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1.
Tower yarders have recently been introduced to forestry in Turkey. Clarification of the productivity and cost of logging using the tower yarder is often requested because the cost for machinery is a significant factor in all calculations concerning mechanized operations. Machines are often extremely expensive compared with the low cost of labor in developing regions. In this study, a new logging system using a tower yarder was compared with a conventional system using a stationary yarder in terms of productivity and cost. The research was conducted in the northeast of Turkey, in 1989 and 1992. The productivity of the tower yarder and the stationary yarder was found to be 5.655 m3/h and 5.002 m3/h, respectively. Harvesting cost was analyzed based on observed productivity. The harvesting costs of the tower yarder and the stationary yarder were found to be 47,410 TL/m3 and 17,553 TL/m3, respectively. With the tower yarder, the machine cost reached 93.1 % of the harvesting cost while the machine cost using the stationary yarder reached 71.1%. A part of this paper was orally presented at the 3rd Annual Meeting of the Japan Forest Engineering Society (1996).  相似文献   

2.
Cable yarding systems are widely used in mountainous forests of Austria. The goal of this paper is to determine optimal road spacing (ORS) of yarding operations by tower yarder in Styria to help logging planners minimize logging costs. A total of 591 working cycles were used to develop the multiple regression model using stepwise method to predict yarding time per cycle. The production and cost in whole tree uphill yarding were 6.70 m3/PSH and 27.60 Euro/m3, respectively. The roading, yarding and installation cost per cubic meter were computed for different yarding distances and graphed as a function of road spacing. The minimum total cost and ORS were 42.88 Euro/m3 and 261 m, respectively for one-way yarding. For two-way yarding, the minimum estimated total cost, ORS and optimal road density would be 38.48 Euro/m3, 373 m and 26.8 m/ha, respectively. The results showed increasing harvested volume decreases ORS and that increased roading cost increases ORS. The load volume has a significant effect on ORS.  相似文献   

3.
A winch and a sulky can transform a farm tractor into an effective small-scale logging machine, closely resembling a wheeled cable skidder. The additional cost of these implements is very small, but they offer significant benefits when extracting timber under the conditions of small-scale forestry. The authors developed a productivity model for skidding timber with wheeled farm tractors, equipped with winch and sulky. The origin data pool contained over 300 individual skidding cycles, extracted from 8 separate tests. Statistical analysis of the data allowed calculating a simple mathematical relationship for estimating skidding productivity as a function of significant work conditions, such as: piece size, winching distance, tractor power, skidding distance and crew size. This model can provide useful directions to prospective users, contributing to operation planning, costing and optimization. It can predict a large proportion of the variability in the data and was successfully validated using reserved cycle records, extracted from the same data pool and not used for model development. Depending on tractor power and piece size, the average turn volume and productivity can exceed respectively 2 m3 per cycle and 4 m3 per Scheduled Machine Hour (SMH). Top performance can reach 8 m3 SMH−1, with heavy tractors and large logs.  相似文献   

4.
Multipurpose tree species （MPTs） were studied in an agroforestry arboretum under subtropical humid climate in Northeast India. Out of 12 MPTs planted under agroforestry systems, Acacia auriculiformis in spacing of 2 m × 2 m （2500 stems·hm^-2） could have the potentiality to meet the timber/fuelwood requirement due to its high wood production of 635 m^3·hm^-2 with mean annual increment （MAI） of 2.54×10^-2 m^3.treel.a^-1 in a short rotation period of 10 years. Thus, A. auriculiformis is a short rotation forest tree species suitable to grow in subtropical humid climate. On the other hand, at 16 years of age, Eucalyptus hybrid and Michelia champaca in spacing of 3 m × 3 m （1111 stems.hm^2） produced appreciably high timber volume of 315 m^3.hm^-2 and 165 m^3.hm^-2 with MAI of 1.77×10^-2 m^3.tree^-1·a^-1 and 0.92×10.2 m^3.tree^-1.a^-1, respectively. At 16 years of age, Gmelina arborea produced a timber volume of 147 m^3.hm^-2 with MAI of 1.47×10^-2 m^3.tree^-1.a^-1 followed by Samania saman （140 m^3.hm^-2）, Albizziaprocera （113 m^3·hm^-2） and Tectona grandis （79 m3.hm^-2） with MAI of 1.40, 1.13 and 0.78 × 10^-2 m^3 .tree^-1a^-1, respectively in 4 m × 4 m spacing （625 stems.hm^-2）. Gliricidia maculata and Leucaena leucocephala could be used as live fences around the farm boundary to supply their N-rich leaves for mulch as well as manure to crops. In agroforestry arboretum, direct seeded upland rice （Oryza sativa - variety, AR-11）, groundnut （Arachis hypogaea - variety, JL-24） and sesamum （Sesamum indicum - variety, B-67） were grown during the initial period upto 8 years of tree establishment. Under other MPTs, there was a reduction in crop productivity as compared to open space. After 8 years of tree establishment, horti-silvi and silvi-pastoral systems were developed and pineapple （Ananas comosus - variety Queen）, turmeric （Curcuma longa -variety RCT -1） and cowpea （Vigna sinensis - variety Pusa Barsati） as forage crop were raised. The productivity of p  相似文献   

