适应价格的用材林主伐决策模型的研究

本文研究了木材价格的变化为一自相关随机过程时用材林采伐的随机决策分析问题,分析了用材林经营决策中的不确定性因素及其对经营决策的影响,建立了一个针对主伐的木材市场价格随机变动的适应价格的主伐决策模型,利用动态规划求得在一个给定决策期内的主伐最优经营策略,对应这个策略有一个最大的期望效益。并进一步分析了在价格波动情况下和不同贷款利率下的最优策略。     

Optimal forest stock and harvest with valuing non-timber benefits: a case of US coniferous forests

How much to cut and to remain, as well as when to cut is an important decision-making issue in forest management. Unlike forest age, forest stock and harvest levels are applicable to both plantations and natural forests. This paper investigates the optimal forest stock and harvest with the consideration of both timber and non-timber benefits. The impacts of the discount rate, silvicultural cost, marginal timber benefit, and marginal non-timber benefit on the optimal forest stock and harvest are also examined. The results indicate that forest stock should be thickened when non-timber benefits are valued in addition to timber. The optimal steady state stock increases with a decrease in the discount rate, or an increase in marginal non-timber benefit. However, the impacts of the discount rate, marginal timber benefit, and marginal non-timber benefit on the optimal steady state harvest are ambiguous. In addition, a decrease in the discount rate has the same effect on the optimal steady state stock and harvest as an increase in the ratio of marginal non-timber benefit to marginal timber benefit. These theoretical results are illustrated through an empirical example of the US coniferous forests.     

基于最优轮伐期模型的超限额采伐现象及其约束机制分析

文中将最优轮伐期模型应用于对超限额采伐现象的研究,认为由于国有森工企业的利润大多来自于木材销售收入,而企业领导的任期是有限的,他们只关心自己任期内的业绩,导致企业经营的目标实际上是短期木材收益的最大化,而不是我们所期待的可持续木材与生态综合收益最大化,甚至也不是私人拥有森林时所追求的长期木材收益的最大化。他们会设法突破政府设定的采伐限额,增加采伐量,造成森林资源加速衰退的不良后果,不仅生态功能迅速萎缩,木材产量也无法长期维持下去。同样的情形在国有林场短期租赁给私人经营时也极易发生。为尽量杜绝这种现象,有必要通过建立有效的监督和惩罚机制使超采所带来的额外收益小于被发现时上缴罚款的数学期望值,以此从根本上遏制住企业超限额采伐的动机。     

An interactive multiobjective approach to harvest decisions in forest planning

A hierarchical approach to forest planning is formulated, where harvest schedules are first determined, followed by a decision about harvest methods (harvest regime). Choice of harvest methods is particularly important because of concerns about harvest‐related site disturbance. In the decision model developed in this article, determination of a harvest regime is expressed as a multiple‐objective decision incorporating maximization of net present value and minimization of cumulative site disturbance for different site classes, subject to maintaining high levels of production, an even flow of timber, and avoiding adjacency violations. The search for preferred harvest regimes is performed interactively over a set of non‐dominated harvest schedules with alternative aspiration levels identified for the various objectives to reflect values of different stakeholders.     

A simulation model for economic analysis of timber/forage production alternatives in rocky mountain aspen stands

A simulation model was developed to analyze possibilities for timber and forage joint production in Rocky Mountain aspen stands. Given harvest possibilities from timber yield tables and information concerning site characteristics, the model calculates the physical production levels for timber and forage, and then uses these figures to make an economic analysis based on present net worth and financial maturity criteria. The model was applied to different sets of sites, harvest possibilities, and costs and revenues. The results indicated that the optimal joint production strategy varies with the economic criterion, the discount rate and harvest strategy.     

