农田防护林采伐年龄的探讨

针对我国平原农区农田防护林建设的现状及近年来的研究成果,对防护林的数量成熟龄、工艺成熟龄、防护成熟龄、经济成熟龄进行了深入探讨,提出了各种成熟龄的确定方法。在生产实践中,农田防护林的采伐年龄应取４种成熟龄的上限,当在伐期龄不能采伐时,宁可推迟也不要提前采伐。同时,对防护林成熟的可变性、成熟龄的表示方法、林带本身对成熟龄的影响及伐期龄的应用等问题进行了讨论。     

迭部县森林资源永续利用调整方案的探讨

本文以迭部县森林资源的经济收益为主,考虑收益的时间性(利息)等因素,兼顾森林生态环境及生态效益,利用二类调查材料,采用线性规划理论,建立森林资源变化动态模型及线性方程组;利用微机求出不同调整期与轮伐期的森林调整方案,进行多方案选优,最终确定出最合理的森林调整方案,将现有的森林调整为法正林结构。     

马家庄林场用材林合理调整的可行性分析

该文针对山西管涔林局马家庄林场经营的现状,采用线性规划方法,拟合6种优化方案对其用材林进行调整。利用经济分析手段对方案综合比较,认为调整期60a,轮伐期40a 效益现值最大,即使今后木材价格下趺29.3%,仍能保本经营,而不致亏损。     

西江林场杉木的经济轮伐期

根据市场趋势调整林业经营对策,是林业生产的重要课题,而各类用材林经济轮伐期的确定则是重中之重．就此,根据西江林场近10 a来杉木用材林调查数据和有关资料,用土地纯收益法、内部收益率模型、净现值一般模型处理计算,对西江林场杉木林用材林的经济轮伐期作了初步探讨,得出杉木轮伐期为13-15 a．依此可大大缩短杉木林的经营周期,对加速资金周转,提高经营效益,解决两危问题增强林业生产积极性和活力等都有一定的作用．     

短轮伐期巨尾桉合理主伐期研究

通过对巨尾桉轮伐期为5a、6a、7a的林木蓄积量、出材量、营林成本、经济效益进行了分析比较,探讨了主伐期对经济效益的影响,以期为林场确定合理的轮伐期提供参考依据。     

综合轮伐期研讨

从分析综合轮伐期的相关因素入后，对目标综合轮伐期、期初综合轮伐期、期末综合轮伐期三者进行比较，提出未来森林资源一种设计模型，并举例进行验证。     

森林经营规划中的综合轮伐期研究

从分析综合轮伐期的相关因素入手，对目标综合轮伐期、期初综合轮伐期、期末综合轮伐期三者进行比较，提出未来森林资源利用三种设计模型，并举例进行验证。     

“分期平衡法”在编案工作中的运用──浅谈“分期平衡法”与“线性规划”

在森林经营方案的编制工作中，关于合理年伐量的确定，除了用运筹学中线性规划原理和方法，分别对各森林经营类型建立森林收获调整模型，通过模型求解，得到合理的采伐面积，既可以改善年龄结构，达到调整的目的（法正状态），保证调整期（一个轮伐期）内最大的采伐收获，即利用线性规划调整森林收获量以外，一般常用公式有轮伐期公式、成熟度公式、第一林龄公式、第二林龄公式、平均生长量公式和蓄积量结合生长量公式进行计算。这六种计算公式，在具体工作中运用时，要在理解公式适应范围的基础上，根据各个经营单位（编案单位）林分结构特…     

推荐一本好书——《杨树》专著

杨树是我国人民熟知和热爱的树种。它分布广,轮伐期短,经济上见效快。我国北部及中部大面积的防风固沙林和农田防护林,其主要树种就是杨树;平原绿化与四旁植树的重要树种也是杨树。可以说,杨树在林业建设中占有重要位置。而过去尚缺乏一部系统     

