Suckering response of aspen to traffic-induced-root wounding and the barrier-effect of log storage

In a growth chamber, we tested how the seasonal timing of placing a physical barrier (simulating a possible effect of log storage) and inflicting root damage impacted aspen (Populus tremuloides Michx.) root systems and their suckering capability. Roots from 4-year-old saplings were used, and one half of these root systems had the above-ground portion cut in the winter (dormant) while the other half was cut during the growing season in the summer. Damage was inflicted to the roots by driving a large farm tractor over them, and a covering treatment was applied using a polystyrene board to prevent suckers from emerging from the soil. Soil temperatures for the winter-cut root systems were kept at 5 °C over the growing season, using a water bath, while for the summer-cut root systems soil temperatures were maintained at 17 °C over the growing season. In the winter-cut root systems, both log storage and root wounding caused a 40% reduction in living root mass and carbohydrate reserves, as well as reducing sucker numbers and their growth performance. In the summer-cut root systems log storage and root wounding reduced living root mass by approximately 35% as well as sucker growth, but had less of an impact on the number of suckers produced.     

Root carbohydrates and aspen regeneration in relation to season of harvest and machine traffic

Season of harvest has often been suggested as a driver for the erratic success of aspen (Populus tremuloides) sucker regeneration, partially due to root carbohydrate reserves and soil conditions at the time of harvest. A field experiment in western Manitoba, Canada, assessed root suckering and root carbohydrates of aspen in response to season of harvest and machine traffic. Six sites (120 m × 120 m) were selected within two large mature aspen stands slated for summer harvest. Plots (50 m × 50 m) were hand-felled (without machine traffic) in mid-summer, late summer, winter, and one plot was left uncut as a control. Season of cut with no traffic had no effect on sucker density, height or leaf dry mass per sucker. During the dormant season, root starch reserves were highest in the winter cut plots, however, just prior to suckering, this difference in carbohydrate reserves among the three seasons of harvest disappeared and by the end of the first growing season root reserves in all three seasons of cut had recovered to near control levels. Adjacent plots that were conventionally harvested in the summer and impacted by logging traffic had similar sucker densities but had 19% less height growth of suckers and 29% less leaf dry mass per sucker compared to suckers in plots harvested at the same time without traffic. After one growing season, root carbohydrate levels were similar whether or not machine traffic was used; however, the reduction in leaf dry mass in plots with machine traffic could have negative implications for carbohydrate accumulation and growth. The study suggests that the phenological state of the mature aspen plays a very small role in aspen regeneration and that harvesting practices and site conditions are likely the main drivers of aspen regeneration success.     

The influences of conifer succession, physiographic conditions and herbivory on quaking aspen regeneration after fire

Fire suppression over the last century has increased conifer expansion and dominance in aspen-conifer forests, which appears to be a driving force behind aspen decline in some areas. The primary objective of this study was to examine how increasing conifer dominance affects aspen regeneration vigor following the return of fire. The influence of physiographic features and herbivory on aspen regeneration vigor were also examined. The study was conducted in the Sanford fire complex located in the Dixie National Forest in southern Utah, USA, where more than 31,000 hectares burned in the summer of 2002. Seven years after the burn (at 66 locations) we measured aspen regeneration density and height as response variables and former stand composition and density (the burned trees were still standing), soil characteristics, slope, aspect and presence or absence of herbivory as independent variables. Aspen regeneration (root suckering) densities ranged from <500 to 228,000 stems/hectare with an average of 37,000 stems/hectare. Post-fire aspen regeneration density was most strongly correlated with pre-fire stand successional status (as measured by stand composition and species abundance), with percent conifer abundance (R² = −0.55) and overstory aspen density (R² = + 0.50) being the most important. Average aspen suckering densities ranged from approximately 60,000 stems/hectare in what were relatively pure aspen stands (>90% aspen) to less than 5000 stems/hectare in stands where conifer abundance was greater than 90%. Soil C, N, and P showed positive correlations (R² = 0.07 to 0.17) with aspen regeneration vigor, while soil texture had a relatively weak influence on sucker regeneration. Aspen regeneration densities were 15% lower on north facing aspects compared to east, west and south facing aspects with slope steepness showing no correlation with regeneration vigor. Regeneration density was significantly lower (8%) at sites with evidence of herbivory versus sites where herbivory was absent. Overall, the aspen regeneration response in the Sanford fire complex was strong despite high wildlife densities, which may be related to disturbance size. Where the maintenance of aspen is desired in the landscape we recommend promoting fire when the percentage of overstory conifer stems is greater than 80% or overstory aspen density is less than 200 overstory stems/hectare.     

