On the effect of volatile stumpage prices on the economic attractiveness of a silvicultural transformation strategy

This paper evaluates the economic attractiveness of a silvicultural transformation strategy, focussing on risk, as a result of the volatility of stumpage prices. Based on a situation of a 58-year-old spruce stand [Picea abies (L.) Karst.], which can be found near Freising (Upper Bavaria, Germany), a growth model (silva 2.2) was used to project the stand development. Growth simulations were conducted for a specific transformation strategy, from regular to irregular age structure on the one hand, and for a conservative silvicultural strategy (thinning, clear-cut, reforestation), on the other hand. The transformation strategy was aimed at achieving an uneven-aged stand structure. It was based on early initiation, small-scale regeneration cuts carried out frequently and periodically. The harvests were, therefore, more evenly distributed over the time period analysed. Unlike transformation, even-aged silviculture consisted of relatively strong thinning up to age 68, followed by weak or no interventions up to age 98, the rotation age, aiming to maximise mean value increment. Both strategies were modelled over a time period of 198 years. Based on the growth data, a Monte Carlo model was used to estimate the financial results of both strategies. The stumpage price was assumed as a random variable with a probability density which follows a normal distribution. From the results of 1000 simulations for each strategy, distributions of the net present value (NPV) were calculated. Due to the complexity of the growth model silva, the calculations, being valid not for a forest enterprise but for one single stand, were restricted so that the time for every intervention was fixed, regardless of the stumpage price. Since the revenues produced by transformation were more evenly distributed over time than those achieved by the conservative even-aged strategy, the latter was far more influenced by very low or very high prices at the time of the clear-cuts. This fact caused a much smaller variation in NPV of the transformation. Parallel to this result, the probability of producing a deficit (that is to achieve a negative NPV) was lower for the transformation. The financial effect shown in this study in favour of transformation certainly compensates for a potentially higher risk of storm damage during the transformation treatment.     

Stand-landscape integration in natural disturbance-based management of the southern boreal forest

Forest ecosystem management, based partly on a greater understanding of natural disturbance regimes, has many variations but is generally considered the most promising approach to accommodating biodiversity concerns in managed forested regions. Using the Lake Duparquet Forest in the southeastern Canadian boreal forest as an example, we demonstrate an approach that attempts to integrate forest and stand-level scales in biodiversity maintenance. The concept of cohorts is used to integrate stand age, composition and structure into broad successional or stand development phases. Mean forest age (MFA), because it partly incorporates historic variability of the regional fire cycle, is used as a target fire cycle. At the landscape level, forest composition and cohort objectives are derived from regional natural disturbance history, ecosystem classification, stand dynamics and a negative exponential age distribution based on a 140 year fire cycle. The resulting multi-cohort structure provides a framework for maintaining the landscape in a semi-natural age structure and composition. At the stand level, the approach relies on diversifying interventions, using both even-aged and uneven-aged silviculture to reflect natural stand dynamics, control the passage (“fluxes”) between forest types of different cohorts and maintain forest-level objectives. Partial and selective harvesting is intended to create the structural and compositional characteristics of mid- to late-successional forest types and, as such, offers an alternative to increasing rotation lengths to maintain ecosystem diversity associated with over-mature and old-growth forests. The approach does not however supplant the necessity for complementary strategies for maintaining biodiversity such as the creation of reserves to protect rare, old or simply natural ecosystems. The emphasis on maintaining the cohort structure and forest type diversity contrasts significantly with current even-aged management in the Canadian boreal forest and has implications for stand-level interventions, notably in necessitating a greater diversification of silvicultural practices including more uneven-aged harvesting regimes. The approach also presents a number of operational challenges and potentially higher risks associated with multiply stand entries, partial cutting and longer intervals between final harvests. There is a need for translating the conceptual model into a more quantitative silvicultural framework. Silvicultural trials have been established to evaluate stand-level responses to treatments and operational aspects of the approach.     

