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.     

Modelling near-natural silvicultural regimes for beech – an economic sensitivity analysis

Near-natural silvicultural regimes for beech (Fagus sylvatica L.), in the form of uneven-aged selective felling, receive increasing interest in Denmark. This is partly due to the ability of this system to preserve the forest climate and maintain important ecological functions such as bio-geochemical cycling and biodiversity conservation. The optimal age to convert from even-aged management to uneven-aged selective felling seems to be as early as possible, about 55 years, when sufficient natural seeding can be expected. A fixed conversion period of 100 years is assumed. This regime, here analysed by the use of a so-called chessboard model, appears to be economically superior to clear felling if the regime is initiated in medium-aged stands down to the age of 55 years, assuming a high site quality and a real discount rate of 3% per annum. Uneven-aged selective felling seems to be economically superior to even-aged natural regeneration, assuming that: (i) the stumpage prices of regeneration harvests are increased by 10%, or (ii) the diameters of regeneration harvests exceed those of even-aged management by about 17% simultaneous with an identical increase of the maximum stumpage price. Clear felling seems to be the more profitable regime only if: (i) the stand is close to the economic optimal rotation age for clear felling, and (ii) when the stumpage prices of regeneration harvests achieved by use of the uneven-aged selective management regime are reduced by 10% or more due to quality defects caused by prolonged rotation ages. The above results are sensitive to variation of stumpage prices, but less so to variation of regeneration costs associated with near-natural management systems. However, the near-natural silvicultural regimes may be unable to fulfill the liquidity objectives following from the application of traditional management systems.     

Effects of initial stand states on optimal thinning regime and rotation of Picea abies stands

Abstract

This study analysed the effects of young stand characteristics on optimal thinning regime and length of rotation periods for even-aged Norway spruce [Picea abies (L.) Karst.] stands. Stand development was based on a distance-independent, individual-tree growth model. The young stand data were collected from 12 well-stocked Norway spruce stands in southern Finland. Results showed that optimal thinning regimes and rotation period depend on site quality and initial stand characteristics. At the first thinning, optimal thinning type depended on initial density. Thinning from both ends of the diameter distribution turned out to be optimal for initially dense stands. At the second and subsequent thinnings, thinning from above was clearly superior. At a low interest rate, thinning from below was optimal for the first thinning regardless of stocking level. For the study data, optimal rotation periods varied from 61 to 92 years at 3% interest rate. The high variation in length of rotation period was due to the sensitivity of optimal length of rotation period to site qualities, initial stand structure and density.     

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.     

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.     

ROTATION

The computer model ROTATION was developed to calculate and compare optimal rotation ages for even-aged forest stands according to mean annual increment, money yield table, forest rent, land expectation value, present net worth, internal rate of return, and financial maturity criteria. The program was written in Microsoft QuickBasic and h e input variables consist of volume yield data, stumpage price, land cost, stand establishment cost, stand management cost, and the rate of interest. Results are displayed in tabular format and values indicating the optimal rotation age based on each of the seven criteria are presented. A representative example is included which incorporates normal yield data for ponderosa pine (Pinus oonderosa Doual. ex Laws.) and commercial timber management revenues and expenditures approximating those currently countered in the Sierra Nevada and southern Cascades, USA. Potential users of ROTATION include forest managers and natural resource educators.     

Optimising the management of even-aged Pinus sylvestris L. stands in Galicia, north-western Spain

The study developed management instructions for even-aged Pinus sylvestris stands in Galicia (north-western Spain). Although these stands are highly productive, no silvicultural management schedules have been proposed so far for them on the basis of systematic analyses. This study used data from 2160 optimisation runs to develop the management instructions. Land expectation value was used as the objective function. Different prices of timber assortments were considered and the discounting rate was varied from 0.5 to 5%. The method employed to find the optimal management schedules of stands was the combination of a stand simulator and an optimisation algorithm. The simulator uses an earlier growth and yield model for Pinus sylvestris in Galicia to predict the future development of the stand with a given management schedule while the optimisation algorithm seeks the best management schedule among all the possible alternatives. The results show that optimal rotation lengths vary widely between 42 and 170 years, high discounting rates and good site quality resulting in the shortest rotations. Four thinnings were found to be suitable for all sites and discounting rates. With discounting rates higher than 1% the commercial thinnings should gradually decrease the stand basal area towards the end of the rotation.     

