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.     

Herb layer vegetation of south Swedish beech and oak forests—effects of management and soil acidity during one decade

Effects of forest management and soil acidity on herb layer vegetation were studied after 10 years on 190 permanent plots in south Swedish beech (Fagus sylvatica) and oak (Quercus robur) forests. Species richness generally increased with management intensity, mainly due to establishment of ruderal species from the seed bank. Species richness of the typical forest flora was unaffected by management. Moderate management of oak stands favoured several species which are commonly found in semi-natural pastures. Classification and ordination of the data showed that the main floristic gradient within Swedish beech and oak forest vegetation is related to soil acidity. Species richness of the typical forest flora was strongly positively correlated with soil pH in beech forests, but this correlation was weaker in oak forests. The number of herbaceous plants with a broader habitat range increased with pH only in the oak forest plots. Long term changes in the forest environment, which may affect the vegetation, are the decline of grazing 150-50 years ago and soil acidification mainly caused by atmospheric pollutants during the last 50 years. In the one-decade perspective of this study, however, we did not find a general trend towards a more acid-tolerant flora. Neither could we find a general decrease of pasture species in currently ungrazed oak stands. The results indicate that most typical forest plants are well adapted to and partly depend on occurrence of canopy gaps and soil disturbance. If canopy thinning is followed by periods of canopy closure the characteristic shade tolerant flora of Swedish beech and oak forests may be able to persist as long as soil chemical limits of existence are not exceeded.     

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%.

     

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.     

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.     

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.     

Abundance response of western European forest species along canopy openness and soil pH gradients

In order to better understand the structure and composition of forest plant communities, we aimed to predict the abundance of understory herbaceous species locally at the stand level and according to different environments. For this, we seeked to model species distributions of abundance at a regional scale in relationship with the local stand structure (canopy openness) and regional soil resources (soil pH).Floristic inventories, performed in different light and soil conditions located in 1202 records of north eastern France, were used to analyze the combined effect of canopy openness and soil pH on the abundance of 12 common western European forest species: Anemone nemorosa, Deschampsia flexuosa, Festuca altissima, Hedera helix, Lamium galeobdolon, Lonicera periclymenum, Molinia caerulea, Oxalis acetosella, Pteridium aquilinum, Rubus fruticosus, Rubus idaeus, and Vaccinium myrtillus. Ordinal regression models relating species abundance responses to their environment were developed.For most species (eight out of 12), distribution was significantly affected by canopy openness and soil pH. Differences among low-abundance (i.e. cover <25%) and high-abundance (i.e. cover >25%) responses were noted for 11 species along the canopy openness gradient and four species along the pH gradient. The present study quantifies optimal light and soil nutrient requirements for high-abundance responses and quantifies light and soil nutrients tolerance conditions for low-abundance responses. The combination of both factors highlights the pre-eminence of pH conditions occurrence and canopy openness for species abundance.The models developed by this study may be used to define canopy openness thresholds in function of soil characteristics to control the development of species during forest regeneration. The species-specific reactions on local canopy openness along a regional soil gradient illustrate the need for a species-specific management approach.     

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.     

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.     

Regeneration of commercial tree species in a logged forest in the Selva Maya, Mexico