Private forest investment and long-run sustainable harvest volumes

Private timberlands in the United States have the biological potential to provide larger quantities of timber on a sustainable basis than they do today. Most opportunities for increasing growth and harvest lie on nonindustrial private lands in the South. Past studies, based on fixed scenarios of future prices, also suggest that many of these opportunities for intensified management can be undertaken with positive economic returns. Translation of these physical and apparent economic potentials into projections of future management and harvest requires a model of private timber management investment behavior. This study examines the dynamics of investment in private forest management according to a model of timber markets and timber supply in which intertemporal levels of private investment, harvest, and timber prices are all endogenous. The results of this model are used to examine the extent and types of possible future private management investments and how these will affect timber supply. In addition, the sensitivity of these projections to variations in key market and behavioral determinants is examined through simulation of alternative scenarios involving reduced public timber harvest and constraints on planting investment of nonindustrial private owners.The base case illustrates the substantial potential of timberlands for increased growth and harvest. This requires, however, investments in planting well beyond those observed in recent years. Given this, the area in planted forests would almost triple within the next 30 years. Expanded investment would allow immediate increases in timber harvest and sustained increases in timber inventory, with virtually no trend in softwood log prices. Projected increases in plantation area would concentrate timber production on fewer hectares, with more hectares managed passively. Naturally regenerated forests in the future would cover at least three-quarters of the private timberland area, with hardwoods continuing to dominate. Restricting nonindustrial private plantation investment to levels observed in the recent past markedly alters projections for softwoods, thus raising prices and reducing timber harvest relative to the base case across the full projection period. In contrast, reductions in public timber harvest alone result in increased prices and reduced total cut in the near term, but have limited impact on the outlook three-five decades hence, because private investment effectively compensates for public timber harvest reductions.     

Snag density varies with intensity of timber harvest and human access

Many species of vertebrates depend on snags (standing dead trees) for persistence, and limited research suggests that snag density is lower in areas of intensive timber harvest and increased human access. While intensive timber harvest is one source of potential snag loss, ease of human access to forest stands may also facilitate loss via firewood cutting of snags. Accordingly, we hypothesized that density of snags (number of snags/ha) would decline in forest stands with increasing intensity of timber harvest and increasing ease of human access. We tested our hypothesis by sampling stands under varying levels of timber harvest and access on National Forest land in the northwestern United States. Stands with no history of timber harvest had 3 times the density of snags as stands selectively harvested, and 19 times the density as stands having undergone complete harvest. Stands not adjacent to roads had almost 3 times the density of snags as stands adjacent to roads. Unharvested stands adjacent to non-federal lands and closer to towns had lower snag density, as did stands with flat terrain in relation to nearest road. Our findings demonstrate that timber harvest and human access can have substantial effects on snag density. Meeting snag objectives for wildlife will require careful planning and effective mitigations as part of management of timber harvest and human access.     

Selective Logging and Regeneration of Timber Species in the Maya Biosphere Reserve in Guatemala

This study explores the regeneration of 12 selected timber species within an area of selective logging in a neotropical rainforest in Guatemala. A part of the Maya Biosphere Reserve, in which timber harvest is performed by the cooperative Unión Maya Itzá, makes up the study area. We report the results of an inventory of 12 species over an area of 300 ha and detailed recording of saplings and seedlings for 10 selected timber species in five 1-ha plots. In the latter, characteristics of gaps (gap size and location, and vegetation cover) were also recorded. The recorded density of timber seedlings and saplings in the study area was low. The low present density of future harvestable timber species suggests that the total volume of harvested trees will decline from harvest to harvest in the future if an interval between subsequent logging events of 25 yr is used and if the logging intensity prescribed by the current management plan is upheld. Measures needed for forestry in this region to be sustainable are discussed.     

Financial optimisation of target diameter harvest of European beech (Fagus sylvatica) considering the risk of decrease of timber quality due to red heartwood

A mature, average stand of European beech was generated based on characteristic data of trial plots. Some 27 different strategies of target diameter harvest, were simulated for up to 80 years with the help of a distance-dependent single-tree growth simulator. The treatments were differing in the size of the target diameter, the beginning and the end of the harvest. Based on a statistical model, the probability of the occurrence of more than 30% of red heartwood at the front-side diameter was calculated for three sections of each log. Using the predicted probability, the decrease of timber quality due to red heartwood for different treatment strategies was assessed. The harvested volume and the predicted timber quality for different harvesting strategies were used to calculate the net revenue achieved in each simulation period with the help of a calculation program. The net present value for variable interest rates of the different harvesting strategies was calculated, assuming free land rent. Using a linear programming approach, optimal areas for different treatment strategies of a modelled forest of 100 ha were calculated under 4 different scenarios. The results of the optimisation showed how the increasing interest rates replaced higher target diameters out of the optimal solution. In contrast to that the treatments with higher target diameter became more important with increasing restrictions concerning budget or ecological constraints.     