Regeneration dynamics of planted seedling-origin aspen (<Emphasis Type="Italic">Populus tremuloides</Emphasis> Michx.)

Aspen (Populus tremuloides Michx.) is a foundational tree species of the North American boreal forest. After disturbance, clonal aspen stands quickly achieve canopy closure by sending up numerous clonal shoots (root suckers) from their lateral root system. Controlled aboveground disturbance will commonly induce prolific root suckering and thereby increase stem density in clonal aspen stands, but it is unclear if increases in stem density will be observed in planted seedling-origin aspen stands. The objectives of this study were to determine (1) overall root suckering response of planted aspen to aboveground disturbance; (2) if different cut heights of the stem or infliction of root damage impact the number of root suckers produced. We found that planted aspen regenerated readily after disturbance, averaging five root suckers per cut tree. However, individual response was highly variable, ranging from zero to 29 root suckers per root system. Of the cut trees, 75% produced at least one root sucker and 60% produced at least one stump sprout. Cutting trees close to the soil surface produced more root suckers than leaving a 25 cm stump. While root system size (mass and length) was well correlated with aboveground measures of planted aspen, root suckering was not related to root system size. As a result of increased forest reclamation efforts in the boreal forest region the planting of aspen has become a more common practice, necessitating a better understanding of the regeneration dynamics and root suckering potential of these planted and seedling-origin aspen forests.     

Does mechanical site preparation affect trembling aspen density and growth 9–12 years after treatment?

Trembling aspen (Populus tremuloides Michx.) density and growth were assessed 9–12 years after stand establishment to determine whether mechanical site preparation (MSP) affects crop tree quality. Study sites were either treated with disc trenching or ripper ploughing and planted with white spruce (Picea glauca (Moench) Voss) seedlings immediately after harvest (treated) or were undisturbed since harvest (control). Stands were surveyed during the summer of 2002 with standard regeneration survey plots. Results show that aspen stem density and height were lower in MSP-treated areas relative to untreated areas. Diameter growth rates were unaffected by treatment, however the percentage of stem discolouration was higher in untreated control stands compared to site prepared areas. The results of this study indicate that there are no long-term benefits to carry out MSP for aspen promotion. However, as MSP does not appear to seriously harm the aspen crop, we suggest that this treatment can still be used on sites where aspen densities may be low without treatment (e.g., sites with extremely low soil temperatures, poor soil aeration, or vigorous competitive vegetation) or where a mixture of aspen and planted spruce are desired.     

Effects of soil temperature and time of decapitation on sucker initiation of intact Populus tremuloides root systems

Abstract

In a growth chamber experiment, root suckering of aspen (Populus tremuloides Michx.) was assessed in relation to timing of cutting and soil temperature. Aspen seedlings were grown in large pots for 3 years before experimentation. In a 2×2 factorial experiment, 3-year-old seedlings were cut at the end of the dormant period or after leaf flush and grown at two soil temperatures (8 or 20°C) for 39 days. Root systems were evaluated for suckering response and carbohydrate reserve status. There were no differences between the two soil temperatures and times of cut in the number of sucker buds initiated on the roots, but the number of buds that developed into suckers was much greater at 20°C. Cutting the dormant seedlings delayed suckering by nearly a week, resulting in smaller suckers at the time of harvest. However, cutting the seedlings when dormant produced almost twice the number of suckers than when cutting occurred after leaf-out. Total non-structural carbohydrates (TNC) of roots declined from 35.6% of dry weight at the end of the dormant season to 21.6% at the time of leaf-out, but there were no differences between the soil temperature and timing of cut treatments. After the 39 day growth period, root systems had 7% lower root TNC in the 20°C treatment than in the 8°C treatment, likely to support the development of the emerging suckers and higher respiration demands.     

