Single-tree Selection System Research Articles

Variable-density thinning designs for harvester-based operations in Northern Europe

ABSTRACT Variable-density thinning (VDT) can be used to start the conversion of young homogeneous conifer plantations to the single-tree selection system. A design for VDT is presented, which is adapted to harvester-based operations in northern Europe without prior tree marking and the low target diameters in the region. Six treatment cells with a size of 10 × 10 m are placed along a 30 m stretch of a strip road with treatments gap (removing all but understory trees), skip (no thinning), and four treatment cells with crop tree-based crown thinning, which removes two dominant competitors of 1–4 crop trees per cell. Skips might in later thinnings be converted into gaps, which is why skips and gaps are placed systematically in the 2 × 3 treatment blocks. Assignment of the crop tree number variants to treatment cells are decided by the harvester operator based on the given stand structure and presence of crop trees meeting all selection criteria. So far, five operations have confirmed the practicality of this design and given some insight into the learning process of harvester operators with these new methods.

Effects of single tree selection cutting on vascular plant species diversity components in temperate forests of Hyrcanian region

Temperate forests in northern Iran are one of the most important natural ecosystems with the highest economic value and a key role in the conservation of forest biodiversity in Iran. We studied vascular plant species diversity components (alpha, beta and gamma) of herb and tree layers on 120 plots at six sites in forests managed by single tree selection and forests that have been left unmanaged for more than 30 years in the Hyrcanian forest zone in northern Iran. Generalized linear mixed models (GLMM) were used to analyse the effect of management on stand properties, tree and herb layer local diversity and soil characteristics. Despite the differences in herb layer local α-diversity, forest management did affect neither community composition of the herb layer nor regional γ-diversity. Also, species richness as well as α- and γ-diversity of the tree layer was significantly higher in managed forests, while β-diversity showed no directional response across herb and tree layers. According to constrained ordination analysis, main drivers for explaining variance in plant species composition were soil organic matter, total nitrogen, potassium, phosphorous, pH and forest structural variables (basal area, number of trees per hectare and canopy cover) in herb and tree layers. We found that in Hyrcanian forests single tree selection management promotes environmental conditions that effectively contribute to increased diversity of the herb and tree layers at the local and regional scale compared to unmanaged forests. The higher diversity of herb and tree layers is likely being driven by higher within-stand heterogeneity, improved light availability in managed forests due to lower stocking density and larger canopy gaps, or also results from topsoil disturbances through wood extraction. This study indicated that single tree selection system has the potential to be used in order to improve biodiversity conservation, and these results can be useful for development of management guidelines and decision-making processes.Because it may not be specific enough to dismiss or prioritize forest management regimes, based only on their impact on plant diversity, further assessments of forest management effects on other crucial factors (such as fauna diversity, structural diversity and forest ecosystems services) are needed.

Norway spruce (Picea abies (L.) H. Karst.) selection forests at Siljansfors in Central Sweden

Continuous cover forestry (CCF) is a type of forest management which is based on ecological principles and avoids clearfelling as much as possible. A specialised form of CCF is the selection system which relies on inhomogeneous size structures in mixed-species forests and on the harvesting of individual dominant trees. The selection system was originally invented by upland farmers in Central Europe some 500 years ago and is fairly uncommon in Northern Europe. In our research, we studied two more or less mono-species Picea abies selection forests at Siljansfors in Central Sweden that have a comparatively low final stem diameter of 50 cm. We involved dynamic demographic equilibrium modelling to identify an ideal size structure as a reference that ensures sustainability. We compared this reference with the observed empirical stem-diameter distributions and found that both stands are indeed advancing towards the structure typical of single-tree selection systems. One stand is particularly close to this ideal, sustainable structure whilst the other requires more goal-orientated management in the future. Our research confirmed that selection forests with largely only one conifer species and a fairly small final diameter are possible at this latitude. We could also show that the dynamic demographic model can be converted to a simpler static model that is easier to apply in forest practice. Since selection stands are rare in Fennoscandia, the two stands studied at Siljansfors have been and will continue to be important research and management demonstration sites in the future.

