Hardwood Content Research Articles

The influence of fibrous suspension flow regimes on the formation of tissue paper manufactured from different furnish compositions

Abstract The present work was based on analysis of the flow regime of fibre suspensions, that corresponds to furnishes and process conditions typically established for tissue paper manufacturing, i.e., under the common range of stock consistencies at the machine headbox and most usual furnish compositions. The flocculation potential of fibre suspensions used for toilet papers, facial tissues, paper towels and table napkins were evaluated on the principles of analytical concepts for fibre agglomeration propensity. The results show crowding numbers from 5.0 to 69.0, depending on the type of fibre or fibre blending ratios. The findings regarding agglomeration factors indicate that flow regimes are mainly in semi-concentrated and around gel state zones but reached the concentrated flow regime, in extreme conditions of fibre morphology and stock consistency. The influence of hardwood and softwood mixture ratios on the fibre suspension features is shown and discussed for common formulations of tissue base paper. The effect of fibre length and coarseness on the flocculation potential and the impacts of fibre suspension flow regimes on the structural properties of tissue paper, such as the formation uniformity are discussed, demonstrating the reasons for the preferred use of high hardwood content in furnish balance for tissue paper manufacturing.

Phylogenetic community structure and stable isotope analysis of the parasitoid community associated with Eastern spruce budworm,Choristoneura fumiferana(Lepidoptera: Tortricidae)

AbstractEastern spruce budworm,Choristoneura fumiferanaClemens (Lepidoptera: Tortricidae), is a major pest of eastern North American forests. Outbreaks of spruce budworm occur every 30–40 years, causing high tree mortality.Researchers have established that higher proportions of hardwood trees within stands (higher hardwood content) may reduce the defoliation and mortality of balsam fir and spruces during spruce budworm outbreaks. One mechanism posited to explain these patterns is that hardwood trees positively impact the parasitoids of spruce budworm. Indeed, parasitism of spruce budworm by parasitoids has been found to be impacted by hardwood content. However, more research is needed to understand how hardwood content impacts the parasitoid community as a whole.In this study, we trialled the use of two analyses, phylogenetic community structure and stable isotope analysis, to examine how hardwood content influenced the parasitoid community associated with spruce budworm.We found that phylogenetic community structure differed between forest stands with different hardwood content. Furthermore, the trophic relationships between several parasitoids and caterpillars on balsam fir or hardwood trees changed within and between years.Our study highlights the potential of these two analyses for understanding how hardwood content influences the parasitoid community associated with spruce budworm.

Hardwood mixtures facilitate leaf litter decomposition and soil nitrogen mineralization in conifer plantations

Productivity in conifer plantations can be increased by hardwood mixture. However, the underlying mechanisms that govern the relationship between hardwood mixture and productivity remain poorly understood, particularly with respect to nutrient cycling. We investigated how and to what extent hardwood mixtures alter nitrogen amounts in leaf litterfall, leaf litter decomposition rates, and soil nitrogen mineralization rates in an experiment that used different thinning intensities (i.e., a non-thinned “control” group with few hardwoods, a 33%-thinned “weak” group with a small amount of hardwoods, and a 67%-thinned “intensive” group with abundant hardwoods) in a conifer Cryptomeria japonica plantation (38-year old). Most of the hardwoods were 15-year old trees that have been regenerated after the first thinning. The annual leaf litterfall amount for the conifer was highest in the control group and lowest in the intensive group, whereas the reverse was true for hardwoods, although the hardwoods’ annual leaf litterfall amount was approximately half that of conifers, even in the intensive group. Consequently, the annual amount of leaf litterfall of hardwoods and conifers combined was lowest in the intensive group. However, the total amount of nitrogen in the annual leaf litterfall of hardwoods and conifers combined did not differ according to thinning intensity, because the mass-based nitrogen concentration in the leaf litterfall of hardwoods was twice that of conifers. The leaf litter decomposition rate in hardwoods was approximately three times faster than that in conifers irrespective of thinning intensity, mainly due to the lower carbon-to-nitrogen (C:N) ratio. Thus, the total amount of nitrogen in the decomposed leaves of hardwoods and conifers combined, calculated by multiplying the total amount of nitrogen in the annual leaf litterfall of hardwoods and conifers by the decomposition rate and summing the results, was highest in the intensive group. In soil from shallow depths (0–10 cm), the nitrogen mineralization rate increased in the order of control, weak, and intensive, attributable primarily to the C:N ratio, which decreased in the same order. The results indicated that increasing the hardwood content by intensive thinning significantly enhances the availability of soil inorganic nitrogen in conifer plantations, by facilitating leaf litter decomposition and soil nitrogen mineralization. These findings indicate that hardwood mixtures can increase forest productivity by enhancing nitrogen cycling.

