Managing forests infested by spruce beetles in south-central Alaska: Effects on nitrogen availability,understory biomass,and spruce regeneration

In Alaska, an outbreak of spruce beetles (Dendroctonus rufipennis) recently infested over one million hectares of spruce (Picea spp.) forest. As a result, land management agencies have applied different treatments to infested forests to minimize fire hazard and economic loss and facilitate forest regeneration. In this study we investigated the effects of high-intensity burning, whole-tree harvest, whole-tree harvest with nitrogen (N) fertilization, and conventional harvest of beetle-killed stands 4 years after treatment, as well as clear-cut salvage harvest 6 years after treatment. We measured available soil ammonium and nitrate and estimated N loss from leaching using in situ cation and anion resin exchange capsules. We also assessed spruce regeneration and responses of understory plant species. Availability and losses of N did not differ among any of the management treatments. Even a substantial application of N fertilizer had no effect on N availability. Spruce regeneration significantly increased after high-intensity prescribed burning, with the number of seedlings averaging 8.9 m⁻² in burn plots, as compared to 0.1 m⁻² in plots that did not receive treatment. Biomass of the pervasive grass bluejoint (Calamagrostis canadensis) was significantly reduced by burning, with burn plots having 9.5% of the C. canadensis biomass of plots that did not receive treatment. N fertilization doubled C. canadensis biomass, suggesting that N fertilization without accompanying measures to control C. canadensis is the least viable method for promoting rapid spruce regeneration.     

Ecosystem management based on large-scale disturbance pulses: A case study from sub-boreal forests of western Quebec (Canada)

The northern Témiscamingue region (western Québec) sustained regional-scale pulses of natural disturbances during the 1850–2000 period, such as severe fires during the 1908–1926 period, two severe spruce budworm outbreaks that occurred in 1909–1918 and 1974–1984, and two birch dieback episodes around 1940 and 1980. These disturbances produced synchronous fluctuations in forest characteristics over large spatial scales. In this paper, we review possible responses of flora and fauna to pulsed large-scale disturbance events and speculate on whether they should be emulated to reduce the impacts of forest management on non-timber resources. The importance of large-scale disturbance pulses for biodiversity and forest ecosystem integrity is potentially great, but this aspect has been poorly investigated by previous research, and thus there is little information available to guide forest management. Large-scale, synchronous disturbances could be emulated by clustering harvesting activities in time, for example by creating “harvest pulses” of 10–20 years, separated by periods of 50–100 years or so with low harvest rates. A potential disadvantage of this strategy is that when our capacity to predict future natural disturbances is low, there is a higher probability of accidentally taking the forest ecosystem outside of the range of natural variability compared with a status quo forest management scenario. From a socio-economic perspective, another potential disadvantage is in creating irregular wood flows to the forest transformation industry. Nonetheless, in a context where the forest has been over-disturbed in the recent past, a forest management strategy involving fluctuating harvest rates could provide the means for faster ecosystem recovery compared with a status quo strategy. We recommend that the potential importance of disturbance pulses for boreal and sub-boreal ecosystems be more thoroughly investigated by future research to inform management and conservation policies.     

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.

Post-harvest Regeneration of Lowland Black Spruce Forests in Northeastern Ontario

Success of natural regeneration has been a concern since the introduction of heavy machinery in harvesting. The objective was to compare the effect of three operational harvest methods careful logging around advanced growth (CLAAG), group seed tree (GST), and group seed tree followed by shearblading site preparation (SHE) on natural regeneration in the Clay Belt region of Ontario. A total of 30 stands, 562 cluster sample plots, were surveyed. Total density of black spruce regeneration did not differ, but height structure of black spruce regeneration did among harvest methods. The CLAAG method resulted in highest total regeneration density of other conifers. Decreasing density of other conifers from the CLAAG to GST to SHE sites indicated that the CLAAG method protected advance regeneration as expected and the SHE method removed advance regeneration in the path of the shearing blade. Both black spruce and other conifer regeneration densities increased with increasing time since harvest. Stocking of black spruce, all conifers, or all tree species did not differ significantly among harvest methods, nor did it change with time since harvest. Stocking was nonlinearly related to regeneration density. Models developed in this study predict that full stocking (i.e., 60%) can be reached based on regeneration density of 5000 stems per ha regardless of crop species choice preference. However, the existing stocking criterion for assessing black spruce regeneration may be problematic.     