5.
The relative effects of irradiance and soil water on alley-cropped herbage are poorly understood. Our objective was to determine effects of irrigation on herbage productivity when tall fescue [Lolium arundinaceum (Schreb.) Darbysh.] was grown in two sites, a meadow and a loblolly pine (Pinus taeda L.) alley (620 trees ha−1), near Booneville, Arkansas. Three tall fescue entries were space planted in the meadow and pine alley with or without irrigation. Herbage mass and nutritive value were determined at 8-week intervals for 2 years. Mean daily PAR was 33.9 (2004) and 37.5 mol m−2 d−1 (2005) in the meadow, while the pine alley received 5.6 mol m−2 d−1 (17% of the meadow) in 2004 and 4.3 mol m−2 d−1 (11% of meadow) in 2005. Effect of tall fescue entry tended to be small relative to site and irrigation. Irrigation compensated for evapotranspiration in the meadow, but not in the pine alley when summer rainfall was about normal (2004) or low (2005). Nevertheless, site (PAR) had a greater effect on herbage specific leaf weight, leaf elongation rate, tillers plant−1, mass tiller−1, and total nonstructural carbohydrate concentration than soil water. Irrigation might have had greater impact on herbage productivity if more water had been applied or if canopy cover had been less extreme. Silvicultural practices should be imposed to improve penetration of solar irradiance to the alley crop.  相似文献   

6.
Plant biomass, species diversity and net primary productivity are presented for herb layer of banj oak (Quercus leucotrichophora A. Camus)-chir pine (Pinus roxburghii Sarg.) mixed forest in Kumaun, central Himalaya, India. The species diversity declined from a maximum (3.56) in September to a minimum (2.11) in December. The monthly live shoots biomass exhibited a single peak growth pattern with highest live shoot biomass of 185 g·m-2 in August. The seasonal pattern showed that the maximum above-ground production (131 g·m-2) occurred during the rainy season and the minimum (1 g·m-2) during winter season. The below-ground production was maximum during winter season (84 g·m-2) and minimum during summer season (34 g·m-2). The annual net shoot production was 171 g·m-2 and total below-ground production was 165 g·m-2. Of the total input 61% was channeled to above-ground parts and 39% to below-ground parts. Transfer of live shoots to dead shoots compartments and that of dead shoots to litter compartments was 61% and 66%, respectively. The total dry matter disappearance was 61% of the total input within annual cycle. The herb layer showed a net accumulation of organic matter, indicating the seral nature of the community.  相似文献   

