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1.
Mechanised harvesting operations are becoming more prevalent in South Africa, with the realisation that motor- manual and manual harvesting operations pose significant health and safety risks to workers. However, the potential damage caused by single-grip harvester feed rollers and delimbing knives on the log surface during debranching and debarking of eucalypts pulp logs may negatively affect fibre recovery as opposed to manually debarked logs, which show little or no log surface damage. Compared with manual debarking, this study investi- gated the influence of two mechanised debarking treatments on wood fibre loss on eucalypt log assortments debarked by harvester head feed rollers and delimbing knives. The two mechanised debarking treatments consisted of three and five feed roller passes along the stem surface. In addition to quantifying the magnitude of this fibre loss, a financial evaluation was done to calculate the value of these losses. The three- and five-pass debarking treatments caused significant fibre losses of 1.425 green tonnes per hectare (gt ha?1) and 2.275 gt ha?1, respec- tively, as opposed to manually debarked logs, which produced no fibre losses. Wood fibre losses in terms of total potential (or available) wood mass for three- and five-pass mechanically debarked trees were 1.06% and 1.70%, respectively. These represent a fibre value loss of R441.75 ha?1 and R705.25 ha?1 for three- and five-pass operations, respectively. For the 6.48 million gt y?1 currently mechanically debarked for the South African pulp and paper industry, this equates to fibre value losses of R21.36 million and R34.10 million annually for three- and five-pass operations, respectively. 相似文献
2.
Mechanised harvesting operations are growing in popularity in South Africa, as motor-manual and manual harvesting operations pose significant health and safety risks to workers. Potential damage inflicted by single-grip harvester feed rollers and delimbing knives on the log surface during debranching and debarking of eucalypts may affect chip size distributions during chip production. Chip size is important as it influences pulp quality and recovery in the kraft pulping process. The study investigated the influence of two mechanised debarking treatments in eucalypts (three feed roller passes and five feed roller passes along the stem surface) with feed-roller-induced log surface damage on pulp value recovery. The two mechanised treatments were compared against chips produced from manually debarked logs with no surface damage. In addition, the effect of two log drying periods (one week and two weeks) and three log classes (base, middle and top logs) on chip quality were also analysed. An economic evaluation was conducted to quantify potential recoverable pulp value losses associated with debarking treatments and log drying periods. Logs subject to manual debarking produced significantly less undesired sized chips than both three-pass and five-pass mechanically debarked logs and therefore had significantly greater pulp value recovery. Mechanically debarked logs had a projected pulp value recovery of R62, R86 and R123 less per bone dry tonne of chips produced from base, middle and top logs, respectively, when compared with manually debarked logs with no log surface damage after a one-week log drying period. Mechanically debarked logs also had a projected pulp value recovery of R77, R40 and R59 less per bone dry tonne of chips produced from base, middle and top logs, respectively, when compared with manually debarked logs with no log surface damage after a two-week log drying period. Logs dried for two weeks also produced significantly less under-sized chips than chips produced from one-week-dried logs and therefore had greater pulp value recovery. However, two-week-dried logs produced wood chips with significantly more over-thick chips than logs dried for one week. The volume of undesirable-sized chips produced during chipping increased with decreasing log size. 相似文献
3.
Hybrid poplar plantations are increasing worldwide and are often accused of impoverishing bird communities. We conducted 124 bird point counts in a landscape where plantations, semi-natural forests and farmland occupied similar surface areas. As expected, birds occurred at higher densities in areas dominated by forests than dominated by plantations, mostly due to the scarcity of late-successional forest birds in plantations. Contrary to expectations, bird communities were the poorest in farmland dominated areas and the most specialised in areas dominated by young plantations. Indeed, many grassland species, including some of conservation concern in Europe, frequently used young plantations. However, plantations have probably depleted grassland bird communities by fragmenting open areas, while playing a limited positive role on forest species. Total length of unpaved roads had a positive effect on community specialisation index, while total length of paved roads and mean forest/plantation patch size played no role. Bird density increased with the development of the understory vegetation in mature poplar plantations. We conclude that poplar should not be planted at the expense of areas of high conservation value; in other cases, they may increase the overall diversity of bird communities. At the plantation scale, we advocate stopping understory removal as soon as possible and maintaining old trees and hedgerows alongside or within plantations to provide suitable breeding habitats for bird species that may be foraging in the plantations. 相似文献
4.
