Successional process of Picea crassifolia forest after logging disturbance in semiarid mountains: A case study in the Qilian Mountains,northwestern China

Selective logging is the most widely employed method of commercial timber production in Asia, and its impact on forest structure, composition, and regeneration dynamics is considerable. However, the successional processes in forest communities after logging in semiarid mountains are poorly understood. To provide more information on these processes, we used data from tree rings, direct and indirect age determinations, and field measurements of stand structure to reconstruct the historical disturbance regime, stand development patterns, and successional processes in a natural Picea crassifolia forest community in the Qilian Mountains of northwestern China. The results showed that the density of P. crassifolia forest increased significantly after logging. The densities of second growth forests 30 and 70 years after logging disturbance had increased to 2874% and 294% of primary forest's density, respectively. Logging disturbance did not alter tree species composition of logged stands. However, the diversity of understory species changed significantly among the successional phases. Logging disturbance decreased the spatial heterogeneity of second growth forest. The spatial distributions of recruitment were affected by the location of the remaining trees. There was less recruitment near the remaining trees than near forest that had been cut. In addition, logging disturbance also induced a growth release for the trees on the sites sampled. Our results imply that the succession and regeneration of P. crassifolia forest may be improved if the remaining trees could be retained relative uniform distribution pattern, thinning or selective logging could be performed to height density, exotic shrubs could be removed or the shrubs cover could be reduced during the earlier successional stages.     

Small mammals and retention islands: An experimental study of animal response to alternative logging practices

The integration of forest biodiversity conservation with wood production is a key part of ecologically sustainable forest management. This can be a particular challenge at the stand-level when high-intensity silvicultural systems like clearfelling are employed. Alternative logging practices to clearfelling that result in partial stand retention are being widely promoted in many parts of the world. We present new findings from a replicated block experiment designed to examine the responses of small terrestrial mammals to the retention of islands of forest within otherwise clearfelled harvest units. Our experiment was conducted in the Mountain Ash (Eucalyptus regnans F. Muell) forests of the Central Highlands of Victoria, south-eastern Australia. We quantified the effects of four treatments on small terrestrial mammal abundance: (1) an uncut (‘control’) area of forest; (2) a 1.5 ha retained island within an otherwise clearfelled area; (3) three 0.5 ha retained ‘islands’ within an otherwise clearfelled area; and (4) a traditionally clearfelled area of forest, over the different stages of harvesting operations from pre-cut to post-cut to post-burn.     

小波分析在集材拖拉机齿轮箱故障诊断中的应用

本文介绍了一种处理非线性信号的新方法,小波分析方法。描述了小波变换的基本构造及其特性,从理论角度,讨论了该变换在集材拖拉机变速箱中的应用及前景。     

中国主要林产品海外市场贸易政策变动分析

2005年以来在国际林产品贸易中木材来源问题受到越来越多的关注,重要林产品进口国纷纷出台相关法规以确保进口林产品木材来源的可靠性。作为林产品国际贸易链重要组成部分的中国林业产业,有必要充分了解这些市场新要求,提升企业管理水平,以确保在林产品国际市场上的综合竞争优势。文中比较分析了近些年新出台的主要林产品国际贸易规则及对中国的潜在影响。     

Enrichment of logging gaps with moabi (Baillonella toxisperma Pierre) in a Central African rain forest

Studies of regeneration in African rain forests suggest that without silvicultural treatments, natural succession in logging gaps may not result in the establishment of timber species. In this paper we present the results of an experimental enrichment planting with moabi (Baillonella toxisperma Pierre), a valuable and important timber species harvested in Central Africa. Although forest gaps are generally considered as favourable for the regeneration of this species, a survey conducted in a forest concession in south-eastern Cameroon provided an estimate of only 12.7 seedlings ha⁻¹, suggesting that the species was, in fact, poorly represented in logging gaps within the study area. To further investigate the dynamics of the moabi in logging gaps, 795 seeds were sown in 15 logging gaps and 410 nursery-raised seedlings were planted in 15 other gaps. A biannual monitoring program over a 30-month period showed a lower survival rate for seedlings from sowing (75.9%) compared to that of nursery-raised seedlings (95.3%). Planted seedlings reached an average of 229.3 cm tall whereas seedlings from sowing were 167.5 cm tall, with the observed difference roughly corresponding to the average height of the nursery-raised seedlings at the time they were introduced to the logging gaps. After 30 months, the diameters of planted seedlings (16.8 mm) were also greater than those of the directly sown individuals (12.5 mm). Forest gap characteristics significantly influenced the growth of the plants. Factors accounting for the differences were total solar radiation, the soil content of coarse sand, the topographic position of the gap, the vegetation cover and the density of Macaranga spp. Whilst total solar radiation had a positive influence on growth, the remaining factors had impacted growth negatively. A streamlined technique was tested by planting 7 seedlings in 250 gaps. Without additional site maintenance, 29.3% of the moabi seedlings emerged naturally from the competing vegetation after 24 months. With biannual maintenance some 89.4% of seedlings became successfully established. Clearance operations had no significant influence on the height of plants whilst plant diameter was greater in cleared gaps. The total cost of the enrichment technique was 5.5 EUR per gap without maintenance and 7.5 EUR per gap with a single maintenance measure. Whilst long-term monitoring is needed, this study suggests a high survival rate of moabi introduced in logging gaps, and a growth rate 10 times higher than previously reported under canopy cover. These findings, combined with the low costs of the enrichment technique, support the use of silvicultural measures in logging gaps to restore the forest.     

