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.     

Influence of skidder traffic and canopy removal intensities on the ground flora in a clearcut-with-reserves northern hardwood stand in Minnesota,USA

We investigated the effects of skidder traffic intensity, soil disturbance intensity, and canopy removal intensity on the richness, diversity, composition, and cover of the entire ground flora (woody and herbaceous vegetation ≤2 m tall), various individual life forms, invasive/noxious species, and species with different requirements with respect to moisture, nutrients, heat, and light (synecological coordinates) in a mesic northern hardwood stand 6 years after a clearcut-with-reserves regeneration harvest removed 50–100% of the canopy. Skidder traffic was restricted to a network of trails and a global positioning system (GPS) tracked skidder movement to quantify the number of passes at pre-established sampling points along the anticipated soil disturbance gradient on and off skid trails. Soil disturbance intensity within the top 15 cm of soil was quantified by relativized resistance to penetration (RRP) compared to untrafficked plots; post-harvest increases in RRP ranged from 81 to 272%. Regression analysis and ordination revealed a pattern of increasing difference from pre-disturbance composition with increasing skidder traffic (i.e., forest floor disturbance), with increased RRP (i.e., soil compaction) and (less so) canopy removal intensity. The ground flora shifted from interior forest species such as Anemone quiquefolia, Aralia nudicaulis, Clintonia borealis, Maianthemum canadense, and Oryzopsis asperifolia to more ruderal, invasive/noxious, and disturbed-forest species such as Aster lateriflorus, Cirsium spp., Phleum pretense, Rubus idaeus, and Trifolium spp. The relative resistance of the initial ground flora to change (inverse of the distances between pre- and post-harvest samples in ordination space) was nonlinearly related to skidder traffic intensity and linearly related to RRP, indicating that the largest compositional changes occurred with the first few passes of the skidder. Mean plot scores for the synecological coordinates revealed that the post-harvest species were on average less demanding of water and nutrients; the opposite was true for light. Plots exposed to less skidder traffic and RRP had higher herb cover and higher nutrient scores; those with more skidder traffic and higher RRP levels had higher shrub cover and higher light scores. We conclude that protection of the ground flora from forest floor and soil disturbance requires careful planning of skid trail networks. Concentrating skidder traffic to a designated skid trail system can result in less area disturbed and spatially connected networks of larger, untrafficked remnant forest patches that may maintain species that are sensitive to forest floor and soil disturbance.     

Soil moisture content as a predictor of soil disturbance caused by wheeled forest harvesting machines on soils of the Western Carpathians

Limiting surface soil disturbance caused by forest harvesting machines is an important task and is influenced by the selection of efficient and reliable predictors of such disturbance. Our objective was to determine whether soil moisture content affects soil load bearing capacity and the formation of ruts. Measurements were conducted in six forest stands where various machines operated. We measured the formation of ruts along skid trails in connection with varying soil moisture content. Soil moisture content was determined through the gravimetric sampling method. Our results showed that severe(rut depth16–25 cm) to very severe disturbance(rut depth [26 cm)occurred in forest stands where the instantaneous soil moisture exceeded its plasticity limits defined through Atterberg limits. Atterberg limits of soil plasticity ranged from 26 to 32 % in individual stands. Regression and correlation analysis confirmed a moderately strong relationship(R = 0.52; p \ 0.05) between soil moisture content and average rut depth. This confirmed that soil moisture is a suitable and effective predictor of soil disturbance.     

Impact of mechanized harvesting on compaction of sandy and clayey forest soils: results of a meta-analysis

Context

Nowadays, harvest operations are predominantly performed fully mechanized using heavy tractors or forestry machines. The resulting soil compaction may negatively affect the soil ecosystem.

Aims

We wanted to draw general conclusions concerning the impact of mechanized harvesting on forest soil bulk density and the influencing factors.

Method

Therefore, we combined the data of several studies using a meta-analysis approach.

Results

The impact decreased from the surface towards deeper soil layers. At 0?C10?cm depth, the impact on clayey soils was highest although not significantly different from the impact on sandy soils. Higher initial bulk densities, i.e., on already compacted forest soils, generally led to smaller extra increases of bulk density after machine traffic. For sandy soils, the impact was also significantly smaller when machines were lighter. No significant relationship was observed between the compaction degree and traffic intensity.