Damages and growth effects after selective mechanical cleaning

An annual survey of damages and growth was conducted two and three years after selective mechanical cleaning in two Norway spruce plantations‐7 and 11–16 years old—and one 11‐year‐old lodgepole pine plantation. The base machine was a modified Bruunett Mini with a rotating disc with two short steel flails, mounted at the tip of the crane. The results show that very few damages were caused by the cleaning device. 5–8% of the seedlings were driven over or otherwise damaged by the wheels and these seedlings show high mortality and great growth reduction. In stands with 1.5–4 m high trees, the trees are often damaged when they are straddled by the machine, which causes growth and quality losses. 14–25% of the undamaged seedlings in Norway spruce stands showed a 25 % annual height growth reduction the first two years after cleaning due to soil compaction and to possible root damage.     

Emulating natural disturbances as a forest management goal: Lessons from fire regime simulations

Emulating natural forest disturbance is an increasingly popular forest management paradigm that is considered a means of achieving forest sustainability. Adopting this goal requires a sound understanding of natural disturbances at scales that correspond to management policies and strategies. In boreal forest landscapes driven by periodic stand-replacing fires this requires knowledge of fire regime characteristics, especially their spatial and temporal variability as well as stochasticity. The major goal of this study was to demonstrate the utility of fire regime simulation modeling to explore the variability of fire regime characteristics, with respect to formulating and assessing forest management strategies. We conducted a modeling experiment in a boreal forest landscape of northwestern Ontario, Canada, to examine its long-term fire regime in relation to forest policies on harvest size distribution. We used BFOLDS, a spatially explicit fire regime model that simulates individual fire events mechanistically in response to fire weather, fuel patterns, and terrain. The fire regimes in four large eco-regions were modeled for a 200-year period under three fire-weather (cold, normal, and warm) scenarios, with replications. We found that fire size distribution in all eco-regions followed power law under all weather scenarios, but their slopes and intercepts varied among eco-regions and fire weather scenarios. Warming fire weather increased burn rates and fire numbers in all eco-regions, albeit to different degrees. Overall, the variability among eco-regions was higher than the variability among fire weather scenarios, and among replicates. Comparisons of simulated fire size classes with those from an 86-year long fire history showed that empirical data cannot capture the variability that could be revealed by simulation modeling. We also show that fire size distribution is spatially heterogeneous within eco-regions, and provide several suggestions for forest policy directions with respect to forest harvest size distributions and harvest rates, based on the variability of fire regime characteristics. An assessment of present forest policies of emulating natural disturbances that guide forest harvest sizes showed that these are incongruent with simulated fire size distributions under all scenarios with one exception. Overall, this study illustrates the value of scenario simulation modeling to explore and quantify the variability of forest fire regime, for use in forest policies and strategies that attempt to emulate natural disturbance.     

A concept for the calculation of financial losses when changing the forest management strategy

The objectives of nature conservation can often only be realised by changing forest management regimes. Thus far, mainly institutional regulations have been used to achieve these goals. However, in Germany there is strong political interest in encouraging contract-based forest management whereby forest owners receive financial compensation for losses when changing over forest management regime. Such compensation is commonly paid in the German agricultural sector but is absent in forestry.When managing forests for social convenience, forest enterprises are faced with financial losses. With regard to practical experience in forestry there is a considerable lack of information about the economic consequences.To estimate the losses related to changes in silvicultural treatment, a calculation scheme based on the annuity method has been developed and figures have been calculated for different tree species and age classes. The annual timber production value determined per ha and year is documented in tables and, as shown by examples, could be applied to evaluate typical changes in forest management such as the renunciation of forest production, change of tree species, premature harvest and the preservation of mature stands.Standardised annual timber production values for different tree species, yield classes, management schemes etc. can be helpful to estimate the financial losses for forest-land owners when changing the management strategy. These financial losses can also be interpreted as the minimum price which has to be offered to forest land owners when a contract-based forest management is striven for by the government.     