Tree quality and value: results in northern conifer stands after 65 years of silviculture and harvest

Despite the importance of financial outcomes to stand-level forest management decision-making, long-term assessments are rare. We compared the quality and value of mixed, northern conifer (Picea–Abies–Tsuga) stands in Maine, USA, treated with a range of silvicultural systems and exploitive cuttings for 65 years. Ten replicated treatments — single-tree selection and uniform shelterwood systems, commercial clearcutting, fixed and guiding diameter-limit cutting, and no cutting — were assessed for quality and value of standing and harvested trees. Selection systems resulted in good tree quality and high stand value, particularly when applied on a short cutting cycle, but small harvest volumes were not always commercially operable. Shelterwood system resulted in good tree quality, but changes in species values over time influenced financial outcomes. In contrast, commercial clearcutting and fixed diameter-limit cutting resulted in poor tree quality and low residual stand value after multiple harvests. Guiding diameter-limit cutting resulted in high stand value and is more appropriately characterized as a silvicultural system than exploitive harvesting when applied with harvest volume limits and seed tree retention. Overall, treatments focused on short-term financial gain led to degraded stand conditions, while those that sought to grow high-quality trees resulted in desirable outcomes over the long term.

The impact of consecutive, shelter and single tree selection system on quantitative characteristics of oriental beech forest in the Muzisay section forest, plan of Haftkhal2, Neka forest

ارزیابی روش‌های مدیریتی در جنگل برای تعیین شیوۀ مناسب مدیریت پایدار ضروری است. به همین دلیل برخی از پارامترهای کمی جنگلی که به‌صورت متوالی ابتدا به شیوۀ تدریجی ‌پناهی و سپس تک‌گزینی بهره‌برداری شدند و پارسل شاهد مقایسه شد. برای این منظور پارسل شاهد و بخش‌هایی از پارسل‌های مجاور آن در راشستان‌های سری موزیسای جنگل‌های هفت‌خال نکا انتخاب شدند. نمونه‌برداری در شبکه‌ای به ابعاد 150 در 200 متر در قطعات ده‌آری صورت گرفت. قطر برابرسینۀ همۀ درختان قطورتر از 5/12 سانتی‌متر و ارتفاع 8 درخت اندازه‌گیری شد. نتایج نشان داد که از سال 1380 تا سال 1398 فراوانی راش در پارسل‌های بهره‌برداری‌شده از 51/81 درصد به 2/96 درصد افزایش و فراوانی ممرز از 41/14 درصد به 9/2 درصد کاهش یافت. فراوانی راش در پارسل شاهد از 9/89 درصد به 7/93 درصد رسید، ولی در فراوانی ممرز تغییری ایجاد نشد. متوسط تعداد در هکتار، در پارسل شاهد از 5/275 اصله به 83/245 اصله کاهش یافت، ولی در پارسل‌های بهره‌برداری‌شده از 32/259 اصله به 81/315 اصله افزایش یافت. حجم در هکتار در قطعات بهره‌برداری‌شده از 47/481 سیلو به 31/426 سیلو کاهش یافت، ولی در پارسل شاهد از 4/454 سیلو به 27/528 سیلو در هکتار افزایش یافت. هر دو عرصۀ تحت بررسی دارای ساختار ناهمسال تقریبا منظم بودند. ساختار حجمی در هر دو عرصه نزدیک به نرمال بوده است. در مجموع به‌جز قطر برابرسینه، تفاوت بین پارسل شاهد و توده‌های بهره‌برداری‌شده در دیگر پارامترهای تحت بررسی معنی‌دار نشد. در واقع بهره‌برداری از جنگل به شیوۀ تک‌گزینی در جنگل تحت بررسی سبب تخریب نشد.