Evaluation of forest management systems under risk of wildfire

We evaluate the economic efficiency of even- and uneven-aged management systems under risk of wildfire. The management problems are formulated for a mixed-conifer stand and approximations of the optimal solutions are obtained using simulation optimization. The Northern Idaho variant of the Forest Vegetation Simulator and its Fire and Fuels Extension is used to predict stand growth and fire effects. Interest rate and fire risk are found to be critical determinants of the superior stand management system and timber supply. Uneven-aged management is superior with higher interest rates with or without fire risk. Alterations in the interest rate affect optimal stocking levels of uneven-aged stands, but have only minor effects on the long-run timber supply. Higher interest rates reduce rotation length and regeneration investments of even-aged stands, which lead to markedly reduced timber supply. Increasing fire risk increases the relative efficiency of even-aged management because a single age cohort is less susceptible to fire damage over the course of the rotation than multiple cohorts in uneven-aged stands. Higher fire risk reduces optimal diameter limit under uneven-aged management and decreases optimal rotation length and planting density under even-aged management.     

Efficiency of Iranian forest industry based on DEA models

Data Envelopment Analysis (DEA) is a mathematical tech-nique to assess relative efficiencies of decision making units (DMUs). The efficiency of 14 Iranian forest companies and forest management units w...     

Population dynamic and management of <Emphasis Type="Italic">Pinus oocarpa</Emphasis> and <Emphasis Type="Italic">Tabebuia rosea</Emphasis> within silvopastoral systems in Central America

Silvopastoral systems—the management of trees within pastures from natural regeneration or planting—are a strategy to promote sustainable livestock systems and ecosystems services. Timber is one of the products from these systems with potential to increase family revenues. The management of natural regeneration and population dynamics of trees is a feasible way to harvest timber and maintain environmental services. In this research, we modeled the population dynamics of Pinus oocarpa and Tabebuia rosea, two important timber species of silvopastoral systems in Central America. The results showed that farmers manage a significant density of different tree species from natural regeneration. However, only the species with well-known uses or desired services are allowed to remain. The natural regeneration is more impressive in silvopastoral systems with natural grass than those with exotic grass. Farming practices, for instance use of fire for weed control, are the main reasons for low rates of natural regeneration in pastures with exotic grass. The models of population dynamics for both species showed that the sustainable timber harvest plans are a viable activity in pasturelands under natural-regeneration management plans. Innovative farmers are willing to adopt silvicultural practices and management of population dynamics to increase timber revenues and sustainability if forestry regulations for sustainable use of trees in farms are simplified.     

Mixed forests and a flexible harvest policy: a problem for conventional risk analysis?

The famous “Faustmann” equation, which allows for identifying the most profitable tree species on a given unstocked piece of land, assumes constant timber prices. In reality, timber prices may fluctuate dramatically. Several authors have proven for monocultures that waiting for an acceptable timber price (reservation price) before harvesting (flexible harvest policy) increases the net present value of forest management. The first part of this paper investigates how efficient a flexible harvest strategy may be applied in mixed forests and whether the optimal species mixture is changed under such harvest policy. Mixtures of the conifer Norway spruce [Picea abies (L.) Karst] and the broadleaf European beech (Fagus sylvatica L.) were investigated. In order to evaluate mixed forests, the risks and the correlation of risks between tree species as well as the attitude towards risk of the decision-maker (risk-aversion is assumed) were considered according to the classical theory of optimal portfolio selection. In the second part we took up a recent critique on modern financial theory by Mandelbrot. Whether or not the assumption of normally distributed financial flows, which are supposed to occur under risk, would be appropriate to evaluate the risk of forest management was investigated. Market and hazard risks as well as their correlation were integrated in the evaluation of mixed forests by means of Monte-Carlo simulations (MCS). The risk of the timber price fluctuation was combined with the natural hazard risk, caused mainly by insects, snow and wind. Applying the μ-σ-rule, the mean net present value (NPV) from 1,000 simulations and their standard deviation were used for the optimisation. Given a low-return, risk-free interest rate to assess potential species mixtures of the Norway spruce and European beech, optimal proportions of European beech increased according to the theory of optimum portfolio selection with growing risk aversion from 0 (ignorance of risk) to 60% (great risk-aversion). In relation to a fixed harvest policy, the net present value of both, Norway spruce and European beech, could be increased significantly. Since the hazard risks of European beech were substantially lower compared with the Norway spruce (relation of susceptibility 1:4) beech benefited more from the flexible harvest policy. A comparison of simulated frequency distributions of the NPV with the expected density functions under the assumption of a normal distribution revealed significant differences. Only in the case of European beech was the general shape of the simulated frequency distribution similar to a normal distribution (bell-shaped curve). However, the density of NPV close to the mean was much greater than expected under the assumption of a normal distribution. Consequently, the frequency of a negative NPV for a European beech forest was greatly overestimated when applying the normal distribution. Though the shape of the simulated frequency distribution was rather different from a normal distribution for Norway spruce the simulated part of negative NPV was quite well approximated by the normal distribution. Therefore the simulated and expected frequencies of negative NPV were similar in case of Norway spruce; only a slight underestimation was seen in the assumption of a normal distribution. It can be concluded that actually simulated frequencies of negative NPV seem to be better measures for risk than computed probabilities of negative NPV, which assume normal distribution. As the risk for European beech was greatly overestimated by the conventional assumption of a normal distribution, the optimal proportions of European beech were surely rather underestimated according to the theory of portfolio. MCS on optimum mixtures derived by the classical portfolio theory seems necessary to test the robustness of such mixtures.