Glen Murphy John Lyons Michael O’Shea Garret Mullooly Enda Keane Ger Devlin 《European Journal of Forest Research》2010,129(6):1057-1067
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. 相似文献
5.
随着天然用材林资源日趋枯竭,杨树人工林在世界范围内在林业和农村发展中的重要性不断增加。本文回顾了国外近年来杨树资源加工利用的最新进展,并就国内杨树人工林的布局、定向培育和龙头产品的确定,建立工业人工林基地及发展林工联合企业等问题提出了建议。 相似文献
6.
Jaco-Pierre van der Merwe Pierre Ackerman Reino Pulkki Dirk Längin 《Southern Forests》2016,78(2):159-167
Mechanised harvesting operations are becoming more prevalent in South Africa with the realisation that motormanual and manual harvesting operations pose significant health and safety risks to workers. The damage inflicted by single-grip harvester feed rollers and delimbing knives on log surfaces during debranching and debarking eucalypts, may affect eventual chip quality. Chip quality influences pulp quality and recovery in the kraft pulping process. This study investigates the influence of two mechanised debranching and debarking treatments on Eucalyptus pulp logs (threeand five-feed roller passes along the stem surface) by feed rollers and delimbing knives on chip uniformity, size and purity. The two mechanised treatments to three log classes (base, middle and top logs) were compared with chips produced from manually debarked logs. Manually debarked logs produced significantly less undesirable-sized chips than both three and five-pass processed logs. The volume of undesirablesized chips produced during chipping also increased with decreasing log size. Manually debarked logs produced chips with significantly less bark than three-pass-processed logs (0.008% vs 0.062%), and five-pass-processed logs produced chips with significantly less bark than three-pass-processed logs (0.018% vs 0.062%). Middle logs also produced chips with significantly less bark than base logs (0.016% vs 0.056%), and top logs produced chips with significantly less bark than base logs (0.017% vs 0.056%). In all cases the bark content on logs was considerably less than the maximum of 1.0% generally specified by kraft pulp mills. 相似文献
7.
The incidence of damage caused by grey squirrels in the Turinplain was studied to assess the impact this alien species ishaving on the highly fragmented Piedmont environment, in particularon profitable cereals, poplar plantations and semi-natural woodlands.The survey of damage was conducted both by interviews to localfarmers and growers and by direct assessment using the NearestNeighbour Method on plantations and woodlands, studying randomlychosen plots in the Turin plain to gain a general overview ofthe situation. The results show a low incidence of damage causedby grey squirrels in the area: little or none was found in semi-naturalwoodlands and in agricultural crops, apart from maize whereless than 1 per cent of fields showed damage, and poplar plantationswhere 5 per cent had signs of bark stripping. Damage on maizecrops was random across the plain, but debarking damage to poplarswas mostly concentrated on the western side of the plain, andtended to occur only in particular years. Damage was concentratedclose to streams and rivers surrounding fields and plantations.The introduction of the grey squirrel in Italy has already causedecological damage such as the extinction of the red squirrelin some areas. Nevertheless, little or no information is availableon the damage this species is causing on woodlands or agriculturalareas. This study is a preliminary survey in order to fill thisgap. 相似文献
8.
From the early 2000s there has been a general shift in South Africa in harvesting and extraction systems from the use of semi- to fully-mechanised systems. Any increase in mechanisation, as is occurring in Zululand, will need to take into consideration damage to stumps and the subsequent ability to regenerate by coppice. In 2002, four types of harvesting and extraction systems, arranged in a randomised complete block design, were used to clearfell a stand of E. grandis × E. urophylla. A motor-manual harvesting system was used to carry out the manual harvesting system (Man). The fully mechanised system (Mech) consisted of a single-grip harvesting head used with a tracked excavator to carry out all felling and processing operations. Two additional systems (Man_Mech_3W and Man_Mech_Flexi) had increased levels of mechanisation over that of the Man treatment. Both these harvesting systems made use of a Bell debarker, with loading carried out by a Bell three-wheeled loader in the Man_Mech_3W, and by a Flexiloader in the Man_Mech_Flexi treatments. Data collected from these four treatments were used to determine the effects of mechanised harvesting systems on type and severity of stump damage, coppicing potential and coppice growth over the rotation. Irrespective of harvesting system, more damage occurred to the top than bottom half of the stump, with a significant decrease in coppice regrowth with increasing stump damage. Most damage and least coppice regrowth occurred in the extraction rows where the damage recorded could be attributed to vehicle movement, tear-outs and/or log stripping. There was no significant difference between the harvesting systems in terms of stump mortality, final stem stocking and rotation-end volume. Thus, individual components within each harvesting system can have a larger impact than the overall harvesting system used. Future research should focus on these components, and where associated damage occurs for a specific component, this should be lessened through management intervention, training or technological improvements. 相似文献
9.