Market impacts of hypothetical fuel treatment thinning programs on federal lands in the western United States

This paper addresses the economics of forest fuel thinning programs on federal lands in the U.S. West, and presents a model of regional timber and product market impacts. The issue of economics is vital to the debate about fire management, and this paper presents market implications of two alternative silvicultural strategies, even-aged and uneven-aged thinning. Projections are based on a regional market model called FTM—West (Fuel Treatment Market model—West), which uses the method of price-endogenous linear programming to project annual market equilibria for softwood timber and wood products in the western United States from 1997 to 2020. The model takes into account variability in tree and log size, as well as economic effects of variable size class on harvest costs, log value, product recovery and mill capacity. Results show large potential market impacts from expanded thinning on federal lands, but impacts vary by silvicultural regime due to differences in size–class distributions of trees available under different thinning regimes. A hypothetical even-aged thinning program (“thin-from-below” strategy) results in net negative market welfare over the projection period (2005–2020), while a hypothetical uneven-aged thinning program (thinning based on stand density index) results in positive net market welfare. Net welfare results are the same over a range of different subsidy and administrative fee assumptions. An implication is that even-aged thinning regimes on federal lands in the U.S. West are less economical and therefore will be less effective.     

Optimizing any-aged management of mixed boreal forest under residual basal area constraints

The current trend of forest management in many countries is reduced use of clear-felling and planting, and increased use of continuous cover management. In Finland, the new forest act of 2014 made all types of cuttings equally allowable on the condition that if the post-cutting residual stand basal area is too low, the stand must be regenerated within certain time frame. Forest landowner can freely choose between evenand uneven-aged management. This study developed a method for optimizing the timing and type of cuttings without the need to categorize the management system as either even-aged or uneven-aged. A management system that does not set any requirements on the sequence of post-cutting diameter distributions is called any-aged management. Planting or sowing was used when stand basal area fell below the required minimum basal area and the amount of advance regeneration was less than required in the regulations. When the cuttings of 200 stands managed earlier with even-aged silviculture were optimized with the developed system, final felling followed by artificial regeneration was selected for almost 50% of stands. Reduction of the minimum basal area limit greatly decreased the use of artificial regeneration but improved profitability, suggesting that the truly optimal management would be to use natural regeneration in financially mature stands. The optimal type of thinning was high thinning in 97–99 % of cases. It was calculated that the minimum basal area requirement reduced the mean net present value of the stands by 12–16 % when discount rate was 3–5 %.     

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.     

Optimal management of uneven-aged Norway spruce stands

An optimization model is specified to analyze forest management without any restrictions on the forest management system. The data on forest growth comes from unique field experiments and is used to estimate a nonlinear transition matrix or size-structured model for Norway spruce. The objective function includes detailed harvesting cost specifications and the optimization problem is solved in its most general dynamic form. In optimal uneven-aged management, stand density is shown to be dominated by limitations in natural regeneration. If the goal is volume maximization, even-aged management with artificial regeneration (and thinnings from above) is superior to uneven-aged management. After including regeneration and harvesting costs, the interest rate, and the price differential between saw timber and pulpwood, uneven-aged management becomes superior to even-aged management. However, in the short term the superiority is conditional on the initial stand state.     

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.     

Thirty Year History of Even-Aged Management

Abstract

Forests of Turkey were severely degraded and depleted as a result of mismanagement particularly during the application of uneven-aged management periods. With the beginning of a national call for planning, all forests except fir-dominated stands are planned for management under even-aged management methods. This paper explains and discusses the results of application of even-aged management on Calabrian pine forests and Eastern spruce forests in Turkey. As shown in 1973 with the first timber inventory, the implementation of even-aged management failed in the first planning period to create an optimal forest structure. It was observed, however, that even-aged management is beginning to accomplish an optimal forest structure in Calabrian pine forests with successful silvicultural treatments. In contrast, implementations of the even-aged management method on spruce forests was found unsuccessful so far. It is concluded that the method would be implementable in spruce-dominated forests and the other light-demanding commercial tree species as well if the silvicultural plans are prepared carefully based on site classification, and if the welfare system of the forest villagers in Eastern Black Sea region is improved.     

