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Conifer growth, Armillaria ostoyae root disease, and plant diversity responses to broadleaf competition reduction in mixed forests of southern interior British Columbia
Canadian Journal of Forest Research
Abstract
Broadleaf trees are routinely removed from conifer plantations during vegetation management treatments, but whether the removal increases tree productivity or affects root disease and plant diversity is unknown. The effects of manual and chemical reduction of paper birch (Betula papyrifera Marsh.) and trembling aspen (Populus tremuloides Michx.) on conifer survival, growth, root disease incidence, and plant community diversity were investigated for 5 years in Douglas-fir (Pseudotsuga menziesii var. glauca (Beissn.) Franco) and lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) plantations in southern interior British Columbia. Broadleaves were reduced by manual, girdling, and cut-stump glyphosate treatments for 5 years but most severely following cut-stump glyphosate and with a delay due to slow death following girdling. Conifer survival was reduced for 35 years following manual cutting or girdling of birch because of a 1.5- to 4-fold increase in mortality due to Armillaria ostoyae (Romagn.) Herink, but this did not occur following cut-stump glyphosate treatment of birch or manual cutting of aspen. Conifer diameter increased with treatment intensity and productivity of the vegetation complex. Competition thresholds were identified for diameter but not survival, although Armillaria-caused mortality tended to increase near the minimum growth threshold. Structural diversity increased following manual cutting and cut-stump glyphosate because birch dominants were removed and understory layers increased, but species richness and diversity were unaffected. Forest managers can expect increased conifer growth with birch removal but also small increases in mortality due to Armillaria ostoyae root disease following manual treatments and loss of large birch trees in all treatments.
... Simard et al. (2001) reported on three of the four sites we have reported here (Mabel Lake, Enterprise Creek and Johnson Lake), that Douglas-fir mortality was primarily due to infection by A. ostoyae with a significant increase in mortality noted in brushed Douglas-fir one-year post treatment but not thereafter. Baleshta et al. (2015) reported from other BC southern interior sites that Douglas-fir mortality, post birch thinning, showed an increase in A. ostoyae mortality only to year two (Baleshta et al. 2005) with no significant treatment differences noted at year 5. Simard et al. (2005) indicated brushing increased Douglas-fir A. ostoyae related mortality through three years, but not through five years. It appears that in the longer-term (> 2 -3 years post treatment) Douglas-fir mortality is not directly related to birch competition, nor brushing activities and that the impacts of A. ostoyae on survival (and growth) are due to local incipient factors influencing Armillaria spread (Baleshta et al. 2015). ...
... Manual brushing of birch often induces re-sprouting and an increase in the number of stems (Peterson et al. 1997;Simard et al. 2005). In this study, brushing reduced the height and cover of birch and other broadleaves, at least in the short term. ...
... The height of the regenerating birch (and other broadleaves) post brushing remained significantly shorter than those in the control plots over the entire 10-year assessment period; however, broadleaf cover was found to rapidly recover such that no significant treatment difference was noted at or after year 3. This is contrary to the observations of Simard et al. (2005) where manual cutting of aspen and birch resulted in significant cover reductions over 5 years despite high rates of sprouting. ...
Manual brushing is used to minimize the competitive effects of paper birch (Betula papyrifera Marsh) and associated broadleaved trees on young Douglas-fir (Pseudotsuga menziesii var. glauca) in southern interior British Columbia. Effects of brushing broadleaved trees, predominantly birch, on interior Douglas-fir survival and growth were studied on four sites. Treatments were applied when plantations were five to nine years old. Through 10 years post treatment, brushing did not affect Douglas-fir survival, but increase height by 22 % and stem diameter by 31 % and the differences were greater than seen at five years. After 10 years, linear models described a declining Douglas-fir height or diameter with increasing broadleaved tree density. Boundary line analysis was used to describe maximum treatment response to broadleaved density and two distance independent competition indices for birch and broadleaves, combining either cover or density with relative heights (CRH, DRH, respectively). A negative exponential relationship was fit to 10-year Douglas-fir heights and diameters with increasing values CRH or DRH. Competition thresholds for density, CRH and DRH were not apparent. The quantile regression results indicated the 10-year response of young Douglas-fir diameter to
brushing occurred primarily with the largest 55 % to 85 % of the population, CRH and DRH respectively.
... Moreover, conifer productivity has been shown to increase, following complete removal of broadleaves from the forest (Simard et al. 2001). As a result, intensive broadleaf control has been justified to enhance conifer productivity (Lavender et al. 1990;Wagner et al. 2005) but there are increasing concerns about the associated costs to forest health, timber production and detrimental effects on biodiversity (Simard et al. 2005;Kelty 2006). It was shown by different investigations that removal of broadleaves increased the rate of disease and in-sect infestations among residual conifers (Taylor et al. 1994;Simard et al. 2001;Hawkins et al. 2012a) as well as reduced the habitat quality for cavity nesting birds (Aitken et al. 2002). ...
... In addition, extensive removal of broadleaf species has the potential to reduce the diversity of stand types in semi-natural landscapes, where the landscape should include a mosaic of managed pure conifer and mixed coniferbroadleaf plantations (Lautenschlager 2000). Simard et al. (2005), Paquette and Messier (2011) and Hawkins et al. (2012a) suggested that yields may be greater in mixed species stands than in pure stands while Frivold and Frank (2002) and Fahlvik et al. (2005) reported that the effect of tree mixture on yield is unclear. ...
... Moreover, they also reported that spruce-birch mixed stands are more productive than the single species stand. Some other investigations in mixed stands also suggested greater productivity than that of pure stands of either species (Simard et al. 2005;Newsome et al. 2010). According to Kelty (2006) more than two species combinations provide the greatest yield compared to pure stand. ...
Current British Columbia forest regulations drive the regeneration management towards pure conifer stands rather than remaining in a mixed-species condition. This approach may result in unnecessary vegetation control. The main objective of this investigation was to study the impact of variable paper birch densities on white spruce growth in 15–20 years old stands for management implications. Regression analysis was used to examine the effect of birch density and two competition indices to predict spruce growth. A mixed model ANOVA showed that spruce mean annual DBH and basal area increment differed significantly among sites and density. From the regression analysis it appears that birch density up to 4,000 stems·ha–1 had no significant influence on spruce growth which is much higher than the current BC reforestation guideline (1,000 stems·ha–1 broadleaves). Similarly, birch relative density index (RDI) had to exceed 3 to affect spruce DBH growth significantly on all sites except one. On most sites, spruce had a larger DBH than birch. Our results also suggest that rather than following the current broadcast approach to vegetation management, a targeted approach could enhance forest productivity and stand diversity.
... When conifer seedlings in this forest type are regenerating following harvest, they can also suffer significant levels of A. ostoyae infection and mortality when contacting inoculated root systems remaining in the soil (Morrison et al. 1991). Any subsequent silviculture treatment that increases the pathogen inoculum load, such as brushing, spacing, or thinning, can cause additional mortality among susceptible seedlings (Cruickshank et al. 1997;Morrison et al. 2001;Simard et al. 2005). While root extraction, or stumping, has been the treatment of choice for mitigating A. ostoyae root disease in young conifer plantations in British Columbia (Morrison et al. 1991), retaining resistant paper birch in intimate mixture also appears to reduce disease incidence among the neighboring susceptible conifers (Morrison et al. 1988). ...
... In a separate mixed plantation, Simard and Hannam (2000) similarly found that reductions of 8-year-old paper birch from 2500 to 50 stems·ha -1 significantly improved diameter growth of interior spruce. Simard et al. (2005) tested the effect of broadcast weeding over 20 sites using three methods and found that Douglas-fir diameter increased by 37% and 17% following the cut-stump glyphosate and girdling treatments, respectively, when broadleaf density was reduced below 4400 stems·ha -1 , or 15% cover. By contrast, it was unaffected by manual cutting, where most broadleaf trees vigorously sprouted back to an average density of 10 812 stems·ha -1 , or 25% cover. ...
... Differences in conifer species responses to weeding reflect earlier predictions based on shade-tolerance rankings (Simard and Sachs 2004). Simard et al. (2005) found that lodgepole pine, for example, responded to smaller decreases in paper birch density than interior Douglas-fir. Lodgepole pine is a relatively shade-intolerant species and highly plastic in its response to increasing light availability (Wright et al. 1998), allowing it to respond more readily to moderate increases in light than Douglas-fir. ...
Vegetation-management practices are applied in temperate-zone forests on the assumption that changing the competitive environment between conifers and unwanted vegetation will improve conifer productivity. We review this assumption using research examining interactions between paper birch (Betula papyrifera Marsh.) and conifers in the highly productive Interior Cedar Hemlock zone of British Columbia. We have found that both competition and facilitation are important in young plantations, where paper birch competes for light, reducing growth of shade-intolerant conifers, but having a facilitative effect on shade-tolerant conifers. This facilitative effect may result from greater ectomycorrhizal diversity, population sizes of Armillaria ostoyae (Romagn.) Herink antagonistic bacteria, and associative nitrogen fixation in plantations where interior Douglas-fir (Pseudotsuga menziesii var. glauca (Beissn.) Franco) is mixed with paper birch. Where paper birch is manually cut or girdled, conifers grow faster in diameter, but more die as a result of A. ostoyae root disease, and these responses increase with increasing weeding intensity. The weeding treatments do not affect plant community species richness but reduce paper birch dominants and increase understory structural diversity. British Columbia forest policy has been slow to respond to these findings, and we suggest that as a result, the forested landscape incurs substantial risk. We propose additional pathways for managing Interior Cedar Hemlock mixtures to ensure that the natural mix of forest types in the landscape is maintained.
... Interspecific competition can negatively affect conifer resource acquisition and growth (Wagner et al. 2004). However, plant communities can also have positive effects on conifer regeneration (facilitation) through long-term nutrient accretion, coinoculation with beneficial soil microbes, or protection from environmental or biotic elements, such as drought, frost, herbivores, or pathogens (Berkowitz et al. 1995;Callaway and Walker 1997;Powell and Bork 2004;Haskins and Gehring 2005;Simard et al. 2005). Such balancing between competitive and facilitative effects is important to understanding the effects of vegetation removal on forest productivity, composition, and diversity over the long term (Kimmins 2003). ...
... Current studies report only the outcome of competitive effects on tree growth (Simard and Heineman 1996;Simard et al. 1998 or focus primarily on nutrient dynamics (Brockley and Sanborn 2003), leaving unknown the dynamic interplay between light, water, nutrient, and microclimatic effects on productivity over time. In spite of this knowledge gap, reforestation practices in these forests remain guided primarily by simple competition models for light British Columbia Ministry of Forests 2000), even though it is known that light accounts for only a moderate portion of the variation in conifer productivity (Comeau et al. 2003;Simard et al. 2005). ...
... The substantial mortality increases we observed with alder and herb removal contrasts with the findings of many North American vegetation management studies showing that mortality decreases (Wagner et al. 2004). Vegetation management models do not take into account noncompetitive effects on survival (Wagner et al. 1989), but recent studies show that vegetation removal has the potential to increase conifer mortality on certain sites by enhancing killing frosts, browsing, root disease, and nutrient deficiencies (Brockley and Sanborn 2003;Baleshta et al. 2004;Simard et al. 2005). ...
We suggest that the net outcome of interactions between regenerating conifers and early seral deciduous species depends on trade-offs between competition and facilitation over time. Vegetation management treatments that dramatically reduce competitive effects of deciduous species may constrain the ability of conifers to optimize resource trade-offs (e.g., increased growth response to light at the expense of increased drought mortality), potentially affecting long-term productivity. In a 15-year study in southern interior British Columbia, we investigated whether lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) survival, growth, and resource availability differed among manipulated stand compositions, from pure pine stands to mixtures with native N2-fixing Sitka alder (Alnus viridis subsp. sinuata (Regel) Á. Löve & D. Löve) or herbs. We found that pine growth increases were sustained only in pure stands, where alder and herbs were completely removed, corresponding with short-term increases in light, soil and air temperature, and soil nitrate. However, this came at a significant cost to survival (through loss of protection from browsing, desiccation, and sun scald), as well as dramatic depletions in soil nitrogen mineralization over the longer term. Our results support a competitionfacilitation trade-off hypothesis, suggesting that treatment-imposed shifts in resource availability over time could negatively affect forest productivity.