我国杨树速生丰产林合理轮伐期研究概况

通过比较分析国内有关不同立地条件、造林密度下,杨树林分平均胸径、蓄积连年生长量和蓄积年均生长量的生长变化,探讨找出在不同栽培目标和条件下,杨树林的最适轮伐期,为我国杨树林的经营和采伐管理提供科学的指导和建议。综合分析国内现有研究表明:不考虑经济效益,若以培育大径材林为目标,建议最适栽植密度可为500株/hm~2(4.0 m×5.0 m),合理轮伐期可定为10 a;若以培育中径材林为目的,建议最适栽植密度可为2 500株/hm~2(2.0 m×2.0 m),合理轮伐期可定为7 a;若以培育小径材林为目的,建议最适栽植密度可为4 444株/hm~2(1.5 m×1.5 m),合理轮伐期可定为7 a。若考虑经济效益,建议大、中、小径材的合理轮伐期可分别确定为9~11 a、6~7 a和5~7 a。同时,本文重点讨论了国内研究存在的“研究不够系统全面,指导生产实践的适用性不广”“经济效益的评价方法未统一,评价指标不一致,最适轮伐期的确定存在一定难度”“缺少对生态效益评价方面的系统研究”等3个方面的问题和建议。     

纸浆材人工林复合轮伐期的讨论

针对我国纸浆材人工林的经营现状和存在的问题,本文提出了复合轮伐期的概念。纸浆材人工林实行复合轮伐期经营的材积收获量,将比单一轮伐期经营高出20%,再加上复合轮伐期生产的大径锯材市场价格高的因素,相应的经济收益将高出更多。复合轮伐期充分利用了地力和林木生长的潜力,它不仅是纸浆材轮伐期和大径锯材轮伐期的复合,也是经营目的的复合,体现了现代林业多目标培育林木的经营原则。     

Increasing rotation periods during a time of decreasing profitability of forestry — a paradox?

The profitability of forestry in Germany decreased during recent decades because of more or less constant prices for forest products, increasing input prices and limited success in rationalisation. However, the volume of growing stock increased significantly during this period since forest enterprises have chosen longer rotation periods. This is especially true for state owned and community owned forests but also at least partly for private forests. It is normally not an alternative for the owners of forest enterprises in Germany to sell the forests completely, but on a first glance increasing investments in standing timber during a time of decreasing profitability of forestry seems to be inconsistent with economic theory. On the one hand this observation could be explained as the result of non-timber values. However, this paper is focused on another approach, which is an expanded Faustmann model in line with soil rent theory and focused on timber production. Profitable rotations in the future have the effect of shortening the optimal rotation period because an investment in standing timber causes opportunity costs by delaying the establishment of the next generation of the forest. Unprofitable future rotations have the opposite effect, if the landowner is forced to reforest. In case investments in reforestations are not profitable decision-makers have good reasons not to cut the mature stands, in spite of the fact that the internal rates of return of investments in standing timber are low in comparison with investments on the financial market. Empirical data for the period 1954–1998 mostly from guidelines for forest valuation are used together with inflation corrected interest rates to show that optimal rotation length increased over time. Nevertheless we have to recognise that the observed rotation periods are distinctly longer than the calculated optimal rotation lengths. Other factors which may also explain the investments in forestry are discussed later.     

A modeling analysis of the interaction between forest age and forest responsiveness to increasing CO2 concentration

Typically, forests have rotations of 10-200 years. On that time scale, anthropogenic increases in atmospheric carbon dioxide concentration ([CO2]) and the associated changes in climate are expected to be substantial. These changes will, therefore, almost certainly affect the growth of presently established forest stands. Most studies on the effects of increasing [CO2] on tree growth have been made with young plants. However, the growth of trees within a forest stand varies with age. As a consequence, it is difficult to infer from the available experimental data how rising [CO2] will affect forest productivity over a full rotation. In this study, various mechanisms that may account for the slowing of forest growth with age were introduced into the forest growth model CenW, to assess how these processes affect the modeled growth response to increasing [CO2]. Inclusion of allocation shifts with tree height, individual tree mortality, changing respiration load and nutrient dynamics or age-based reductions in photosynthetic capacity had only small effects on the response to increasing [CO2]. However, when photosynthesis of mature trees was decreased as a function of size, then the growth response to increasing [CO2] was reduced because, at the same age, trees were larger in elevated than in ambient [CO2]. No simple and generally valid interactions between increasing [CO2] and forest age were identified because of the large number of interacting processes, all of which are incompletely understood. Important age x climate change interactions on productivity must occur in real forests and need to be considered to understand likely future trends. However, these interactions are complex and difficult to test. It is therefore not yet possible to predict with confidence the modification of the CO2 response by forest age.     