Impact of silvicultural system on natural regeneration in Western Himalayan moist temperate forests of Pakistan

Site conditions (topography, aspect, moisture availability, humus thickness, light exposure, and grazing activities) play a vital role in the germination and regeneration process. The research was conducted in the Himalayan moist temperate forest. The research site was divided based on the silvicultural system (group selection system and single-tree selection system) into 148 plots and 150 plots, respectively. The group selection system was examined on the site of 2 ha which was clear-felled under a project in the 1980's. The present study examined the impact of silvicultural systems on regeneration. The frequency table was used, and relative frequency was calculated for the species and silvicultural system, density per m2 was also calculated. Diversity indices were calculated through taxa, dominance, Simpson’s index, Shannon index, evenness, equitability, and fisher alpha. Ten taxa were found in both silvicultural systems, with individual repetition of 17 and 15 taxa, respectively. Group selection is more compact visibly as compared to the single-tree selection system. The single-tree selection system is more diversified in species composition, stand structure, moisture availability, and less humus availability. The study also highlights future predictions for the conservation of these forests, which are highly sensitive and a hotspot for wildlife and climate change phenomena. Silvicultural practices such as silvicultural system, cleaning, weeding, thinning operations are regularly practiced, which can reduce the negative impact on these productive forests.

Sustainability of High-Value Timber Species in Mixed Conifer–Broadleaf Forest Managed under Selection System in Northern Japan

Understanding the sustainability of high-value timber species in managed forests provides useful information for the management of these species in the long-run. Using nearly 50 years of census data in long-term permanent plots, we investigated the sustainability of three high-value timber species—monarch birch (Betula maximowicziana Regel), castor aralia (Kalopanax septemlobus (Thunb.) Koidz), and Japanese oak (Quercus crispula Blume)—in cool-temperate mixed forest under a selection system in northern Japan. We used stocking, demographic parameters, and species proportions of these species as measures of sustainability. Results showed that the tree density and basal area of the three high-value timber species increased during the study period. Moreover, the basal area increment of these species showed an increasing trend across census periods. However, while no significant differences in the tree mortality of these species were observed, the numbers of in-growth fluctuated across census periods. Increasing trends in species proportions of monarch birch and Japanese oak were observed. Even though there were some fluctuations across census periods, especially in smaller diameter classes, diameter distribution curves of high-value timber species followed a reversed J-shaped pattern. The results revealed that the sustainability measures of high-value timber species can be achieved in forest stands managed under single-tree selection system. In addition, the results also indicated the changing structure and composition of the forest stand. The stocking and basal area increment of conifers decreased while those of broadleaves increased. The proportion of conifers decreased to 33.01% in 2008–2016 from 48.35% in 1968–1978. The results of this study would be useful for adapting silvicultural practices and harvesting practices as well as for simulating various silvicultural and management options for high-value timber species.

Conceptual decision-making framework for the sustainable harvesting of forest and woodland species for medicinal tree bark in southern Africa

Tree bark is widely used in traditional medicine in southern Africa. The growing demand for medicinal bark requires scientifically sound harvest systems for sustainable use. A conceptual framework and decision matrix are presented to aid forest managers in selecting the most appropriate system for the sustainable harvesting of particular species. The conceptual framework is based on the results of experimental bark harvesting of selected forest and woodland tree species in southern Africa, where tree response to bark stripping was assessed. The extent and rate of bark regrowth and the susceptibility of the exposed wood to fungal and insect damage, are of particular importance to assess harvest options. The decision matrix groups species based on tree response to bark stripping, and identifies the most appropriate harvest option for a particular species. Species-specific harvest prescriptions are formulated and alternatives to strip harvesting are identified where avoidance is advised. The conceptual framework and decision matrix were applied to forest woodland species on which experimental bark harvesting was conducted in Malawi, South Africa and Zambia. Of the 22 species studied, 10 have the potential for strip harvesting, based on extent of bark regrowth and susceptibility to fungal and insect damage. These were assessed further in terms of prescriptions for strip harvesting. For the remainder, full-tree harvesting in a single-tree selection system would be the most viable harvest option. Alternatives to strip and full-tree harvesting are also discussed.

Assessing small-stem density in northern hardwood selection system stands

Data from three uneven-aged northern hardwood stands in New York State were analyzed to assess the effects of understory American beech (Fagus grandifolia Ehrh.) density on changes of small stems within the 2.54 to 5.08 cm diameter class during the first cutting cycle under single-tree selection system. Findings show that the amount of understory American beech on a regeneration plot, quantified using a species index value (SIV), affects the abundance of other species. Results reveal the future plot-level stocking of these small trees for (i) all species (including American beech) as related to time since cutting and residual basal area or (ii) non-beech species as influenced by beech interference (SIV), time since cutting, and residual basal area. Findings indicate that for plots with limited understory beech, small-stem stem density will increase from postcut levels to a peak at 8–12 years after selection system cutting and then decrease. The higher the residual basal area is, the sooner the numbers of small trees reach a peak level and the fewer are present of that threshold size. Findings confirm that no or only minimal numbers of small non-beech trees develop on plots with high levels of understory American beech (SIV ≥ 0.5).