Hardwood-softwood composition influences early-instar larval dispersal mortality during a spruce budworm outbreak

Spruce budworm (Choristoneura fumiferana Clem.) defoliation of balsam fir (Abies balsamea (L.) Mill.) has been shown to be less severe in stands with higher hardwood (broadleaved trees) content during both building and declining phases of budworm outbreaks. Reduced defoliation associated with forest composition could be explained by habitat fragmentation and/or natural enemy hypotheses, which posit higher early-instar larval dispersal loss or more intense parasitism in hardwood-softwood mixed stands than in pure balsam fir stands, respectively. We carried out field studies in 27 hardwood, mixedwood, and softwood plots with varied balsam fir-hardwood composition to assess effects of forest composition on: 1) first- and second-instar larval dispersal loss, and 2) stage-specific spruce budworm density and parasitism rates. Results indicated that increasing hardwood content increased second-instar (L2) dispersal losses. Stand type significantly affected dispersal loss of L2 larvae, both measured directly for three years and sampled on balsam fir seedlings. Post-hoc pair-wise comparisons indicated that L2 dispersal loss was less in softwood than in mixedwood or hardwood stand types based on measurements on ground traps and less in softwood and mixedwood than in hardwood stands based on sampling budworm larvae on regeneration. This suggested that high early-instar larval dispersal loss is a plausible explanation for the decreased spruce budworm density and balsam fir defoliation associated with increasing hardwood content. Stand type did not significantly affect parasitism rates.

Disentangling variables that influence growth response of balsam fir regeneration during a spruce budworm outbreak

Height increment of balsam fir (Abies balsamea (L.) Mill.) regeneration during a spruce budworm (Choristoneura fumiferana Clem.) outbreak can be affected by a variety of variables including defoliation, ground vegetation competition, canopy openness, the height of regeneration, and stand type. To disentangle how these variables interact to determine regeneration height increment, we sampled 36 plots in two regions showing contrasting climate, regional vegetation, and budworm outbreak severity. Linear mixed-effects models were used to analyze the effects of these five variables on height increment of balsam fir regeneration. In the Amqui (early defoliation) plots, height increment was significantly affected by a “cumulative defoliation × height of regeneration × hardwood content” interaction. Defoliation significantly reduced height increment when regeneration was >30 cm tall in softwood and mixedwood plots, but regeneration <30 cm tall in softwood and mixedwood plots and all regeneration in hardwood plots had light defoliation, which did not reduce height increment. Results were even more complex for the North Shore (late defoliation) plots, where there were three significant 3-way interactions affecting height increment: “height × hardwood content × ground vegetation cover”, “hardwood content × canopy openness × cumulative defoliation”, and “hardwood content × ground vegetation cover × cumulative defoliation”. Canopy openness was >25% in all softwood plots, and height increment substantially declined with increasing cumulative defoliation; however, in mixedwood and hardwood plots, canopy openness was <25% and height increment increased with defoliation. In softwood plots, height increment declined sharply with increasing cumulative defoliation at all ground vegetation cover levels, but in mixedwood and hardwood plots, height increment increased or decreased slightly with increasing cumulative defoliation. Results showed that the variables affecting height increment have surprisingly complex interactive effects.

Effects of Hardwood Content on Balsam Fir Defoliation during the Building Phase of a Spruce Budworm Outbreak