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.     

Species Interactions in the Dynamics of Even- and Uneven-Aged Boreal Forests

Many boreal tree stands are neither clearly even-aged nor clearly uneven-aged. The stands may undergo a series of stages, during which an even-aged stand is transformed into two-storied mixed stand, and finally to multistoried or uneven-aged stand structure. The species composition often changes during the succession of stand stages. This study developed models for stand dynamics that can be used in different stand structures and species compositions. The model set consists of species-specific individual-tree diameter increment and survival models, and models for ingrowth. Separate models were developed for Scots pine, Norway spruce, and hardwood species. The models were used in a growth simulator, to give illustrative examples on species influences and stand dynamics. Methods to simulate residual variation around diameter increment and ingrowth models are also presented. The results suggest that mixed stands are more productive than one-species stands. Spruce in particular benefits from an admixture of other species. Mixed species improve diameter increment, decrease mortality, and increase ingrowth. Pine is a more beneficial admixture than birch. Simulations showed that uneven-aged management of spruce forests is sustainable and productive, and even-aged conifer stands growing on medium sites can be converted into uneven-aged mixed stands by a series of strong high thinnings.     

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.     

Tree size distribution and abundance explain structural complexity differentially within stands of even-aged and uneven-aged structure types

Characterizations of physical structural complexity are an important surrogate for the potential of forested stands to provide desired ecosystem services such as biodiversity. Distinguishing between stands with different structural conditions is not only a necessary feature of useful structural metrics and indices, but how such measures vary among stands can reveal clues to the ecological processes driving structure. We used stand inventory metrics and indices of structural complexity to differentiate between even-aged and uneven-aged structure types using 10 stem-mapped coniferous stands of each type distributed across Switzerland. Within each structure type, we further explored relationships among stand inventory metrics and structural indices over a roughly 10-year period of management intervention. The even-aged and uneven-aged structure types were clearly differentiated using both stand inventory metrics and spatially explicit structural complexity indices. Overall, structural complexity within even-aged stands was strongly related to, and best predicted by, metrics including the distribution of basal area among canopy layers, while complexity in the uneven-aged stands was most strongly related to, and best predicted by, metrics including measures of abundance. Although predictive models could be developed for canopy position mixture, diameter differentiation, and small-scale structural complexity (but not spatial aggregation) using only stand inventory metrics, the prediction success after only a single management intervention was lower than expected. These results indicate that research to explore small-scale structural complexity requires detailed spatially explicit inventory data and that management to enhance structural complexity may require the manipulation of different attributes in stands of even-aged (diameter distribution) and uneven-aged (total abundance) structure types.     

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 %.     

Productivity and optimal management of the uneven-aged hardwood forests of Hyrcania

Hyrcania is a productive region near the southern coast of Caspian Sea. Her forests are mostly uneven-aged beach-dominated hardwood mixtures. There is increasing willingness to treat these forests without clear-felling, following the ideas of continuous cover management. However, lack of growth and yield models have delayed this endeavor, and no instructions for uneven-aged management have been issued so far. This study developed a set of models that enable the simulation of stand development in alternative management schedules. The models were used to optimize stand structure and the way in which various initial stands should be converted to the optimal uneven-aged structure. The model set consists of individual-tree diameter increment model, individual-tree height model, survival model, and a model for ingrowth. The models indicate that the sustainable yield of the forests ranges from 2.2 to 7 m³ ha^?1 a^?1 in uneven-aged management, depending on species composition. Better ingrowth would substantially enhance productivity. The optimal stand structure for maximum sustained yield has a wide descending diameter distribution, the largest trees of the post-cutting stand being 80–100 cm in dbh. If cuttings are conducted at 30- or 40-year intervals, they should remove 20–40 largest trees per hectare. Despite moderate growth rate, uneven-aged management produces high incomes, 850–1,000 UDS ha^?1a^?1, because the timber assortments that are obtained from the removed large trees have very high selling prices. Optimal conversion to uneven-aged structure showed that the steady-state stand structure depends on initial stand condition and discount rate when the length of the conversion period is fixed. Discount rates higher than 1 % lead to reduced wood production, heavy cuttings, and low basal areas of the steady-state forest.     