恒被林及其育林体系

恒被林很早就被提出来了,但其育林体系直到现在才得到推行,这个育林体系不包括皆伐,要求林冠永远地覆盖林地,而不使土壤裸露。这个育林体系既能维护森林环境,不影响森林景观和森林结构的变化,又能培育与收获木材,很符合现代的森林经营观念。英国的恒被育林体系包括:群状与单株择伐,渐伐,带状与群状渐伐,有计划的群状采伐,伐块范围不超过0.25hm2,采用人工栽植或天然更新或两者结合以形成复层异龄混交林。对于同龄纯林可采用上述育林体系进行改造。     

Silvicultural systems for southern bottomland hardwood forests

Silvicultural systems integrate both regeneration and intermediate operations in an orderly process for managing forest stands. The clearcutting method of regeneration favors the development of species that are moderately intolerant to intolerant of shade. In fact, clearcutting is the most proven and widely used method of successfully regenerating bottomland oak species in the South. The seed-tree method of regeneration favors the establishment of light-seeded species. Mechanical soil scarification may be necessary if the desired species requires bare mineral soil for establishment. The shelterwood method of regeneration can provide for the development of heavy-seeded species, but has produced highly variable results with southern bottomland oaks. The single-tree selection method of regeneration favors the development of shade-tolerant species. When single-tree selection is applied repeatedly to stands containing commercially valuable shade-intolerant species, composition will gradually shift to less-valuable, more-tolerant species. Consequently, the single-tree selection method of regeneration is not recommended for any commercially valuable bottomland hardwood tree species. Group selection, in its strictest application, creates only small openings that usually fail to allow sufficient light to the forest floor for satisfactory establishment and development of shade-intolerant bottomland species. Patch cutting, a combination of uneven-aged (group selection) and even-aged (clearcutting) silviculture, designed to create larger openings, has been successfully used to produce an uneven-aged stand that consists of many small, irregularly shaped, even-aged groups. Silvicultural systems should include a planned program of intermediate operations designed to enhance the growth and development of those species favored during the regeneration process. Improvement cutting and commercial thinning are increasingly common in southern bottomland hardwood forests. Other partial cuttings employed today in bottomland hardwood forests typically involve some form of crop-tree release. Specific recommendations for the selection of silvicultural systems are presented for the eight most important species groups found in southern bottomland hardwood forests.     

Emulating natural disturbances: the role of silviculture in creating even-aged and complex structures in the black spruce boreal forest of eastern North America

Ecosystem-based forest management is based on the principle of emulating regional natural disturbance regimes with forest management. An interesting area for a case study of the potential of ecosystem-based forest management is the boreal forest of north-western Québec and north-eastern Ontario, where the disturbance regime creates a mosaic of stands with both complex and simple structures. Old-growth stands of this region have multi-storied, open structures, thick soil organic layers, and are unproductive, while young post-fire stands established following severe fires that consumed most of the organic soil show dense and even-sized/aged structures and are more productive. Current forest management emulates the effects of low severity fires, which only partially consume the organic layers, and could lead to unproductive even-aged stands. The natural disturbance and forest management regimes differ in such a way that both young productive and old-growth forests could ultimately be under-represented on the landscape under a fully regulated forest management regime. Two major challenges for ecosystem-based forest management of this region are thus to: (1) maintain complex structures associated with old-growth forests, and (2) promote the establishment of productive post-harvest stands, while at the same time maintaining harvested volume. We discuss different silvicultural approaches that offer solutions to these challenges, namely the use of (1) partial harvesting to create or maintain complex structures typical of old-growth stands, and (2) site preparation techniques to emulate severe soil burns and create productive post-harvest stands. A similar approach could be applied to any region where the natural disturbance regime creates a landscape where both even-aged stands established after stand-replacing disturbances and irregular old-growth stands created by smaller scale disturbances are significant.     