Defoliation by spruce budworm (Choristoneura fumiferana Clem.) on balsam fir (Abies balsamea (L.) Mill.) is more severe in fir than in mixed fir-hardwood stands. Previous studies assumed that defoliation in fir-hardwood stands was reduced in proportion to percent hardwood regardless of outbreak severity. We tested the influence of stand composition on defoliation during the first 5 years of a spruce budworm outbreak near Amqui, Quebec, by sampling 27 fir-hardwood plots selected to represent three percent hardwood basal area classes (0%–25%, 40%–65%, and 75%–95%). Balsam fir defoliation was significantly lower (p &lt; 0.001) as hardwood content increased, but the relationship varied with overall defoliation severity each year. Annual plot defoliation in fir-hardwood plots, estimated using: (1) defoliation in pure fir plots and the assumption that defoliation in fir-hardwood plots was reduced in proportion to percent hardwood; (2) a generalized linear mixed-effects model with defoliation in pure fir plots, percent hardwood, and interaction as fixed-effects; and (3) Random Forests prediction incorporating 11 predictor variables, resulted in r = 0.77, 0.87, and 0.92 versus measured defoliation, respectively. Average defoliation severity in softwood plots and percent hardwood content were the most important variables in Random Forests analysis. Data on average defoliation level in softwood stands, as an indicator of overall outbreak severity, improves prediction of balsam fir defoliation in mixed stands.

Ecoregional Patterns of Spruce Budworm—Wildfire Interactions in Central Canada’s Forests

Wildfires and outbreaks of the spruce budworm, Choristoneura fumiferana (Clem.), are the two dominant natural disturbances in Canada’s boreal forest. While both disturbances have specific impacts on forest ecosystems, it is increasingly recognized that their interactions also have the potential for non-linear behavior and long-lasting legacies on forest ecosystems’ structures and functions. Previously, we showed that, in central Canada, fires occurred with a disproportionately higher frequency during a ‘window of opportunity’ following spruce budworm defoliation. In this study, we use Ontario’s spatial databases for large fires and spruce budworm defoliation to locate where these two disturbances likely interacted. Classification tree and Random Forest procedures were then applied to find how spruce budworm defoliation history, climate, and forest conditions best predict the location of such budworm–fire interactions. Results indicate that such interactions likely occurred in areas geographically bound by hardwood content in the south, the prevalence of the three major spruce budworm host species (balsam fir, white spruce and black spruce) in the north, and climate moisture in the west. The occurrence of a spruce budworm–fire interaction inside these boundaries is related to the frequency of spruce budworm defoliation. These patterns provide a means of distinguishing regions where spruce budworm attacks are likely to increase fire risk.

Forest overstory composition and seedling height influence defoliation of understory regeneration by spruce budworm

Abstract Higher hardwood content in stands results in lower defoliation of overstory balsam fir (Abies balsamea (L.) Mill.) caused by spruce budworm (Choristoneura fumiferana Clem.). To determine whether higher overstory hardwood content also reduced defoliation and mortality of balsam fir regeneration of varying height classes during a spruce budworm outbreak, we sampled 36 plots representing three classes of hardwood content (0–25%, 40–65%, and 75–95%) across a gradient of fir-hardwood stands. Twenty-seven plots were sampled in nine stands near Amqui, Quebec in an early stage spruce budworm outbreak (3 years of defoliation), and nine plots were sampled in three stands in the North Shore of Quebec in a later stage budworm outbreak (7 years of defoliation). Linear mixed-effects models with repeated measures (years) were used to analyze differences in defoliation of fir regeneration as a function of hardwood content, six height classes, and three years (2013, 2014, 2015). In the Amqui plots, defoliation of fir regeneration was significantly related to all factors and interaction terms except for hardwood content, while in the North Shore plots, defoliation was significantly related to all factors and the hardwood content x height class and hardwood content x year interaction terms. Defoliation of balsam fir regeneration was 85% higher in softwood than in hardwood stands in 2013 and 2014 in the North Shore plots, when the budworm outbreak was severe. Defoliation was at least 10% higher on regeneration taller than 30 cm than on smaller regeneration in the Amqui plots in 2015 and over 15% higher in the North Shore plots. In general, balsam fir regeneration in softwood stands had higher levels of defoliation than in hardwood stands when defoliation was severe, and regeneration taller than 30 cm had higher defoliation than smaller regeneration.