... The increasing risk of Armillaria with increasing AH:M suggests that warmer, drier annual conditions favour Armillaria infection, possibly because drought increases tree stress and susceptibility (Coakley et al. 1999) to a range of agents (Spittlehouse 2008). Silviculture treatment factors did not contribute to the Armillaria model, contrasting with previous reports of increased incidence of Armillaria associated with manual brushing (Simard et al. 2005). ...
... Decreasing lodgepole pine density, which could be the result of either site characteristics or silviculture treatment (e.g., juvenile spacing), increased the risk of mountain pine beetle damage. Brushing likewise strongly increased risk, probably because it increased lodgepole pine growth rates (e.g., Simard et al. 2005), which has been associated with increased susceptibility to beetle attack (Amman 1972). Four temperature-related climatic factors contributed to the model predicting mountain pine beetle presence, and three of them (MCMT, NFFD, and eFFP) suggest increased risk associated with warmer winter conditions, a phenomenon that has elsewhere been documented (Williams and Liebhold 2002). ...
... Lodgepole pine mortality is likely to increase as environmental factors such as drought (Coakley et al. 1999) predispose them to damage from pathogens or insects (Manion 1991). To some extent, silviculture treatments such as brushing may relieve lodgepole pine stress by reducing competition (e.g., Simard et al. 2005); however, other treatments (e.g., juvenile spacing) appear to increase the risk of a variety of agents (pine needle cast, Dothistroma, mountain pine beetle, sequoia pitch moth, and pine terminal weevil). Careful planning, particularly in prescribing lodgepole pine for planting, may offset the frequency with which serious damage occurs. ...
Lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) has been extensively planted throughout interior British Columbia, and as a result may be particularly susceptible to climate-induced changes in the range and severity of common damaging agents. We quantified the presence of 14 damaging agents in sixty-six 15- to 30-year-old pine stands. Hard pine stem rusts, primarily western gall rust, were present on every site. We used logistic regression to predict individual agent presence from climatic, location, site, and treatment factors and calculated odds ratios to evaluate whether risk to lodgepole pine increases or decreases as these factors change. Risk of damage from serious agents (stem disease, root disease, and mountain pine beetle) increased with increasing latitude; however, in several of these models, risk also increased as temperature of the coldest month got warmer. We also found evidence that increasing risk of damage from agents that are currently less serious (sequoia pitch moth, pine needle cast, and pine terminal weevil) was associated with warming and (or) increasingly dry climatic conditions. Given the predominance of lodgepole pine in northerly ecosystems and the prediction that climate change effects will increase with latitude, our results suggest the need to consider potential increases in damage from diseases and insects during silviculture planning and timber supply prediction.
... The relationship of relative stem volume increment (RSTV, relative to maximum observed per site) to DRD was explored using non-linear regression to describe the growth impact of increasing mixedwood competition. The exponential model similar to that used by Simard et al. (2005) was found to best describe the relationship ( Fig. 3 and Table 5b). Following Wagner et al. (1989) we approximated a minimum tree growth response competition threshold by site, based on 20% of the maximum observed DRD level (Wagner, 2000;Simard et al., 2005). ...
... The exponential model similar to that used by Simard et al. (2005) was found to best describe the relationship ( Fig. 3 and Table 5b). Following Wagner et al. (1989) we approximated a minimum tree growth response competition threshold by site, based on 20% of the maximum observed DRD level (Wagner, 2000;Simard et al., 2005). This DRD level was determined to be 0.02, 0.022 and 0.028 for McKinley Lake, Teardrop and Tyee Lake, respectively. ...
... Since DRD is the sum of the closest three neighbour/pine DBH ratios divided by their distances to the select pine, one can easily calculate an average threshold distance (ATD) dependent on the average neighbour/pine DBH ratio (ATD = neighbour/pine DBH ratio/(minimum response level/3)). Similarly, we can determine an ATD for maximum growth (5-10% of maximum DRD) (Wagner, 2000;Simard et al., 2005). Minimum and maximum growth response ATD are then available to apply at the individual pine level as a site specific tool to assess growth potential and guide mixedwood management treatments. ...
Three lodgepole pine and aspen mixedwood sites located in the central interior of British Columbia within the Sub Boreal Spruce (SBS) biogeoclimatic zone were chosen to study the neighbourhood aspen competition and canopy light environment of 14–19-year-old lodgepole pine. All three sites had previously been established as separate research trials designed to explore various silviculture options for controlling aspen competition (aspen brushing, herbicide, thinning and untreated areas). For each site, 33–36 pine trees were selected to represent the observed range of light regimes under the influence of various aspen competition levels. At each sample pine, competition and stand measurements were made and a series of vertical canopy light measurements from the top to the base of the live crown. After an evaluation of a variety of competition indices, the index DRD; sum of the ratio of each of the three nearest neighbour's DBH to the subject pine divided by their distance and, amount of available light at the top of the crown (DIFNt) were found as the best overall predictors of pine stem volume growth. A site specific exponential relationship of relative pine stem volume growth to DRD was found and minimum growth response competition thresholds were determined, which could provide useful targets where maximizing pine volume is intended. Evaluation of both linear and non-linear models of DIFNt versus height growth indicated the response to be linear across the observed range of available light. Implications for management are discussed.
... In contrast, for 30-year-old P. menziesii no reduction in root pathogen-caused mortality rate was found from growing it in mixture with nonhost species. Also in British Columbia, experimental removal of naturally regenerated broadleaves B. papyrifera and Populus tremuloides (quaking aspen) generally caused a 1.5-to 4-fold increase in mortality of planted P. menziesii for 3-5 years due to A. ostoyae infection, though the effect depended on removal method (Gerlach et al., 1997;Baleshta et al., 2005;Simard et al., 2005). In Southwest Lapland and in North Karelia, Finland, modeling of observational data showed that the incidence of M. pinitorqua on young P. sylvestris was greater in the presence of both Populus tremula (aspen, also a host species), and Salix spp. ...
... This was linked to increases in light and soil moisture levels caused by the thinning. In higher altitude British Columbia forests infested with A. ostoyae, the diameter growth of planted P. menziesii was 27% greater after experimental removal of the naturally regenerated broadleaves B. papyrifera and P. tremuloides compared with untreated controls, and the increase was greater with higher intensity removal treatments, however height growth was not significantly affected (Gerlach et al., 1997;Baleshta et al., 2005;Simard et al., 2005). In a second experiment, diameter growth of P. contorta var. ...
Invasive pathogens threaten the ability of forests globally to produce a range of valuable ecosystem services over time. However, the ability to detect such pathogen invasions—and thus to produce appropriate and timely management responses—is relatively low. We argue that a promising approach is to plan and manage forests in a way that increases their resilience to invasive pathogens not yet present or ubiquitous in the forest. This paper is based on a systematic search and critical review of empirical evidence of the effect of a wide range of forest management options on the primary and secondary infection rates of forest pathogens, and on subsequent forest recovery. Our goals are to inform forest management decision making to increase forest resilience, and to identify the most important evidence gaps for future research. The management options for which there is the strongest evidence that they increase forest resilience to pathogens are: reduced forest connectivity, removal or treatment of inoculum sources such as cut stumps, reduced tree density, removal of diseased trees and increased tree species diversity. In all cases the effect of these options on infection dynamics differs greatly amongst tree and pathogen species and between forest environments. However, the lack of consistent effects of silvicultural systems or of thinning, pruning or coppicing treatments is notable. There is also a lack of evidence of how the effects of treatments are influenced by the scale at which they are applied, e.g., the mixture of tree species. An overall conclusion is that forest managers often need to trade-off increased resilience to tree pathogens against other benefits obtained from forests.
... Pine growth response has been found more variable in southern BC where drier climatic conditions may impact aspen productivity . From a total of 13 study locations in southern interior BC, pine diameter growth response to brushing treatments was noted as positive on eight sites found in the Interior Douglas-fir (IDF), Interior Cedar Hemlock (ICH) and Montane Spruce (MS) biogeoclimatic zones (Simard et al. 2001, Prasad 2002, Simard et al. 2005. Pine height response results were variable, noted as positive, negative or not significant depending on the site. ...
... However, much of this work does not present treatments where zero or near zero aspen competition exists, but rather relies on small neighbourhood plot assessments of aspen taller than the subject pine to quantify and interpret the impacts of competition. Without a quantitative measure of a near zero aspen competition neighbourhood (pine monoculture), the interspecific competition range is truncated and maximum pine response is undefined (Wagner 2000, Simard et al. 2005. The results presented here represent stand-level assessments that compile competitive impacts across the various DBH classes that exist, influenced by not only light and canopy space competition but also underground resource competition as part of the stand dynamics of the stem exclusion phase. ...
Six lodgepole pine plantations located in the Sub Boreal Spruce (SBS) biogeoclimatic zone of northern interior British Columbia were chosen to study the impacts of aspen competition on the growth and yield of lodgepole pine. The six sites from four different zonal variants (dw2, dw3, dk1 and mc2) ranged in age from 22 to 39 years. Site preparation treatments occurred on all sites: drag scarification, disking, or a broadcast burn post clear-cut logging. Four of the sites received at
least one operational brushing treatment for aspen (chemical or manual). At each site, 30 pine trees (CP) were selected as plot centres to represent the observed range of aspen competition. A series of nested plots up to 7.98 m radius was used to evaluate effects of % pine composition on stand density and stand volume using linear and non-linear models. At five of the six sites total volume was unchanged across the range of pine composition. The growth interaction between aspen and pine was found to be a linear relationship of competitive reduction where pine volume, basal area and merchantable volume was highly sensitive to any increase in aspen density or composition.
... The high richness of regenerating tree species in our harvesting treatments ought to promote ecosystem productivity due to niche partitioning and synergies among species (Tilman, 1999;Ares et al., 2010;Thompson et al., 2011;Forrester and Bauhus, 2016;Liang et al., 2016). The greater broadleaf densities in the lower retention treatments in particular will help protect the conifers against root pathogens according to earlier studies in these forests (Baleshta et al., 2005;Simard et al., 2005), enhance nutrient availability (Prescott et al., 2004;Zhang et al., 2012), and promote bird diversity (Aitken and Martin, 2007). The enhancement of shade tolerant species in small gaps of the higher retention treatments will also promote a shift toward later successional stand structures, which would provide habitat for more old-growth dependent plants, birds, and mammals . ...
Clearcutting reduces proximity to seed sources and mycorrhizal inoculum potential for regenerating seedlings. Partial retention of legacy trees and protection of refuge plants, as well as preservation of the forest floor, can maintain mycorrhizal networks that colonize germinants and improve nutrient supply. However, little is known of overstory retention levels that best protect mycorrhizal inoculum while also providing sufficient light and soil resources for seedling establishment. To quantify the effect of tree retention on seedling regeneration, refuge plants, and resource availability, we compared five harvesting methods with increasing retention of overstory trees (clearcutting (0% retention), seed tree (10% retention), 30% patch retention, 60% patch retention, and 100% retention in uncut controls) in an interior Douglas-fir-dominated forest in British Columbia. Regeneration increased with proximity to legacy trees in partially cut forests, with increasing densities of interior Douglas-fir, western redcedar, grand fir, and western hemlock seedlings with overstory tree retention. Clearcutting reduced cover of ectomycorrhizal refuge plants (from 80 to 5%) while promoting arbuscular mycorrhizal plants the year after harvest. Richness of shrubs, herbs, and mosses declined with increasing harvesting intensity, but tree richness remained at control levels. The presence of legacy trees in all partially cut treatments mitigated these losses. Light availability declined with increasing overstory cover and proximity to leave trees, but it still exceeded 1,000 W m−2 in the clearcut, seed tree and 30% retention treatments. Increasing harvesting intensity reduced aboveground and belowground C stocks, particularly in live trees and the forest floor, although forest floor losses were also substantial where thinning took place in the 60% retention treatment. The loss of forest floor carbon, along with understory plant richness with intense harvesting was likely associated with a loss of ectomycorrhizal inoculum potential. This study suggests that dispersed retention of overstory trees where seed trees are spaced ~10–20 m apart, and aggregated retention where openings are <60 m (2 tree-lengths) in width, will result in an optimal balance of seed source proximity, inoculum potential, and resource availability where seedling regeneration, plant biodiversity, and carbon stocks are protected.
