第六讲(二)轮伐期

轮伐期是表示林业生产周期的一种方式。具体地说就是用材林中采取皆伐或伐区式渐伐的经营单位进行永续利用的生产周期。所以,凡是采用皆伐或伐区式渐伐的经营类型,都要确定轮伐期。对于理想的法正林(即各龄级的森林面积相等)来说,轮伐期就是森林成熟龄,或叫森林主伐年令。     

大兴安岭林区森林主伐方式的探讨

本文通过对大兴安岭林区森林植被结构特征,建群树种的更新特点的分析和对正在施行的各主伐方式效果的评价,认为带状间隔皆伐和二次渐伐适于本林区森林结构及更新特点,而择伐不适用,应加以限制。     

周恩来的林业观

近段时间，笔者通过阅读《周恩来选集》、《周恩来经济文选》等一些著作，深入领会周恩来总理在60年代调整时期就伐林与育林问题的几次重要讲话，受益非浅。我国林业既要解决森林覆盖率低与生态环境差的问题，又要解决木材资源有限与国民经济发展需要大量木材的问题。周恩来针对二者之间的矛盾，提出了“伐木与育林，重点放在育林”，越伐越多，越多越伐，青山常在，永续作业的林业发展方针。周恩来认为，国民经济发展迫切需要木材，不采伐是不行的；没有木材，钢、煤、矿都上不去。但是，采伐必须同育林相结合，不能多于育林。“用剃光头的…     

经营性大强度渐伐

经营性大强度渐伐是在经营性采伐的基础上,为了维护森林的生态效益和森林的景观,促进天然更新,同时获取年平均单位面积的最大经济收入,采取的强度较大的渐伐方法。渐伐是在山区的人工林中进行,加大了渐伐强度,减少了渐伐次数,维持了森林的生态效益和森林景观。     

适合渐伐的林分

采伐与更新是森林经营的重要内容,采用的方式也是经营合理与否的最主要指标。建国三十多年来,我国森林采伐基本上只采用了大面积皆伐和择伐。这种状况很不适应我国广阔的地域,繁多的森林类型和材种类型。本译文介绍的渐伐,在国外正广泛地应用。这对某些(特别是阳性) 树种的天然更新,对保护森林环境及发挥森林防护效益有着极为重要的意义。在我国也有很多森林类型,像云冷杉林,落叶松林,红松林等也都可以考虑应用渐伐。     

四不象伐区的形成和改造

“四不象”伐区的由来从森林经理学来讲,根本没有“四不象”这个术语。所谓“四不象”实际是有的林区在多年的木材生产过程中不重视科学,不按采伐方式办事,只凭“长官意志”搞“自由伐”或“随便伐”的产物。它既不象择伐,又不象渐伐,更不是采育兼顾伐,似乎是皆伐又不是皆伐的一种残破伐区。群众称之为“四不象”伐区。     

森林主伐与更新的关系

文章主要阐述了森林主伐方式有皆伐、渐伐、择伐,分别不同方式加以论述森林主伐与更新的关系,主要有皆伐迹地更新、渐伐迹地更新和择伐迹地更新。     

世界主要林业国家山区林区木材采运工业发展趋势

据1971年世界主要林业国家山区林区木材采运国际学术讨论会发表的论文和介绍的情况,简介世界主要林业国家山区林区木材采运工业的发展趋势如下。一、采伐方式西欧国家,由于没有原始的成过熟林,因此,森林经营都是小规模的,以永续利用为原则。采伐方式有皆伐、群状择伐、择伐和渐伐等。趋于用精选苗人工更新。美国、加拿大和日本等国家,基本上采用皆伐方式,然后进行机械更新。二、集材方式坡度在25°以下时,一般采用带绞盘机或液压抓钩的轮式或履带式拖拉机原条集材。同时,配备大功率的推土机,舖设集材道和运材岔线。     

渐伐和择伐对土壤酶活性的影响

为研究和论证鸟克兰西部地区最适当的采伐方式,在伊凡诺——弗兰科夫斯克林场木材采伐作业区(里沃夫地区),进行了营林、植物、气象、水文和土壤方面的研究。在分析土壤物理化学特性的同时,确定了林中枯枝落叶层,对照地,二次带状下种渐伐和三次群状择伐作业区的土壤生物活性。渐伐是在冬季进行的,第二次渐伐是在第一次渐伐后经过5年进行的。对照地未渐伐。在第二次带状下种渐伐作业区,     

汪清林业局采育林经营技术

本文对汪清林业局采育林经营技术进行了分析,结果表明:自对天然异龄林实施采育择伐经营技术以来,使经营区的森林覆盖率逐年提高,由1966年的66.60%,上升为2007年的95.95%;采育林生长量6.240 m3.hm-2.a-1,比全局经营林分的平均生长量高出1.650 m3.hm-2.a-1;改善了林分结构,红松、云冷杉、紫椴、水曲柳等主要建群种的比例逐年增加,促进了森林顶级群落的恢复,实现了"青山常在,永续利用"的森林经营目标。     

Establishment of the Second Rotation in the Jutland Heath Plantations

The paper describes briefly the silvicultural methods used toregenerate stands of pure Norway spruce (Picea abies Karst.)or Norway spruce mixed with a small proportion of Silver fir(Abies alba Mill.) on the poor heath soils of Jutland. Regenerationafter clear felling, uniform shelterwood, and shelterwood stripfelling is described. The last method has advantages over theother two.     