Conclusions

We observed clear compaction on both clayey and sandy soils, especially in case of low initial soil compaction degrees and heavy machines. The compacted initial state of many forest soils, the long recovery period, and the generally high impact of the first passes that is frequently mentioned in literature all count in favour of designated skid trails and an adjustment of the machine type to the job.     

Mitigating effects of slash on soil disturbance in ground-based skidding operations

Reinforcement of skid trails with slash has been shown to reduce soil disturbances, but there have not been any studies documenting the mitigating effects following traffic of harvest equipment traffic on steep mountainous skid trails. The objective of this study was to quantify potentially mitigating effects of slash cover on soil compaction and rutting on skid trails in mountainous hardwood forests. The effects of the placement of no slash (bare soil), light density slash (7.5 kg m^?2) and heavy density slash (17.5 kg m^?2) in a skid trail following one, five, and nine machine passes on both gentle slopes <20% and steep slopes >20% in a downhill skidding operation by a steel-tracked skidder were studied. Bulk density and rut depth increased following harvest equipment traffic on both slope gradients. Compared to bare soils, soil bulk density was not significantly reduced by light slash density; however, soil bulk density was significantly reduced by heavy slash up to five machine passes on steep slopes. Light and heavy slash significantly reduced rut depth in both slope classes. The study revealed a high protective role of slash, particularly on steep skid trails. However, benefits of slash to mitigate soil compaction were limited to five passes, after which the slash deteriorated and only provided benefits against rutting.     

Long-term assessment of soil physicochemical properties and seedlings establishment after skidding operations in mountainous mixed hardwoods

One of the basic requirements for sustainable forest management in mixed broadleaved stands is to provide suitable conditions for natural regeneration of trees. These conditions include, but are not limited to, the frequency, quality and the composition of seedling species. Compacted soil layers caused by forest machinery traffic are the most common problem affecting seedling establishment and growth after skidding operations. In this study, we evaluated the frequency, quality, diversity of seedling species and physicochemical properties of soil on 10-, 20- and 30-year-old abandoned skid trails. Further comparison to the values of the mentioned above parameters in control areas allowed for the evaluation in terms of natural recovery processes, under varying traffic intensity and the longitudinal slope of the skid trails in a mixed broadleaved forest. Results showed that there is a significant positive trend of recovery for soil physicochemical properties and ecological characteristics (density and quality) of seedling growing on the skid trails. The time required to recover soil properties and ecological attributes of seedlings increased with increasing traffic intensity and slope of the skid trail. Our results showed that it takes 20 and 30 years to fully recover the chemical and physical properties of the soil, respectively. On the 30-year-old skid trails, density and species diversity indices were fully recovered, but the quality of the seedlings was not restored to the control conditions. The results suggest the importance of a proper planning of the skid trail network, avoiding in particular skid trails with a slope gradient higher than 20%.

     

Application of a Small-Scale Equipment System for Biomass Harvesting

The small-scale harvesting equipment system has been and continues to grow in use in forestry operations in some regions in the world. This harvest system can include a range of equipment types, such as feller-bunchers or chainsaws, skidders or farm tractors, and chippers. These machines are generally smaller, lower cost and less productive than larger, more advanced forestry machines. The objective of this project was to investigate the feasibility of a small scale harvesting system that would produce feedstock for a biomass power plant. The system had to be cost competitive. A boom-type feller-buncher, a small grapple skidder and a chipper were tested as a small-scale system. In this study, feller-buncher and skidder productivity was determined to be 10.5 m³ per productive machine hour, and production for the chipper was determined to be 18 m³ per productive machine hour. Production from the system did not reach the desired levels of 4 loads/day (25 m³/load); however, the system was able to produce about 3 loads/day. The results showed that the system currently could fill a roadside van for $16.90/m³, but suggested machine modifications could potentially reduce the system cost to $12.73/m³. Residual stand damage was minimal, especially on flatter ground and not operating on a slash layer. Soil disturbance from the harvesting system was predominantly undisturbed or classified as a shallow disturbance.     