Comparing the Quantity and Structure of Deadwood in Selection Managed and Old-Growth Forests in South-East Europe

The knowledge about the impact of selection silviculture on deadwood components is fairly scarce. This study compared two Dinaric old-growth forests (OGFs) with adjacent managed forests (MFs) in which the single-tree selection system has been applied for a century. The comparisons were made in terms of the current amounts of coarse woody debris (CWD), distribution of its decay stages, and diameter structure of different CWD types (snags, logs, stumps). The relationship between the volume of live and dead trees was also examined. In both OGFs and MFs, the most snags were found in the third decay stage, while the volume of logs and stumps increased from the first to fifth decay class. The study showed the clear advantage of OGFs over adjacent selection MFs in terms of CWD volume, whereas the basal area of live trees and growing stock were not always reliable indicators for distinguishing between MFs and OGFs. The diameter distribution of individual CWD types (snags, logs, stumps) also differed significantly between selection MFs and OGFs in all tested pairs. This fact, along with the significant differences in CWD volume, indicates that selection silviculture should be amended to incorporate practices that ensure more natural management of deadwood components.

Single-tree selection system effects on forest soil macrofauna biodiversity in mixed oriental beech stands

Hyrcanian temperate forests are of importance due to their genetic variation, biodiversity, commercial productions and many other ecosystem services. Over the past decades the selection silvicultural system (mostly single-tree selection) has been the dominant method to manage and utilize these forest ecosystems. This study aimed to assess the effect of single-tree selection silvicultural system on mixed beech stands of eastern Hyrcanian temperate forests using soil macrofauna as bioindicator. Therefore 91 forest treefall gaps have been selected of which 36 gaps were natural gaps in managed stands, 41 gaps were human created gaps and 14 gaps were natural gaps in virgin stands. In each gap 3 soil profiles and in each profile 3 soil samples were taken at 3 depths, including litter layer, shallow (0–10cm) and deep (10–20cm) soil. Macrofauna of all soil samples were extracted and identified to class level and weighed. Diversity (Shannon and Simpson) and evenness indices were calculated for all soil samples. Results showed that most important macrofauna based on biomass were Clitellata, Gastropoda, Chilopoda and Diplopoda in the study area. In the litter layer of all gaps Gastropoda (snails) have the most amount of biomass followed by Chilopoda (millipedes), while in shallow and deep soil Clitellata (earthworms) and Chilopoda were the main classes based on biomass. There was no significant difference in diversity and evenness indices among the three gap groups (virgin, natural and artificial) which indicates that the single-tree selection system has not intensive and irrecoverable effects on the soil macrofauna of the studied forest stands after about 10 years.

Stand structural complexity of mixed old-growth and adjacent selection forests in the Dinaric Mountains of Bosnia and Herzegovina

Research results on the structure of European OGF are often contradictory; while some researchers stress equilibrium structures, others suggest that this rarely happens due to biomass accumulation. If the former were the case, then there would be a fairly strong argument that OGF should serve as natural references for selection management. At the same time, mountain mixed selection forests are in many regions considered to be the most “natural” type of MF, and thus to a large extent similar to corresponding OGF. However, because there are few old-growth forests (OGF) left in Europe, comparisons between OGF and selection-managed forests (MF) are rare. Since nature-based silviculture should follow natural processes and not exclude any species from its natural range, in this study we compared two mixed OGF and neighboring MF (Piceo-Abieti-Fagetum illyricum) in the Dinaric Mountains of Bosnia and Herzegovina. The MF were managed by the single-tree selection system for almost a century. The results indicated that this management approach yielded a statistically significant difference in tree species composition and presence of large-diameter trees. The cumulative diameter distributions, however, were similar in OGF and MF as both exhibited the shapes that are considered to provide demographic equilibrium. On the species level, though, this was the case only for beech. Species occurrence matrices indicated significant dominance of young European beech (Fagus sylvatica L.) trees over silver fir (Abies alba Mill.) and Norway spruce (Picea abies L. Karst) in OGF. Nevertheless, based on the results from MF, the study highlights the crucial role of silvicultural measures that may potentially provide targeted long-term coexistence of the studied broadleaved and coniferous tree species.