Water and element fluxes during the regeneration of Norway spruce with European beech: Effects of shelterwood-cut and clear-cut

The regeneration of mature Norway spruce with European beech using the shelterwood silvicultural system is a good example of continuous cover forestry. In contrast, the regeneration may also start with clear-cut plots, which often occur after calamities like wind-throw or bark beetle attack. During regeneration the forest ecosystem becomes a highly dynamic system. Nutrient losses from the soil may occur as the element turnover is affected by the reduced nutrient uptake of forest trees as well as the enhanced mineralisation and nitrification due to higher soil temperature and soil moisture. Continuous cover forestry may help to reduce these nutrient losses. In order to test this, we investigated water and element fluxes of two chronosequences. The first investigated regeneration in the shelterwood system, while the second concerned itself with regeneration on clear-cut plots. In a shelterwood-cut about 30% of the mature spruce trees are removed and young beech trees are planted. Some 10 years later a secondary felling is carried out and at age 20 of the beech regeneration the final harvest of the mature trees occurs. Thus, the studied time steps were (a) the first 5 years after the initial cut and planting, (b) 10-year-old beech regeneration after the second shelterwood cut and (c) 20-year-old beech regeneration after the final harvest.Our results indicate that nutrient losses with seepage water – especially nitrogen, calcium and magnesium – occur during the first years after the clear cut and, to a lesser extent, after secondary felling on the selective-cut plot. This may temporarily affect seepage water quality due to elevated nitrate concentrations, which reached values of more than 100 mg l⁻¹. In the time span between planting and an age 20 of the beech regeneration, total losses of nitrogen from the main rooting zone reach 230 kg ha⁻¹ after clear cut. Preliminary estimates of the total nitrogen loss in the shelterwood system range between 150 and 230 kg ha⁻¹ indicating either significantly lower or equal losses of nutrients. In the second case, however, element output is distributed more equally over the 20-year-period than after clear felling where 85% of the nitrate leaching occurs during the first 3 years.     

Dynamics of ecosystem services in <Emphasis Type="Italic">Pinus sylvestris</Emphasis> stands under different managements and site quality classes

Timber and biodiversity are considered two antagonistic ecosystem services (ES), largely influenced by silviculture and site ecological conditions. In order to address the trade-offs between these two ES over time, we performed a retrospective study at compartment level in the Pinus sylvestris forests of the Spanish Central Mountain System. Archival data from Management Plans for eight forests with contrasting silvicultural systems (uniform shelterwood system, group shelterwood system, irregular shelterwood system,) and three different site quality classes were analysed. Timber production was assessed through stand volume, harvested timber volume and a stand volume index. Biodiversity was examined through structural diversity (Gini index, Shannon tree size diversity index, Simpson’s reciprocal index and evenness index, all applied to diameter classes) and the abundance of large living trees. For all silvicultural systems investigated, stand volume and harvested timber volume have grown since the beginning of the management plans (beginning of the twentieth century in some forests). The largest yields of timber corresponded to the best quality sites with more intensive silvicultural treatments (uniform and group shelterwood systems). The uniform shelterwood system showed lower figures for structural diversity, though not always significant. The best site qualities maintained notable structural diversity values, even under the most intensive management system. The application of the different management systems over decades has revealed a synergy between timber production and structural diversity, particularly in those systems maintaining more than one age class, although results are conditioned by forest harvesting history. The interaction between historical silvicultural treatment and site quality has been identified as an important source of information to understand forest dynamics and functioning of ES provision.     