Spatial impacts of soil disturbance and residual overstory on density and growth of regenerating aspen

We examined spatial aspects of harvesting impacts on aspen regeneration at 25 sites in northern Minnesota. These sites had been clearcut or partially harvested 4–11 years ago. At each site, residual overstory, which was composed of trees other than aspen, soil disturbance, and tree regeneration were determined along transects leading away from skid trails into the neighboring stand. We characterized spatial extent of soil disturbance as soil strength using an Eijkelkamp soil cone penetrometer. Soil disturbance dropped off very quickly at the edge of skid trails, suggesting that the impact of harvesting traffic on areas adjacent to skid trails is minor. On skid trails, disturbance levels were higher on sites harvested in summer than on sites harvested in winter. Even after adjustment for differences in soil disturbance, stands harvested in winter had higher regeneration densities and greater aspen height growth than stands harvested in summer, suggesting that aspen regeneration was more sensitive to a given level of soil disturbance on summer-harvested sites versus on winter-harvested sites. Soil disturbance and residual overstory interactively reduced aspen regeneration densities and height growth, indicating that avoidance of soil disturbance is even more critical in partially harvested stands. Predictions based in the spatial patterns of impact found in this study indicated that harvesting conditions may have a great impact in future productivity of a site.     

Importance of different tree fractions for epiphytic lichen diversity on Picea abies and Populus tremula in mature managed boreonemoral Swedish forests

Abstract

Knowledge of the canopy lichen flora of managed forests is poor, but needs more focus since, for example, slash (tops, branches and twigs) harvest for biofuel may pose a threat to epiphytic lichen diversity. This study compared lichen species richness, density and composition between stems, tops, branches and twigs of mature Norway spruce (Picea abies) and aspen (Populus tremula) in managed boreonemoral forests in south–central Sweden. The stems were also compared with the slash fractions pooled together. All comparisons were made separately for each tree species. In total, 30 lichen species were found on Norway spruce and 46 on aspen. No significant differences in species richness or species density between fractions were found for Norway spruce, whereas aspen tops were significantly less species rich and species dense than the other fractions. Moreover, aspen slash was significantly more species dense than the stem. The lichen species composition of the stems clearly differed from that of the tops, branches and twigs in both tree species. Thus, lichen communities other than those removed with stems by conventional forestry are removed from the stands owing to slash harvest. However, these species are rather common and widespread in Sweden. The impact of slash harvest on the epiphytic lichen flora may therefore be of minor importance in forests established after clear-cutting or on former arable land.     

Effect of stock type characteristics and time of planting on field performance of aspen (Populus tremuloides Michx.) seedlings on boreal reclamation sites

Aspen (Populus tremuloides Michx) has great potential as a reclamation species for mining sites in the boreal forest, but planting stock has shown poor field performance after outplanting. In this study we tested how different aspen seedling characteristics and planting times affect field outplanting performance on reclamation sites. We produced three different types of aspen planting stock, which varied significantly in seedling size, root-to-shoot ratio (RSR), and total non-structural carbohydrate (TNC) reserves in roots, by artificially manipulating shoot growth during seedling production. All three stock types were then field-planted either in late summer, late fall, or early spring after frozen storage. Seedlings were outplanted onto two reclaimed open-pit mining areas in the boreal forest region of central and east-central Alberta, Canada, which varied significantly in latitude, reclamation history, and soil conditions. Overall, height growth was better in aspen stock types with high RSR and TNC reserves. Differences in field performance among aspen stock types appeared to be more strongly expressed when seedlings were exposed to more stressful environmental site conditions, such as low soil nutrients and moisture. Generally, aspen seedlings planted with leaves in the summer showed the poorest performance, and summer- or fall-planted seedlings with no shoot growth manipulation had much greater stem dieback after the first winter. This indicates that the dormancy and hardening of the stem, as a result of premature bud set treatments, could improve the outplanting performance of aspen seedlings, particularly those planted during summer and fall.     