... Other examples are highly general pathogens that may inhabit several tree species. Good examples are generalist Armillaria species that may disperse during thinning from stumps of broadleaved trees to conifers and cause root rot (Simard et al. 2005), although opposite observations have also been made (Gerlach et al. 1997). Furthermore, exotic tree species grown together with native ones may support local pathogens. ...
The boreal forests of Fennoscandia are largely dominated by Norway spruce and Scots pine. Conifer monocultures have been favoured in forest management during the last decades. Recently, concern has risen that forests consisting of only one tree species could be vulnerable to biotic damage. Additionally, environmental and societal changes are placing new demands on forest utilization, thus shifting the focus to alternative forest management options providing a wider scale of ecosystem services. It has been proposed that mixed forests are better than monocultures with respect to biodiversity, risk management and recreational value. By synthesising research studies, we provide an overview of current knowledge on how to combine wood production and other ecosystem services in mixed boreal forests in Fennoscandia. We addressed the following questions in more detail: what are the effects of mixed forests on soil properties, understorey vegetation, biodiversity, wildlife, resistance to and resilience against damage, forest productivity and the multiple use of forests? Furthermore, what are the silvicultural possibilities for establishing and managing mixed forests?
Based on this review, mixed forests appear to provide a higher output of most ecosystem goods and services, including higher biodiversity and improved risk management, soil properties and multiple-use values. The most serious challenge is the browsing by cervids, which damages sapling stands. There is potential to establish single-storied mixed forests with current regeneration methods and material. Further research is particularly needed on the silvicultural practices suited for mixed boreal forests.
... Stand type also plays a significant role in maintaining biological diversity. Mixedwood stands are reportedly more diverse and provide more benefits than just conifer or broadleaf stands (Simard et al. 2005;Paquette and Messier 2011;Hawkins et al. 2013b). Therefore, stand type was also considered as a component of potential vegetative diversity where mixedwood stands were assigned the highest diversity score (5 out of 5) followed by broadleaf (3.5 out of 5) and conifer (1.5 out of 5) stands and projected on the map for each polygon (Appendix C iii). ...
Insect outbreaks are natural phenomena that play a critical role in the development, senescence, and rebirth of forests. However, the damage caused by large-scale epidemics can have landscape scale consequences that are often poorly understood. The recent mountain pine beetle (MPB) outbreak in Canada has impacted a record >18.5 million hectares of pine forests, placing forest values at risk and significantly impacting forest-dependent communities within the region. To assess this impact, an ecosystem service-based approach was applied. Based on land cover information and monitoring data, four ecosystem services were assessed and mapped: merchantable timber, water provisioning, aboveground carbon storage, and vegetation diversity (supporting habitat). Timber is the most impacted provisioning ecosystem service followed by water provisioning, with peak stream flow in affected watersheds being positively related to mortality percent. Effects on carbon storage are substantial, with 20% of total timber aboveground carbon in dead pine trees. These effects may be mitigated, however, by the growth response of residual live trees and forest regeneration. The potential vegetation diversity showed a positive response to MPB-caused tree mortality. The results of our study may help with setting management priorities in response to large-scale biotic damage in forests in British Columbia and elsewhere.
... Herbicide treatments significantly reduced trembling aspen cover, height, and density, as well as low shrub cover in this boreal ecosystem. Similar reductions in broadleaf tree cover have been reported for other northern forests [9,[23][24][25][26]. Other studies [9,11,27] have also reported reductions in shrub cover following glyphosate application. ...
Glyphosate herbicide is widely used to control bluejoint reedgrass (Calamagrostis canadensis (Michx.) Beauv.), trembling aspen (Populus tremuloides Michx.), and other competing species in regenerating white spruce (Picea glauca (Moench) Voss) plantations in Alberta, Canada. In 2004, we initiated a study to examine the effects of the aerial application of glyphosate herbicide on plant community diversity and tree growth near Calling Lake, Alberta. Four treatments were applied: (a) no treatment (control); (b) herbicide application in the first growing season after harvesting; (c) herbicide application in the third growing season after harvesting; and (d) herbicide application in the second and fourth growing seasons after harvesting (two treatments). After 11 growing seasons, species richness was not significantly affected by treatment, while Shannon and Simpson index values were highest in areas treated with herbicide in the first growing season. Herbicide treatment did not have a significant effect on the cover of bluejoint reedgrass after 11 growing seasons, but did significantly reduce trembling aspen and paper birch cover and height. Application of glyphosate in the second and fourth growing seasons resulted in the greatest reductions to aspen cover and height, as well as significant increases in spruce diameter at age 11. Simulations with the Mixedwood Growth Model indicate that all tested herbicide treatments will reduce aspen volume while increasing spruce volume at age 90, with the largest impacts evident where two treatments were applied.
... Model results suggested superior fits when all NN species were used except for the LL site where superior fit was found with aspen NN (Table 7). Simard et al. (2005) used a similar model to describe lodgepole pine response to increasing broadleaf competition (primarily aspen). The exponential Table 6. ...
Six lodgepole pine plantations located within the Sub Boreal Spruce (SBS) biogeoclimatic zone of the northern interior of British Columbia were chosen to study the impacts of neighbourhood aspen competition on the growth of planted lodgepole pine (22-39 years old). At each site, 30 pine trees (CP) were selected as plot centres across the observed range of aspen competition. Information on the six nearest neighbours (NN) and a variety of competition indices were evaluated using linear and nonlinear models. Competition indices based on diameter or height relative to size were found as the best overall predictors of CP growth. Proximity of NN to the CP was found to be inconsistent as a predictor of growth. Individual pine and aspen NN modelling suggested aspen competition had the greatest influence on CP growth restriction. The results do not support aspen thresholds for optimizing the growth of free growing pine plantations. It is recommended that performance-based standards be developed that account for aspen competition intensity and provide guidance for the management of pine stand productivity.
... Early successional species and shade-intolerant species such as white birch and trembling aspen have higher light use efficiency when compared to late successional species (Valladares and Pearcy 1998;Valladares and Niinemets 2008). These relationships are similar when considering conifers: shadeintolerant conifers like lodgepole pine (Pinus contorta) or jack pine (Pinus banksiana) have higher growth following thinning when compared to shade-tolerant conifers such as Douglas fir (Pseudotsuga menziesii) or black spruce (Simard et al. 2005;Goudiaby et al. 2012). However, the competitive abilities of early successional species decline as mixed stands develop (Simard et al. 2004). ...
Key message: In mixed forest plantations in sub-boreal forests with high levels of natural regeneration ingrowth, competition must be quantified differently for each species, with distant-independent indices working better for the planted species and distant-dependent indices for ingrown balsam fir. Although broadleaved competition hinders growth of coniferous species more than coniferous competition, the differentiation between clades is not important enough to improve growth predictions. Context: The use of ecosystem-based forest management has changed how forest stands are tended. This shift in the management paradigm has led to a higher tolerance in natural ingrowth regeneration in plantations. The correct way of quantifying competition must thus be assessed to develop growth simulators. Aims: An individual tree relative basal area increment (RBAI) growth model for white spruce, balsam fir and other coniferous and broadleaved species was calibrated. Methods: Using data obtained from 94 sample plots in 48 white spruce plantations from Eastern Quebec, we considered both linear and nonlinear models of RBAI as a function of site index, tree size and tree competition. The tested distance-dependent and distance-independent indices were also discriminated according to competitor clade (conifers or broadleaves). Results: The best competition index for balsam fir was distance-dependent whereas a distant-independent one was retained for the other species groups. Moreover, broadleaved competitors had stronger effect on RBAI for white spruce growth when compared to coniferous competitors. Conclusion: Competition must be quantified depending on if the species is planted or ingrown. However, dividing competition into clades (i.e. coniferous versus broadleaved) is not necessary, at least in the present study.
... The trees in these and other forests are considered foundational species (Simard 2009), and the traits of foundational trees have been shown to have heritable effects on the associated networking mycorrhizal fungi (Rosado et al. 1994a, b), bird and arthropod communities (Whitham et al. 2006), soil microbes (Schweitzer et al. 2008), and potentially gene regulation of connected neighbours connected (Song et al. 2015 ) and the biochemistry of subsequent generations of seedlings (Karst et al. 2015 ), suggestive of group selection. As such, group selection may help explain why forest productivity and tree disease resistance in communities of Douglas-fir, paper birch, their inter-linking mycorrhizal fungi and associative soil microbes are enhanced compared with monocultures of Douglas-fir alone (Simard et al. 2005). However, studies are needed to test whether groups actually do benefit from MN-driven plant behaviour changes. ...
Adaptive behavior of plants, including rapid changes in physiology, gene regulation and defense response can be altered when linked to neighbouring plants by a mycorrhizal network. Mechanisms underlying the behavioral changes include mycorrhizal fungal colonization by the mycorrhizal network or interplant communication via transfer of nutrients, defense signals or allelochemicals. We focus this review on our new findings in ectomycorrhizal ecosystems, but also review recent advances in arbuscular mycorrhizal systems. We have found that the behavioral changes in ectomycorrhizal plants can depend on environmental cues, the identity of the plant neighbor and the characteristics of the mycorrhizal network. The hierarchical integration of this phenomenon with other biological networks at broader scales in forest ecosystems, and the consequences we have observed when it is interrupted, indicates that underground 'tree talk' is a foundational process in the complex adaptive nature of forest ecosystems.
Published by Oxford University Press on behalf of the Annals of Botany Company.
... Looking at DBH projections, the results indicate DBH is also increasing at a greater rate than the projected pure spruce stand at SI 50 = 21.4 (Fig. 6). These findings are also supported by observations in the central BC interior (Hawkins, Dhar 2011) and in the southern BC interior mixedwood forest (Simard et al. 2005; Simard, Vyse 2006 ). Some other investigations also reported that mixedwood stands showed greater productivity than single species stands (Man, Lieffers 1999; Legare et al. 2004; Kelty 2006). ...
Interest in conifer-broadleaf mixedwood forests has greatly increased due to continuous demand for
hardwood products and a shift towards more biological or ecosystem-based management. In British Columbia, more than 30% of the productive forest land is a conifer–broadleaf mixture and current forest regulations are more conifer biased rather than maintaining a mixed-species condition. The aim of this study was to examine the impact of paper birch on white spruce growth. Spruce growth data from 10 to 18 years old complex stands indicate that radial, height, and stem volume was not impacted by retaining up to 3,000 stems·ha–1 of birch. Similarly, growth and yield model projections suggest spruce-birch stands would be more productive up to a threshold birch density (3,000 stems/ha) than pure spruce stands. At a 4% real interest rate, the removal of birch from these stands does not appear to be warranted as an investment. The results suggest that instead of encouraging uniform broadleaf removal across conifer
plantations, mixed species management strategies could enhance the forest productivity, stand diversity and resilience.
... Traditional models of forest dynamics predict that regeneration patterns are controlled by competitive interactions with neighbours (Oliver & Larson, 1997), but this study showed that facilitation by networks increased regeneration performance and affected interspecific interactions between paper birch and Douglas-fir, encouraging a more diverse tree community. These tree-species-rich forests are also more resilient to insect attack and disease than pure Douglas-fir forests, as shown when deciduous species are removed by weeding or thinning (Morrison et al., 1988;Baleshta et al., 2004;Simard et al., 2005). Forest ecosystems are dynamic, and this is illustrated by dynamic patterns and processes in mycorrhizal networks. ...