Simulated cavity tree dynamics under alternative timber harvest regimes

We modeled cavity tree abundance on a landscape as a function of forest stand age classes and as a function of aggregate stand size classes. We explored the impact of five timber harvest regimes on cavity tree abundance on a 3261 ha landscape in southeast Missouri, USA, by linking the stand level cavity tree distribution model to the landscape age structure simulated by the LANDIS model. Over 100 years, mean cavity tree density increased constantly under all timber harvest regimes except for even-aged intensive management. This was due in large part to the continued maturation of the numerous stands that were >70 years old at the start of the simulations. However, compared to the no harvest (control) regime, the uneven-aged, the mixed, the even-aged long rotation, and the even-aged intensive harvest regimes reduced the cavity tree density by 9–11, 11–13, 15–18, and 28–34%, respectively, as more old stands were cut. Forest managers and planners can use this information to evaluate the practical consequences of alternative timber harvest regimes and consider the need for activities such as cavity tree retention.     

Decision support for evaluating landscape departure and prioritizing forest management activities in a changing environment

We evaluated changes (hereafter, departures) in spatial patterns of various patch types of forested landscapes in two subwatersheds (“east” and “west”) in eastern Washington, USA, from the patterns of two sets of reference conditions; one representing the broad variability of pre-management era (∼1900) conditions, and another representing the broad variability associated with one possible warming and drying climate-change scenario. We used a diagnostic set of class and landscape spatial pattern metrics to compare current spatial patterns of test subwatersheds against the two sets of reference conditions. In a companion decision support model built with the EMDS modeling system, we considered the degree of departure in the subwatersheds, relative to the two sets of reference conditions along with two additional criteria (vulnerability to severe wildfire and timber harvest opportunity), to determine the relative priority of landscape restoration treatments, and the potential for timber harvest to underwrite the treatments. In the decision support model, the current spatial pattern conditions of physiognomic types, cover types, forest structural classes, and those of late-successional and old forest patches of the two subwatersheds were compared against the two sets of reference conditions. The degree of departure in spatial patterns of physiognomic conditions was moderate in both subwatersheds in the pre-management era and climate-change comparisons. The situation was similar for the cover-type departure analysis, but spatial patterns of cover types increased in similarity to the reference conditions in the western subwatershed under the climate-change scenario. Spatial patterns of structural conditions showed a high degree of departure in both subwatersheds when compared to either set of reference conditions, but similarity improved in the eastern subwatershed under the climate-change scenario. Spatial patterns of late-successional + old forest structure were strongly similar to the broad envelope of conditions represented by the pre-management era reference in the western and moderately similar in the eastern subwatershed, but declined in both subwatersheds when compared with the climate-change reference conditions. When the degree of departure in spatial patterns of all patch types was considered along with vulnerability to severe wildfire and timber harvest opportunity, the eastern subwatershed rated higher priority for landscape improvement using either set of reference conditions. We conclude by considering uncertainties inherent in the analysis approach, types of sensitivity analysis needed to investigate model performance, and broad implications for forest managers.     