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.     

Spatial patterns in mixed coniferous even-aged,uneven-aged and conversion stands

Different methodological approaches from the field of spatial statistics, the index of cluster size (ICS) and quadrat methods such as the two-term and three-term local quadrat variance (TTLQV and 3TLQV) and the new local variance (NLV) were tested to find a simple spatial measure to classify mixed coniferous uneven-aged, even-aged and conversion stands in the central Black Forest area of Germany. Altogether six stands were analysed with regularly distributed sample plots of 0.25 ha (50×50 m), each subdivided into 25 quadrats of 10×10 m. In each of the quadrats, diameter at breast height (dbh) for trees of the overstory (dbh>7 cm) was assessed and classified into three diameter classes. Height measurements were used to develop specific stand height curves for each stand and to calculate the standing volume per tree and per quadrat. The even-aged stands showed a regular distribution of the standing volume, while the conversion and uneven-aged stands were more clustered. This was detected using ICS, which proved to be a simple but very efficient measure for stand structure. The ICS also showed a highly random distribution of small and medium trees and a regular distribution of large trees of the overstory in the uneven-aged stand. Large and medium trees of one even-aged stand were also regularly distributed while conversion stands showed a regular, random or slightly clustered distribution of these trees. The more uneven the ages in the stands were, the larger were the phases detected by the NLV. The findings of the ICS were generally supported by the TTLQV and 3TLQV. The more uneven the ages in a stand were, the less clustered were the trees of different sizes of the understory. Clustering also decreased with increasing height of understory trees. The patterns detected in the investigated stands were related to the effect of different management regimes. Implications for the management of conversions stands based on the findings of the study are given.     

Growth and productivity of black spruce in even- and uneven-aged stands at the limit of the closed boreal forest

The increasing commercial interest and advancing exploitation of new remote territories of the boreal forest require deeper knowledge of the productivity of these ecosystems. Canadian boreal forests are commonly assumed to be evenly aged, but recent studies show that frequent small-scale disturbances can lead to uneven-aged class distributions. However, how age distribution affects tree growth and stand productivity at high latitudes remains an unanswered question. Dynamics of tree growth in even- and uneven-aged stands at the limit of the closed black spruce (Picea mariana) forest in Quebec (Canada) were assessed on 18 plots with ages ranging from 77 to 340 years. Height, diameter and age of all trees were measured. Stem analysis was performed on the 10 dominant trees of each plot by measuring tree-ring widths on discs collected each meter from the stem, and the growth dynamics in height, diameter and volume were estimated according to tree age. Although growth followed a sigmoid pattern with similar shapes and asymptotes in even- and uneven-aged stands, trees in the latter showed curves more flattened and with increases delayed in time. Growth rates in even-aged plots were at least twice those of uneven-aged plots. The vigorous growth rates occurred earlier in trees of even-aged plots with a culmination of the mean annual increment in height, diameter and volume estimated at 40–80 years, 90–110 years earlier than in uneven-aged plots. Stand volume ranged between 30 and 238 m³ ha⁻¹ with 75% of stands showing values lower than 120 m³ ha⁻¹ and higher volumes occurring at greater dominant heights and stand densities. Results demonstrated the different growth dynamics of black spruce in single- and multi-cohort stands and suggested the need for information on the stand structure when estimating the effective or potential growth performance for forest management of this species.     