Factors affecting soil-based natural regeneration of <Emphasis Type="Italic">Abies sachalinensis</Emphasis> following timber harvesting in a sub-boreal forest in Japan

Natural regeneration of Abies sachalinensis on soil was studied in a natural sub-boreal forest managed by single tree selection cutting located within the Hokkaido Tokyo University Forest. First, seedlings of A. sachalinensis on skid trails, soil mounds, soil pits, and undisturbed soil were counted, and their areas were measured. Most seedlings were found on skid trails. Seedling densities of A. sachalinensis on sites with soil disturbance, with the exception of soil pits, were significantly greater than that on undisturbed soil. Second, densities of Sasa senanensis, heights of S. senanensis, and seedling densities of A. sachalinensis on skid trails and undisturbed soil in both a closed-canopy stand and in a canopy gap were compared. Seedling density of A. sachalinensis on skid trails in the closed-canopy stand was significantly greater than that in the canopy gap. Average density and average height of S. senanensis, which is known to interfere with regeneration of many woody species, were significantly greater on skid trails and undisturbed soil in the canopy gap than those in the closed-canopy stand. It could be concluded from this study that both crown closure and soil disturbance are essential for natural regeneration of A. sachalinensis on soil in sub-boreal forests.     

An operational UAV-based approach for stand-level assessment of soil disturbance after forest harvesting

The effectiveness of generating virtual transects on unmanned aerial vehicle-derived orthomosaics was evaluated in estimating the extent of soil disturbance by severity class. Combinations of 4 transect lengths (5–50 m) and five sampling intensities (1–20 transects per ha) were used in assessing traffic intensity and the severity of soil disturbance on six post-harvest, cut-to-length (CTL) clearfell sites. In total, 15% of the 33 ha studied showed some trace of vehicle traffic. Of this, 63% of was categorized as light (no visible surface disturbance). Traffic intensity varied from 787 to 1256 m ha^?1, with a weighted mean of 956 m ha^?1, approximately twice the geometrical minimum achievable with CTL technology under perfect conditions. An overall weighted mean of 4.7% of the total site area was compromised by severe rutting. A high sampling intensity, increasing with decreasing incidence of soil disturbance, is required if mean estimation error is to be kept below 20%. The paper presents a methodology that can be generally applied in forest management or in similar land-use evaluations.     

Effects of wheeled cable skidder on rut formation in skid trail — a case study in Hyrcanian forest

The impact of skidding operations on forest soils can be divided into three major categories: soil profile disturbance, soil compaction, and soil puddling and rutting. The present study was designed as a factorial experiment in the Kheyrud Forest with a Timberjack cable skidder to evaluate the influences of number of machine passes and soil moisture of skid trails on rutting over a fine-grained soil, and to quantify these effects. The effects of soil moisture of 20% 30%, 30% 40% and 40% 50% and different levels of compaction were studied. Compaction treatments were applied using different numbers of skidding passes (1, 5, 10, 15, 20, 25, 30 times). Result shows that an increase in the number of machine passes could increase rut depth, but the majority of rutting was occurred after the initial few machine passes. Also rut depth at soil moisture of 40% 50% was higher than rut depths at soil moisture of 30% 40% and 20% 30%. The average rut depth in soil with 20% 30%, 30% 40% and 40% 50% moisture was 17, 22 and 35 cm, respectively. Rut depths were increased significantly with soil moisture and number of machine passes. It is suggested that skidding operations should be planned when soil conditions are dry in order to minimize rutting., but if skidding must be done under wet conditions, the operations should be stopped when machine traffic could create deep ruts.     

Comparison of ground disturbance of frozen peatland during stump harvesting using a stump drill and rake

ABSTRACT

Tree stumps could be a source of renewable energy, contributing to a reduced dependence on fossil fuels. In Finland, stumps are currently harvested when the ground is not frozen to avoid co-removal of large amounts of soil and stones. Hence, the machinery used for stump extraction is not operated year-round. On peatlands, stumps could potentially be harvested when the ground is frozen. However, peatlands are highly sensitive to ground disturbance. There is, therefore, a need to identify equipment that causes low ground disturbance. In this study, peatland ground disturbance at stump level caused by stump harvesting using either a stump drill or a conventional stump rake was evaluated and compared in winter conditions. Results show that the stump drill caused up to 90% less ground disturbance per harvested stump than the conventional stump rake, but harvested 32–53% of the stump wood. Additionally, the size and shape of the disturbed areas changed between the harvesting year and following year, indicating that frost heaving plays a role in filling holes caused by stump extraction. The stump drill also consumed similar time to the conventional stump rake when harvesting Scots pine stumps on mineral soils, but far more when harvesting Norway spruce stumps.     