Evaluating harvest costs and profit of commercial thinnings in softwood stands in west-central Maine: A case study

Precommercial thinning (PCT) is a common silvicultural treatment in the management of young conifer forests. The positive effects of PCT on tree growth are well documented, however, there have been few operational studies of thinning productivity associated with later harvests in such stands and associated cost comparison with high-density, small-diameter stands. In the winters of 2012/2013 and 2013/2014 a long-term herbicide and PCT study in west-central Maine was commercially thinned using cut-to-length (CTL) and whole-tree (WT) harvesting systems in PCT and non-PCT stands, respectively. Thinning prescriptions consisted of three nominal removal intensities (33%, 50%, and 66% of the standing softwood volume) in a randomized block design with three to four replications. Stand density, basal area, hardwood content, and removal intensity were not significant in explaining variation in harvester and feller-buncher productivity. An analysis of unit cost of production indicated that wood chip production using a WT system in non-PCT stands is less costly than the production of roundwood using a CTL system in PCT stands. Profit, however, is similar for products harvested by either system. Our conclusion is that the WT system used in the study is economically feasible to treat highdensity, small-diameter stands in a commercial thinning.

Estimating forest vulnerability to the next spruce budworm outbreak: will past silvicultural efforts pay dividends?

Silvicultural treatments recommended to reduce damage by spruce budworm (SBW; Choristoneura fumiferana Clemens) include reducing balsam fir (Abies balsamea (L.) Mill.) abundance and age and increasing spruce (Picea spp.) and hardwood content. To evaluate the effect of these measures on forest timber supply, we assessed stand characteristics, disturbance history, and timber supply for an intensively managed eastern Quebec forest from 1985 to 2004, encompassing a major SBW outbreak. During this time, mean stand age declined from 55 to 51 years, and proportions of areas in balsam fir stands declined (42% to 27%), spruce–fir stabilized (12% to 11%), and mixedwoods increased (32% to 52%). We estimated forest vulnerability using softwood volume reductions following simulated outbreak scenarios of different severity (low, moderate, and high) and different effects of hardwood content in reducing spruce–fir defoliation. Volume reductions for outbreaks simulated to begin in either 1985 or 2004 were similar, ranging from 15%–46% (no hardwood effect in reducing defoliation) to 13%–39% (given a maximum hardwood content effect) for light and severe outbreaks, respectively. Considering the net detrimental effect of increased hardwood content on softwood timber supply, we question the dividends of promoting hardwoods and recommend increasing the combined use of plantations and weeding treatments to increase spruce content.

Growth and mortality of balsam fir- and spruce-tolerant hardwood stands as influenced by stand characteristics and spruce budworm defoliation

Balsam fir (Abies balsamea (L.) Mill.)-tolerant hardwood and spruce (Picea sp.)-tolerant hardwood stands were compared along a gradient of hardwood composition (12–82%). Using permanent sample plot data, influences of stand hardwood content, past spruce budworm (Choristoneura fumiferana Clem.) defoliation, insecticide spraying, and stand and site characteristics on survivor growth and mortality of the fir–spruce (spruce budworm host species) component of these stands were determined. Balsam fir basal area, spruce basal area, and percent hardwood were significantly related to fir–spruce survivor growth. Balsam fir mixedwood plots had four to five times higher fir–spruce cumulative mortality (3.7–13.3m2ha−1) than spruce mixedwood plots (1.0–2.9m2ha−1) from 1990 to 2004, and sustained higher wind-related mortality after the budworm outbreak ended in the late 1980s to early 1990s. A mortality regression tree model indicated that initial balsam fir basal area, % tolerant hardwood basal area, maximum cumulative defoliation from 1983 to 1987, and spruce budworm outbreak zone (north, central, south New Brunswick) all significantly influenced fir–spruce mortality. Results demonstrated differences in stand dynamics between these stand types, with lower spruce budworm vulnerability and higher longevity and more stable structure of spruce mixedwood than of fir mixedwood.

The Severity of Budworm-Caused Growth Reductions in Balsam Fir/Spruce Stands Varies with the Hardwood Content of Surrounding Forest Landscapes