Forests have been diminishing world-wide because of land-use changes and are experiencing additional stress from climate change. While CO2 enrichment, warming and nutrient pollution are increasing forest productivity and belowground carbon sequestration in North America and Europe, increases in drought, extreme weather events and deforestation practices are also pushing disturbance regimes outside of their natural range. Wide-spread forest diebacks or decline are already occuring in response to increasing drought, wildfire, and insect and disease attacks with climate change. These have the potential to outweigh any positive effects of climate change factors on increased belowground carbon allocation to mycorrhizas, soil microbes or roots. Recovery of these forests is uncertain given the changing dynamics between climate, trees and their mutualists, as well the changing severity and extent of disturbances. The potential for positive feedbacks from dying forest respiration to atmospheric CO2 levels is high. Humans can play an important role in mitigating forest mortality and assisting migration of species, thus dampening the impacts of climate change. Mycorrhizas play an important role in the recovery and organization of forests, and it therefore follows that conservation of mycorrhizal fungal communities should help stabilize forests and soils with climate change. Mycorrhizal networks form rapidly following disturbance in the interior Douglas-fir forests of British Columbia, providing critical water and nutrients to establishing seedlings. In mature Douglas-fir forests, most trees, even those of different species, ages and sizes, are connected by a mycorrhizal network. The extensive networks of large hub trees facilitate regeneration of younger trees in the understory, helping them tolerate the stressful environmental conditions. Mycorrhizal networks and hub trees are foundational to the organization of forests because they create favorable local conditions for tree establishment and growth. Therefore, conserving hub trees and mycorrhizal networks appears important to the conservation, regeneration and restoration of forests. Conserving forests, mitigating or managing forest diebacks or declines, and assisting migration of tree species are all important strategies for adapting to the effects of climate change.
Restoring vegetation in degraded ecosystems is an increasingly common practice for promoting biodiversity and ecological function, but successful implementation is hampered by an incomplete understanding of the processes that limit restoration success. By synthesizing terrestrial and aquatic studies globally (2594 experimental tests from 610 articles), we reveal substantial herbivore control of vegetation under restoration. Herbivores at restoration sites reduced vegetation abundance more strongly (by 89%, on average) than those at relatively undegraded sites and suppressed, rather than fostered, plant diversity. These effects were particularly pronounced in regions with higher temperatures and lower precipitation. Excluding targeted herbivores temporarily or introducing their predators improved restoration by magnitudes similar to or greater than those achieved by managing plant competition or facilitation. Thus, managing herbivory is a promising strategy for enhancing vegetation restoration efforts.
In 2017, a 5 year strategy and needs assessment survey documented consultations with Southern Interior Industry and BCTS staff highlighting priority research gaps to address key operational silviculture questions. The need for long term monitoring data documenting the effects of thinning birch competition within Douglas-fir plantations was considered a high priority. As a result, remeasurement of four PROBE sites (Simard 1993) allowed for the assessment of both the birch and Douglas-fir components over 19 years post birch thinning.
Treatments included 600 and 2500 stems per hectare (sph) of retained birch, as well as untreated controls. These treatments were established at each site, where planted Douglas-fir and retained birch were tagged and repeatedly measured over a 19-year post-treatment period in combination with vegetation assessments and silviculture surveys. Significant early increases in Douglas-fir diameter and crown length associated with birch thinning were not found >5 years post treatment, although Douglas-fir were visually larger through to 19 years. Retained birch diameter and crown size were significantly larger within the 600 sph thinning plots compared to both the 2500 sph retained birch and the untreated control plots from years 3 to 19. Douglas-fir and retained birch tree volume increments over the 5- to 19-year post-treatment period were 150% and 260% larger, respectively, in the 600 sph treatment plots than in the controls.
Over the 19-year period, Douglas-fir/birch height and crown size allometric ratios indicated that the height and crown growth rate of Douglas-fir was greater than that of birch after year 5, which indicated that Douglas-fir canopy dominance increased over time. Stand-level densities indicated by year 19 total density were significantly less in the thinned treatments due to significant declines in broadleaf density. Even though by year 19 post treatment, conifer densities were 3300–4800 sph across all treatments, only 600 sph were free-growing. Conifer ingress, noted since treatment establishment (9–14 years post planting), together with birch densities of 1100–2700 sph has resulted in overstocked stands that contain, on average, between 4500 and 7600 total sph at year 19. Prediction of Douglas-fir tree growth in relation to neighbourhood competition was influenced by large variations in local density, species composition, and cover across the treatments. Douglas-fir crop tree size distribution was explored across the treatments using diameter–frequency plots, density functions, and cumulative stem volume growth patterns. Several management implications are provided highlighting opportunities for future composition and density treatments.
Broadcast weeding of naturally regenerating paper birch (Betula papyrifera) to improve performance of conifer crop trees is common in forest plantations in British Columbia, Canada, but such treatments are costly, reduce biodiversity and may increase disease. To investigate whether alternative treatments can enhance conifer performance with minimal loss of other ecosystem services, we examined effects of selective removal of paper birch in two interior Douglas-fir (Pseudotsuga menziesii var. glauca) plantations on Douglas-fir growth and survival, and cover and height of residual birch and the understorey plant community. Douglas-fir-centred birch-free patches of varying radius (0 to 2.5 m) were created by single and repeated manual cutting and Triclopyr® application. The “threshold brushing radius,” defined as the birch removal radius at which Douglas-fir performance was optimized, was 2.0 m at the more productive site and 1.5 m at the less productive one. Armillaria root disease, the major Douglas-fir mortality agent, spiked in the 1.0 m radius manual cutting treatment at one location. The greatest reductions in birch and understory plant abundance occurred following the most intensive treatments. Selective brushing treatments are an effective alternative to broadcast removal of paper birch for increasing conifer performance, and have less impact on the plant community.
Lodgepole pine is extensively planted across western Canada but little is known about development of these stands beyond the juvenile stage. We quantified stocking status and damage incidence in sixty-six 15- to 30-year-old lodgepole pine plantations that had previously been declared free-growing in the southern interior of British Columbia. The stands were located in six biogeoclimatic zones: Engelmann Spruce-Subalpine Fir (ESSF), Montane Spruce (MS), Interior Cedar-Hemlock (ICH), Interior Douglas-fir (IDF), Sub-Boreal Spruce (SBS), and Sub-Boreal Pine-Spruce (SBPS). Freegrowing standards were no longer met on 27% of plantations, with the worst performance (70% no longer free-growing) in the Interior Cedar-Hemlock forests. Natural regeneration was common but it was half the size of lodgepole pine. Biotic damage, especially hard pine stem rusts, was the dominant factor reducing free-growing densities. Stands were at greater risk of reduced stocking where summer precipitation was higher or soil moisture regimes were wetter and where stands had been broadcast-burned prior to planting or received secondary treatments of brushing or pruning. Reforestation policies that encourage widespread planting of lodgepole pine, particularly in areas where lodgepole pine has limited natural occurrence such as in the ICH zone, should be reconsidered given that health problems are extensive and are expected to increase with climate change.
Ponderosa pine (Pinus ponderosa) in the Black Hills National Forest, SD, USA, was surveyed for Armillaria root disease (ARD). The root pathogen Armillaria ostoyae occurred on ponderosa pine seedlings, saplings, pole‐size trees and large‐diameter trees. The mean incidence of aboveground disease symptoms by stem count was low (0.2%), but in certain areas, the incidence was higher, affecting the regeneration success and tree longevity. Symptomatic ponderosa pine were in areas characterized by having higher elevation, greater annual precipitation, more seedlings, bigger large‐diameter trees and greater odds of past harvesting activity than in areas without root disease. Stump density was positively spatially correlated with root disease incidence. No particular soil type was related to disease occurrence; though, in areas with symptomatic trees, soil available water holding capacity (AWC) was greater and soil permeability was less where root disease was present. Spatial analysis confirmed the relationships found in linear correlations, with soil AWC and stump density positively and soil permeability negatively correlated with per cent infected stems ha−1 and basal area infected.
Critical height ratios for predicting competition between trembling aspen and lodgepole pine were identified in six juvenile stands in three south-central British Columbia ecosystems. We used a series of regression analyses predicting pine stem diameter from the density of neighbouring aspen in successively shorter relative height classes to identify the aspen-pine height ratio that maximized
R
2
. Critical height ratios varied widely among sites when stands were 8–12 years old but, by age 14–19, had converged at 1.25–1.5. Maximum
R
2
values at age 14–19 ranged from 13.4% to 69.8%, demonstrating that the importance of aspen competition varied widely across a relatively small geographic range. Logistic regression also indicated that the risk of poor pine vigour in the presence of aspen varied between sites. Generally, the degree of competition, risk to pine vigour, and size of individual aspen contributing to the models declined along a gradient of decreasing ecosystem productivity.
In southern British Columbia, juvenile trembling aspen is managed primarily as a competitor with conifers rather than for its ecological and economic value. As a result, brushing treatments have been applied on a widespread basis and this practice is likely to continue in the near future. Given the potential for climate change to affect our valuation of aspen, we require a better understanding of factors that affect its development, its competitive ability with conifers and its responses to brushing. We used data from 11 aspen management experiments to examine the influence of climate and site factors on aspen height, cover, and density in 17–24 year-old control stands and 9–16 years after manual cutting or girdling. Models explained 64% and 89% of the variation in aspen height in control and manually brushed stands, respectively, but were poor for girdling. Increasing length of the frost-free period was associated with increasing aspen height in control stands, whereas drier summer conditions on cool aspects favoured height growth of aspen suckers following manual cutting. We also examined the influence of climate and site factors on three simple competition indices that describe the height and density of aspen relative to conifer height, and then tested how well these indices predicted conifer growth. The density of aspen taller than conifers accounted for 39% of the variation in lodgepole pine diameter and the ratio of aspen/conifer height accounted for 33% of the variation in Douglas-fir height, suggesting that aspen competition was only moderately important to conifer growth. Our findings imply that aspen may become more productive with warmer summers provided it is not limited by summer moisture availability and that mixed stand management is a viable option in southern interior stands.
We used manual cutting to manipulate trembling aspen (Populus tremuloides Michx.) density and spatial arrangement in relation to crop lodgepole pine (Pinus contorta Dougl. Ex Loud. var. latifolia Engelm.) on two sites in contrasting dry, cool to cold ecosystems of south-central British Columbia. In the dry, cool interior Douglas-fir ecosystem (IDFdk3), we reduced the density of tall aspen (aspen at least as tall as target pine) to 0 (broadcast removal), 1000, 2500, or 4000 stems/ha when the planted lodgepole pine was 6 years old. Eight years later, pine height/diameter ratio (HDR) was significantly lower in the broadcast removal and 1000 stem/ha treatments than in the control. There were no other significant growth responses and pine survival and vigour were good regardless of treatment. In contrast, in a dry, cold sub-boreal pine spruce ecosystem (SBPSxc) where treatments were applied at a stand age of 11 years, naturally regenerated lodgepole pine stem diameter increased significantly in the broadcast removal treatment relative to the untreated control within 2 years. After 4 years, HDR had declined significantly relative to the control where tall aspen density was ≤1000 stems/ha. There were no significant pine responses where 2500 tall aspen stems/ha were retained or where tall aspen were removed only within a 1-m radius around pine. The greater difference in height (height differential) between aspen and pine at the SBPSxc than the IDFdk3 site may partly explain the differing response of lodgepole pine to treatment. Trends of decreasing sucker density with increasing aspen retention were evident at both sites, but differences were significant (p ≤ 0.05) only at the SBPSxc site.
Vegetation management treatments are often applied to high-elevation, Ericaceous shrub-dominated sites in southern interior British Columbia to facilitate reforestation. We studied the effects of manual cutting on an established vegetation community and newly planted to 2-year-old Engelmann spruce (Picea engelmannii Parry ex Engelm.) over a 10-year period. Spruce survival was significantly higher in the treatment than the control 3 years after brushing (p = 0.020). Although differences in survival continued to be large after 10 years (79% versus 61%), they were no longer significant due to increased between-site variability. Relative height estimates indicated that brushed spruce were taller relative to the vegetation canopy than control spruce throughout the 10 years assessment period, but growth responses were small even where significant. The cutting treatment significantly increased ground-level diameter after 3 and 5 years, but not after 10 years. The loss of statistical significance is attributed to ongoing mortality of small diameter suppressed stems in the control. After 10 years, shrub cover was still lower in the cutting treatment than the control, but height had recovered within 3 years. Manual cutting increased Shannon diversity in the first year post-treatment (p = 0.039), after which it returned to control levels. There were no differences in species richness. A competition index based on the first year relationship between spruce and vegetation cover and height (CRHTS1) explained 33% of the variation in spruce diameter 10 years after treatment, and first year total shrub cover (COVTS1) explained 28% of the variation. R2 values increased slightly over time, suggesting that vegetation competition was still affecting at least some surviving seedlings when they were 10–12 years old. Thresholds for spruce diameter of 139 and 64% were identified for CRHTS1 and COVTS1, respectively.