Signals controlling root suckering and adventitious shoot formation in aspen (Populus tremuloides)

We determined the effects of removal of leaves, stem axillary buds, or the entire shoot on root suckering (adventitious shoot formation by roots) and basal stem sprouts in 3- and 4-year-old potted seedlings of aspen (Populus tremuloides Michx.). The greatest number of root suckers (67.9 +/- 8.5 per plant) emerged after excision of the entire shoot. Defoliated and debudded stems were the major source of inhibitory agents for root suckering, although axillary buds and developing new leaves also exerted a significant inhibitory effect. Removal of mature leaves had only a minor effect on root suckering. Removal of a continuous band of bark (girdling) at the base of the stem consistently stimulated growth of adventitious shoots from the stem below the girdle and occasionally promoted root suckering. Exogenous application of indole-3-acetic acid to excised stumps inhibited root suckering and basal stem sprouting. Naphthylphthalamic acid (NPA), an auxin polar transport inhibitor, had no effect on root suckering or stem sprouting when it was applied to the bark of the basal stem. However, NPA significantly increased root suckering when it was applied to the exposed surface of xylem after girdling. These results suggest that polar transport of auxin in the xylem parenchyma is an important inhibitor of root suckering. On decapitated stems, vacuum extraction of xylem sap from the root system lowered the frequency of root suckering compared with decapitation alone, indicating that substance(s) originating in the root system also play a significant role in controlling root suckering.     

The effects of mechanical site preparation and subsequent wildfire on trembling aspen (Populus tremuloides Michx.) regeneration in central Alberta,Canada

The objective of this study was to assess the regeneration response oftrembling aspen (Populus tremuloides Michx.) to differentmechanical site preparation (MSP) techniques commonly used in operationalforestry (disc trenching, drag scarifying and blading) and the specificmicrosites created by each treatment. This study was designed to measureregeneration after at least the first two growing seasons, however a largewildfire burned 80% of the study sites at the beginning of the second growingseason. Consequently, only limited second year data were presented, butregeneration from the first growing season following the fire was alsoassessed.Results indicated that microsites where the forest floor was disturbed and theparent root system was only lightly injured were more conducive to suckeringthan undisturbed microsites or where the root system was severely injured.Also,the fire disturbance after the first growing season resulted in increasedsuckering relative to the untreated controls in the first year. These resultssuggest that aspen sites with thick organic layers or vigorous competition fromother species can benefit from MSP when applied before the first growingseason.In addition, if first year suckering is inadequate, subsequent disturbancessuchas prescribed fire have the potential to improve suckering provided the parentroot system remains intact.     

Regeneration of Populus nine years after variable retention harvest in boreal mixedwood forests

Aspen and balsam poplar regeneration from root suckers were assessed in boreal mixedwood forests nine years after logging in a variable retention experiment (EMEND Project—Ecosystem Management Emulating Natural Disturbance) located north of Peace River, Alberta, Canada. Five levels of retention of mature trees (2%, 10%, 20%, 50% or 75% of the original basal area) were applied in stands dominated by aspen, white spruce or mixtures of the two species. Basal area of aspen (or that of aspen plus balsam poplar combined) prior to logging strongly influenced sucker density of aspen (or aspen + balsam poplar combined) and in some cases their growth. Nine years after harvest there was a decline in sucker density and volume ha⁻¹ with increasing retention levels of aspen (or both poplars combined); sucker density declined by 50% when only 20% of the original basal area was left in the stand. Retaining mature spruce trees in the stand had little influence on the number of suckers but did affect their total volume ha⁻¹. Thus, we suggest that by knowing stand aspen and balsam poplar density prior to logging and varying levels of retention of aspen and balsam poplar or conifers at harvest, the density of Populus regeneration can be predicted by managers, thereby allowing them to create a range of mixedwood conditions.     