E. Somarriba 《Agroforestry Systems》1992,18(1):69-82
Both model and field estimations were made of the damage inflicted to coffee plants due to the harvest of timber shade trees (Cordia alliodora) in coffee plantations. Economic analyses were made for different coffee planting densities, yields, and both coffee and timber prices.Damage due to tree felling and log skidding should not be a major limitation to the use of timber shade trees in coffee plantations. The timber price that would balance all discounted losses and benefits to zero, for scenarios with and without trees ranged between 8–20 US $/m3 (current overbark log volume at the saw mill yard is US$ 66/m3). There will be lower margins for coffee damage in high yielding plantations, specially in years of good coffee prices. Nevertheless, the use of timber shade trees is recommended even in these scenarios. 相似文献
10.
《Southern Forests》2013,75(4):195-200
At least 200 000 m3 of timber is harvested annually using semi-mechanised harvesting systems on the Viphya forest plantations in Malawi. Although these systems have long been used on the Viphya, no investigation on their productivity has so far been reported. Additionally, the absence of localised productivity analyses in Malawi has created a paucity of information on appropriate timber harvesting systems for production maximisation and cost minimisation. The objective of this study was to compare the production rates and operational costs of chainsaw/grapple skidder (semi-mechanised) and feller-buncher/grapple skidder (mechanised) harvesting systems in order to determine the economic feasibility of mechanised systems in the Viphya forest plantations. The study was conducted in Pinus kesiya compartments at the Kalungulu and Champhoyo forest stations of the Viphya forest plantations. A work study approach was followed to capture harvesting time and volume data for the semi-mechanised system. Secondary work study data were used to simulate productivity of the mechanised system on similar compartment conditions. A timber-harvesting costing model was used to analyse the results. The study showed that the simulated mechanised system was associated with lower operating costs and inventories with higher production rates than the semi-mechanised system. The cost marginal difference was US$0.89 m–3. It was therefore established that migration to mechanised systems could optimise timber harvesting productivity on the Viphya in future, if optimal volumes are available to ensure the efficient application of the mechanised harvesting system. 相似文献
11.
Much research effort is being devoted to developing forest management practices with limited impacts on biodiversity. While the impact of poplar Populus sp. plantations on biodiversity is relatively well-known at the landscape scale, the impact of alternative management practices at the plantation scale has received much less attention. Yet biodiversity is likely to be impacted by the choice of the poplar clone, stem density at plantation, type and duration of the understory control, and age at which the poplars are harvested. In this study, we investigated the impact of these factors on herbaceous plant communities with data from plant surveys conducted in 85 young (2–5 years) and 96 mature (11–17 years) hybrid poplar high-forest plantations in northern France. On average, ruderal or generalist plants contributed to 40.5% of the plot species richness; tall herbs (60.2%), forest (26%) and meadow plants (13.8%) contributed to the remaining 59.5% more specialised species. Soil moisture and soil nitrogen were major determinants of plant communities: wet soils were favourable to tall herbs, while meadow and forest species preferred moist soils; a significantly lower diversity of the three species groups was reported in the nutrient richer soils (in mature plantations only for forest plants). Mean species richness decreased with plantation age except for forest species. Plant communities in young plantations showed little differences in composition according to the type of understory control (chemical, mechanical or both). The development of a shrubby layer in mature plantations was restricted to the drier soils and was detrimental to both meadow plants and tall herb species. Effects of previous land use on forest and tall herb species were found only in young plantations, suggesting a rapid reset of plant communities for these two groups. This may not be the case for meadow species as the influence of previous land use was significant in mature plantations only. Finally, clone type and stem density at plantation had no significant impact on plant communities. Adjusting age at which the poplars are harvested seems the only effective way to drive plant communities in high-forest poplar plantations: delaying poplar harvest (probably beyond 15–20 years) would benefit forest plants, while advancing poplar harvest (about 10 years) would benefit tall herbs, especially in wet soil conditions. 相似文献
12.