Forest harvesting and wildfire were widespread in the upper Great Lakes region of North America during the early 20th century. We examined how long this legacy of disturbance constrains forest carbon (C) storage rates by quantifying C pools and fluxes after harvest and fire in a mixed deciduous forest chronosequence in northern lower Michigan, USA. Study plots ranged in age from 6 to 68 years and were created following experimental clear-cut harvesting and fire disturbance. Annual C storage was estimated biometrically from measurements of wood, leaf, fine root, and woody debris mass, mass losses to herbivory, soil C content, and soil respiration. Maximum annual C storage in stands that were disturbed by harvest and fire twice was 26% less than a reference stand receiving the same disturbance only once. The mechanism for this reduction in annual C storage was a long-lasting decrease in site quality that endured over the 62-year timeframe examined. However, during regrowth the harvested and burned forest rapidly became a net C sink, storing 0.53 Mg C ha−1 yr−1 after 6 years. Maximum net ecosystem production (1.35 Mg C ha−1 yr−1) and annual C increment (0.95 Mg C ha−1 yr−1) were recorded in the 24- and 50-year-old stands, respectively. Net primary production averaged 5.19 Mg C ha−1 yr−1 in experimental stands, increasing by < 10% from 6 to 50 years. Soil heterotrophic respiration was more variable across stand ages, ranging from 3.85 Mg C ha−1 yr−1 in the 6-year-old stand to 4.56 Mg C ha−1 yr−1 in the 68-year-old stand. These results suggest that harvesting and fire disturbances broadly distributed across the region decades ago caused changes in site quality and successional status that continue to limit forest C storage rates.
We characterize variation in radial and height growth of saplings of 11 tree species across a range of light levels in boreal, sub-boreal, subalpine, and temperate forests of northwestern British Columbia. Shade-tolerant species had the greatest response to an increase in light at low-light levels but had low asymptotic growth at high light. Shade-intolerant species had weaker responses to increases at low light but had the highest growth rates at high light. The effects of climate on intraspecific variation in sapling response to light were also related to shade tolerance: across different climatic regions, the most shade-tolerant species varied in their response to low light but not high light, while shade-intolerant species varied only in their high-light growth. Species with intermediate shade tolerance varied both their amplitude of growth at high light and the slope of the growth response at low light. Despite the interspecific trade-offs between high- and low-light growth, there was a striking degree of overlap in the light response curves for the component species in virtually all of the climatic regions. Successional dynamics in these forests appear to be more strongly governed by interspecific variation in sapling survival than growth.
The paper presents a comprehensive review of the biomass equations for 65 North American tree species. All equations are of the form M = aDb, where M is the oven-dry weight of the biomass component of a tree (kg), D is diameter at breast height (DBH) (cm), and a and b are parameters. Equations for the following tree components were included in the review: total aboveground biomass, stem wood, stem bark, total stem (wood and bark), foliage, and branches (wood and bark). A total of 803 equations are presented with the range of DBH values of the sample, sample size, coefficient of determination R2, standard error of the estimate, fitting method used to estimate the parameters a and b, correction factor for a bias introduced by logarithmic transformation of the data, site index and geographic location of the sampled stand(s), and a reference to the paper in which the equation (or the data) was published. The review is a unique source of equations that can be used to estimate tree biomass and/or to study the variation of biomass components for a tree species.
The coarse-scale population structure of pathogenic Armillaria (Fr.) Staude species was determined on ap- proximately 16 100 ha of relatively dry, mixed-conifer forest in the Blue Mountains of northeast Oregon. Sampling of recently dead or live, symptomatic conifers produced 112 isolates of Armillaria from six tree species. Armillaria spe- cies identifications done by using a polymerase chain reaction based diagnostic and diploid-diploid pairings produced identical results: 108 of the isolates were Armillaria ostoyae (Romagn.) Herink and four were North American Biologi- cal Species X (NABS X). Five genets of A. ostoyae and one of NABS X were identified through the use of somatic incompatibility pairings among the putatively diploid isolates. Armillaria ostoyae genet sizes were approximately 20, 95, 195, 260, and 965 ha; cumulative colonization of the study area was at least 9.5%. The maximum distance between isolates from the 965-ha A. ostoyae genet was approximately 3810 m, and use of three estimates of A. ostoyae spread rate in conifer forests resulted in age estimates for the genet ranging from 1900 to 8650 years. Results are discussed in relation to possible mechanisms that influenced the establishment, expansion, and expression of these genets; the ge- netic structure and stability of Armillaria; and the implications for disease management in this and similar forests. Résumé : La structure grossière des populations des espèces pathogènes d'Armillaria (Fr.) Staude a été établie sur une
The frequency of Armillaria species in precommercial thinning stumps and the interaction at root contacts between Douglas-fir (Psendotsuga menziesii (Mirb.) France) crop trees and stumps colonized by Armillaria ostoyae (Romagn.) Herink were investigated at sites in four biogeoclimatic zones along a transect from the coast through the southern interior of British Columbia. The frequency of stumps colonized by A. ostoyae and Armillaria sinapina Berube & Dessureault varied among lower, mid, and upper slope transects. On coastal sites, A. sinapina dominated fresh hygrotopes and A. ostoyae dominated slightly dry hygrotopes, and the frequency of both fungi was low on moist hygrotopes. On interior sites, A. ostoyae was found over all hygrotopes, but with lower frequency on the driest sites. The distribution of the two Armillaria species on sites is apparently determined by anoxia associated with periodic soil saturation, by drying of the soil, and by host response limiting spread of pathogenic species, At root contacts between colonized stump roots and crop tree roots, transfer and infection by A. ostoyae occurred more frequently in moist biogeoclimatic zones than dry ones. Lesion size on crop tree roots was related to inoculum volume at some sites and to stump root diameter at others. The percentage of lesions on roots at which crop trees formed callus was associated with tree bole volume. The results indicate that there will be crop tree mortality following precommercial thinning, especially where inoculum levels are high in the Interior Cedar-Hemlock and Interior Douglas-fir biogeoclimatic zones.
The trembling aspen (Populus tremuloides Michx.) white spruce (Picea glauca (Moench) Voss) mixed woods near Fort Nelson are distinguished by the large size of individual trees, longevity, and the low occurrence of internal decay in trembling aspen. The development of these forest ecosystems has had limited documentation and may be significantly different than those described in other portions of the boreal forest. At five study stands, stem analysis techniques were used to examine the patterns of height and radial growth over time according to species and structure type. There were two patterns of species establishment that were consistent with the stand structure. In codominant stands, recruitment periods for trembling aspen and white spruce overlapped. The stratified stands were consistently associated with a 29- to 58-year lag in white spruce recruitment. Spruce that were codominant with aspen at the time of sampling had sustained periods of rapid height and diameter growth. White spruce that were later to establish on site had slower rates of height and diameter growth. White spruce ages indicated that a dominant recruitment episode was more common than continuous recruitment. Height and diameter growth of trembling aspen were similar in both stand types. The differences in trembling aspen growth patterns between stands were due to site quality. The white spruce in codominant stands did not appear to go through a period of suppression and then release associated with stand-level trembling aspen mortality, as commonly described for other boreal mixedwoods. The vigor and longevity of trembling aspen in Fort Nelson appear to prolong the period of trembling aspen domination of mixed stands well beyond the time periods observed in other boreal ecosystems.
Treatments that reduce neighbour density are widely applied in the belief they will improve conifer growth in mixed forests. However, our understanding of stand composition and age effects on competition is poor. We used neighbourhood analysis for 748 target conifer trees to examine interspecific competition within 11-, 25-, and 50-year-old mixed, even-aged stands of paper birch (Betula papyrifera Marsh.), Douglas-fir (Pseudotsuga menziesii var. glauca (Beissn.) Franco), western redcedar (Thuja plicata Donn ex D. Don), and western larch (Larix occidentalis Nutt.) in southern interior British Columbia. Critical neighbourhood height and distance were identified where competition accounted for the greatest variation in target conifer diameter. Competition processes were emperically examined using relative height indices. We found that critical neighbourhood distance increased with stand age and was greater for larch than for cedar. Critical neighbourhood height was higher for cedar than for Douglas-fir or larch in the 11-year-old stands but lower in the older stands. The most important competitors in the 11-year-old stands were tall neighbours, whereas those in the older stands were short neighbours. We found asymmetrical relationships between target conifers and neighbours for all species and age-classes, indicating a resource preemption mode of competition. To be useful in developing prescriptions for competition management in mixed species stands, competition indices should consider neighbour identity and critical height for each target species. Assessment radius must also be sufficiently large to adequately characterize competition.
Armillaria ostoyae (Romagn.) Herink. causes serious damage to forest tree species worldwide. In this study, Hypholoma fasciculare (Huds. ex Fr.) Kummer was inoculated, after logging, into areas in south-central British Columbia that had been identified as having high levels of A. ostoyae. Hypholoma fasciculare was successfully established in a variety of different types of trials, as indicated by growth of H. fasciculare mycelium into roots of inoculated stumps and the presence of fruiting bodies on and around stumps. Three to five years after treatment, inoculated plots had biologically and statistically significantly lower levels of mortality attributable to A. ostoyae.Key words: Hypholoma fasciculare, Armillaria, biocontrol, woody debris.
Five years after spacing a young, 11 m tall paper birch (Betula papyrifera Marsh.) stand, we examine relationships between growth of understory white spruce (Picea glauca (Moench) Voss), subalpine fir (Abies lasiocarpa (Hook.) Nutt.), and level of birch retention. Our objectives were to evaluate the effectiveness of selected measures of competition for estimating the effects of the residual birch and to evaluate the influence of residual birch densities on growth responses of naturally regenerated subalpine fir and white spruce. Basal area of Scouler willow (Salix scouleriana Barratt) and birch were found to effectively predict light transmittance (diffuse noninterceptance). The best models for predicting 4-year volume growth of subalpine fir and white spruce incorporate initial crown volume of the subject trees and transmittance as independent variables. Lorimer's index and Hegyi's index gave similar results to those obtained using basal area and transmittance, suggesting that there is little benefit in including measurements of proximity in a competition index. For both species, the correlation between basal area increment and light was substantially stronger than observed for volume increment. However, height increment of both subalpine fir and spruce was only weakly correlated with measured light levels. The ratio of height increment to volume increment decreased with both increasing initial height and transmittance for subalpine fir and white spruce.
This study investigated the stand structure in pine, spruce and deciduous forests in the border district of Finland and Russia. A total of 46 mature forest stands was selected as pairs, the members of each pair being as similar as possible with respect to their forest site type, age, moisture and topography. The stands were then compared between the two countries by means of basal areas and number of stems. The proportions of dominating tree species were 2-12% lower, and correspondingly the proportions of secondary tree species higher, in Russian forests. The density of the forest stock was also higher in each forest type in Russia. The forests in the two countries differed most radically in terms of the abundance of dead trees. The amount was two to four times higher in Russian deciduous and spruce forests, and in pine forests the difference was 10-fold. The stand structures indicated that Russian coniferous stands, in particular, were more heterogeneous than intensively managed pine and spruce stands in Finland.
Mortality from Armillaria root rot is a major concern of forest management. Field experiments were conducted in Minnesota to evaluate interspecific differential susceptibility and to assess whether density or species composition, specifically the proportion of conifers in a plot, influences seedling mortality from Armillaria spp. Seedlings of 10 tree species (six conifers and four hardwoods) were planted at four densities in several species mixtures on recently logged sites. Species differed significantly in susceptibility (p < 0.0001); balsam fir (Abies balsamea (L.) Mill.), tamarack (Larix laricina (Du Roi) K. Koch), and black spruce (Picea mariana (Mill.) BSP) showed the greatest infection and mortality. Hardwood species and eastern white pine (Pinus strobus L.) showed negligible mortality. There was a trend (p = 0.1) toward increased root infection with increasing density of the three species that showed significant mortality. Their mortality rates were 5.6, 8.7, 10.2, and 10.8% in plots with 2-, 1-, 0.5-, and 0.25-m spacing, respectively. Mortality increased significantly (p = 0.001)with an increase in the proportion of conifers in a plot. Mortality in the three most susceptible species was reduced by 75% when grown in aspen-rich rather than in conifer-rich plots. Thus, seedling mortality was related to species identity, planting density, and proportion of conifers, suggesting that selected diversity (mixtures of conifers with hardwoods rather than conifer monocultures) reduces disease impact.