7.
Two tests were conducted with a new model of mini-forwarder, specifically designed for thinning operations. The tested machine resembles a conventional industrial forwarder, with tandem bogies and central articulation, but is much smaller and lighter. The machine was tested on forest plantations established on ex-farm land: such plantations offer favorable and homogeneous work conditions, which allowed reasonably accurate productivity figures to be obtained with a relatively small number of observation hours (about 10.5 h). Despite the relative inexperience of the driver, the tests indicated a productivity of between 3.1 and 3.8 m3 per scheduled machine hour (SMH) over an extraction distance of about 400 m. Extraction costs ranged from 12.4 to 15.1 € m−3 at the calculated machine rate of 47.6 € h−1. Compared to older models derived from recreation vehicles or tracked wheelbarrows, the machine tested in this study offers a better performance and a much more comfortable workplace, with the operator sitting inside an enclosed and insulated cab. Fitted with four bogies and provided with a much longer wheelbase, the new forwarder is likely to be safer than tracked machines when surmounting obstacles, and it certainly offers a much smoother ride to the operator. Nevertheless, the tested machine is still much narrower than industrial forwarders and does not enjoy the same lateral stability. Hence, the machine is ideal for sneaking between trees and climbing over obstacles, but once on a slope it must be driven straight along the grade and never across it, unless with much caution. Like all hydrostatically driven vehicles, the tested mini-forwarder is not suited to long-distance extraction (>1 km): if run at high speed for too long, its hydrostatic transmission tends to overheat, forcing the operator to make frequent stops.  相似文献   

8.
In recent years there has been an increasing interest in developing spatial statistical models for data sets that are seemingly spatially independent.This lack of spatial structure makes it difficult,if not impossible to use optimal predictors such as ordinary kriging for modeling the spatial variability in the data.In many instances,the data still contain a wealth of information that could be used to gain flexibility and precision in estimation.In this paper we propose using a combination of regression analysis to describe the large-scale spatial variability in a set of survey data and a tree-based stratification design to enhance the estimation process of the small-scale spatial variability.With this approach,sample units(i.e.,pixel of a satellite image) are classified with respect to predictions of error attributes into homogeneous classes,and the classes are then used as strata in the stratified analysis.Independent variables used as a basis of stratification included terrain data and satellite imagery.A decision rule was used to identify a tree size that minimized the error in estimating the variance of the mean response and prediction uncertainties at new spatial locations.This approach was applied to a set of n=937 forested plots from a state-wide inventory conducted in 2006 in the Mexican State of Jalisco.The final models accounted for 62% to 82% of the variability observed in canopy closure(%),basal area(m2·ha-1),cubic volumes(m3·ha-1) and biomass(t·ha-1) on the sample plots.The spatial models provided unbiased estimates and when averaged over all sample units in the population,estimates of forest structure were very close to those obtained using classical estimates based on the sampling strategy used in the state-wide inventory.The spatial models also provided unbiased estimates of model variances leading to confidence and prediction coverage rates close to the 0.95 nominal rate.  相似文献   

9.
Fine root biomass, rates of dry matter production and nutrients dynamics were estimated for 1 year in three high elevation forests of the Indian central Himalaya. Fine root biomass and productivity were higher in closed canopied cappadocian maple forest (9.92 Mg ha−1 and 6.34 Mg ha−1 year−1, respectively), followed by Himalayan birch forest (6.35 Mg ha−1 and 4.44 Mg ha−1 year−1) and Bell rhododendron forest (6.23 Mg ha−1 and 2.94 Mg ha−1 year−1). Both fine root biomass and productivity declined with an increase in elevation. Across the sites, fine root biomass was maximal in fall and minimal in summer. In all sites, maximum nutrient concentration in fine roots was in the rainy season and minimum in winter. Fine root biomass per unit basal area was positively related with elevation, Bell rhododendron forest having the largest fine root biomass per unit of basal area (0.53 Mg m−2) and cappadocian maple the least (0.18 Mg m−2). The production efficiency of fine roots per unit of leaf biomass also increased with elevation and ranged from 1.13 g g−1 leaf mass year−1 in cappadocian maple forest to 1.28 g g−1 leaf mass year−1 in Bell rhododendron forest. Present fine root turnover estimates showed a decline towards higher elevations (0.72 year−1 in cappadocian maple and 0.58 year−1 in Bell rhododendron forest) and are higher than global estimates (0.52).  相似文献   