Conversion of Norway spruce forests in the face of climate change: a case study in Central Europe

Steadily increasing damage to Norway spruce forests in Europe has caused researchers and managers to consider whether these forests can be converted to more stable ecosystems. In a central European mountain region, we investigated whether management systems (MSs) specified by regional stakeholders provide sound alternatives to the currently applied management. We used the forest model Sibyla to explore whether the tested MSs differ in their sensitivity to climate change in terms of altered biomass production, stand structure, forest damage, and financial outcome. The tested MSs were no-management (NM), currently applied management (BAU), and management based on the preferences of forest managers (FM) or on the preferences of other stakeholders (OSH). With NM, spruce remained dominant during the simulation period 2010–2100, and the rate of damage significantly increased. Spruce also remained dominant with FM, while the abundance of non-spruce species significantly increased with BAU and OSH. The rate of salvage logging converged at 50% of the total harvest for all MSs up to 2050. Climate change reduced biomass production (?15%) with all MSs but had a negligible effect on biodiversity indicators. The average initial value of the simulated stands was 20,000 € ha^?1 and the nominal value in 2100 was between 1900 and 10,900 € ha^?1. The Net Present Value calculated with the 2% interest rate was negative during the whole simulation period (?5600 to ?18,500 € ha^?1 in 2100). Effect of climate change on all financial indicators was negative. Our findings indicate that secondary spruce forests are highly vulnerable and that the systems proposed by both forest managers and other regional stakeholders failed to significantly reduce forest damage and stabilize forest production.     

德国北部挪威云杉林可持续经营中期计划的实例分析

可持续森林经营理论为中期林业计划和收获调整提供了丰富的模型选择,其不同的方法可应用于各种特定的场合和不同经营类型.本文简要回顾了传统的森林计划方法,一种称为"多林分发展"的概念可以用于任意的经营系统,这个概念把森林看作由一系列林分组成,在每一个林分中可以预先制定多种经营措施的选项,每种选项都可以通过木材或其它产品以及消耗的资源计算出一个目标值.这种简单的概念可以应用到大量的不同森林经营场合,它为森林经营者制定切实可行的森林措施和评价森林经营计划提供方法.在本研究中,以德国北部一片包括21个小班的挪威云杉林班的一个中期计划为例,说明"多林分发展"这一经营系统在实际生产中的应用.每个小班具有不同的初始状态,每个小班预设了若干经营选项,根据小班的初始状态、生长模型为各种选项计算各时期的木材产出.在林班的水平上,经营目标方程包括两个组成部分:净现值和均衡木材收获值.用模拟退火的方法来优化总体目标方程值.优化的总体解决方案在为每个小班选定合适的经营选项的同时,在全林的水平上获得最优的经济和均衡产出组合.     

Growth and yield models for uneven-sized forest stands in Finland

Uneven-sized forestry is gradually gaining popularity and acceptability also in the Nordic countries. This is because of the willingness of the public and some forest owners to avoid clear-fellings and pursue more near-nature forest structures. It has also been realized that the profitability of uneven-sized forestry may be competitive with even-aged forestry. In Finland, management of uneven-sized stands is hampered by the lack of information about the dynamics of such stands, and about the yield and profitability of uneven-sized forestry. This study developed models which allow managers to simulate the growth and yield of uneven-sized stands in Finland, making it possible to predict the yield and analyze the sustainability of different management options. The model set consists of individual-tree diameter increment, height and survival models, and a model for ingrowth. The modeling data consisted of two long-term field experiments of uneven-sized forest management, a set of temporary sample plots measured earlier for growth modeling purposes, and the sample plots of the third National Forest Inventory of Finland. The application area of the models covers all growing sites, all main tree species, and the whole surface area of Finland. According to the models, the sustainable harvest of a fertile (Oxalis-Myrtillus site) uneven-sized Norway spruce forest varies between 5.5 and 7 m³ ha⁻¹ a⁻¹ in Central Finland, depending on the length of the cutting cycle, stand density, and shape of the diameter distribution. It is profitable to harvest large diameter classes more heavily than small ones. Due to the large amount of data the models for diameter increment are highly significant and reliably show the growth level of trees in uneven-sized stands. The weakest models are the ingrowth models, which are based on a clearly smaller data set than the other models.     