Spatial patterning and population structure of a common woodland herb, Trillium erectum, in primary and post-logging secondary forests

We investigated the population age structure and spatial patterning of a common understory perennial, Trillium erectum var. album, in primary and post-logging secondary (industrially logged in the early 1900s) cove forests of the southern Appalachian Mountains. Within each of 8 T. erectum populations (4 in primary forest and 4 in secondary forest), we mapped the locations of all T. erectum plants in a 10 m × 10 m plot located within the center of each population. We recorded the height and life stage of each plant and excavated a randomly selected subset for age determination. Trillium erectum populations in primary forests displayed a somewhat stronger and more consistent spatial structure than those found in secondary forests. However, aside from being on-average younger due to a higher concentration of juveniles, age structures of secondary forest populations were similar to those of primary forests and both forest types had similar maximum plant ages. Our results, when considered with the life history of the species, suggest that logging did not eliminate T. erectum from secondary forests. Rather, residual plants and patches of plants that survived logging provided the propagules needed to expand and reestablish populations following logging. This relatively rapid recovery stands in stark contrast to the slow recovery observed by others in post-agricultural secondary forest. When considered in the context of other studies of post-disturbance recovery in secondary forests, our results suggest that the full history of a site must be carefully considered when examining the impacts of disturbance on forest perennial herbs.     

Forests and water: a policy perspective

Asian policymakers need to know how changes in land uses and practices related to forests affect flooding, dry season stream flow, and water quality. Based on their beliefs about these relations, policymakers often ban logging or introduce expensive projects. Many key stakeholders believe that logging and deforestation increase flooding and the damage floods cause, but there is only evidence for this in relation to smaller and less severe floods. It is also widely believed that logging and clearing forest reduce dry season stream flow, but whether that actually occurs depends on rainfall patterns, soils, topography, geology, and the type of vegetation. Forests generally improve water quality, although not always. More research is needed on the magnitude of the water quality effects, particularly as regards drinking water.     

A conceptual model to characterize disturbance severity in forest harvests

I present a three-dimensional disturbance severity model and illustrate the potential usefulness of the model for characterizing disturbance conditions caused by forest harvesting. Disturbance is most often described in terms of disturbance type, size and frequency, with less emphasis on severity. In addition, studies of disturbance impacts have emphasized the dominant tree and woody understory layers, overlooking the species-rich herbaceous layer. For a wide range of harvesting treatments (clearcutting to selection systems with and without site preparation), I characterized disturbance severity based on hypothesized patterns of canopy removal, understory vegetation removal and forest floor and soil modification. To illustrate the application of the model, I plotted the data from three studies in North American coniferous and mixed coniferous–deciduous forests in the three-dimensional diagram of disturbance severity, using actual measures of the degree of disturbance on each axis or estimates inferred from other related variables. The plotted points showed general agreement with the hypothesized ranges of disturbance severity for the treatments represented in these studies. The three axes of disturbance severity can be affected differently depending on disturbance type, emphasizing the importance of characterizing the degree of disturbance on each of these three axes. Short-term responses of the herbaceous layer are strongly influenced by disturbance severity on each of these three axes. Disturbance conditions must be quantified before vegetation indicators of these conditions can be identified. The conceptual model provides a framework for comparing forest harvesting treatments to natural disturbance events. These comparisons are critical to designing ecologically sustainable forest management strategies.     

Treefall gaps of certified,conventionally managed and natural forests as regeneration sites for Neotropical timber trees in northern Honduras

Forest certification programmes promote sustainable management of the world's forests. Certification can be given to a forest management system that fulfils certain environmental, social and economic criteria.