Proportional basal area method for implementing selection silviculture systems in longleaf pine forests

Proportional basal area (Pro-B) was developed as an accurate, easy-to-use method for making uneven-aged silviculture a practical management option. Following less than 3 h of training, forest staff from a range of professional backgrounds used Pro-B in an operational-scale field study to apply single-tree selection and group selection systems in longleaf pine (Pinus palustris Mill.) stands. Field crews achieved precision levels often within 3%–5% of the 11.5 m2·ha−1 target residual basal area. By aggregating many diameter classes into only three diameter-class groups, Pro-B improves efficiency by requiring tree markers to remember only three fractions, while making a single pass through the stand. Trees of large size, specific species and with good form, broad crowns and cavities can be retained, while adjusting spacing to release residuals. Systematic quantification of marking trees for removal enables different individuals to obtain similar results. Early observations revealed encouraging levels of pine regeneration and stand development, along with continuing good volume growth rates of 3% per year. Although less certain until one or more cutting cycles are completed, these early tests indicate that a stable mature forest structure should develop, which is characterized by the presence of large trees and natural regeneration.

Vulnerability of uneven-aged forests to storm damage

Uneven-aged forests are assumed to have a high stability against storm damage but have rarely been analysed for vulnerability to storm damage due to a lack of a sufficient empirical database. Here we model storm damage in uneven-aged forest to analyse major factors that may determine the sensitivity of this type of forests to storms based on a broad database. Data are derived of public forests in the canton Neuchâtel in West Switzerland that are dominated by silver fir and Norway spruce and managed since the beginning of the 20th century following a single-tree selection system. A unique dataset of periodical (every 5–10 years) full inventories measuring the diameter of every single tree including salvage cuttings was available for the investigation. The time series reached back until 1920 and covered an area of 16 000 ha divided into 3000 divisions. The effect of a major winter storm (‘Lothar’) in December 1999 on these forests was investigated using a subset of 648 divisions. The influence of the vertical stand structure on the vulnerability of storm damage was studied using logistic regression models. To facilitate the analyses, an index of closeness to a J-shaped distribution (LikeJ) based on the number of trees in different diameter classes was developed. Besides structural indices, variables representing stand characteristics, soil-related and topography-related variables were included. The results of our study show that the overall damage level of the investigated forests was rather low. The variables that entered the model for the unevenaged stands were different to those that are normally significant for even-aged stands. While variables like stand structure, the timing of the harvesting and topographic variables entered a multivariate statistical model as significant predictors, standard predictors for storm damage in even-aged stands such as stand density, thinning intensity or species composition were not significant. We hypothesize that the uneven-aged structure of the investigated forests may be one reason for the low damage level we observed but emphasize the need for more detailed research to support this conclusion.

Analisi storica e modellizzazione della dinamica del carbonio in foresta attraverso il Carbon Budget Model: un esempio per la Provincia Autonoma di Trento