We characterize variation in radial and height growth of saplings of 11 tree species across a range of light levels in boreal, sub-boreal, subalpine, and temperate forests of northwestern British Columbia. Shade-tolerant species had the greatest response to an increase in light at low-light levels but had low asymptotic growth at high light. Shade-intolerant species had weaker responses to increases at low light but had the highest growth rates at high light. The effects of climate on intraspecific variation in sapling response to light were also related to shade tolerance: across different climatic regions, the most shade-tolerant species varied in their response to low light but not high light, while shade-intolerant species varied only in their high-light growth. Species with intermediate shade tolerance varied both their amplitude of growth at high light and the slope of the growth response at low light. Despite the interspecific trade-offs between high- and low-light growth, there was a striking degree of overlap in the light response curves for the component species in virtually all of the climatic regions. Successional dynamics in these forests appear to be more strongly governed by interspecific variation in sapling survival than growth.
Ten-year response of plant communities to disk trenching, plowing, rotoclearing and windrow burning was studied on two contrasting sites to address concerns that mechanical site preparation reduces structural and species diversity. Cover and height of all species on randomly located subplots within 0.05- to 0.075-ha treatment plots were used to develop indices of volume, structural diversity, and species diversity; to ordinate the plots; and to correlate species diversity with crop-tree performance. At both sites, community response was strongly influenced by the severity of site preparation. On a boreal site dominated by willow (Salix L. spp.), green alder (Alnus crispa (Ait.) Pursh ssp. crispa) and trembling aspen (Populus tremuloides Michx.), site preparation increased structural diversity and had little effect on species diversity. High-severity treatments increased non-native species abundance 10- to 16-fold while only marginally enhancing growth of planted white spruce (Picea glauca (Moench) Voss) over medium-severity treatments. On a nutrient-poor sub-boreal site, species diversity declined with increasing treatment severity and with increasing lodgepole pine (Pinus contorta var. latifolia Engelm.) stem volume. Velvet-leaved blueberry (Vaccinium myrtilloides Michx.) was highly sensitive to mechanical disturbance. Moderate mechanical treatments appear to improve conifer performance while causing little change to plant communities, but high severity treatments can cause substantial change.
The degree of herbivory and the effectiveness of defense varies widely among plant species. Resource availability in the environment
is proposed as the major determinant of both the amount and type of plant defense. When resource are limited, plants with
inherently slow growth are favored over those with fast growth rates; slow rates in turn favor large investments in antiherbivore
defenses. Leaf lifetime, also determined by resource availability, affects the relative advantages of defenses with different
turnover rates. Relative limitation of different resources also constrains the types of defenses. The proposals are compared
with other theories on the evolution of plant defenses.
Most obligate cavity-nesting birds are considered to be nest-site limited, either by time or energy to excavate or to acquire suitable holes for nesting. We examined rates of nest-cavity reuse for a rich community of cavity-nesting birds in mixed forests in interior British Columbia. Using a sample of 402 cavity-reuse cases over five years, we measured cavity reuse for 20 cavity-nesting bird and mammal species (three guilds), and examined the relationship between nest-cavity reuse and features of cavities, nest trees, and forest stands. Eight percent of used cavities were destroyed between years. Reuse rates were 17% for the cavities of weak excavators such as nuthatches and chickadees, 28% for formerly active woodpecker nests, and 48% for cavities previously used by secondary cavity nesting birds, but there was considerable species variation within all guilds. Nest cavities in aspen that were deep with large entrances had the highest reuse. At the forest stand level, cavities in trees close to edges and in sites with more edge habitat had greater reuse. Reused cavities tended to be occupied in sequential years rather than being inactive for a year. With increasing amounts of managed landscapes, availability of suitable cavities for forest nesting vertebrates is decreasing. Reuse of existing cavities might help mitigate the problem of nest-site limitation.
Intensive forest management has changed both local and regional characteristics of Fennoscandian forest. However, quantitative documentation of landscape transformations is rare. In this study, five forest landscapes were examined in order to define and quantify forest landscape transformation in southern Finland from the 1940s to the 1970s and 1990s. These areas of 140-200 km2 contained both private and state-owned forests. Digital aerial photographs of each area were classified into no-canopy forest (clear-cut and seedling stands, open mires) and closed-canopy forest (young and mature stands). Patch density, mean patch size, largest patch index and edge density calculated for closed-canopy patches indicated fragmentation from the 1940s to the 1970s and recovery from the 1970s to the 1990s. Trends were very similar in both ownership groups. Thus, fragmentation of closed-canopy forests has not progressed continuously in southern Finland, but shows different patterns depending on the period. However, the recovery observed between the 1970s and 1990s does not necessarily mean an increased abundance of the natural old-growth areas that are needed to host many of the currently threatened species.
Thresholds define the time when management action is required to prevent a loss in yield, but have remained relatively elusive in forest vegetation management. Hundreds of studies quantifying the effects of competing vegetation in young forest stands, however, have produced reasonably consistent patterns and magnitudes of tree responses. These consistencies reveal a set of general guidelines that can be used to assist forest managers in deciding when vegetation management treatments are needed. Among the variety of vegetation management thresholds that have been defined, competition and critical-period thresholds can be interpreted from existing forest vegetation research. Competition thresholds define the vegetation density at which yield loss begins to occur and varies depending on whether the manager's objective is to maximize survival, height increment, basal area growth, or biomass. These interactions also appear to vary depending on whether woody or herbaceous plants are the principal competitors. The critical-period threshold defines the time period when vegetation control must occur to prevent yield loss. Results from one critical-period study indicate that capturing the potential for conifer growth requires control of vegetation for the first several years after planting.
We examine use of the neighborhood approach for quantifying interspecific competition around Douglas-fir seedlings that were planted in early-successional forest vegetation. We manipulated woody and herbaceous vegetation in the neighborhoods of >685 trees on four sites in the Oregon Coast Range for five years. We sought the best neighborhood expression of interspecific competition by systematically examining the influence of various measures of woody-neighbor abundance, height, distance, and spatial arrangement in regression models that predict the annual basal area and height growth of Douglas-fir. We identified the optimum neighborhood height and radius for each year. Visual estimates of shrub species cover provided the best assessment of neighbor abundance. Stratifying the neighborhood by the height of shrubs relative to the height of the Douglas-fir improved regression models and quantified patterns of competitive asymmetry. Differences in the response of Douglas-fir height and basal area to neighborh...
The 6-year effects of differing levels of Sitka alder (Alnus viridus spp. sinuata (Regel) Á. Löve & D. Löve) retention (0, 500, 1000, and 2000 clumps/ha) on the development of retained alder and on the growth and foliar nutrition of 7-year-old naturally regenerated lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) were evaluated in a sub-boreal ecosystem in the central interior of British Columbia. Alder development was inversely related to alder retention density, with the largest height and crown width increments occurring at the lowest alder densities. Low to moderate levels of alder cover did not significantly inhibit the diameter or height growth of lodgepole pine. Even under high alder cover, growth was not reduced until alder cover exceeded 45%. Over the 6-year response period, lodgepole pine diameter and height increments under high alder cover were reduced by 10% and 12%, respectively, relative to the no-alder treatment. The effect of alder density on lodgepole pine foliar N was strongly linear, with the highest N levels measured in the high alder retention treatment. However, the positive impact of alder retention on foliar N resulted in probable imbalance of N relative to S and possibly P and K. Unless alleviated, nutritional imbalances may preclude reliable assessment of the competitive effects (i.e., light and soil resources) of alder density, if any, on lodgepole pine growth.
We examine use of the neighborhood approach for quantifying interspecific competition around Douglas-fir seedlings that were planted in early-successional forest vegetation. We manipulated woody and herbaceous vegetation in the neighborhoods of > 685 trees on four sites in the Oregon Coast Range for Eve years. We sought the best neighborhood expression of interspecific competition by systematically examining the influence of various measures of woody-neighbor abundance, height, distance, and spatial arrangement in regression models that predict the annual basal area and height growth of Douglas-fir. We identified the optimum neighborhood height and radius for each year. Visual estimates of shrub species cover provided the best assessment of neighbor abundance. Stratifying the neighborhood by the height of shrubs relative to the height of the Douglas-fir improved regression models and quantified patterns of competitive asymmetry. Differences in the response of Douglas-fir height and basal area to neighborhood height suggested that neighbor influences on height growth were asymmetric, while effects on basal area growth were symmetric. Shrub neighbors whose crowns intermingled with that of the Douglas-fir had the greatest influence on Douglas-fir growth and defined the optimum neighborhood radius. The competitive influence of neighboring shrubs decreased rapidly as their distance increased beyond the optimum neighborhood radius. Accounting for neighbor spatial arrangement using two measures of angular dispersion did not improve the models. The best neighborhood dimensions for Douglas-fir seedlings changed with time, apparently with the dynamics of vertical structure in the plant community. The neighborhood approach was effective for (1) evaluating various approaches forest managers might use to quantify competing vegetation, (2) examining the dynamics of competitive effects, (3) quantifying asymmeteric competition, (4) determining the relative competitive effects of woody and herbaceous vegetation, and (5) documenting the differing response of tree height and basal area growth to neighboring plants.
We compared wildlife utilization of recent clearcuts subjected to three regeneration scenarios commonly used in boreal balsam fir (Abies balsamea (L.) Mill.) forests: natural regeneration, plantation of black spruce (Picea mariana (Mill.) BSP) followed by herbicide release (glyphosate), and plantation of black spruce followed by manual release (brushsaw). The wildlife species studied were songbirds, small mammals and the snowshoe hare (Lepus americanus Erxleben). Surveys were conducted during the 2 years preceding and the 5 years following conifer release. The abundance of songbirds decreased the second and third years after both types of release, and the abundance of the red-backed vole (Clethrionomys gapperi Vigors) was reduced for 2 years following herbicide release. Snowshoe hares rarely used the stands during the 8 to 10 years that followed logging, so conifer release did not affect them. In this study, the short- and mid-term effects of the regeneration scenarios on wildlife may have been mitigated by the poor quality of clearcuts as wildlife habitats at the time of release and by the fact that plantations, like naturally regenerated sites, had a heterogeneous vegetation and a well-developed herb and shrub cover. In the humid balsam fir forest, where vegetation growth is slow and snow cover deep, the size and distribution of clearcuts would have greater effects on wildlife in the short and mid term than the regeneration scenario used for forest renewal. A landscape management approach inspired by natural disturbance dynamics is proposed as a mitigation measure.Nous avons comparé l'utilisation par la faune d'aires de coupe soumises à trois scénarios de régénération courants dans la sapinière boréale, soit la régénération naturelle, la plantation d'épinette noire (Picea mariana (Mill.) BSP) dégagée chimiquement (glyphosate) et la plantation d'épinette noire dégagée mécaniquement (scie débroussailleuse). Notre étude a porté sur les passereaux nicheurs, les petits mammifères et le lièvre d'Amérique (Lepus americanus Erxleben), inventoriés pendant les 2 ans antérieurs aux dégagements et les 5 ans suivants. Les principaux effets observés ont été une diminution de l'abondance des passereaux nicheurs 2 et 3 ans après tout dégagement et de celle du campagnol à dos roux (Clethrionomys gapperi Vigors) pendant 2 ans après un dégagement chimique. Le lièvre n'a pas été affecté par les dégagements car il a rarement fréquenté les sites pendant les 8 à 10 ans qui ont suivi la coupe. Dans cette étude, l'impact à court et moyen terme des scénarios de régénération sur la faune pourrait avoir été mitigé par la pauvreté faunique des sites au moment des travaux de dégagement et par le fait qu'à l'instar des sites régénérés naturellement, les plantations affichaient une végétation hétérogène ainsi que des strates herbacée et arbustive basse bien développées. Dans la sapinière boréale pluviale, où la croissance de la végétation est lente et l'enneigement important, la superficie et la répartition des parterres de coupe auraient beaucoup plus d'impacts sur la faune à court et moyen terme que le scénario utilisé pour les remettre en production. Une stratégie d'aménagement à l'échelle du paysage, inspirée de la dynamique des perturbations naturelles, est proposée comme mesure de mitigation.