Nutrient and heavy metals in decaying harvest residue needles on drained blanket peat forests

Harvest residue decomposition can significantly contribute to nutrient and heavy metal exports to receiving water courses. This study monitors the nutrient and heavy metal dynamics in decaying Sitka spruce and lodgepole pine harvest residue needles on Atlantic blanket peat forests in the west of Ireland. Using the litterbag method, harvest residue was placed both within and between furrows in two uncut forest and two clear-cut sites. On the clear-cut sites, the litterbags were positioned outside the harvest residue piles (i.e. brash windrows). Over the 2-year monitoring period, the needles decomposed slower at the clear-cut sites than the uncut forest sites, with mass losses of 46–55 and 58–77 %, respectively. Approximately 20 % less phosphorous (P) was released from the decaying needles at the clear-cut sites, while nitrogen (N) was released only at the uncut sites. Tree species was a significant factor contributing to nutrient and heavy metal release and accumulation patterns, with higher concentrations of aluminium (Al), nickel (Ni), cadmium (Cd) and zinc (Zn) in the decaying spruce needles than in pine. Conversely, the spruce needles showed accelerated depletion of calcium (Ca) and magnesium (Mg) relative to the pine. The harvest residue needle positioning (inside furrow/between furrows) and the site soil characteristics contributed significantly to Al transformations in spruce needles and iron (Fe) in both spruce and pine needles, with more accumulation occurring inside the furrows where Al and Fe contents of the peat were high. Manganese (Mn) was released from the needles in three of the four sites with a total release of over 90 % within 2 years. In the remaining site, where the Mn content of the peat was high, an accumulation of Mn in the needles was observed. The decomposition of needles on blanket peat catchments may be a significant source of P to receiving water courses, owing to their fast release of P, but not a likely source for N export.     

Management tools for optimal allocation of wood fibre to conventional log and bio-energy markets in Ireland: a case study

A set of tools are described for optimal allocation of wood fibre at an operational planning level. These were applied to a case study in Ireland. Allocation was based on optimising net value recovery (delivered price minus harvesting and transportation costs) while meeting market demands and operational constraints (mainly crew capability and productivity limits). Two new models were developed to predict harvesting costs and transportation costs for Irish forest conditions. A new model was developed to link Sitka spruce biomass expansion factors to optimal log-making algorithms so that log and bio-energy product yields could be estimated for individual harvest areas. An existing operational allocation model based on a tabu search heuristic procedure was used. The case study included 16 forest harvest areas and 12 processing plants (saw logs, pallet logs, stakes, pulp, bio-energy slash bundles, etc.). New terrestrial lidar scanning procedures were used to obtain representative stem profiles from over 4,000 trees for the 16 forests. We demonstrated that optimal allocation of bio-energy and log products, while complex, can be achieved through the use of appropriate management tools.     

Price Adapted Timber Harvest Decision Model

研究了木材价格的变化为一自相关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;建立了一个木材市场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．     

Inherited narrow crown form, harvest index and stem biomass production in Norway spruce, Picea abies

The effect of crown form on stem biomass production was investigated in an 18-19-year-old Norway spruce stand (Picea abies (L.) Karst.). The harvest index was 0.271 in pendula trees, which have a heritable narrow crown form, and 0.235 in normal-crowned trees and the dry weights of stem biomass were 2.57 kg and 3.37 kg, respectively. However, the production of stem biomass per crown projected area was more than twice as much in pendula trees as in normal-crowned trees. Results indicate that the crown form of pendula spruce is less plastic than that of normal-crowned spruce suggesting that such trees might maintain a high stemwood yield per unit ground area with increasing stand density. Because pendula spruce has a higher harvest index and a less flexible crown than normal-crowned spruce, it might be useful for crop tree ideotype breeding.     