Determination of optimal rotation period for management of lumbering forests in Kenya

This study estimates the optimal rotation period of various tree species in Kenya and applies it in the management of lumbering forests through optimal synchronization of forest plantations to achieve a steady supply to lumbering firms. The optimal rotation period of three tree species, pine, cypress, and eucalyptus, was estimated using data from Kenya Forest Service. A combined application of Chang simple production model and ? Faustmann? model? reveals the optimal biological harvest age is 25 years for pine, 25 years for cypress, and 14 years for eucalyptus. However, introducing the prices and using the Faustmann optimal rotation model at the current market interest rate of 10.5%, the Faustmann rotation age for pine stand will be maximized at 12.67 years, cypress at 23.5 years, and eucalyptus at 38.4 years. The research further indicates significant variability in land expectation value and soil rent of various species and proposes an inclusion of “species” as a variable in forest land valuation. In the conclusion, nonmarket factors affecting the optimal yield were further explained and recommendations on sustainable yield production were suggested.     

Ground-dwelling invertebrates in reforested conifer plantations

Plantation forests are an important part of the forest estate in many countries. In Ireland, they cover around 9% of the land area and many that are commercially mature are now being felled and reforested. The potential biodiversity value of such second rotation forests has yet to be determined, yet this may be particularly significant in Ireland where cover of semi-natural woodland is only 1%. Invertebrates are a vital component of forest biodiversity, functioning as decomposers and pollinators, herbivores, predators and prey. Spiders and Carabid beetles are often used in biodiversity assessment as they are easily captured using pitfall traps, are taxonomically well known and respond to changes in habitat structure. This study aimed to examine spider and Carabid beetle diversity in second rotation Sitka spruce (Picea sitchensis) plantations at different stages of the forest cycle (5, 8–12, 20–30, 35–50 years), and compare the spiders captured in second rotation forests with those from first rotation. Spider and beetle diversity was influenced by stand structural development in second rotation plantations with numbers of forest-associated species increasing over the forest cycle. Overall, spider richness declined over the forest cycle and this was related to decreasing cover of field layer vegetation and fewer open-associated species. In contrast, total beetle richness increased and became more specialised over the forest cycle which may be related to slower colonisation of disturbed areas by beetles in comparison with spiders, and fewer open specialists at the early stages of second rotation. Spider assemblages were distinguished between rotations. This may be related to differing habitat conditions in second rotation forests including dryer soils with lower pH, differing vegetation complexity and presence of brush piles. Few of the forest species accumulated during first rotation were retained and the early stages of second rotation forest cycle was characterised by a generalist open fauna. Nonetheless, as the forest cycle progressed the spider assemblages between rotations became more similar. Current forest policy supports retaining over-mature trees and creating a mosaic of different aged stands within a plantation. Such measures may provide refuge for forest species after clearfell. In countries where forest fragments exist in a landscape dominated by agriculture, consideration should be given to the capacity of mature forest adjacent to felled stands to support forest species, and to the configuration of over-mature areas retained after felling.     

Long-term effects of establishment practices on plant communities across successive rotations in a loblolly pine (Pinus taeda) plantation

Implementation of repeated, high-intensity short rotations in forest plantations raises concerns about the effects of such practices on herbaceous layer biodiversity and overall sustainability. To investigate these concerns, we conducted a comparative study of second and third rotation plant communities in a loblolly pine plantation in the Piedmont of North Carolina. The second rotation stand was established in 1960 using conventional practices and was harvested in 1981, leaving two plots in each of three blocks as “historical” plots representing the second rotation. The third rotation was planted in 1982, and a 2 × 2 factorial experiment was established within an area that had been complete-tree harvested, using two site preparation (drum-chop versus shear, pile, and disk) and two cultural (vegetation control versus no vegetation control) treatments in each of three blocks. Presence/absence data for vascular plant taxa were collected in the second rotation historical plots at year 22 and also in the third rotation treatment plots at year 18 and analyzed using non-metric multidimensional scaling (NMDS) ordination, indicator species analysis, analysis of species richness, and computation of species turnover. Results indicated overall similarities in the herbaceous layer from year 22 in the second rotation to year 18 in the third rotation, while revealing some key differences in species composition, including persistence of disturbance-responsive species associated with the vegetation control treatment in the third rotation plots. The addition of these species largely accounted for an increase in species richness from the second to the third rotation. Species composition in low intensity third rotation plots (chop, no vegetation control) most closely resembled that of the second rotation plots of similar age. In addition, differences in species composition due to soil and topographic differences within the study persisted through both rotations, while compositional effects of treatments implemented at the beginning of the third rotation diminished with time. We conclude that more intensive silvicultural practices, such as site preparation and vegetation control, reduce initial competition from woody species and thus permit the persistence of early successional species, increasing overall diversity. From the larger perspective of the entire study, the second and third rotation stands converged to similar species composition after approximately two decades post-planting despite early treatment-related differences in the third rotation. It remains to be seen whether additional harvests, rotations, and intensive practices will continue to support a functioning understory plant community in these short rotation plantation forests.     

