compensate for leaf area losses by maintaining longer crowns. We measured canopy closure (i.e., the inverse of crown shyness), crown radius and length, and green litterfall in stands of various height, relative density, and site index. Canopy closure decreased with stand height and increased with site index and relative density. Green litterfall increased with height and relative density. Crown radius and crown length reached a plateau by 8-10 m height, despite increased spacing between tree boles with increasing stand height. Crown radius increased with height and site index but declined with relative density and slenderness coefficient. Crown length also increased with height and site index but declined with slenderness coefficient. Despite the fact that, in tall stands, where >50% of the sky was not covered by crowns, there was not an accompanying increase in crown length to take advantage of the apparent increase in light transmission to the lower crown. [ABSTRACT FROM AUTHOR]

1 Crown collisions induced by tree sway are hypothesized to reduce crown closure and leaf area in maturing cold temperate forests. These declines are thought to lead to the decline in productivity when a stand ages. 2 We tethered groups of lodgepole pine ( Pinus contorta Dougl. Ex Loud. Var. latifolia Engelm.) trees in a web pattern at 10 m height, in four 15-m tall stands in western Alberta, Canada, to determine whether preventing crown collisions would increase crown cover and leaf area. 3 The stands all had less than 65% crown closure at the beginning of study. Photographs of the canopy were taken in each control and webbed plot in 1998 and at the same point in 2004. Six years after webbing, crown cover had increased by 14.4%, compared to a 2.1% increase for the control plots. 4 Webbing also resulted in significant increases in mean branch length, leaf area per branch and foliage density of individual branches from top and middle sections of the crown. Polishing of branches, caused by chronic contact with adjacent trees, was three times as common on control trees compared to webbed trees. The mean leaf area per tree was larger for the webbed trees. 5 Crowns of webbed trees were more symmetrical than those of control trees. Trees from webbed plots, however, had a decline in leaf area density. The branches of control trees were typically curved upward with twigs pointed inward, making the crowns more compact compared to the outwardly expanding crowns of trees from the webbed plots. 6 The fact that crowns expanded laterally after webbing, despite little change in light regime, provides strong evidence against the hypothesis that loss of crown closure in maturing stands is caused by a lack of light. 7 The study indicates that the decline in crown closure and leaf area in maturing and tall stands is at least partly related to wind-induced sway of trees abrading the edges of crowns. [ABSTRACT FROM AUTHOR]

Investigates the tree sway and crown collision behavior of even-aged lodgepole pine stands of different structure in Alberta, Canada. Comparison between Two Creeks and Chickadee stands; Factors that create spatial heterogeneity in light within and below the canopy; Determinants of the amount of intercepted wind and the magnitude of wind loads; Description of several approaches to defining crown collisions; Correlations between crown collision frequency, slenderness coefficient and density.

Discusses the results of a study, which explored the influence of partial harvesting and forest floor disturbance on nutrient availability and understory vegetation in boreal mixedwoods in Alberta. Factors that influence the establishment and growth of planted white spruce; Description of the forest floor disturbance treatments used in the study; Effects of harvest type on soil temperature, magnesium availability and plant density and cover.

Analyzes the sucker regeneration of trembling aspen in the boreal mixedwood forests in North America. Factors that control aspen suckering; Description of the physiological processes of sucker initiation; Role of temperature in determining early sucker development; Information on the dynamics of sucker stands; Impact of the number of mature aspen trees retained after logging on the number of suckers formed.

Presents a study to evaluate the regeneration response of trembling aspen to different mechanical site preparation techniques commonly used in operational forestry. Consideration of techniques such as disc trenching, drag scarifying and blading; Role of the specific microsites created by each treatment; How a fire disturbance after the first growing season resulted in increased suckering relative to the untreated controls in the first year.

Presents a study of crown dimensions, crown leaf areas, and leaf area densities were determined on individual trees in 96 juvenile Populus tremuloides Michx. stands in central Alberta, Canada. Crown radius, height, leaf area, and leaf area density that were well explained by stem diameter at 30 cm (D[sub30]); Leaf area index, estimated using the LAI-2000, that reached a maximum of 4 m² m[sup-2] in some stands by age 9 and decreased after age 25; Leaf area indices for the same stands, estimated by allometric relationships, that were greater than 7 m[sup4]; Horizontal overlap between adjacent tree crowns declined from 68 to 38% of crown width with increasing average D[sub30] from 1.5 to 15.0 cm; Data that was used to calibrate MIXLIGHT, a spatially explicit light transmission model, to predict the range of light conditions in the understory of juvenile stands; Light predictions that were validated in 18 additional plots in which light transmission was measured; Measured light transmission that ranged from 4 to 68% of above canopy light among sites and from 16 to 53% within a mapped site; MIXLIGHT that predicted transmission well for average stand light levels (R² = 0.80); Individual positions within the mapped stand where there was a strong relationship between predicted and observed light (R² = 0.92), there was underprediction at high light and over at low light.