The relationship between shelterwood cuts and crown thinnings and the abundance and distribution of birds in a southern New England forest

Forest regeneration methods such as shelterwood treatments have been shown to substantially increase the diversity of bird species, specifically of species that prefer early seral forests, now rare in the eastern United States. Stand improvement techniques such as thinnings have also been found to increase avian diversity under some conditions. A sustainably managed forest, however, must simultaneously apply regenerative harvesting with stand improvements, and the effect of such treatment combinations on bird community composition is not clear. We compared bird distribution and abundance on shelterwood cuts, crown thinnings, and unmanaged stands at the Yale Myers Forest, a large privately owned and actively managed forest in southern New England. Bird abundance and species diversity was highest in shelterwood cuts and lowest in unmanaged forest, with thinnings being intermediary. Different suites of species inhabited the three treatments, with 18 of 49 common species differing significantly in their abundances between treatments. Characteristics of the vegetation that were directly influenced by silvicultural intervention, including canopy openness, seedling regeneration and vertical structural diversity, appeared to be the dominant drivers of bird abundance. The abundances of some species or groups of species were correlated with the number of trees retained in the implementation of the forestry practices. In conjunction with the conservation of a variety of mature forest habitats, regenerative cuts and stand improvement techniques can be used together to sustain a diverse assemblage of bird species.     

Recruitment of tree species in mixed selection and irregular shelterwood forest stands

Context

Recruitment is an important process in forest stand dynamics, especially in uneven-aged stands. Continuous recruitment is a prerequisite for diverse, uneven-aged silvicultural systems, but patterns may vary significantly.

Aims

The main goals of the study were to examine the recruitment of the main tree species in selection and irregular shelterwood stands in silver fir?CEuropean beech?CNorway spruce forests and to determine the main predictors of the recruitment occurrence.

Methods

Data from 5,486 permanent inventory plots were used to study recruitment of saplings into the tree layer (diameter at breast height ??10?cm).

Results

Recruitment rate differed significantly between selection (7.6?trees?ha^?1?year^?1) and irregular shelterwood (26.1?trees?ha^?1?year^?1) stands. Shade-tolerant fir and beech recruited with higher probability in selection stands, while light-dependent sycamore recruited with higher probability in irregular stands. In addition, forest types, soil pH, stand basal area, mean diameter, and the basal area of the same tree species with respect to recruitment were found to be important predictors of recruitment occurrence.

Conclusions

The application of different uneven-aged silvicultural systems and their forms makes it possible to considerably influence the future tree species composition of uneven-aged forests.     

Managing forest complexity through application of disturbance–recovery knowledge in development of silvicultural systems and ecological rehabilitation in natural forest systems in Africa

How can we accommodate the diversity in tree species and sizes in mixed-species/size/age stands in the sustainable management of natural forests and woodlands in Africa for diverse timber and non-timber forest products and services, and during rehabilitation of degraded forests? The evergreen moist tropical to warm-temperate forests, from the equator to 34°S, generally function through relative shade tolerance. The tropical, strongly seasonal, drier deciduous woodlands generally function through adaptation to fire and/or grazing/browsing. Silvicultural systems, when implemented, are often not aligned with the ecological characteristics of the particular forest systems or the specific targeted species. This paper presents the concept of using the basic disturbance–recovery processes, with recovery development via stand development stages, as the basis for the development of silvicultural systems suitable for maintenance of forest complexity. Grain analysis and stem diameter distributions, analysed from resource inventories, are used to determine the specific shade- or fire-tolerance characteristics of key economical and ecological tree species. The gained knowledge of the ecosystem and species characteristics (including modes of regeneration, i.e. from seed or vegetative regrowth) and processes is used to simulate the ecological disturbance–recovery processes through the development of mixed silvicultural systems, such as a single-tree selection system, a group felling system and a coppice management system in the same forest. Very similar concepts are used to develop rehabilitation strategies to recover the processes towards regrowth stands of diverse species and structure: through stands of introduced plantations and invader tree species; and through early regrowth stages in deciduous woodlands and evergreen forests, after fire, slash-and-burn traditional agriculture, charcoal production or open-cast mining.     

Comparative mast seed production in unmanaged and shelterwood white pine (Pinus strobus L.) stands in central Ontario

The effect of the seed cut of the uniform shelterwood silvicultural system on white pine seed production, seed characteristics, and seed viability during 2 mast seeding events was examined in operationally harvested second growth, white pine-dominated forest stands in central Ontario. Seed traps placed along transects in unmanaged and shelterwood stands in each of 3 blocks were used to monitor seed production in 2000 and 2006 (4 and 10 years after harvesting). During these 2 mast seed years between 386,000 and 2,730,600 seed ha^?1 were produced among study stands. Total seed production expressed on a per hectare and unit pine basal area basis did not differ by harvest treatment or among blocks in either year. Variability in seed production among stands was primarily due to differences in stand structure, with seed production positively related to white pine basal area. Seed characteristics were largely similar between harvested and unmanaged stands and between seed years. Seed viability was relatively high in both years, with seed from shelterwoods germinating slightly slower than those from unmanaged stands. Seed quality, as estimated by laboratory germination performance, was higher in 2006 than 2000, likely due to improved seed development and maturation in the warmer, wetter growing season of 2006. Our results suggest that the seed cut of the uniform shelterwood system applied to second growth white pine stands is unlikely to adversely affect white pine seed production, seed quality, or potential for natural regeneration during mast seeding events.     