The impact of landscape design planning on the timber production and financial outputs of a forest plantation in Ireland

Significant expansion has occurred in Ireland's forest estate since the 1950s. However, the design of the monocultural plantations established in the 1950s and 60s is now considered insensitive to local landscapes and re-design intervention and transformation is needed to improve integration into the environment. This case study was carried out in Laracus forest, Co. Donegal. The rotation of all stands in this 581-ha property has reached the final production phase, with coupes scheduled for clearfelling from 2003 to 2015. The implications of forest re-design for both the volume production in the current rotation and the financial return of the current and subsequent rotations were examined. Results indicated a volume loss due to design planning for the current rotation of 5.6% compared to the volume produced under the standard regime. In financial terms, this represents a loss of 4.6%. For the subsequent rotation, a significant financial gain of 22% in net present value was achieved as a result of redesigning the plantation. The overall financial out-turn for the property, when both the current and subsequent rotations were considered, was a 3.4% lower net present value for the design plan than for the standard regime. This result represents a lower impact of design planning in Laracus than most other forest restructuring studies have reported.     

合理利用森林土壤资源提高森林土壤生产力的研究

论述了世界范围内森林土壤资源被破坏、人工林地力衰退、产量逐代下降,严重地威胁着人类对有限的森林土壤资源的永续利用、引起广大林业工作者普遍关注的状况。阐述了维护、恢复森林土壤功能,合理地利用森林土壤资源,提高森林土壤生产力的途径。     

Wood Production Potentials of Fenno-Scandinavian Forests Under Nature-Orientated Management

In Finland, Norway and Sweden forest management is presently changing towards a more nature-orientated management. In this study the European Forest Information SCENario (EFISCEN) model was applied to determine how this change might affect the potential for wood production in the three countries. Three different management regimes, traditional, traditional with nature conservation (''conservation''), and longer rotations with nature conservation (''conservation +''), were combined with two alternative felling levels. The results show that conserving 6.1-8.8% of the older forests in the southern regions had no limiting effects on production levels, as foreseen by the European Timber Trend Studies V by the UN-ECE for Finland and Sweden. Under the conservation + scenario, maximum sustainable felling levels decreased to 84, 79 and 72% of the present levels in Finland, Norway and Sweden, respectively. Increasing the rotation length put more pressure on the older age classes and thus did not increase the average age of the forest. If the consumption of wood increases as quickly as indicated by other studies, it will be hard to fulfil that demand and at the same time conserve considerable areas of forest in the southern regions of the countries.     

A model of carbon storage in forests and forest products

This paper discusses the general formulation of a model that describes carbon storage in a forest and its timber products as a function of the forest growth curve, the rotation period and the carbon retention curves for the timber products. After a number of rotations, the rotation-averaged quantity of stored carbon approaches an asymptotic value. It is shown that, when forests are managed for maximum sustained yield of biomass, the contribution to asymptotic carbon storage from timber products is about 2.5D/T* times the contribution from living trees, where D is the characteristic decay time for reconversion of timber products to carbon dioxide, and T* is the normal rotation period for maximum sustained yield. For a given value of D/T*, carbon storage can be optimized if the policy of maximizing sustained yield is relaxed. For D/T* < 1, as the rotation period is increased indefinitely, the asymptotic level of carbon storage increases monotonically toward the value of the carbon content of living trees at maturity, g(f). For D/T* > 1, there is a finite, optimal rotation period, T(o), greater than T*, for which asymptotic carbon storage is greater than g(f). As D/T* tends to large values, however, T(o) tends to T*, so that, in this limit, management for maximum sustained yield also ensures maximum carbon storage. From initial planting, the time taken to reach asymptotic carbon storage decreases as the normal rotation period, T*, decreases, but increases almost linearly with increasing decay time of timber products, D. This result qualifies the short-term value of any particular planting strategy.