Characteristic site disturbance due to harvesting and extraction machinery traffic on sensitive forest sites with peat soils

The effects of wood harvesting and extraction machinery traffic on sensitive forest sites with peat soils were characterised with the objective of quantifying the threshold levels beyond which significant site impacts (compaction and rutting) would occur. The treatments involved running the machines in selected extraction racks (i.e., 3 m wide machine routes) while conducting normal wood thinning and extraction operations comprising one and two passes by the harvester and the forwarder with full payload, respectively. Soil disturbance thresholds were established by testing the level of significance of the difference in induced soil damage and compaction before and after machine traffic treatments. For volumetric soil water content lying between 10.0 and 14.9%, threshold cone penetration resistance levels for two 600/55–30.5 tyres were found to range from 594 to 640 kPa for deep-raised peat soil with initial strength lying between 524 and 581 kPa. In general, the proportion of the total rut depth data in each rack that exceeded the threshold level of 21.5 cm was about 5%. The threshold value corresponds to sinkage equivalent to 15% of the overall wheel diameter of the harvester, above which machine mobility would be hampered considerably. In addition, after harvester traffic the mean rut depth per unit rack length was 10.2×10⁻² cm/m, and it ranged from 0.7 to 24.7×10⁻² cm/m.     

Soil physical properties degrade further on skid trails in the year following operations

Short-term recovery of soil physical properties on skid trails was investigated upon cessation of skidding operations and 1 year later. Bulk density and porosity were assessed at three levels of traffic intensity and two slope gradients. Compared to undisturbed areas, bulk density increased, total porosity and macroporosity decreased, and microporosity increased in the compacted areas immediately after skidding. In all cases, changes were significantly greater when traffic intensity was higher and when slopes were steeper. Surface soil compaction did not show any recovery over the 1-year period, illustrating the persistent effects of compaction on soil structure. In fact, surficial compaction further increased and macroporosity further decreased after 1 year of recovery, compared to immediately after skidding. While these changes may reflect inherent small-scale site variability or differences in soil moisture content at times of sampling, direct negative physical impacts on newly exposed soil (such as by raindrops), in addition to the loss of organic matter after canopy removal and skidding, likely delayed any physical recovery, particularly on heavily trafficked trails on steeper slopes. These results raise serious concerns about long-term resilience to traffic on forest soils and indicate the necessity to properly retire skid trails to avoid further soil degradation as trails age.     

Torque required to twist and cut loose Scots pine stumps

Abstract

Stump wood is a possible source of renewable energy, but before its potential as a fuel can be utilised to a high degree, new harvesting techniques should be developed to reduce the environmental impact (notably ground disturbance) of harvesting stumps. The forces required to lift and drag stumps out of the soil are known. In this study, two unknown and important parameters were addressed: the torque required to uproot stumps by twisting them and the torque required to cut lateral roots around stumps. A new, improved stump-twisting rig was designed and used in trials with 28 Scots pine (Pinus sylvestris) trees (breast-height diameter over bark, 153–427 mm). The measured torque requirements ranged from 10 to 50 kNm. Twisting stumps required more torque than cutting lateral roots around stumps and the required torque increased with increases in stump size. The results indicate that a wrist on a big feller-buncher, but not a conventional rotator used on forest machines, should be able to generate sufficient torque to cut the roots around stumps such as those used in this study.     

Assessing the effects of initial soil characteristics,machine mass and traffic intensity on forest soil compaction

An extensive field trial was set up in eight forest stands to examine the influence of soil texture (two stands on sand, four on loam to silt loam, two on clay), machine mass (light, heavy) and traffic intensity (one and five skidding cycles) (i.e. pass back and forth on the skid trail) on soil compaction after mechanized harvesting. Dry bulk density (BD), penetration resistance (PR), micro-topography and soil carbon dioxide (CO₂) concentration were applied as response variables for soil compaction. Significant effects on BD were nearly absent (<7% increase) and occurred occasionally for PR (60–70% increase, up to 150% on clay soils). Especially for loam to silt loam and clay soils, this was in contrast with the expectation. The negligible compaction degrees for loam to silt loam are attributed to high initial compaction levels that prevented further compaction, as was found by general linear modelling (GLM) for both BD and PR. For clay soils the small compaction degrees can be explained by the high water contents that result in plastic deformation instead of strong compaction degrees, as was confirmed by the micro-topographical measurements. GLM also revealed a significant impact of machine mass (BD) and soil water content (BD, PR) on the compaction degree. Soil texture, traffic intensity and position in relation to the wheel tracks generally turned out to have an insignificant influence. With regard to clear interactions the influence of traffic intensity depends on the position in relation to the wheel tracks and the machine that was used (PR).     