Forecasting landscape-scale,cumulative effects of forest management on vegetation and wildlife habitat: A case study of issues,limitations, and opportunities

Forest landscape disturbance and succession models have become practical tools for large-scale, long-term analyses of the cumulative effects of forest management on real landscapes. They can provide essential information in a spatial context to address management and policy issues related to forest planning, wildlife habitat quality, timber harvesting, fire effects, and land use change. Widespread application of landscape disturbance and succession models is hampered by the difficulty of mapping the initial landscape layers needed for model implementation and by the complexity of calibrating forest landscape models for new geographic regions. Applications are complicated by issues of scale related to the size of the landscape of interest (bigger is better), the resolution at which the landscape is modeled and analyzed (finer is better), and the cost or complexity of applying a landscape model (cheaper and easier is better). These issues spill over to associated analyses that build on model outputs or become integrated as auxiliary model capabilities. Continued development and application of forest landscape disturbance and simulation models can be facilitated by (1) cooperative efforts to initialize more and larger landscapes for model applications, (2) partnerships of practitioners and scientists to address current management issues, (3) developing permanent mechanisms for user support, (4) adding new capabilities to models, either directly or as compatible auxiliary models, (5) increasing efforts to evaluate model performance and compare multiple models running on the same landscape, and (6) developing methods to choose among complex, multi-resource alternatives with outputs that vary over space and time.     

Impact of bark beetle (Ips typographus L.) disturbance on timber production and carbon sequestration in different management strategies under climate change

The likely environmental changes throughout the next century have the potential to strongly alter forest disturbance regimes which may heavily affect forest functions as well as forest management. Forest stands already poorly adapted to current environmental conditions, such as secondary Norway spruce (Picea abies (L.) Karst.) forests outside their natural range, are expected to be particularly prone to such risks. By means of a simulation study, a secondary Norway spruce forest management unit in Austria was studied under conditions of climatic change with regard to effects of bark beetle disturbance on timber production and carbon sequestration over a time period of 100 years. The modified patch model PICUS v1.41, including a submodule of bark beetle-induced tree mortality, was employed to assess four alternative management strategies: (a) Norway spruce age-class forestry, (b) Norway spruce continuous cover forestry, (c) conversion to mixed species stands, and (d) no management. Two sets of simulations were investigated, one without the consideration of biotic disturbances, the other including possible bark beetle damages. Simulations were conducted for a de-trended baseline climate (1961–1990) as well as for two transient climate change scenarios featuring a distinct increase in temperature. The main objectives were to: (i) estimate the effects of bark beetle damage on timber production and carbon (C) sequestration under climate change; (ii) assess the effects of disregarding bark beetle disturbance in the analysis.Results indicated a strong increase in bark beetle damage under climate change scenarios (up to +219% in terms of timber volume losses) compared to the baseline climate scenario. Furthermore, distinct differences were revealed between the studied management strategies, pointing at considerably lower amounts of salvage in the conversion strategy. In terms of C storage, increased biotic disturbances under climate change reduced C storage in the actively managed strategies (up to −41.0 tC ha⁻¹) over the 100-year simulation period, whereas in the unmanaged control variant some scenarios even resulted in increased C sequestration due to a stand density effect.Comparing the simulation series with and without bark beetle disturbances the main findings were: (i) forest C storage was higher in all actively managed strategies under climate change, when biotic disturbances were disregarded (up to +31.6 tC ha⁻¹ over 100 years); and (ii) in the undisturbed, unmanaged variant C sequestration was lower compared to the simulations with bark beetle disturbance (up to −69.9 tC ha⁻¹ over 100 years). The study highlights the importance of including the full range of ecosystem-specific disturbances by isolating the effect of one important agent on timber production and C sequestration.     