One of the main threats to the sustainability of community forestry in the Selva Maya is insufficient regeneration of commercial tree species. We evaluated the regeneration status of 22 commercial tree species in a managed semideciduous tropical rain forest in Southern Mexico. The study was carried out in six harvesting areas along a 16-year chronosequence. In each area, 10 transects (1000 m²) were established and all trees >50 cm height and <10 cm diameter were recorded. We evaluated the relationships between seedling and sapling abundance, and canopy cover and disturbance condition (closed forest, canopy gap, log landing, skid road, primary road and secondary road). The area occupied by closed forest canopy increased with age of harvesting area (65–91% of sampled area), while the area occupied by canopy gaps decreased (22–9%). Log landings occupied less than 1% of the sampled area. The predominant canopy cover was 75–80% in all harvesting areas, even in the most recently harvested areas. The highest densities of seedlings and saplings, of both shade tolerant and intolerant species, were found in log landing and skid trails, followed by secondary roads. Even Simarouba glauca, a shade tolerant species, displayed higher densities in sites with ≤65% of canopy cover. Our results support previous findings and indicate that the levels of disturbance caused by existing harvesting procedures may be inadequate to promote sufficient regeneration of not only light demanding desirable species but also for some of the evaluated shade tolerant species of commercial interest. Seedling and sapling densities exhibited by Swietenia macrophylla, for example, are insufficient to support current harvesting rates. The application of a spatial mixed system with patch-cuts of different sizes, a consequence of group felling, could be applied to provide the necessary conditions for the regeneration of the main commercial species.     

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.     

Explaining conifer dominance in Afrotemperate forests: Shade tolerance favours Podocarpus latifolius over angiosperm species

We contrasted the regeneration success of angiosperm canopy species with that of Podocarpus latifolius to test whether this conifer was sufficiently shade tolerant to be favoured on infrequently disturbed and well-shaded sites. Seedling and sapling population structures were measured in several habitats representing a light gradient in warm temperate forest in the Drakenberg mountains of South Africa. The angiosperm-dominated forest was well-shaded (∼5.5% PAR) and lacked ground vegetation. Seedlings of angiosperm canopy species were abundant but the absence of saplings indicated regeneration failure. In contrast, P. latifolius was represented by all size classes beneath the intact canopy indicating continuous regeneration in angiosperm-dominated forest. Angiosperm regeneration was similarly poor in forest gaps, which were dominated by grasses, ferns and vines. P. latifolius entered the advanced regeneration in gaps by establishing in shade before gap formation. The floor of the Podocarpus-dominated forest was less shaded (∼7.5% PAR) than angiosperm-dominated forest and dominated by grass, which suppressed most conifer regeneration. Gaps in Podocarpus forest were more than double the size of gaps in angiosperm forest and dominated by vines and understorey shrubs. There was no clear winner of the angiosperm–conifer contest in Podocarpus forest gaps. Consequently, gaps maintain limited angiosperm diversity in Podocarpus forest. Angiosperm canopy species regenerated continuously in the high light (∼11.5% PAR) thicket environment. Few seedlings of P. latifolius were recorded in the thicket environment. Our findings are consistent with the hypothesis that shaded and infrequently disturbed forest sites favour shade-tolerant conifers over relatively light-demanding angiosperm species. The outcome of the competitive interaction between angiosperm and conifer at the regeneration phase depends on the relative shade-tolerance of associated species.     

Extent and causes of site damage due to forestry traffic

Increased mechanization in the forestry means usually increased traffic on a ground which is also used as a growth substrate. In this state‐of‐the‐art article it is found that the traffic could have an areal extent of 10–30% of the site area mainly due to yarding at clear‐felling and thinning. In the future there could be up to 6 machine entries on the site till a stand age of 50 year.

Skidding is often recognized as the major cause of soil disturbance with 50–75% of the skid trails considered as apparently compacted. Rut formation after forwarders can also be a problem but harvesters seems to be forgotten or give minor problems.

In order to reduce soil compaction smaller machines must be considered on many sites. Maybe 5–10 tonnes machines with a real mean ground pressure of 60–70 kPa could give, thanks to good tyres, an acceptable level of soil disturbance.

High tractive forces and slip may contribute to the soil disturbance as much as double the ground pressure. Calculations show it is therefore better to carry the load than to skid. However, the change in weight balance of the machine due to the load is still a problem and maybe anti‐slip control could give the machine a better torque distribution.     