Inventory and modelling for forests in transition from even-aged to uneven-aged management

In plantation forestry, as well as in forests managed according to the single tree selection system (Plenter forest), there are well established methods available to control sustainable management in terms of timber resources. If a shift from even-aged to uneven-aged management is intended, there is usually a lack of a clear, numerically defined aim. Then individual tree growth models help to (i) check if certain aims can be achieved at all and (ii) to define these aims more clearly and numerically, e.g. in terms of structural indices. Regular inventories, based on permanent sample plots, help to determine deviations from these aims. As a feedback of these results, management may be changed or aims may be adjusted. Two forest management districts in Austria were investigated. In one of them, continuous cover forestry was intended where, as soon as regeneration has reached a certain height, the upper layer was removed. In the other case, individual tree harvesting has been performed for 30 years, and a single tree selection system is intended. In both cases, permanent inventories based on angle-count sampling have been installed and re-measured at least once after 10 years. Using the individual tree simulator PrognAus it is shown, that the intended management strategy for the single tree selection system leads to an equilibrium of harvests and growth after about 80 years, accompanied by the intended high structural diversity of the stands, while species diversity and between-stand variation cannot be enhanced by much. In the natural regeneration system without single tree selection, species diversity, structural diversity and between-stand variation is enhanced, but during the 100 years simulated no equilibrium between harvests can be reached. Periods where there is a lack of large timber to be harvested occur regularly. From these examples it is concluded that inventories with permanent sample plots, together with individual tree growth simulators are appropriate tools to evaluate forest management changes.     

Beyond Even- vs. Uneven-Aged Management

The effect of forest management has been to override the dynamics produced by natural disturbances with a dynamic of human design. Under even-aged management, the forest is held in an early successional state, providing some habitat for species of open field and edge but little for species of the forest interior. Alternatively, uneven-aged management may maintain forest interior conditions but does not provide the large-scale heterogeneity created by pre-settlement disturbance processes. The traditional choice between even- and uneven-aged management approaches condemns the landscape to one of two mutually exclusive dynamics, causing the loss of natural landscape heterogeieity and the biodiversity it supports. The conservation of biodiversity will require that silviculture move beyond the artificial dichotomy of even- versus uneven-aged management to accommodate the full range of patterns, intensities, and frequencies of the natural disturbance regime. Traditional emphases on "regenerating the stand" and "optimizing growing stock" must be replaced by an emphasis on establishing the appropriate-sized cohort in the context of landscape-scale objectives.     

How to quantify forest management intensity in Central European forests

Existing approaches for the assessment of forest management intensity lack a widely accepted, purely quantitative measure for ranking a set of forest stands along a gradient of management intensity. We have developed a silvicultural management intensity indicator (SMI) which combines three main characteristics of a given stand: tree species, stand age and aboveground, living and dead wooden biomass. Data on these three factors are used as input to represent the risk of stand loss, which is a function of tree species and stand age, and stand density, which is a function of the silvicultural regime, stand age and tree species. Consequently, the indicator consists of a risk component (SMI_r) and a density component (SMI_d). We used SMI to rank traditional management of the main Central European tree species: Norway spruce (Picea abies [Karst.] L.), European beech (Fagus sylvatica L.), Scots pine (Pinus sylvestris L.), and oak (Quercus robur L. and Quercus petraea L.). By analysing SMI over their whole rotation period, we found the following ranking of management intensity: oak<beech<pine?spruce. Additionally, we quantified the SMI of actual research plots of the German Biodiversity exploratories, which represent unmanaged and managed forest stands including conifer forests cultivated outside their natural range. SMI not only successfully separate managed from unmanaged forests, but also reflected the variability of forest management and stand properties across the entire sample and within the different management groups. We suggest using SMI to quantify silvicultual management intensity of stands differing in species composition, age, silvicultural system (even-aged vs. uneven-aged), thinning grade and stages of stand conversion from one stand type into another. Using SMI may facilitate the assessment of the impact of forest management intensity on biodiversity in temperate forests.     

Optimising the management of maize — Grevillea robusta fields in Kenya

The study optimised the management of a Grevillea robusta (A. Cunn.) stand growing in the central highlands of Kenya. The optimisations were conducted separately for even-aged and uneven-aged management system of trees. The management was also optimised with the requirement that maize production under the tree cover must be profitable every year. Technically, the optimisation problems were solved by linking a simulation program with the non-linear optimisation algorithm of Hooke and Jeeves. The simulation program calculated the tree growth, volumes of harvested trees, and maize yields with a given set of management parameters (decision variables). The maize yield predictions and simulated timber yields were converted into gross incomes of which the production costs were subtracted. In even-aged management the objective variable was the soil expectation value with 5% discounting rate. In uneven-aged management the mean annual net income was maximised. The optimal solutions indicated that with both management systems it is optimal to concentrate on wood production. The optimal stand densities were so high that profitable maize production was not possible under the tree cover. The mean annual wood production of the optimal management schedule was more than 50m³ ha^–1. Forcing profitable maize production in the solution decreased the wood production by 57% (even-aged forestry) or 27% (uneven-aged forestry) and net income by 45% (even-aged forestry) or 24% (uneven-aged forestry).This revised version was published online in November 2005 with corrections to the Cover Date.     