Hybrid poplar plantations have become an important component of forest and agricultural landscapes in alluvial floodplains since poplars are among the fastest-growing trees in temperate regions. However, these habitats are thought to decrease biodiversity, including ground beetle diversity, as compared to other traditional land-uses such as grasslands and semi-natural forests. To evaluate the impacts of poplar plantations on carabid diversity, we tested whether carabid assemblages are more affected by land-use type than by canopy cover type in three alluvial floodplains in North-Eastern France. We stratified our 63-plot sampling design according to four habitat types based on land-use and plantation age. Non-metric multidimensional scaling revealed a successional gradient in species composition related to canopy cover progressing from grasslands through young, then adult poplar plantations, to semi-natural forests. Species-level response models showed that many carabid species distinguished the open habitats (grasslands and young poplar plantations) from the closed ones (adult poplar plantations and semi-natural forests). Only a few species preferred one of the traditional land-uses such as grasslands or semi-natural forests. Based on our data, the deleterious effect of poplar plantations on the conservation of ground beetles may not be as high as expected. 相似文献
13.
14.
为了研究苏鲁两省杨树木材变色、变色真菌和造成的损失,于2005—2010年分别对9个县市杨木加工厂进行了调查和定点观察。结果表明,在杨树砍伐后,在露天存放22～80天杨原木和单板存在不同程度边材变色,其变色程度与在露天存放时间有密切关系。春夏之交砍伐的杨木比冬季砍伐的杨木更易变色;3～5年生杨木比8—9年生杨木更易变色;剥皮杨木比带皮杨木更易变色;单板变色比原木更明显,致使单板的经济价值可降低25％～30％。鉴定出引起杨木变色的真菌有23属32种,其中危害最严重的变色菌主要有可可球二孢、交链孢、球孢枝孢。其中不高双孢菌、红紫球二孢、青琐龙孢球二孢在杨木上属于首次报道。 相似文献
15.
《Southern Forests》2013,75(2):133-149
A study of both fibre volume loss and related opportunity cost was performed across the South African softwood sawtimber industry to gain information on the actual utilisation of useful fibre and potential loss or gain of opportunity in terms of potential revenue from both field practices and policy. The study quantified volume losses from high stumps, felling and crosscut saw kerf, log allowances, excessive removal of merchantable wood, incorrect log trimming allocation, and utilisable wood left in-field. Eight treatments were examined: four terminated with merchandising at roadside landing and four at merchandising yards. Within the treatments, felling was either motor-manual or mechanised and compartments were classed by average compartment tree size (less than or greater than 1 m3). Total wood utilisation was found to be 92.07%. Stumps were found to be 7 cm higher than necessary and volume losses because of high stumps were 0.79% and 0.07% for mechanical and motor-manual felling, respectively. For felling saw kerf losses, mechanical felling showed 0.92% loss, whereas motor-manual felling resulted in only 0.15% loss. Incorrect log trimming allowance provided for 0.60% loss. Excessive trimming of logs resulted in 2.02% loss. Volume lost because of crosscutting saw kerf was low at 0.20%, but tops not being extracted resulted in 2.57% loss. Using SIMSAW 6 simulations, these volume losses translated into an additional annual harvested volume of 421 722 m3 or additional 1 278 ha harvested area, R166 million log value and R393 million net lumber value loss. Total loss was lowest (6.49%) in the average tree size class less than 1 m3, which was mechanically felled regardless of merchandising location. For the majority of volume loss categories, motor-manual felling caused greater loss when compared to mechanical felling methods. Log trimming allowance consumed 80 604 m3 annually. The results indicate that the human element may have a greater impact on fibre and value losses than the system choice. Further research is recommended to quantify the effect of the human element. 相似文献
16.
杨树短轮伐期集约栽培的新进展 总被引：8，自引：0，他引：8
本文介绍了参加18届国际杨树会议的17个会员国的杨树栽培新进展、杨树育种和短轮伐期集约栽培的研究动态和成果,还报道了与会外国专家的观感。 相似文献
17.