10.
The Dahurian larch forest in northeast China is important due to its vastness and location within a transitional zone from boreal to temperate and at the southern distribution edge of the vast Siberian larch forest. The continuous carbon fluxes were measured from May 2004 to April 2005 in the Dahurian larch forest in Northeast China using an eddy covariance method. The results showed that the ecosystem released carbon in the dormant season from mid-October 2004 to April 2005, while it assimilated CO2 from the atmosphere in the growing season from May to September 2004. The net carbon sequestration reached its peak of 112 g·m−2·month−1 in June 2004 (simplified expression of g (carbon)·m−2·month−1) and then gradually decreased. Annually, the larch forest was a carbon sink that sequestered carbon of 146 g·m−2·a−1 (simplified expression of g (carbon)·m−2·a−1) during the measurements. The photosynthetic process of the larch forest ecosystem was largely affected by the vapor pressure deficit (VPD) and temperature. Under humid conditions (VPD < 1.0 kPa), the gross ecosystem production (GEP) increased with increasing temperature. But the net ecosystem production (NEP) showed almost no change with increasing temperature because the increment of GEP was counterbalanced by that of the ecosystem respiration. Under a dry environment (VPD > 1.0 kPa), the GEP decreased with the increasing VPD at a rate of 3.0 μmol·m−2·s−1·kPa-1 and the ecosystem respiration was also enhanced simultaneously due to the increase of air temperature, which was linearly correlated with the VPD. As a result, the net ecosystem carbon sequestration rapidly decreased with the increasing VPD at a rate of 5.2 μmol·m−2·s−1·kPa−1. Under humid conditions (VPD < 1.0 kPa), both the GEP and NEP were obviously restricted by the low air temperature but were insensitive to the high temperature because the observed high temperature value comes within the category of the optimum range.  相似文献   

11.
The effects of the warm and dry weather in the southern upper Rhine plain in the southwest of Germany on the carbon balance of the Scots pine forest at the permanent forest meteorological experimental site Hartheim were analysed over a 14-month period. The investigation of the net ecosystem exchange of carbon dioxide (F NEE) of the Scots pine forest started in the extraordinary hot and dry August 2003. Carbon dioxide fluxes were measured continuously using an eddy covariance system and analysed by use of the EDDYSOFT software package. After determining the temperature dependence of the forest ecosystem respiration and the daytime light dependence of the CO2 exchange, monthly and annual carbon balances of the Scots pine forest were calculated. Mean peak daytime F NEE rates observed in August and September 2003 (−6.5±3.6 μmol m−2 s−1) were drastically lower than in August and September 2004 (−11.8±5.2 μmol m−2 s−1), which did not show pronounced deviations from the mean long-term (1978–2002) climatic conditions. In August 2003, the Hartheim Scots pine forest was a distinct CO2 source (35 g C m−2). The estimates of the annual carbon sink strength of the Scots pine forest ranged between −132 g C m−2 (August 2003–July 2004) and −211 g C m−2 (October 2003–September 2004). The main uncertainty in the determination of the carbon balance of the Hartheim Scots pine forest was introduced by the frequently low turbulence levels, i.e. the friction velocity corrected night-time F NEE fluxes.  相似文献   

12.
Agroforestry systems can play a major role in the sequestration of carbon (C) because of their higher input of organic material to the soil compared to sole crop agroecosystems. This study quantified C input in a 19-year old tropical alley cropping system with E. poeppigiana (Walp.) O.F Cook in Costa Rica and in a 13-year old hybrid poplar (Populus deltoides × nigra DN-177) alley cropping system in southern Canada. Changes in the level of the soil organic carbon (SOC) pool, residue decomposition rate, residue stabilization efficiency, and the annual rate of accumulation of SOC were also quantified in both systems. Carbon input from tree prunings in Costa Rica was 401 g C m−2 y−1 compared to 117 g C m−2 y−1 from litterfall at the Canadian site. In southern Canada, crop residue input from maize (Zea mays L.) was 212 g C m−2 y−1, 83 g C m−2 y−1 from soybeans (Glycine max L.) and 125 g C m−2 y−1 for wheat (Triticum aestivum L.), and was not significantly different (p < 0.05) from the sole crop. The average yearly C input from crop residues in Costa Rica was significantly greater (p < 0.05) in the alley crop for maize (134 g C m−2 y−1) and Phaseolus vulgaris L. bean crops (35 g C m−2 y−1) compared to the sole crop. The SOC pool was significantly greater (p < 0.05) in the Costa Rican alley crop (9536 g m−2) compared to its respective sole crop (6143 g m−2) to a 20 cm depth, but no such difference was found for the southern Canadian system. Residue stabilization, defined as the efficiency of the stabilization of added residue (crop residues, tree prunings, litterfall) that is added to the soil C pool, is more efficient in southern Canada (31%) compared to the alley cropping system in Costa Rica (40%). This coincides with a lower organic matter decomposition rate (0.03 y−1) to a 20 cm depth in Canada compared to the Costa Rican system (0.06 y−1). However, the average annual accumulation rate of SOC is greater in Costa Rica (179 g m−2 y−1) and is likely related to the greater input of organic material derived from tree prunings, compared to that in southern Canada (30 g m−2 y−1) to a 20 cm depth.  相似文献   