Soil redox potential in small pondcypress swamps after harvesting

Soil environmental conditions were investigated in nine stillwater swamps dominated by pondcypress (Taxodium distichum var. nutans) in north central Florida. Three swamps were left unharvested (control); three were harvested, but surrounding slash pine plantations were left intact (swamp harvest); and three were harvested along with the surrounding slash pine plantations (swamp+upland harvest). Measurements of soil redox potential (E_h) and other soil and water properties were collected for 5 months before harvesting (December 1993–April 1994) and for 2 years after harvesting (May 1994–May 1996). No significant differences in water level resulted from harvesting, although control swamps became dry and harvested swamps remained flooded shortly after harvesting. E_h in the swamp+upland harvest treatment was lower than in the control treatment for only 1 month (July 1994) after logging but was also lower in areas where the soil was compacted by skidder equipment. Short-term increase in water level and soil compaction by skidder trafficking appear to have minimal long-term effects on soil environmental conditions.     

华北落叶松迹地更新关键技术及其效果评价

近年,随着大部分华北落叶松近成熟林分被采伐利用,迹地更新技术成为经营管理的首选课题。2002~2006年,通过对围场桃山林场迹地更新技术的实践,总结出了"就近育苗、合理育苗、局部整地、加强幼抚"等,是华北落叶松迹地更新的关键技术,且效果明显。     

Clonal variation in root suckering ability of hybrid aspen (Populus tremula L. × P. tremuloides Michx.)

Current information on the root sucker ability of hybrid aspen (Populus tremula L. × P. tremuloides Michx.) is in most cases based on clone mixtures. In this study, we could separate the performance among clones by using two experimental sites with monoclonal plots of the crossing. The natural regeneration was followed for 2 years after harvest of the formerly planted stands, clear-cut at 22 and 25 years of age, respectively. We found that clonal differences were present in the number of root suckers produced per area unit and their biomass production. However, all included clones produced sufficiently many root suckers for a successful regeneration. To receive a more complete evaluation of the root sucker dynamics for future selection on the clonal level, further studies are needed where vitality, self-thinning and effects of thinning measures are coupled to the goal of the aspen forestry.     

Management tools for optimal allocation of wood fibre to conventional log and bio-energy markets in Ireland: a case study

A set of tools are described for optimal allocation of wood fibre at an operational planning level. These were applied to a case study in Ireland. Allocation was based on optimising net value recovery (delivered price minus harvesting and transportation costs) while meeting market demands and operational constraints (mainly crew capability and productivity limits). Two new models were developed to predict harvesting costs and transportation costs for Irish forest conditions. A new model was developed to link Sitka spruce biomass expansion factors to optimal log-making algorithms so that log and bio-energy product yields could be estimated for individual harvest areas. An existing operational allocation model based on a tabu search heuristic procedure was used. The case study included 16 forest harvest areas and 12 processing plants (saw logs, pallet logs, stakes, pulp, bio-energy slash bundles, etc.). New terrestrial lidar scanning procedures were used to obtain representative stem profiles from over 4,000 trees for the 16 forests. We demonstrated that optimal allocation of bio-energy and log products, while complex, can be achieved through the use of appropriate management tools.     

Economic analysis on log damage during logging operation in Caspian Forests

Waste wood was studied in an economic enterprise by logging, function, tree species and log size in four Caspian hardwood sites. Damaged logs were recorded with additional information obtained for the location, dimensions and type of damage. The data were analyzed statistically to determine significant differences of damage during logging process. The results indicated that animal harvesting systems cause more volume (40.5% of log volume) and value loss (89.5 $·m^?3) to logs than mechanized harvesting systems (13.9% and 6.0 $·m^?3), also bucking resulted in significantly more volume (9.9% of log volume) and value loss (5.5 $·m^?3) when compared to skidding (0.2% of log volume and 0.2 $·m^?3), decking (0.4% of log volume and 0.2 $·m^?3) and loading (0.2% of log’s volume and 0.3 $·m^?3) operations. Study showed that the processes of skidding, decking and loading of logs have very little impact on damage levels. Volume and value losses of damaged logs are not sensitive to tree species and log size. The information from the field study is important in creating new guidelines or training to help minimize hardwood log damage during the timber harvesting process.     