The relationship between aboveground symptoms and belowground incidence of Armillaria ostoyae (Romagn.) Herink on conifers in 13- to 24-year-old stands was investigated at five sites in each of the dry, moist, and wet climatic regions in the Nelson forest region, British Columbia. All trees > 1.3 m in height in 0.01-ha circular plots centred on a tree killed fewer than two or more than five years previously or located where there were no symptomatic trees were removed from the soil by an excavator. The location and host response at each A. ostoyae lesion on root systems were recorded. Significant differences in belowground incidence were seen among climatic regions and plot types, with distance from the centre of plots, and between planted and naturally regenerated trees. Belowground incidence was related to the percentage of putatively colonized stumps within and adjacent to plots. There were significant differences among climatic regions in the intensity of infection, host reaction to infection, and percentage of diseased trees showing aboveground symptoms. These results have implications for interpreting results of surveys for Armillaria root disease in juvenile stands and for tending of such stands.
Working Paper 64, published 2002, was the last of that series. The use of trade, firm, or corporation names in this publication is for the information and convenience of the reader. Such use does not constitute an official endorsement or approval by the Government of British Columbia of any product or service to the exclusion of any others that may also be suitable. Contents of this report are presented for discussion purposes only. Funding assistance does not imply endorsement of any statements or information
The relationship between aboveground symptoms and belowground incidence of Armillaria ostoyae (Romagn.) Herink on conifers in 13- to 24-year-old stands was investigated at five sites in each of the dry, moist, and wet climatic regions in the Nelson forest region, British Columbia. All trees >1.3 m in height in 0.01-ha circular plots centred on a tree killed fewer than two or more than five years previously or located where there were no symptomatic trees were removed from the soil by an excavator. The location and host response at each A. ostoyae lesion on root systems were recorded. Significant differences in belowground incidence were seen among climatic regions and plot types, with distance from the centre of plots, and between planted and naturally regenerated trees. Belowground incidence was related to the percentage of putatively colonized stumps within and adjacent to plots. There were significant differences among climatic regions in the intensity of infection, host reaction to infection, and percentage of diseased trees showing aboveground symptoms. These results have implications for interpreting results of surveys for Armillaria root disease in juvenile stands and for tending of such stands.
We compared wildlife utilization of recent clearcuts subjected to three regeneration scenarios commonly used in boreal balsam fir (Abies balsamea (L.) Mill.) forests: natural regeneration, plantation of black spruce (Picea mariana (Mill.) BSP) followed by herbicide release (glyphosate), and plantation of black spruce followed by manual release (brushsaw). The wildlife species studied were songbirds, small mammals and the snowshoe hare (Lepus americanus Erxleben). Surveys were conducted during the 2 years preceding and the 5 years following conifer release. The abundance of songbirds decreased the second and third years after both types of release, and the abundance of the red-backed vole (Clethrionomys gapperi Vigors) was reduced for 2 years following herbicide release. Snowshoe hares rarely used the stands during the 8 to 10 years that followed logging, so conifer release did not affect them. In this study, the short- and mid-term effects of the regeneration scenarios on wildlife may have been mitigated by the poor quality of clearcuts as wildlife habitats at the time of release and by the fact that plantations, like naturally regenerated sites, had a heterogeneous vegetation and a well-developed herb and shrub cover. In the humid balsam fir forest, where vegetation growth is slow and snow cover deep, the size and distribution of clearcuts would have greater effects on wildlife in the short and mid term than the regeneration scenario used for forest renewal. A landscape management approach inspired by natural disturbance dynamics is proposed as a mitigation measure.
This study was designed to test the hypothesis that herbicide (glyphosate, active ingredient) application for conifer release would reduce species diversity (measured as richness, Simpson's index, and Shannon-Wiener index) of both plant and small mammal communities over a 5-year period in young sub-boreal spruce (Picea engelmannii Parry ex Engelm. x Picea glauca (Moench) Voss) forest. Four treated and four untreated (control) sites were studied near Prince George in central British Columbia, Canada. Crown volume index of shrub vegetation was reduced by herbicide application. Species richness of shrubs was reduced in the first year after treatment and remained lower on treated sites throughout the 5-year period. Both indices of shrub diversity, however, were not different over the 5 years. Herbicide treatment initially reduced crown volume index of herbaceous vegetation, but values quickly recovered to untreated levels by the second year after treatment. Herbaceous species diversity was not affected by herbicide treatment. Diversity of small mammal communities apparently was not affected by herbicide application. In general, diversity of plant and small mammal communities seemed to be maintained, and hence, these treatment sites may not lower overall diversity of a forested landscape. Silvicultural practices, such as conifer release with herbicides or alternative methods, may contribute to a diversity of stand structures and wildlife habitats if appropriately designed and implemented.
Mean age, mean and top heights and yield were studied in 20 mixed stands of birch (Betula pubescens Ehrh. and B. pendula Roth) and Picea abies (L.) Karst. and nine mixed stands of birch and Pinus sylvestris L. in south-eastern Norway. Each mixed stand and the adjacent pure coniferous stand (control) were growing under the same site conditions and had not been commercially thinned. There were no significant differences in mean age at breast height or in top heights between birch and conifers in the mixed stands, while mean height was significantly higher for birch than for spruce. A growth index was calculated based on total volume and age at breast height. For the spruce sites the growth in young mixed stands (birch Keywords: ABIES; BETULA; DYNAMICS; FORESTS; GROWTH; INDEX; MIXED; PENDULA; PICEA; PINUS; PUBESCENS; QUALITY; SITE; STAND; SYLVESTRIS; YIELD Document Type: Research Article DOI: http://dx.doi.org/10.1080/028275802753626782 Publication date: April 1, 2002 More about this publication? Editorial Board Information for Authors Subscribe to this Title ingentaconnect is not responsible for the content or availability of external websites (document).ready(function() { var shortdescription = (".originaldescription").text().replace(/\\&/g, '&').replace(/\\, '<').replace(/\\>/g, '>').replace(/\\t/g, ' ').replace(/\\n/g, ''); if (shortdescription.length > 350){ shortdescription = "" + shortdescription.substring(0,250) + "... more"; } (".shortdescription a").click(function() { (".originaldescription").slideDown(); return false; }); }); Related content In this: publication By this: publisher In this Subject: Forestry By this author: Frivold, Lars Helge ; Frank, Jon GA_googleFillSlot("Horizontal_banner_bottom");
Most obligate cavity-nesting birds are considered to be nest-site limited, either by time or energy to excavate or to acquire suitable holes for nesting. We examined rates of nest-cavity reuse for a rich community of cavity-nesting birds in mixed forests in interior British Columbia. Using a sample of 402 cavity-reuse cases over five years, we measured cavity reuse for 20 cavity-nesting bird and mammal species (three guilds), and examined the relationship between nest-cavity reuse and features of cavities, nest trees, and forest stands. Eight percent of used cavities were destroyed between years. Reuse rates were 17% for the cavities of weak excavators such as nuthatches and chickadees, 28% for formerly active woodpecker nests, and 48% for cavities previously used by secondary cavity nesting birds, but there was considerable species variation within all guilds. Nest cavities in aspen that were deep with large entrances had the highest reuse. At the forest stand level, cavities in trees close to edges and in sites with more edge habitat had greater reuse. Reused cavities tended to be occupied in sequential years rather than being inactive for a year. With increasing amounts of managed landscapes, availability of suitable cavities for forest nesting vertebrates is decreasing. Reuse of existing cavities might help mitigate the problem of nest-site limitation.
In this study the effects of thinning, fertilization and pruning on the vigour of Douglas fir (Pseudotsuga menziesii) and its susceptibility to Armillaria root disease were explored. Tree vigour was defined as the relative capacity for tree growth, expressed as the above-ground biomass increment per unit of photosynthetic tissue, or growth efficiency (GE). It has been hypothesized that trees with higher GE can better resist pathogen attack, and that GE can be used as a predictor of tree susceptibility to disease. In a previous study, four Douglas fir plantations were thinned, fertilized and pruned in all combinations, and the effects of these treatments on tree vigour were measured after 10 years. Root disease was not a factor in the initial study design, and mortality was ignored until 8 years after the treatments were applied. The results of an earlier study were utilized and the correlation between Armillaria root disease incidence and the effects of earlier stand treatments on tree growth was tested. Armillaria ostoyae was the primary mortality agent in the study area. Disease incidence on infested subplots ranged from 2 to 20%. Armillaria ostoyae incidence was the highest at medium tree density (6.1%), slightly lower on the low density (5.6%), and lowest on the unthinned plots (3.8%). There were no significant correlations between disease incidence and previous tree growth. The vigour of trees that became symptomatic or died by 1993 was not significantly different in 1983–85 from the vigour of trees that remained asymptomatic. On these sites, in areas of infestation, A. ostoyae is killing the largest, fastest growing trees, as well as less vigorous trees. Armillaria continues to cause mortality, regardless of the growth efficiency or growth rate of the host.
1 It is useful to distinguish between the immediate effects of species richness on ecosystems and those which become apparent on a longer time scale, described here as filter and founder effects.
2 Relationships between plant diversity and ecosystem properties can be explored by classifying component species into three categories – dominants, subordinates and transients. Dominants recur in particular vegetation types, are relatively large, exhibit coarse‐grained foraging for resources and, as individual species, make a substantial contribution to the plant biomass. Subordinates also show high fidelity of association with particular vegetation types but they are smaller in stature, forage on a more restricted scale and tend to occupy microhabitats delimited by the architecture and phenology of their associated dominants. Transients comprise a heterogeneous assortment of species of low abundance and persistence; a high proportion are juveniles of species that occur as dominants or subordinates in neighbouring ecosystems.
3 A ‘mass ratio’ theory proposes that immediate controls are in proportion to inputs to primary production, are determined to an overwhelming extent by the traits and functional diversity of the dominant plants and are relatively insensitive to the richness of subordinates and transients. Recent experiments support the mass ratio hypothesis and the conclusion of Huston (1997) that claims of immediate benefits of high species richness to ecosystem functions arise from misinterpretation of data.
4 Attribution of immediate control to dominants does not exclude subordinates and transients from involvement in the determination of ecosystem function and sustainability. Both are suspected to play a crucial, if intermittent, role by influencing the recruitment of dominants. Some subordinates may act as a filter influencing regeneration by dominants following major perturbations.
5 Transients originate from the seed rain and seed banks and provide an index of the pool of potential dominants and subordinates at specific sites. Where the landscape carousel operates against a background of declining diversity in the reservoir of colonizing transients, we may predict that a progressive loss of ecosystem functions will arise from the decline in the precision with which dominants can engage in the re‐assembly and relocation of ecosystems.
Patterns of survival and stem-volume growth for planted seedlings of ponderosa pine (Pinus ponderosa Dougl. ex Laws.) competing with various levels of woody and herbaceous vegetation were derived from three previous studies—one in Oregon and two in Montana. Negative hyperbolic curves of opposite concavity describe the relation between the abundance of woody or herbaceous vegetation and (1) the survival and (2) the stem volume of the pine seedlings. From these curves, two types of competition thresholds for managing forest vegetation are identified: (1) maximum-response threshold—a level of vegetation abundance where additional control measures will not yield an appreciable increase in tree performance; and (2) minimum-response threshold—a level of vegetation abundance that must be reached before additional control measures will yield an appreciable increase in tree performance. The maximum- and minimum-response thresholds for pine stem volume occurred at lower levels of vegetation abundance than those for pine survival. Thus, forest managers may need to consider ponderosa pine survival and stemvolume growth as separate objectives when managing woody and herbaceous vegetation in young plantations. Knowledge of maximum- and minimum-response thresholds also can be used to improve herbicide prescriptions.