13.
A dramatic decline in forest cover in eastern Africa along with a growing population means that timber and poles for building and fuelwood are in short supply. To overcome this shortage, the region is increasingly turning to eucalyptus. But eucalyptus raises environmental concerns of its own. Fears that it will deplete water supply, affect wildlife and reduce associated crop yields have caused many countries in the region to discourage farmers from planting this exotic. This paper is part of a series of investigations on the growth and water use efficiency of faster growing eucalyptus hybrids, which was introduced from South Africa to Kenya. The hypothesis is that the new hybrids are more efficient in using water and more suitable for the semi-arid tropics than existing eucalyptus and two popular agroforestry species. Gas exchange characteristics of juvenile Eucalyptus grandis (W. Hill ex Maiden), two eucalyptus hybrids (E. grandis × Eucalyptus camaldulensis Dehnh.), Grevillea robusta (A. Cunn) and Cordia africana (Lam) was studied under field and pot conditions using an infrared gas analyzer was used to measure photosynthetic active radiation (PAR), net photosynthetic rate (A), stomatal conductance (g s) and transpiration rate (E) at CO2 concentrations of 360 μmol mol−1 and ambient humidity and temperature. A, E and g s varied between species, being highest in eucalyptus hybrid GC 15 (24.6 μmol m−2 s−1) compared to eucalyptus hybrid GC 584 (21.0 μmol m−2 s−1), E. grandis (19.2 μmol m−2 s−1), C. africana (17.7 μmol m−2 s−1) and G. robusta (11.1 μmol m−2 s−1). C. africana exhibited high E values (7.0 mmol m−2 s−1) at optimal soil moisture contents than G. robusta (3.9 mmol m−2 s−1) and eucalyptus (5.3 mmol m−2 s−1) in field experiment and G. robusta (3.2 mmol m−2 s−1) and eucalyptus (4.2 mmol m−2 s−1) in pot-grown trees. At very low soil moisture content, extremely small g s values were recorded in GC 15 and E. grandis (8 mmol m−2 s−1) and G. robusta (14 mmol m−2 s−1) compared to GC 584 (46.9 mmol m−2 s−1) and C. africana (90.0 mmol m−2 s−1) indicating strong stomatal control by the species. Instantaneous water use efficiency ranged between 3 and 5 μmol mmol−1 and generally decreased with decline in soil moisture in pot-grown trees but increased with declining soil moisture in field-grown trees.  相似文献   

14.
An empirical time study was conducted to evaluate the per- formance of the current felling and tree processing methods used in Northern Iran’s Hyrcanian forest. Motor-manual felling is done mostly in winter, while tree processing starts when the felling season ends. We identified the elements of felling and processing work phases, and 142 cycles and 110 cycles were respectively recorded for felling and proc- essing. On the basis of data analysis (time study), we developed statisti- cal models of effective time consumption in the respective work phase and for its total productivity. The production rate of felling with and without delay time was 9.7 and 11.65 trees per hour (0.17 USD·m -3 and 0.21 USD·m -3 ), and the average production cost with and without delay was 1.21 USD and 1.45 USD per tree, respectively. The average produc- tivity of processing was 35 m 3 per effective hour and the average unit cost of processing was 0.22 USD·m -3 .  相似文献   