不同迹地更新红松的效果分析

对不同迹地类型更新红松进行了试验研究,结果表明,红松与落叶松迹地更新红松成活率和保存率不足80％,幼树生长不良,土壤养分含量低,林木质量低劣,而次生林和荒山荒地迹地更新红松,成活率和保存率在90％以上,林木生长迅速,根系发达,土壤养分含量较高,林木质量优异.所以今后营造红松速生丰产林,应以次生林和荒山荒地迹地为宜.     

西非布基纳法索共和国道路网干扰对路边环境Pteleopsis suberosa更新的影响

沿铺面道路和未铺面道路,调查了4种路边环境（缓变区,附近区,中间区和非缓变区）的Pteleopsis suberosa苗木种群结构和其更新机制。沿道路平行线调查了2m&#215;5m的203块样方,记录每个样方内的种苗总数和每个种苗的活枝数。通过评价基部和水平枝芽和挖掘地下根系来确定更新机制。结果表明,在4种路边环境中,单一主干和多主干苗木的总密度及各自密度都有明显的变化（p〈0.05）。所有苗木都是无性繁殖而来,根出条占98%,眠芽蘖和萌生各占1%左右。研究表明,铺面道路和未铺面道路缓变区中等水平土壤的干扰可以刺激Pteleopsis suberosa根出条更新 道路类型（铺面和未铺面）对苗木密度没有影响,但对路边立地的P.suberosa种群的萌生能力来说,道路类型是一个重要变量。P.suberosa是一个耐干扰的物种,受道路网干扰后可以通过根出条繁殖。     

The impact of roe deer (Capreolus capreolus), seedbed, light and seed fall on natural beech (Fagus sylvatica) regeneration

The aim of the present study was to quantify the effects of roe deer browsing relative to the effects of soil preparation, shelterwood density (light) and seed fall. Ultimately, the goal was better silvicultural guidelines to support the use of natural beech regeneration in the close-to-nature forestry context. In spring 1995, an experiment on natural regeneration with three experimental stands (0.28–0.6 ha) was installed in a beech (Fagus sylvatica) dominated broadleaved forest inhabited by a dense roe deer (Capreolus capreolus) population (24 deer km⁻²). The autumn of 1995 offered a large beech mast (stand average 307–1168 beechnuts m⁻²).Treatments installed included fencing to exclude deer, soil preparation, shelterwood thinning, and the relevant control treatments. Roe deer and soil preparation had dramatic effects on regeneration from the moment the seedlings sprouted in the spring 1996. The regeneration sprouted only sparsely in the unprepared seedbed producing only 5 seedlings m⁻² (average across fence treatments) after 2 months, which was reduced to 1 sapling m⁻² 8 years later. Deer had no significant effect on the regeneration density of the unprepared seedbed. In contrast, the cultivated seedbeds produced initially (after 2 months) up to 191 seedlings m⁻² protected by fence, whereas the densities in the unfenced treatments peaked by 22 seedlings m⁻². By the end of the study, these densities were reduced to 22 saplings m⁻² in the permanently fenced mineral soil seedbed and to 2 saplings m⁻² in the unfenced mineral soil seedbed. Regeneration height outside the permanent fence was generally only half the height of the regeneration inside. Additionally, we found significantly positive effects of increasing light and seed fall on regeneration density and of light on regeneration growth.We conclude that the roe deer only reduced the regeneration density of the dense regenerations established in the cultivated seedbeds. However, the regeneration density of the unprepared seedbed was not sufficient to support a future high quality stand. We found no treatment that within the timeframe of this study could support successful regeneration establishment outside the permanent fences. Whether this will change in the future with more time given for the regeneration to establish is yet to be revealed.