Presents a study where trembling aspen (Populus tremuloides Michx.) and white spruce (Picea glauca (Moench) Voss) seedlings were grown at uniform air temperatures but different soil temperatures (5, 15, and 25 C), and gas-exchange and growth characteristics were examined during active growth and early dormancy. Populus tremuloides that had no root growth and limited growth in leaf area and shoot mass compared with the large increases in leaf and shoot mass at 25 C; Picea glauca that had some root growth at 5 C and moderate growth of roots at 15 and 25 C; Differences that did not occur in aboveground mass at the different soil temperatures; Net assimilation and stomatal conductance in Populus tremuloides that were reduced with decreasing soil temperatures; Picea glauca soil temperatures that did not affect these gas-exchange variables; In both species, root mass that was higher in the dormant period than during the growing period, while root volume remained constant; Growth variables of Populus tremuloides that were more suppressed by cold soils than in Picea glauca; Root total nonstructural carbohydrates (TNC) that decreased between the active growth and dormancy period by nearly 50% in Populus tremuloides; Change that did not occur in TNC in Picea glauca; Results that suggest a more conservative use of TNC reserves in Picea glauca combined with a tolerance to cold soil temperatures compared with Populus tremuloides.

Vegetation management treatments are applied on a large proportion of regenerated sites in British Columbia and Alberta to improve survival and early growth of conifers and to meet provincial standards. Conventional techniques like manual brushing and chemical herbicides continue to be widely applied. However, other less familiar methods like sheep grazing can also be a viable option on some sites. Sheep grazing has been demonstrated to offer good to excellent control of both herbaceous and woody vegetation, provided certain conditions are met. Specifically, the dominant vegetation must be palatable to the sheep, the large- and small-scale topography must be relatively even, the treatment must be carried out before the crop trees become severely suppressed or damaged and the animals must be effectively supervised. It is our position that there is an opportunity to increase the use of sheep grazing for vegetation control in some regions of the northern forests of British Columbia and Alberta, thus providing another viable option for forest managers. [ABSTRACT FROM AUTHOR]

Intensive silviculture is practiced in many parts of the world but is rare in the public forests of western Canada. Here, we make the argument that intensive silviculture could be justified in Alberta but has not been implemented due to philosophies and policy decisions by foresters from government, industry and academia. These include adherence to long rotations, management goals that are aimed at sustained total volume yield rather than economic value, limitations in the types of stands that are allowed to be regenerated and models that do not include intensive silviculture options. In Mixedwood Growth Model projections, we demonstrate the potential of intensive silviculture that includes combinations of selecting good sites and thinning to produce merchantable stands by age 50 compared to the standard rotation age of 80 with basic silviculture. There could be even more gains if forest level constraints in timber flow were removed due to the increased growth of regenerating stands. Finally, we examine the attitude and policy changes that we believe are necessary for adoption of more intensive silviculture systems on parts of Alberta's forest landbase. [ABSTRACT FROM AUTHOR]

1. In a growth chamber experiment, an additive series design was used to test the ability of three replacement species (Trifolium pratense, Trifolium repens, and Epilobium angustifolium) to suppress Calamagrosis canadensis, a problem species in the regeneration of Picea glauca in the mixed-wood associations of the boreal forest. The effects of the replacement species on P. glauca seedling were also tested. 2. Seedling of C. Canadensis were planted at three different times (same time as the replacement species, 2 and 4 weeks later than the replacement species) into four different densities of the replacement species (229, 601, 1577 and 4174 plants m−²). Seedlings of P glauca were planted into the same four densities of the replacement species and at the same time as the replacement species. 3. Light transmission through the replacement species' canopies decreased with time and increasing density. After 8 weeks, the deepest shade was cast by T. pratense, which reduced light transmission to as low as 4%. 4. The biomass and mortality of the replacement species were not affected by C. Canadensis or P. glauca. The replacement species did, however, show different rates of density-dependent mortality, which was attributable to different levels of intraspecific competition. 5. Above-ground biomass accumulation, rhizome production, and mortality in C. canadensis was negatively affected by all three replacement species, especially at the latest planting time. Height and biomass of P. glauca seedlings was also reduced by all replacement species. 6. The results indicate that all three replacement species could be used to control seedling establishment by C. canadensis. Differences between the replacement species are discussed in the light of possible applications in the field of forestry. [ABSTRACT FROM AUTHOR]