Forest floor temperature and relative humidity following timber harvesting in southern New England,USA

Forest amphibians, especially salamanders, prefer forests with shaded, cool, and moist forest floors. Timber harvesting opens the forest canopy and exposes the forest floor to direct sunlight, which can increase forest floor temperatures and reduce soil moisture. These microclimatic changes can potentially degrade the harvested stand for amphibian habitat or affect other biotic resources or ecological processes at the forest floor and in the understory. The degree of forest floor disturbance is directly related to the intensity of harvesting, however, the duration of this effect is unknown. We conducted a study of forest floor temperature and relative humidity over a 12-year chronosequence (1993–2004) of timber harvests. We compared simultaneous, paired measurements of temperature and relative humidity at three positions (soil, forest floor, air) in harvested and control sites over three seasonal survey sessions. Vegetation composition and structure were measured at each survey location. Ambient weather conditions were recorded at three open-field locations across the study area.     

Threshold change in forest understory vegetation as a result of selective fuelwood extraction in Nairobi, Kenya

We examined whether heavy fuelwood collection can cause threshold change in understory forest community and evaluated how selective wood extraction might lead to delayed forest recovery in an urban forest of Nairobi, Kenya. Piecewise regression which represents strongest support for threshold change provided the best fit for the relationships between understory floristic composition (i.e. DCA axis 1) and human disturbance gradients (i.e. canopy cover, and distance from the slum), where threshold changes were detected at c.a. 350 m from the slum and c.a. 30% canopy cover. Only one tree species significantly indicated communities beyond the threshold while an aggressive invasive alien plant (IAP) Lantana camara was strongly represented. Total species diversity along the two human disturbance gradients peaked before the threshold was reached, suggesting that decline in species diversity along the prevailing disturbance gradient might be able to forecast threshold change. Tree species richness in the understory rapidly declined as the threshold was surpassed while other growth forms (i.e. shrubs, herbs and climbers) were relatively unaffected. The effect of selective tree cutting was indirectly impacting the forest understory as species richness pattern of preferred and non-preferred species paralleled that of trees and shrubs, respectively. Thickets of L. camara can negatively affect indigenous flora and its establishment was favored under selective fuelwood extraction removing certain tree species while leaving the IAP untouched. Shading can readily eliminate the IAP, but weak tree regeneration beyond the threshold suggested forest recovery might be delayed for longer than expected because of the interaction between selective fuelwood use and the IAP.     

三峡库区云阳县三种类型马尾松林微生物区系及优势种群分析Ⅰ.林地土壤细菌、芽孢杆菌和真菌

为探讨马尾松不同类型林地土壤微生物区系及其季节变化,对三峡库区云阳县马尾松近熟龄天然林、中龄天然林和人工林林地土壤可培养细菌、芽孢杆菌(Bacillus spp.)和真菌进行了分析。结果表明,林地土壤微生物优势种群种类和数量因不同森林类型林地和季节有所差异。中龄天然林的细菌数量显著高于近熟龄天然林和人工林,其四季变化也最大,而近熟龄天然林和人工林则相对平缓。林地土壤细菌优势种群主要是芽孢杆菌(Bacillus spp.)和假单胞菌(Pseudomonas spp.),尤以蜡状芽孢杆菌(Bacillus cereus)居多,在四季中冬季细菌的优势种群数量所占比例最高(近熟龄天然林＞人工林＞中龄天然林),优势种群近熟龄天然林为芽孢杆菌,占39.74%;人工林为假单胞菌,占37.26%;中龄天然林为蜡状芽孢杆菌,占24.91%。三种林地类型土壤的芽孢杆菌在不同季节都以蜡状芽孢杆菌(占20% - 49%)和芽孢杆菌科(Bacillaceae)一种(种名未定)为优势种群。三种林地类型土壤真菌优势种群在秋季所占比例最高,且人工林＞近熟龄天然林＞中龄天然林;优势种群数量及所占比例人工林为核盘菌(Sclerotinia sclerotiorum),33.08%,近熟龄天然林为核盘菌, 31.7%,中龄天然林为瓦克青霉(Penicillium waksmanii), 25.15%。     

Operational impacts to residual stands following ground-based skidding in Hyrcanian Forest, northern Iran