机械运输对伊朗北部山林陡峭集材道土壤的干扰

A study was conducted to investigate the effects of skid trail slope and traffic levels on soil disturbances at two soil depths (0–10 and 10–20 cm). The treatments were set at four traffic levels (2, 7, 12 and 20), two slope classes (<20% and >20%) and two soil depths (0–10 and 10–20 cm). Results show that skidder traffic, longitudinal slope and soil depth have significant effect on soil bulk density in skid trail. Comparison of average soil bulk density in different traffic levels shows that there are significant differences in average bulk density between different traffic levels and control (p<0.05). The average bulk densities in different slopes and soil depths are significantly increased with increase in traffic levels, maximized at 12 passes (p<0.05), but there are no significant differences between 12 and 20 passes. The interaction effects between traffic and soil depth are significant (F _0.05,3=0.109, p<0.001). For all traffic treatments, there are significant differences in soil moisture content between the two slope classes and the two depths (p<0.001). However, the interaction effects between traffic levels and slope classes are not significant (p >0.05), although skidder traffic and slope affected soil moisture content.     

Improvement and evaluation of the feller-buncher head

The high quality forest machines have recently become very popular in Japan. Many improvements on these machines have been made to fit the Japanese forests. This report describes the improvement and evaluation of the feller-buncher head of the prototype machine: FG-35. This head is mounted on the telescopic and knuckle-boom carrier. The prototype machine was improved to cut the trees, felled down on the ground or felled side ways by the storm as in the Kyushu district. And also the machine was improved so that it could be driven well without crashing the chainsaw-bar by the beginners. The testing operation of this machine carried out in Sumita-chou in Iwate and in Kuzu-chou in Oita. The productivity of the machine can be estimated at about 20 m³/h. The results of the improvement on the machine can be said to be good. A portion of this report was presented at the 106th Annual Meeting of the Japanese Forestry Society (1995).     

Soil changes after traffic with a tracked and a wheeled forest machine: a case study on a silt loam in Sweden

Alterations to some soil physical parameters were evaluatedafter passes by a tracked forest machine and a wheeled one ofequal mass (about 20 000 kg). Measurements were made after arange of machine passes, with a maximum of eight. The measuredsoil physical parameters were dry bulk density, penetrationresistance, intrinsic air permeability, saturated hydraulicconductivity, porosity and pore-size distribution. Rut depthwas also measured. Although the wheeled machine caused deeper ruts than the trackedone, alterations caused by the two machines to the measuredsoil parameters were similar, except in the uppermost 5–10cm. The wheeled machine caused a decrease in bulk density at5 cm depth, whereas the tracked machine caused an increase,despite its lower ground pressure.     

Enhancing the regeneration of compacted forest soils by planting black alder in skid lane tracks

Soil compaction due to the use of heavy machinery for timber harvesting has become a widespread problem in forestry. However, only few studies deal with the regeneration of compacted forest soils. In the present study, we examined the potential of accelerating soil regeneration by planting black alder trees (Alnus glutinosa (L.) Gaertn.) in skid lane tracks. In 2003, seedlings were planted into the rut beds of severely compacted skid lanes in two Swiss forest sites. In addition, some of the ruts were filled with compost. In 2009 and 2010, we assessed the success of these measures by analysing physical parameters of soil structure (bulk density, total and coarse porosity and air permeability), root densities and tree growth. Tree growth was exceptionally strong on the skid lanes. Total and coarse soil porosity and air permeability showed significant increase in planted skid lanes as compared to untreated control subplots, approaching values found for untrafficked soil in the immediate vicinity. All soil physical parameters were closely correlated to root mass density. Compost application enhanced tree growth and soil structure regeneration on one site, but had a retarding effect on the other site. Planting black alders has great potential as an environmentally friendly measure to accelerate the structural regeneration of compacted forest soils in temperate humid climates.