A significant portion of the forest harvesting in the cooler regions of North America occurs in the winter when the ground is frozen and can support machine traffic. Climate change may influence the cost of forestry operations by reducing the period of winter access in those cold regions. In this study, we examined the impact of a shortened period of frozen ground conditions on logging operation and costs. To adapt to shorter period of frozen soil conditions, logging contractors might need to provide more machines and labor to complete logging in a shorter period of frozen conditions. The objectives were to calculate the costs of logging operations of a hypothetical forestry company in Alberta, Canada under two conditions: first, when the wood was hauled to the mill directly; and second, when part of the wood was hauled to satellite yards close to the logging area, thereby minimizing the annual number of idle hauling trucks. General Circulation Models were used to predict future winter weather conditions. Using the current type of harvesting machines and hauling directly to the mill, the unit cost of logging operations ($/m3) was projected to increase by an average of 1.6% to 2.5% in 2030s, 2.8% to 5.3% in the 2050s and 4.8% to 10.9% in the 2080s compared to the base year of 2015–2016. With use of satellite yards during the winter logging, the total logging cost will increase over direct haul, by 1.8% to 2.8% in the 2030s, 3.1% to 5.7% in the 2050s and 5.2% to 11.4% in the 2080s. Using satellite yards, however, will provide year-around employment for hauling truckers and more consistent and reliable hauling operations. [ABSTRACT FROM AUTHOR]

Mineral soil-capped, inverted mounds (a layer of organic matter topped by a mineral soil cap on an undisturbed in situ soil horizon) are often created as planting sites for tree seedlings in areas dominatedby a very competitive grass, Calamagrostis canadensis. Mounding, however, has had variable success at slowing the spread of this grass into the planting sites. A series of three field experiments investigated the pattern of rhizome growth of C. canadensis into mounds. Experiment 1 tested the interaction of mound thickness and clonal connections of C. canadensis to plants outside the mounds; experiment 2 the removal of the organic layer containing most of the rhizomes (screefing) prior to mounding, and experiment 3 the effect of mulching and fertilising on penetration and distribution of rhizomes through the mound. The thickness of the mineral soil cap was the most important factordetermining the success of C. canadensis colonisation, while clonal connections were only of importance for shallow mounds. Screefing before creating the mound resulted in a reduction of C. canadensis establishment. Rhizome penetration from plants outside of the mound was not strongly affected by fertilising and mulching. A fourth experiment,conducted in a controlled environment, tested the ability of rhizomes from buried C. canadensis sods to grow through mineral soil caps ofdifferent thickness. The grass sods had different growth potentials which were achieved by a pre-treatment of two levels of light and nutrients, resulting in high and low rhizome carbohydrate concentrations. Low reserves did not reduce the ability of rhizomes to penetrate any thickness of the mineral soil cap. Strategies of C. canadensis establishment on mounds are discussed. [ABSTRACT FROM AUTHOR]

Three experiments were conducted to examine the effects of Calamagrostis canadensis (Michx.) Beauv. on the growth of Populus tremuloides Michx. Containerized seedlings of P. tremuloides were transplanted into large pots and subjected to (1) three soil temperatures (20, 12, and 60C), (2) root competition with C. canadensis, or (3) presence or absence of C. canadensis litter, each at two nutrient regimes. In thefirst experiment, significant differences (p = 0.0001) in pre- and neo-formed leaf area and root and shoot dry weights were observed for plants subjected to the three different soil temperatures. In experiment two, the presence of C. canadensis significantly (p < 0.001) reduced total biomass, plant height, and root collar calliper of P. tremuloides. In the third experiment, a significant interaction (p = 0.027) between C. canadensis litter and nutrient regime was observed, withthe greatest inhibitory effect on P. tremuloides growth resulting from litter at the low nutrient regime. Low soil temperature had the strongest negative effect on P. tremuloides of the four factors investigated. However, direct competition with C. canadensis, low nutrient conditions, and C. canadensis litter likely would add to the growth suppression of P. tremuloides by this grass. The results of this study have significant implications for the management of P. tremuloides after harvesting. [ABSTRACT FROM AUTHOR]