Carefully managed tree plantations offer an opportunity for sustainable biomass production. In recent years, the responses of the Salicaceae to environmental constraints have increasingly been investigated at different levels of biological integration, giving rise to a physiological approach to the function of trees in environmental restoration and monitoring. Significant progress has been achieved by the poplar and willow community in understanding targeted characteristics of complex tree stress responses. The Fifth International Poplar Symposium brought together experts in this area, with the main objective being to improve, coordinate and communicate existing national research on the biological and environmental dimension of multifunctional poplar and willow plantations. The secondary objective was to develop a network of research scientists and extension workers to provide scientific support for subjects interested in using fast-growing poplar and willow species for tree-related environmental projects. The ultimate goal was to build up services for the multipurpose tree plantation network on local-level management in order to obtain maximized benefits from tree crops. The purpose was also to maximize the synergy between local knowledge and global-level processes that require information on multipurpose tree crop production. 相似文献
18.
通过设立固定标准地对杨树的中幼林龄期和近熟林龄期生长情况进行调查分析，了解踊桥区祁县镇不同立地条件下杨树长势，判断林分立地条件对生长量影响的关键因子，并进行了标准地土壤剖面结构、理化性质和土壤养分含量对比，结论如下：影响杨树生长的关键因素是林地土层厚度，分析了杨树低产林形成原因是：土壤层浅、瘠薄、空隙度小、质地粘重。并提出相应对策：杨树低产林改造；加强中幼林抚育、进行土壤改良；发展林下经济改善土壤结构理化性质；营造复层林、间接改良土壤，提高林地综合利用率。 相似文献
19.
伐根嫁接杨树林根系分布特征 总被引：4，自引：3，他引：1
通过对比研究大兴区的伐根嫁接杨树林分和与其地下和地上部分分别相同的植苗造林杨树林分,得出伐根嫁接杨树林根系的特殊分布特征。采用全挖法获取杨树总根量和根型,采用土柱法获取吸收根(细根≤2mm,粗根210mm)。结果表明:伐根嫁接林根系总干重分别是相同地下和地上部分植苗造林的1.83倍和7.38倍;其根系数量多且粗壮,为水平斜生根型,而植苗造林林分为水平根型;伐根嫁接林总细根量和总粗根量分别比两个植苗造林林分提高了86.27%和224.65%,59.06%和65.86%;与植苗造林相比,伐根嫁接林表层的吸收根垂直和水平分布都表现异常,垂直分布中0～10cm土层的细根分布较多,10～20cm土层的分布较少;水平分布中株间0～20cm土层的分布异常多。该结论为伐根嫁接杨树林的生长优势提供了进一步的微观解释。 相似文献
20.
Natascia Magagnotti Carla Nati Gianni Picchi Raffaele Spinelli 《Agroforestry Systems》2011,82(1):77-86
The study compares two product strategies—chips versus firewood—and two technological levels—manual versus mechanized—as applied
to the thinning of walnut agroforestry plantations, established on ex-arable land. Such plantations are widespread all across
Europe, and their establishment was subsidized under the provisions of EU Directive 2080/90, and of regional grant schemes.
Field test data were used to build a simple deterministic model for estimating thinning productivity and cost under varying
work and economic conditions. This model can assist prospective users when checking the profitability of an operation, or
when assessing the competitiveness of alternative options. Removing nurse alder from young walnut plantations yields between
25 and 50 t of fresh biomass per hectare and is crucial to the good development of the stand. The study shows that the removal
of nurse alder from walnut plantations is economically viable, and it can also offer some profits if stand and market conditions
are favourable. As a rule, the average DBH of removal trees should not be smaller than 12 cm. Best results are obtained with
mechanized harvesting, which does not seem to cause heavier stand and soil damage than manual harvesting. Manual harvesting
is preferable only if the annual utilization of machinery is very low, and in this case it should be geared to firewood production.
The manual whole-tree harvesting (WTH) method used in this study offers the lowest performance under all conditions, and should
be replaced with some other manual alternative to WTH. Mechanized WTH offers a significant cost reduction over mechanized
short-wood (SWS) harvesting, but this difference is still rather limited: hence, other parameters come into play when deciding
what system to apply, and namely product price and mass output. In this respect, one also has to consider the cost of managing
the harvesting residue, and that of fertilizing, if soil nutrient depletion is to be feared. 相似文献