Long-term development of soil organic carbon and nitrogen stocks after shelterwood- and clear-cutting in a mountain forest in the Bavarian Limestone Alps

Forest soils store large stocks of soil organic matter (SOM) and are of vital importance for the ecosystem supply with nutrients and water. According to the available literature, depending on management regime and site properties, different negative and positive effects of forest management (particularly of forest thinnings and shelterwood cuttings) on soil organic carbon (SOC) and nitrogen (N) stocks are observed. To elucidate the long-term impact of different shelterwood systems and small clear-cuttings on the OC and N stocks of shallow calcareous soils in the Bavarian Alps, we conducted soil humus inventories on different plots of a mixed mountain forest management experiment started in 1976. The silvicultural multi-treatment experiment consists of a NW-exposed Main Experiment (ME) site with eight plots of different cutting intensity (two unthinned controls, two light shelterwood cuttings = 30 % of basal tree area removed, two heavy shelterwood cuttings = 50 % removed, and two clear-cuttings = 100 % removed) on Triassic dolostone. Additionally, plots were installed at a N-exposed dolostone (ND) site and two sites (FL, FH) on Flysch sandstone (each with one unthinned control and one heavy shelterwood cutting). The shelterwood cuttings from 1976 were repeated in 2003 to re-establish the overstorey basal area as produced by the first cutting in the different plots. Thirty-five years after the first treatments, forest floor SOC and N stocks were significantly decreased (up to ?70 %) at the different shelterwood and clear-cut treatments compared to the unthinned control at the ME site despite vigorous development of natural rejuvenation. Also significantly smaller topsoil (forest floor plus mineral soil 0–10 cm depth) OC stocks (between ?16 and ?20 %) were detected at the thinned compared to the control plots. Differences in topsoil N stocks were also considerable (between ?3 and ?14 %), but substantially smaller than OC stock changes. For the total soil down to 30 cm depth, OC stocks in the differently thinned plots were consistently smaller compared to the unthinned control plots. Comparable to our findings at the ME site, heavy shelterwood plots at the three other sites (ND, FL, and FH) showed significant losses of OC in the forest floor (up to 43 %), mineral soil (up to 38 %), topsoil (up to 38 %), and total soil (up to 34 %). Significant large absolute and relative SOC decreases coincided with sites characterized by large initial humus stocks. Moreover, significant effects of heavy shelterwood cuttings on SOC and N stocks (on average 23 % SOC loss and 13 % soil N loss for the forest floor plus the uppermost 10 cm mineral soil) were detected on a regional level. Our results show that different shelterwood systems are accompanied with a considerable long-term decrease in OC and N stocks in shallow calcareous forest soils of the Bavarian Alps. However, a comparison with a windthrown forest stand at a nearby similar site indicates that SOM losses after thinning operations are small compared to decreases following windthrow or other calamities with subsequent large soil erosion and increased mineralization processes.     

Harvesting intensity versus sustainability in Indonesia

In East Kalimantan (Indonesia), impacts of conventional (CNV) and reduced-impact logging (RIL) on forest ecosystems were compared on the basis of pre- and post-harvesting stand inventories. There was a positive and significant correlation between the proportion of trees damaged by felling and the density of trees felled. Logging intensity ranged from 1 to 17 trees ha⁻¹(9–247 m³ ha⁻¹) and averaged 9 trees ha⁻¹ (86.9 m³ ha⁻¹). The study has shown that with RIL techniques, logging damage on the original stand can be significantly reduced by 50% compared with conventional logging. However, this 50% reduction in logging damage, was dependent on the felling intensity. With a felling intensity of 8 stems ha⁻¹ or less, RIL techniques only damaged 25% of the original tree population whereas 48% were damaged with conventional techniques. Above this felling intensity (i.e. 8 stems ha⁻¹), the effectiveness of RIL in limiting forest damage was significantly reduced, mainly because of the increasing felling damage. Moreover, the removal of all harvestable timber trees, leaving only few potential crop trees, will result in a seriously depleted residual stand. Because of the high damage involved by high felling intensity, leaving few potential crop trees, and the yield capacity of the remaining stand, acceptable harvesting volume will not be reached within the felling rotation of 35 years. It is concluded that silvicultural system based on diameter limit alone, as is the Indonesian system (TPTI), cannot be compatible with sustainability and more sophisticated harvested-selection rules are needed.     

木麻黄防护林持续经营问题初探

木麻黄无性系造林 ,林分密度管理 ,低效林改造 ,抚育间伐技术 ,更新技术等是影响木麻黄防护林持续经营的主要因素。实施生态系统管理 ,采取营造木麻黄混交林、林木施肥等营林技术措施是木麻黄防护林持续经营的主要途径