15.
The use of small-scale harvesting equipment continues to grow in forestry in many regions of the world. This equipment includes various devices and methods used to harvesting that generally are smaller, less expensive and less productive than advanced forestry machines. The objective of this study is to compare the efficiency of five alternative extraction methods implemented in a harvesting unit located in a mixed beech and oak forest ecosystem in northwestern Turkey. A continuous time study was conducted during primary transport operations that included skidding with animal power, skidding with farm tractor, hauling with farm tractor, hauling with forest tractor, and extraction by skyline. Timber was skidded uphill on a skid trail, and an average skidding distance of 100 m for all haulage methods was considered. Average slope of the harvesting unit ranged from 20 to 40 %. Average productivities for respective haulage methods were 3.80, 6.25, 2.80, 5.25 and 10.09 m3/h. Significant differences were found between productivity of haulage methods using one-way analysis of variance. The extraction by skyline, skidding with farm tractor, and hauling with forest tractor were determined to be the most statistically different methods, the productivity of these methods was found significantly higher than the other methods. Skid trails are useful for shortening distances during forest operations and skidding with farm tractor is a productive method in small-scale forestry of Turkey.  相似文献   

16.
Daily net canopy photosynthesis (P n) was predicted for cocksfoot (Dactylis glomerata L.) canopies grown under different light regimes by integration of a leaf photosynthesis model developed for the light-saturated photosynthetic rate (P max), photosynthetic efficiency (α) and the degree of curvature (θ) of the leaf light–response curve. When shade was the only limiting factor, the maximum P n (P nmax) was predicted to decrease approximately linearly from 33.4 g CO2 m−2 d−1 to zero as photosynthetic photon flux density (PPFD) fell from full sunlight (1800 μmol m−2 s−1 PPFD) to 10% of this in a fluctuating light regime. It was also predicted that at 50% transmissivity P nmax was higher for a continuous light regime (10.4 g CO2 m−2 d−1) than for a fluctuating light regime with the same intensity (8.4 g CO2 m−2 d−1). The canopy photosynthesis model was then used to predict dry matter (DM) production for cocksfoot field grown pastures under a diverse range of temperature, herbage nitrogen content and water status conditions in fluctuating light regimes. This prediction required inclusion of leaf area index and leaf canopy angle from field measurements. The model explained about 85% of the variation in observed cocksfoot DM production for a range from 6 to 118 kg DM ha−1 d−1. The proposed model improves understanding of pasture growth prediction through integration of relationships between shade limitations in fluctuating light regimes and other environmental factors that affect the canopy photosynthetic rate of cocksfoot pastures in silvopastoral systems.  相似文献   

17.
The above-ground biomass and production, below-ground biomass, nutrient (NPK) accumulation, fine roots and foliar characteristics of a 8-year-old silver birch (Betula pendula) natural stand, growing on abandoned agricultural land in Estonia, were investigated. Total above-ground biomass and current annual production after eight growing seasons was 31.2 and 11.9 t DM ha−1, respectively. The production of stems accounted for 62.4% and below-ground biomass accounted for 19.2% of the total biomass of the stand. Carbon sequestration in tree biomass reaches roughly 17.5 t C ha−1 during the first 8 years. The biomass of the fine roots (d < 2 mm) was 1.7 ± 0.2 t DM ha−1 and 76.2% of it was located in the 20 cm topsoil layer. The leaf area index (LAI) of the birch stand was estimated as 3.7 m2 m−2 and specific leaf area (SLA) 15.0 ± 0.1 m2 kg−1. The impact of the crown layer on SLA was significant as the leaves are markedly thicker in the upper part of the crown compared with the lower part. The short-root specific area (SRA) in the 30 cm topsoil was 182.9 ± 9.5 m2 kg−1, specific root length (SRL), root tissue density (RTD) and the number of short-root tips (>95% ectomycorrhizal) per dry mass unit of short roots were 145.3 ± 8.6 m g−1, 58.6 ± 3.0 kg m−3 and 103.7 ± 5.5 tips mg−1, respectively. In August the amount of nitrogen, phosphorus and potassium, accumulated in above ground biomass, was 192.6, 25.0 and 56.6 kg ha−1, respectively. The annual flux of N and P retranslocation from the leaves to the other tree parts was 57.2 and 3.7 kg ha−1 yr−1 (55 and 27%), respectively, of which 29.1 kg ha−1 N and 2.8 kg ha−1 P were accumulated in the above-ground part of the stand.  相似文献   