林木生长和收获预估模型的研究动态

从近年来林木生长和收获模型的研究中,可以看出有如下的发展动向:（1）由林分水平模型向径级水平模型、单木水平模型转变;（2）从林木的自然生长模型发展来考虑人为育林措施的经营模型;（3）由简单的人工同龄纯林模型深化到复杂的天然异龄混交林;（4）关注点从测树学调查因子的经验性模型转向生理生态的机理性模型。还就今后我国的林木生长模型研究提出了几点建议。     

Stand structure, competition and growth of Scots pine (Pinus sylvestris L.) in a Mediterranean mountainous environment

The relationship between competition and tree growth was studied in four stands of Pinus sylvestris L. occurring in a continental Mediterranean mountain area (in the Guadarrama range, Spain), i.e., an uneven-aged stand, a stand with oak (Quercus pyrenaica Willd.) understorey, a plantation, and a mature even-aged stand. Competition was measured by a simple size-ratio distance-independent index and was negatively associated with tree diameter. This negative association was stronger in the uneven-aged, plantation and mature even-aged stands than in the stand with oak understorey. Competition was also negatively associated with current diameter increment. This relationship was moderately strong in the mature even-aged stand and weak in the uneven-aged stand and the plantation. In the uneven-aged and the mature even-aged stands, a weakly significant relationship was found between diameter growth and tree size, whereas these parameters were not associated in the stand with oak understorey. The competition index provided a better prediction of growth rate than the alternative use of diameter. Both diameter and basal area growth were greater in the uneven-aged than in the even-aged stands.     

美国怀俄明州西黄松林分碳库和经济收益比较

A forest carbon (C) sequestration project was conducted to evaluate the economic incentives that would be required by landowners to engage in C trading under different management regimes. Costs associated with joint management for C sequestration and timber would be valuable for establishing sound forest C trading systems. In this study, we calculated the C yield and amortized value of three Wyoming, ponderosa pine stands. The management practices examined were, unmanaged, even-aged (regeneration after clear-cut) and uneven-aged (selectively harvested). Costs and revenues associated with three stands were converted into 2006 real dollars using the all commodity producer price index to facilitate a comparison among the net revenues of three stands. Net revenues were annualized using a conservative annual interest rate of 4.5%. Our even-aged stand had the highest annual average C yield of 2.48 Mg·ha⁻¹·a¹, whereas, the uneven-aged stand had the lowest C accumulation (1.98 Mg·ha⁻¹·a⁻¹). Alternatively, the even-aged stand had the highest amortized net return of $276·ha⁻¹·a⁻¹ and the unmanaged stand had the lowest net return of $276·ha⁻¹·a⁻¹ and the unmanaged stand had the lowest net return of 64 ·ha⁻¹·a⁻¹. On the plots examined, an annual payment of $22 for each additional Mg of C sequestered would encourage a change from uneven aged management to an unmanaged stand that sequesters additional C, in the absence of transactions costs.     

关于异龄林大小等级划分标准的探讨

在森林资源调查中,对异龄林用平均年龄和龄组进行归类,会缩小不同林分之间的结构差异,并造成林分年龄的偏低估计。利用海南省热带天然林样地资料。在对异龄林结构进行分析的基础上,提出用占总株数20％的大径级林木来计算异龄林的平均直径、平均树高等林分特征因子,并根据平均直径大小按“径组”（或粗度级）将异龄林分为5级,基本与同龄林的5个龄组相对应。便于对森林资源的统计和汇总分析。提出的径组划分标准可为异龄林的调查和统计提供参考,也为开展这方面的进一步研究提供借鉴。