Risk evaluation and tree improvement as components of intensive forest management in Japan

Forestry practice differs from agricultural crops practice owing to the huge size of trees, their longevity and the variety of uncontrollable conditions under which they grow. Even with intensive forest management, the actual effects of investment of labour and materials in the forest seem to be fairly small because of the size of the forest and the long harvest rotation. Since we expect to produce both a higher quantity and a higher quality of timber with intensive forestry, it is very important to have adequate counter-measures to the fatal or destructive factors which affect forest establishment and growth. In Japan, in the field of forest tree breeding, we are making maps as information sources for decision making, in which iso-lines show the degrees of damage due to fatal factors such as pests and diseases. If there is more than one fatal factor overlapping in an area, it might be difficult to grow forests for commercial purposes. We have to decide how to use the forest land in these areas, or how to take counter-measures such as tending, chemical control, genetic improvement or even a change in the tree species. As forestry has a long harvest rotation, it is necessary to have ‘a quality control system’ in management, in which a follow-up assessment of planting materials, tending techniques in combination with site conditions, and fatal factors will be made. In this situation, forest tree improvement (breeding) seems to be of prime importance in intensive forest management in the future.     

Timber yield projections for tropical tree species: The influence of fast juvenile growth on timber volume recovery

Most growth and yield models for tropical tree species use diameter growth data obtained from permanent sample plots. A potential disadvantage of this data source is that slow-growing, suppressed juvenile trees are included of which only a small fraction will attain harvestable size. If this is the case, the average growth rate of extant juvenile trees will be lower than the historical, juvenile growth rate of trees of harvestable size. Thus, if juvenile growth rates are obtained from permanent plots, future timber yield may be underestimated. To determine the magnitude of this effect we simulated tree growth based on two types of diameter growth data: long-term tree-ring data from harvestable trees (‘lifetime growth data’) and growth data of the last 10 years from trees of all sizes (‘plot-type growth data’). The latter data type is a proxy for growth data from permanent sample plots. Second, we evaluated which percentage of harvestable timber volume at initial harvest is available at second harvest using lifetime growth data. We obtained tree-ring data from 89 to 98 individuals of three Bolivian timber species over their entire size range. Based on these data tree growth simulations were performed for two scenarios: a second harvest in 20, and in 40 years. A realistic degree of growth autocorrelation was incorporated in the growth projections, for both the lifetime and the plot-type growth data.     

Efficacy of riparian buffers in mitigating local population declines and the effects of even-aged timber harvest on larval salamanders

Headwater streams are an important and prevalent feature of the eastern North American landscape. These streams provide a wealth of ecosystem services and support tremendous biological diversity, which is predominated by salamanders in the Appalachian region. Salamanders are ubiquitous throughout the region, contributing a significant biomass that supports ecological and ecosystem processes. One of the greatest threats to salamanders is loss of headwater-riparian habitat through timber harvest. In this study, we measured larval salamander abundance at five headwater streams with different riparian buffer widths retained following logging. By sampling larval salamanders using leaf litter bags, we assessed the impacts of even-aged timber harvest on aquatic larval salamander abundances, where it was found that larvae are negatively impacted by increased stream sedimentation and a decrease in riparian buffer width. We found that retention of a 9-m buffer was effectively no different than complete removal of all riparian forest, and as such, current regulations to protect headwater streams are ineffectual. Furthermore, no significant differences were observed between the 30 m buffer treatment and uncut control treatments suggesting that a 30 m or larger riparian buffer may assuage the in-stream effects of riparian timber harvest. Management guidelines for Appalachian forests should be revised to accommodate the biology of plethodontid salamanders.     

An approach to GIS-based multiple criteria decision analysis that integrates exploration and evaluation phases: Case study in a forest-dominated landscape

The increasing importance and complexity of land and natural resource management are creating a need for ecosystem-based management (EBM). Multiple criteria decision analysis (MCDA) combined with geographic information systems (GIS) can integrate factors related to the triple bottom line of ecological, economic, and social perspectives required by EBM. However, GIS-based MCDA is limited in this role because (i) it rarely integrates or encourages an exploration phase in preparation for structured evaluation and (ii) inexperienced users may find MCDA methods and GIS software difficult to use. This paper presents a novel approach for (i) supporting an exploration phase to help structure a problem and (ii) integrating the exploration and evaluation phases in an easy-to-use software system. The approach was validated through a land-management case study in a forest-dominated landscape with a variety of stakeholders. Case-study participants used the approach to rate areas within a timber harvest plan based on their potential for conflict with conservation values. The case-study decision analysis determined that between 1.3% and 6.6% of the harvest plan area had a conservation rating of 0.30 or higher on a scale of 0–1. The system was made available to the forest industry and other stakeholders to support harvest plan adjustments, demonstrating how such tools can be used to improve and integrate our knowledge of forest ecology and management. Assessment of participant feedback reveals that an exploration phase is effective in helping understand a problem and prepare for multiple criteria evaluation (MCE).