18.
Salal (Gaultheria shallon Pursh), which is widely used for floral greenery, is an important non-timber forest product (NTFP) from the coastal forests of the Pacific Northwest of North America. However, there are no known studies on the impacts of commercial salal harvesting on subsequent growth. A study was therefore initiated to quantify the growth of salal 1 year after commercial harvesting, and to compare this with growth of unharvested salal. The amount of biomass removed from shrubs through commercial harvesting (131 g m−2) was the same as the amount of annual growth in adjacent undisturbed plots (135 g m−2). One year later, the amount of regrowth in previously harvested plots (144 g m−2) was greater than the amount of new growth in adjacent undisturbed plots (111 g m−2). As there was little difference in the weight per current stem, the increased biomass after commercial harvesting was attributed to the observed increase in stem number (60 stems m−2) as compared to undisturbed salal (50 stems m−2). Our study does not incorporate either repeated annual harvesting or variable harvesting intensities, both of which have been anecdotally reported to affect levels of re-growth and therefore sustainability.  相似文献   

19.
From 2002 to 2003, based on the investigation of sample plots and stem analysis of remained plantation communities in the areas of returning farmland to forest in the 1980s in Datong County, Qinghai Province, this paper studies tree productivity and moisture potential productivity of six types of plantations on the land of returning farmland to forest, such as green poplar (Populus cathayana Rehd.) and shrub mixed forest, Asia white birch (Betula platyphylla) and China spruce (Picea asperata) mixed forest, Dahurian larch (Larix gmelinii) pure forest, China spruce pure forest and Asia white birch pure forest and so on. The results show that: in sub-humid region of Loess Plateau, 3 000 trees per hm2 is a proper standard of planting density. Under current condition, the productivity index of green poplar and shrub mixed forest, Asia white birch pure forest, China spruce pure forest, and Asia white birch and China spruce mixed forest with the density of 2 100–3 333 trees per hm2 can serve as potential productivity standard of actual biomass of arbor established forest. In sub-humid area, Thornthwaite Model is adopted to estimate plant climate potential productivity, which is about 8 462 kg&#8226;hm–2&#8226;a–1. The actual potential water productive efficiency of Purplecone spruce (Picea purpurea) and Asia white birch pure established forest are 17.22 and 22.14 kg&#8226;mm–1&#8226;hm–2&#8226;a–1 respectively, and that of green poplar and shrub mixed established forest, and Asia white birch and China spruce mixed established forest are 21.14 and 19.09 kg&#8226;mm–1&#8226;hm–2&#8226;a–1 respectively. The potential productivity of green poplar and shrub mixed forest, Asia white birch and China spruce mixed forest, China spruce pure forest and Asia white birch pure forest which have grown into forest with the density of 3 000 trees per hm2 have attained or been close to that of local climax community, which is local maximum tree productivity at present. These types of forestation models are the developing direction of the returning farmland to forest project.  相似文献   

20.
Most timber harvesting operations in the southern Mediterranean area of Italy can be considered to be in an early stage of mechanization. It is mainly based on agricultural tractors that are sometimes equipped with specific forest-related accessories such as winches, hydraulic cranes, or log grapples. In recent years, there has been an increase of specialized forestry machines working in Calabria, southern Italy, including forwarders, skidders and cable yarders. This study assesses the efficiency and costs of extraction using forwarders, as a mechanized alternative to agricultural tractors and horse logging. Time studies were conducted to quantify the productivity and operational cost of log forwarding for two John Deere forwarders in two different coniferous stands: (A) Calabrian pine and (B) silver fir. The empirical time study included 100 forwarding cycles (i.e., 50 for each site) that were broken down into four different work phase elements. Models for cycle time, total productivity and individual work phases were calculated. The average load per cycle was 11.8 m3 in stand A and 9.97 m3 in stand B and the average one-way forwarding distance was 306 m in A and 597 m in B. The average productivity per scheduled machine hour (SMH) was 14.4 m3 in A and 15.7 m3 in B, while the costs, calculated to be 3.60 €/m3 in A and 4.90 €/m3 in B, were considered lower respect traditional methods.  相似文献   

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