Abstract Tree-ring data collected from balsam fir (Abies balsamea [L.] Mill.) in 31 spruce (Picea spp.)/fir-dominated stands in northern New Brunswick were used to evaluate how radial growth reductions during the last spruce budworm (Choristoneura fumiferana Clem.) outbreak (1972–1992) varied according to the hardwood content of surrounding forest landscapes, insecticide spray history and elevation. Stepwise regression analysis was used to build 12 models describing relationships between mean percent growth reduction (i.e., deviation from mean tree growth averaged over the lifespan of all trees in a stand) and the explanatory variables for years when &amp;gt;80% of stands had growth reductions (1976–1978, 1982–1984, 1990, 1991, and 1994) and for three growth reduction periods (1972–1980, 1981–1985, and 1986–1993). The hardwood content of surrounding forest landscapes entered into all significant regression models (P &amp;lt; 0.05), explaining 12–41% of the variance in budworm-caused growth reductions. Differences in growth reductions among stands were greatest during the initial years of the budworm outbreak (1972–1980), particularly in 1976 when mean reductions were 40% in stands with &amp;lt;50% hardwood and content and 20% in stands in which surrounding hardwood content was &amp;gt;50%. Relationships between variation in growth reductions among stands and elevation or insecticide spray history were weak and less consistent than with landscape hardwood content. Our findings suggest that increasing the hardwood content of forest landscapes could help to reduce the impact of outbreaks on timber supplies.

Effects of Mixed Stand Management to Reduce Impacts of Spruce Budworm Defoliation on Balsam Fir Stand-Level Growth and Yield

Abstract Mixed hardwood-balsam fir stand management has been proposed as one silvicultural technique to reduce spruce budworm damage to balsam fir. An analysis was conducted using published results from New Brunswick, Canada, and northern New England, USA, to assess whether optimum hardwood levels (percent volume) could be determined for various levels of budworm defoliation. The goal was to maximize standing balsam fir volume and to determine trade-offs between reduced damage (hence reduced volumes losses) versus the amount of fir volume lost as a result of allocating growing space to hardwood species. Optimum hardwood levels depended on severity of budworm attack. Below 45% defoliation (5 yr average), the amount of balsam fir volume lost to increased hardwood growing space exceeded the amount of volume protected. As defoliation severity increased above 45%, the optimal hardwood levels increased. At severe levels of defoliation (&gt; 75%) optimal hardwood content was approximately 50% of initial standing volume. The results suggest that mixed stand management can potentially reduce balsam fir volume losses in areas with frequent severe spruce budworm outbreaks. North. J. Appl. For. 16(1):19-24.

The influence of hardwood content on balsam fir defoliation by spruce budworm

Changing stand composition by increasing hardwood content has been suggested as a long-term method for reducing susceptibility and vulnerability of balsam fir (Abiesbalsamea (L.) Mill.) to spruce budworm (Choristoneurafumiferana (Clem.)). Twenty-five mixed balsam fir–hardwood stands were selected in northern New Brunswick, with five stands in each 20% hardwood class (0–20, 21–40%, etc.). Defoliation each year from 1989 to 1993 was significantly (p &lt; 0.0001) related to hardwood content, with r2 ranging from 0.57 to 0.81. As hardwood content increased, defoliation of balsam fir decreased. From 1989 to 1992, the years of moderate to severe defoliation, balsam fir stands with &lt;40% hardwoods sustained 58–71% defoliation, on average, versus 12–15% defoliation in stands with &gt;80% hardwood. A generalized model combining hardwood content and the estimated defoliation in pure softwood stands in a given year explained 77% of the variation in defoliation over stands and years. This study indicated that mixed balsam fir–hardwood stand management, with hardwood content &gt;40%, could substantially reduce losses during spruce budworm outbreaks. Further research is warranted to elucidate the mechanism involved, but our working hypothesis is that greater hardwood content increased the diversity or populations of natural enemies such as birds and parasitoids.

Forest management strategies to reduce spruce budworm damage in the Fundy Model Forest

Spruce budworm (Choristoneura fumiferana) outbreaks cannot be prevented, but the amount of damage that occurs can be managed. Tree species, stand age, hardwood content, and drainage class, as well as the outbreak severity and length, determine the amount of tree mortality during budworm outbreaks. Silviculture and forest management can be used to reduce the incidence of the most damaged stand types across the landscape. The amount of defoliation in mixed balsam fir-hardwood stands is strongly negatively related to hardwood content, especially with hardwoods &gt; 40%. The Spruce Budworm Decision Support System (DSS) links models of stand and forest response to budworm outbreaks and inventory interpretation to a GIS, and can be used to evaluate effects of outbreaks and management on forest structure and timber supply. An example using the Spruce Budworm DSS for a portion of the Fundy Model Forest indicated that losses from a future budworm outbreak could be reduced 34% by directing harvesting and silviculture towards conversion of one-half of the most vulnerable stand types into low susceptibility or non-susceptible species. Key words: decision support system, vulnerability, silviculture, insect damage