Modelling site quality and individual-tree growth in pure and mixed Pinus brutia stands in north-east Greece

? Simulation tools, based on individual tree growth and mortality models can produce the most detailed predictions of forest stand development under different management schedules. These models allow the manager to predict the development of any type of stand (even- and uneven-aged, and pure and mixed stands).

? Different model approaches and predictors are required for pure even-aged or mixed uneven-aged forest stands. This study developed and compared two sets of models which enable tree-level simulation of the development of pure and mixed stands of Pinus brutia in north-east Greece. The first set of models for even-aged forestry consists of site index models, diameter growth models, tree height models, and mortality models. The second set, which is for uneven-aged forestry, uses a past growth index instead of a site index.

? The simulations and overall fitting statistics suggest that the two types of models provide realistic and accurate predictions of forest stand development and allow one to simulate the development of complex Pinus brutia stand structures in Dadia National Park forests.

? The advantages of the two approaches are discussed and it is suggested that the growth index is an effective predictor of site quality and the set of models which used such variable as predictor performed in a similar way as the models using site index, which require more information and a given stand structure (even-aged).

     

Influence of fire and mountain pine beetle on the dynamics of lodgepole pine stands in British Columbia,Canada

An outbreak of the mountain pine beetle (Dendroctonus ponderosae Hopkins; MPB), currently affecting over 10.1 million hectares of lodgepole pine forests (Pinus contorta Dougl.) in British Columbia, Canada, is the largest in recorded history. We examined the dynamics of even-aged lodgepole pine forests in southern British Columbia, which were undergoing this MPB outbreak. Using dendroecology and forest measurements we reconstructed the stand processes of stand initiation, stand disturbances, tree mortality, and regeneration, and explained the current stand structure and the potential MPB impacts in selected stands. Our results indicate that stand-replacing fires initiated even-aged seral lodgepole pine stands in this region. In the absence of fire in the 20th century, multiple MPB disturbances, which each resulted in partial canopy removal, modified the simple one-layer structure of the fire-origin stands by the initiation of post-MPB disturbance regeneration layers, transforming the stands into complex, multi-aged stands. Despite high overstory mortality due to the current MPB outbreak, regeneration layers, which are likely to survive the current outbreak, will provide important ecological legacies and will contribute to mid-term timber supply.     

Adapting a model for even-aged Pinus pinea L. stands to complex multi-aged structures

Stone pine (Pinus pinea L.) stands have been usually managed as even-aged stands. Main objectives in management combine two main commercial productions, timber and pine nuts with other social aspects: soil protection, recreational use and biodiversity conservation. Multifunctional management, together with the occurrence of successive events affecting regeneration have oriented managers to propose a management schedule based on the establishment and preservation of a low-stocking multi-aged complex structure on favourable locations. Despite the recent effort on modelling growth and yield on even-aged stands of stone pine, no studies focusing on modelling dynamics for uneven-aged stands have yet been developed up to present.In this study, a proposal is presented for adapting and calibrating an existing tree-level model, originally developed for even-aged stands of stone pine (model PINEA2), to multi-aged complex stands. Data from four multi-aged trials and 61 plots from the National Forest Inventory were used to adapt the whole set of functions included in the original model. In our study, four different methods have been proposed to adapt the original equations: (1) direct validation and re-parameterization; (2) size class modelling; (3) refit of functions after removing typical even-aged covariates; and (4) multilevel calibration. Adaptation is based on assuming that a multi-aged stand of stone pine can be seen as the sum of independent, smaller, even-aged groups. The low densities of the stands, the early liberation of the most vigorous trees in all size classes and the major importance of root-level competition for water in Mediterranean forests are the main factors explaining these particular dynamics. Results show the suitability of the proposed method, attaining unbiased estimates with a degree of accuracy similar to that achieved in applying the original model to even-aged stands. The adapted model (PINEA_IRR) constitutes a flexible tool for the management and maintenance of stone pine stands, covering a wide range of within stand structural complexity, including forests in transition.