Hyrcanian (Caspian) Forest in northern Iran has a richness of biological diversity, with endemic and endangered species. The usage of ground-based skidding is well accepted practice for the extraction of timber from the forest, but this operation has tended to cause the greatest environmental problems. The aims of the study were to evaluate and comparison of operational impacts, residual stand damage, regeneration, and to quantify these effects such as: the extent of the damage, wounding patterns, size and distribution after logging operations that utilized two different methods: short-log and long-log. A Timberjack cable skidder was used and the study location was in the Kheyrud Forest. Post harvesting assessment of damage to the residual stand was compared along skid trail by 100% inventory method and also for the assessment of regeneration damage along winching strips. The results show that along winching strips the percentage of damage to the regeneration was 44% and 36%, while the tree damages along skid trails reached 2.3% and 4.1% in the short-log and long-log methods, respectively. The greatest average amount of damage to a bole occurred along the first 1 m up from the ground (97%) and also within 4 m of the skidder centerline (80%). These results show that the short-log method causes less damage to the residual stand than the long-log method. Tree location to skidder trail appears to have a significant effect on the number and height of scars on a tree. Well designed and constructed trails should be wide enough to allow wood extraction from the forest. Damage to the residual stand might be reduced by proper planning and training of logging crews.     

Recovery of forest structure and composition to harvesting in different strata of mixed even-aged central Appalachian hardwoods

Context

Implementing nature-based silviculture requires understanding the structural and compositional changes that occur in forested stands under known disturbance types and intensities.

Aims

The objectives were to assess the (a) resistance of hardwood forests to change, (b) their trajectory of recovery following disturbance, and (c) how closely resulting forests resemble original forests.

Methods

We characterized tree structure and composition at three points in time (pre-disturbance, 1-year post-disturbance, and ～15 years following disturbance) along a harvesting disturbance gradient created by removing trees in different forest canopy strata.

Results

Significant differences to pre-disturbance conditions were noted immediately post-harvest for tree basal area, density, species richness, and tree species composition; treatment differences were observed for all parameters except diversity. Plots exposed to the least extreme harvesting disturbances (cutting small and intermediate trees) had returned to pre-disturbance conditions for most parameters after 15 years, while the most extreme harvesting disturbance (cutting large trees) had not yet recovered.

Conclusions

Although not initially resistant, Central Appalachian eastern hardwoods are fairly resilient to the removal of trees in the subcanopy or a mixture of the subcanopy and canopy; only the removal of solely canopy trees (i.e., high grading) and complete removal (i.e., clearcutting) appear to impose harvesting disturbances to which these forests may not be resilient.     

Soil disturbance and post-logging forest recovery on bulldozer paths in Sabah, Malaysia

We examined the extent of soil disturbance associated with bulldozer yarding and the regrowth of woody vegetation on bulldozer paths (skid trails) in selectively logged dipterocarp forest. In an area logged in 1993, using conventional, i.e., uncontrolled, harvesting methods, about 17% of the area was covered by roads and skid trails. In contrast, in a 450-ha experimental area where reduced-impact logging guidelines were implemented, 6% of the area was similarly disturbed. Skid trails in the reduced-impact logging areas were less severely disturbed than those in conventional logging areas; the proportion of skid trails with subsoil disturbance was less than half that in conventional logging areas. Four years after logging, woody plant recovery on skid trails was greater in areas logged by reduced-impact than by conventional methods. Skid trails where topsoil had been bladed off had less woody vegetation than skid trails with intact topsoil. In a chronosequence of logging areas (3, 6, and 18 years after logging), species richness and stem densities of woody plants (>1 m tall, <5 cm dbh) were lower on skid trail tracks than on skid trail edges or in adjacent forest. Both richness and density increased with time since logging, but even 18 years after logging, abandoned skid trails were impoverished in small woody stems compared with adjacent forest. Minimizing soil and stand disturbance during logging appears to allow a more rapid recovery of vegetation on bulldozed soils, but the long-term fate of trees growing on compacted soils remains uncertain.