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Paper birch (Betula papyrifera Marsh.) is routinely chemically or mechanically weeded from Douglas-fir (Pseudotsuga menziesii var. glauca (Beissn.) Franco) plantations to increase conifer productivity, but these practices are controversial because of unknown effects on forest health and diversity. This study examined effects of paper birch density reduction treatments on productivity and disease incidence of Douglas-fir saplings in the southern interior of British Columbia. Five paper birch density treatments (0, 400, 1111, 4444 stems ha−1 and an un-thinned control of >7000 stems ha−1), where paper birch was manually cut at the root collar in 1999, were replicated on four sites in a randomized block design. After 2 years, Douglas-fir survival did not differ significantly among treatments, but where Armillaria ostoyae (Romagn.) Herink was present in untreated stands, mortality due to root disease increased significantly with increasing paper birch thinning intensity. Mean diameter increment and height:diameter ratio of Douglas-fir improved where paper birch was completely removed or partially thinned compared with the control. Mean light transmittance and soil moisture content increased with decreasing paper birch density, but Douglas-fir foliar N status was unaffected. Our results suggest that Douglas-fir growth can be improved and root disease incidence minimized by thinning paper birch to 4444 stems ha−1 in young mixed stands, but that subsequent release treatments may be necessary to maintain Douglas-fir growth rates.
Growth and survival responses of 8 year-old interior spruce to reductions in paper birch density from 2500 to 1000, 50 and 0 overtopping stems ha−1 were examined after five years on a single site in the Interior Cedar Hemlock biogeoclimatic zone of southern British Columbia. Stem diameter increased and height : diameter ratio decreased when birch density was reduced from 2500 to 50 stems ha−1, but there were no further benefits to spruce growth when the entire birch overstory was removed. Spruce growth did not improve where birch was thinned to 1000 stems ha−1, but its potential for release may have been confounded by the higher density of taller conifers in that treatment. Interspecific competition between spruce and paper birch appeared to be primarily for light because spruce responded to dramatic reductions in overstory density but not to reductions in understory sprout density. Spruce survival was unaffected by thinning treatments, indicating that birch density of 2500 stems ha−1 was too low to induce mortality. Armillaria root disease was the main cause of mortality, and spruce leader weevil and Cooley’s spruce gall adelgid were important damaging agents, but the behaviour of these organisms was unaffected by treatment. Stand structure was dramatically changed from a mixed coniferous–deciduous to a predominantly coniferous overstory when birch was thinned to 50 or 0 stems ha−1, which may have negative implications for wildlife. If balancing maximum spruce growth with biodiversity is the primary objective, then between 50 and 1000 stems ha−1 birch should be retained on sites similar to the one used in our experiment. This will require modification of the current legislation governing reforestation in British Columbia.
The aim of this study was to quantify 5-year growth, yield and mortality responses of 9- to 13-year-old naturally regenerated, even-aged paper birch (Betula papyrifera Marsh.) stands to pre-commercial thinning in interior British Columbia. The study included four residual densities (9902–21,807 stems ha−1 (unthinned control), 3000, 1000 and 400 stems ha−1) and four sites with 3-fold within-site replication in a randomised block design. The largest, straightest, undamaged trees were selected to leave during thinning. Thinning reduced stand basal area from 5.90 m2 ha−1 in the control to 2.50, 1.53 and 0.85 m2 ha−1 in the three thinning treatments, representing 42, 26 and 15% of control basal area, respectively. After 5 years, total stand volume per plot remained lower in the three thinning treatments than the control (50.20, 30.07, 18.99 and 11.86 m3 in the control, 3000, 1000 and 400 stems ha−1 treatments), whereas mean stand diameter, diameter increment, height, and height increment were increased by thinning, and top height (tallest 100 trees ha−1) was unaffected. When a select group of crop trees (largest 250 trees ha−1) in the thinning treatments was compared with the equivalent group in the control, there was a significant increase in mean diameter, diameter increment, basal area, basal area increment, and volume increment. Mean height, height increment, top height, and total volume were unaffected by thinning. Crop tree diameter increment was the greatest following thinning to 400 stems ha−1 for all diameter classes. Thinning to 1000 stems ha−1 resulted in lower diameter increment than thinning to 400 stems ha−1 but tended to have higher volume increment. Dominant trees responded similarly to subdominant trees at 400 stems ha−1, but showed the greatest response at 3000 stems ha−1. Results suggest that pre-commercial thinning of 9–13-year-old stands to 1000 stems ha−1 would improve growth of individual trees without seriously under-utilising site resources.
Paper birch (Betula papyrifera Marsh) is considered the most important competitive threat to commercially valuable conifers in the highly productive interior cedar–hemlock forests of British Columbia. It is routinely removed from conifer plantations at high cost to increase conifer growth rates and meet reforestation policy regulations. Competitive effects of paper birch and other neighbours on conifer growth were measured in mixed forests to test the hypotheses that the importance and intensity of interspecific competition were (a) high in young plantations; (b) decrease with stand age; (c) decrease with conifer species shade tolerance. Neighbourhood analysis was applied to 748 target conifer trees in 11 stands that included three stand age classes (11, 25, and 50 years-old) and three target conifer species (Douglas-fir (Pseudotsuga menziesii Mirb. Franco), western redcedar (Thuja plicata D. Don), and western larch (Larix occidentalis Nutt.)). All sites had similar site characteristics and disturbance histories. Regression models were used to examine the importance (model adjusted r2) and intensity (model β1) of neighbour competition on target conifer size. Double logarithmic regression models explained on average 38±3% of the variation in target conifer diameter from the neighbourhood index, NRI . The models indicated that broadleaf neighbours were more important and intense competitors in the 11- and 25-year-old stands, and conifers were more important and intense competitors in the 50-year-old stands. When all broadleaf and conifer neighbours were included in the models, the intensity and/or importance of neighbour competition decreased in the order of 25>50>11-year-old stands, and western larch>Douglas-fir>western redcedar. Instead of encouraging uniform broadleaf removal across most conifer plantations in the BC interior, reforestation policies should take into account the variable effects of broadleaf competition within stands, across stand ages, and with different tree species compositions.
Quantitative synthesis across studies requires consistent measures of effect size among studies. In community ecology, these measures of effect size will often be some measure of the strength of interactions between taxa. However, indices of interaction strength vary greatly among both theoretical and empirical studies, and the connection between hypotheses about interaction strength and the metrics that are used to test these hypotheses are often not explicit. We describe criteria for choosing appropriate metrics and methods for comparing them among studies at three stages of designing a meta-analysis to test hypotheses about variation in interaction intensity: (1) the choice of response variable; (2) how effect size is calculated using the response in two treatments; and (3) whether there is a consistent quantitative effect across all taxa and systems studied or only qualitatively similar effects within each taxon-system combination. The consequences of different choices at each of these stages are illustrated with a meta-analysis to examine the relationship between competition/facilitation intensity and productivity in plants. The analysis used a database of 296 cases in 14 studies. The results were unexpected and largely inconsistent with existing theory: competition intensity often significantly declined (rather than increased) with productivity, and facilitation was sometimes restricted to more productive (rather than less productive) sites. However, there was considerable variation in the pattern among response variables and measures of effect size. For example, on average, competitive effects on final biomass and survival decreased with standing crop, but competitive effects on growth rate did not. On the other hand, facilitative interactions were more common at low standing crop for final biomass and growth rate, but more common at high standing crop for survival. Results were more likely to be significant using the log response ratio (In[removal/control]) as the effect size than using the relative competition intensity ([removal - control]/removal), although the trends for these conceptually similar indices did not differ. When all studies were grouped in a single meta-regression of interaction intensity on standing crop to test quantitative similarity among studies, survival showed the dearest negative relationship. However, when the same regressions were done for each unique combination of taxon and site within each study to test for qualitative similarity among studies, the slopes averaged over studies tended to be negative for biomass and growth rate, but not different from zero for survival. These results are subject to a number of caveats because of the limitations of the available data-most notably, the extension of effects of interactions on individual growth or survival to effects on population distribution and abundance or community structure is highly problematic. Nevertheless, the fact that none of the meta-analyses demonstrated a significant positive relationship between competition and standing crop but that we frequently found negative relationships is an important pattern that has not been apparent from qualitative surveys of individual studies, and it demonstrates the potential power of meta-analysis in ecology. We conclude with recommendations to overcome some of the limitations of the currently available data and meta-analytical procedures.
An updated silvics text for British Columbia. The need for an effective learning tool for silvics - one of the basic required courses in forestry - has been recognized by intructors as well as students across the province. The text prepared 18 years ago by Krajina et al. (1982) specifically for western Canada has become outdated. The silvics text by Burns and Honkala (1990) represents an up-to-date compendium but it is not an effective learning tool, particularly lacking in the linkage of silvics to ecological classification. Consequently, we revised and expanded “Distribution and Ecological Characteristics of Trees and Shrubs of British Columbia” (Krajina et al. 1982) using the available information on silvics, with some modification for BC and the results of recent silvics research done in BC. This material has been consolidated into a format that will help students understand the silvical attributes of tree species as well as the relationships between trees and their environments. To enhance learning, we have selected a series of slides illustrating the salient characteristics for each species and present this visual component on a CD-ROM included with the text. Also included is a large biogeoclimatic zone map of BC. The text, together with the CD-ROM, is intended to facilitate learning of silvics emphasizing its application to silviculture. Forest Sciences, Dept of Peer-Reviewed
Nine-year response of Douglas-fir and the mixed hardwood–shrub complex to chemi-cal and manual release treatments on an ICHmw2 site near Salmon Arm. British Columbia Ministry of Forests
- S W Simard
- J Heineman
Simard, S.W., and Heineman, J. 1996. Nine-year response of Douglas-fir and the mixed hardwood–shrub complex to chemi-cal and manual release treatments on an ICHmw2 site near Salmon Arm. British Columbia Ministry of Forests, Victoria, B.C. For. Resour. Dev. Agree. Rep. 257.
Detection, recogni-tion and management of Armillaria and Phellinus root diseases in the southern interior of British Columbia. British Columbia Ministry of Forests
- D Morrison
- H Merler
- D Norris
Morrison, D., Merler, H., and Norris, D. 1991. Detection, recogni-tion and management of Armillaria and Phellinus root diseases in the southern interior of British Columbia. British Columbia Ministry of Forests, Victoria, B.C. For. Resour. Dev. Agree. Rep. 179.
Control of Armillaria and Phellinus root diseases: 20-year results from the Skimikin stump removal experiment
- D J Morrison
- G W Wallis
- L C Weir
Morrison, D.J., Wallis, G.W., and Weir, L.C. 1988. Control of Armillaria and Phellinus root diseases: 20-year results from the Skimikin stump removal experiment. Can. For. Serv. Pac. For. Cent. Inf. Rep. BC-X-302.
Paper birch managers' handbook for British Columbia. Forestry Canada and British Columbia Ministry of Forests
- E B Peterson
- N M Peterson
- S W Simard
- J R Wang
Peterson, E.B., Peterson, N.M., Simard, S.W., and Wang, J.R. 1997. Paper birch managers' handbook for British Columbia. Forestry Canada and British Columbia Ministry of Forests, Vic-toria, B.C.
Annual report British Columbia Ministry of Forests Boreal plant community diversity 10 years after glyphosate treatment
- Bcmof Victoria
- B C Boateng
- J O Haeussler
- S Bed-Ford
BCMOF. 2003. Annual report 2002/03. British Columbia Ministry of Forests, Victoria, B.C. Boateng, J.O., Haeussler, S., and Bed-ford, L. 2000. Boreal plant community diversity 10 years after glyphosate treatment. West. J. Appl. For. 15: 15–26.
Resource availability and plant antiherbivore defence. Science (Washing-ton
- P D Coley
- J P Bryant
- F S Chapin
- Iii
Coley, P.D., Bryant, J.P., and Chapin, F.S., III. 1985. Resource availability and plant antiherbivore defence. Science (Washing-ton, D.C.), 230: 895–899.
The physical en-vironment as a basis for managing ecosystems. In Creating a forestry for the 21st century: the science of ecosystem manage-ment
- F J Swanson
- J A Jones
- G E Grant
Swanson, F.J., Jones, J.A., and Grant, G.E. 1997. The physical en-vironment as a basis for managing ecosystems. In Creating a forestry for the 21st century: the science of ecosystem manage-ment. Edited by K.A. Kohm and J.F. Franklin. Island Press, Washington, D.C. pp. 229–238.