Cultural entrenchment: Explaining gaps between ecosystem-based management policy and practice in the forests of Newfoundland

Forests in North America have been managed, or unmanaged, under a number of different policy regimes, most recently ecosystem-based management (EBM), which has emerged in response to perceived widespread ecological degradation. But as policy regimes shift, links between stated objectives and the tools or mechanisms to achieve those objectives need to be forged. This case study of forestry on the island of Newfoundland provides an illustration of the gaps between EBM policy and practice, and insights into why EBM can be difficult to implement. Though the case of Newfoundland is unusual because of its isolation, narrow set of economic options, and weak ENGO sector, its adherence to a traditional timber regime offers lessons for the ways that policies move from agenda setting to implementation. In this case, the role of cultural entrenchment—a commitment to timber-based management and to a provincial model of economic support for large-scale industry—created a negative feedback loop that undermined new policy objectives. But a window of opportunity has emerged as a result of pulp and paper industry decline, and so overcoming cultural entrenchment and building a new forest management regime centered on EBM is possible through clearly articulated policy mechanisms and the integration of new forms of expertise.     

The potential rural development impacts of utilizing non-merchantable forest biomass

The development of a market for currently non-merchantable forest material, such as harvest residues or small diameter trees, has been suggested as a possible win-win solution that could: (i) provide a material that can be processed in rural communities reeling from changes in the forest products industry and policy environment; (ii) capture more value from timber management activities; and (iii) provide a financial incentive for treatments to reduce wildfire risk or restore forest stands. Modeling the supply of this material with spatially-explicit potential demand locations allows for a realistic analysis of the feasibility of such a market to stimulate rural development. We model multiple scenarios for the utilization of harvest residues within the current forest products market in western Oregon. Sensitivity analysis explored the effects of cost of the depots on feasibility, including policy designed to support depot establishment through subsidies. Scenarios were also used to assess the effects of increases in federal harvest activities. Results suggest that with relatively high biomass prices, there is some potential for investment in depots to aid rural communities in western Oregon, but there is little change in either the overall feasibility or the location of depot establishment under scenarios of increased federal harvest.     

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。     

Ericaceous shrubs affect black spruce physiology independently from inherent site fertility

Vegetative layering of black spruce (Picea mariana [Mill.] B.S.P.) is the principal mode of regeneration for over mature, uneven-aged stands subject to long fire cycles (>300 years) in northeastern Québec, Canada. However, growth response of black spruce layers following disturbance by fire or harvest can be slow, due to a lag of morphological acclimation and potential nutrient limitation. This phenomenon can be accentuated if black spruce is associated with ericaceous shrubs such as Kalmia angustifolia and Rhododendron groenlandicum, which are known to interfere with conifer growth through direct and indirect competition. Such interactions can result in productive stands being converted to unproductive heathlands. It is not known whether these effects of ericaceous shrubs on black spruce are accentuated on low fertility sites, or if the impacts are independent of inherent site fertility. The objectives of this study were to evaluate the effects of ericaceous shrubs on both resource availability and on functional traits of black spruce advance regeneration across a gradient of site fertility (as defined by a site classification system). We monitored black spruce advanced regeneration physiology and soil nutrient availability over two growing seasons on a gradient of ecological site types in northeastern Québec (Canada). The eradication of competing vegetation favored higher soil NH₄-N and K availability, with increases of 67% and 28% compared to control conditions, respectively. Black spruce photosynthesis rate (A) and foliar K content were higher in plots where vegetation was eradicated, compared to the control plots, but did not vary among ecological site types. Photosynthesis did not appear to be limited by nitrogen or water relations, but was possibly limited by a deficit of foliar K⁺, probably resulting from reduced availability following sequestration by the ericaceous root systems. The absence of interaction between inherent site fertility and the eradication of ericaceous shrubs suggests that vegetation management of ericaceous shrubs must be planned independently from the ecological site type.