Historical analysis and modeling of the forest carbon dynamics using the Carbon Budget Model: an example for the Trento Province (NE, Italy). The Carbon Budget Model (CBM-CFS3) developed by the Canadian Forest Service was applied to data collected by the last Italian National Forest Inventory (INFC) for the Trento Province (NE, Italy). CBM was modified and adapted to the different management types (i.e., even-aged high forests, uneven-aged high forests and coppices) and silvicultural systems (including clear cuts, single tree selection systems and thinning) applied in this province. The aim of this study was to provide an example of down-scaling of this model from a national to a regional scale, providing (i) an historical analysis, from 1995 to 2011, and (ii) a projection, from 2012 to 2020, of the forest biomass and the carbon stock evolution. The analysis was based on the harvest rate reported by the Italian National Institute of Statistics (from 1995 to 2011), corrected according to the last INFC data and distinguished between timber and fuel woods and between conifers and broadleaves. Since 2012, we applied a constant harvest rate, equal to about 1300 Mm3 yr-1, estimated from the average harvest rate for the period 2006-2011. Model results were consistent with similar data reported in the literature. The average biomass C stock was 90 Mg C ha-1 and the biomass C stock change was 0.97 Mg C ha-1 yr-1 and 0.87 Mg C ha-1 yr-1, for the period 1995 -2011 and 2012-2020, respectively. The C stock cumulated by the timber products since 1995 was 96 Gg C yr-1, i.e., about 28% of the average annual C stock change of the forests, equal to 345 Gg C yr-1. CBM also provided estimates on the evolution of the age class distribution of the even-aged forests and on the C stock of the DOM forest pools (litter, dead wood and soil). This study demonstrates the utility of CBM to provide estimates at a regional or local scale, using not only the data provided by the forest inventories, but also by forest management plans.

Potential Yields and Economic Returns of Natural Disturbance-Based Silviculture: A Case Study from the Acadian Forest Ecosystem Research Program

Intrastand variability is promoted by many silvicultural systems designed to emulate natural disturbance regimes (natural disturbance-based silviculture [NDBS] systems) in the eastern United States and Canada but this variability is difficult to model in many growth-and-yield models, limiting application by the region's forest managers. We used a resampling approach to integrate intrastand variability into Forest Vegetation Simulator (FVS) growth-and-yield projections. We subsequently compared potential yield and financial returns over a 100-year period for two NDBS systems monitored in the Acadian Forest Ecosystem Research Program with two conventional systems: a two-stage uniform shelterwood and a single-tree selection system. NDBS systems produced the widest diameter distribution at the end of the harvest rotation and were more effective in recruiting large trees (>24 in.) and more diverse species relative to conventional silviculture systems. Projected merchantable yield and financial return were highest for the single-tree selection, followed by the two NDBS systems and finally the shelterwood; however, if standing merchantable value at the end of simulation was included, the NDBS systems ranked first and third overall financially. Our analysis suggests that NDBS systems are capable of sustaining a greater diversity in forest structure and composition while producing volume yields and financial returns that are competitive with conventional even- and uneven-aged silvicultural systems.

Long-term productivity of helicopter logging in Sarawak

Management of natural forests in the tropics generally involves some type of single-tree selection system that has only a few trees removed per hectare. To reduce the impact of harvesting on the residual stands, logging operations are increasingly moving to low-impact harvesting systems that work with single-tree selection. One low-impact harvesting system is the use of helicopters. However, helicopters are significantly more expensive than ground-based systems, and understanding the factors that influence productivity is critical to profitability of operations. This paper provides an analysis of logging productivity in the tropics using data from four different timber licenses operated by WTK in Sarawak over an 18-year period and using Sikorsky 61F, 64E, and 64F and Kamov KA-32 helicopters. The results show that productivity, measured as average volume produced per hour, is a function of the number of turns per hour, the number of productive hours in a day, the proportion of choker turns, and the type of helicopter. The relatively even hourly production through balancing log size and use of chokers also shows the effect of proper planning in helicopter harvesting.

Le modèle spatial de rendement est-il une solution plus pertinente pour l¿exploitation des forêts tropicales ?

L'expérience de sociétés forestières pratiquant l'abattage sélectif d'arbres individuels au Sarawak montre que leurs opérations ne sont encadrées en général que par une réglementation de base concernant par exemple le diamètre minimum d'abattage, les dimensions maximales des trouées ou les essences autorisées. En général, les aspects sylvicoles ne sont, au mieux, pris en compte qu'implicitement dans les règlements sur l'abattage, et non explicitement dans la planification et les opérations d'abattage. Les sociétés forestières tendent de plus en plus à pratiquer un comptage à 100 % des arbres, associé à une cartographie par GPS, dans le cadre de systèmes d'exploitation à impact faible ou réduit. L'utilisation de systèmes GPS permet d'élaborer des bases de données spatialisées et des descripteurs clés des arbres. Ceux-ci pourraient servir d'appui à la planification d'activités futures basées sur des modèles de croissance et de rendement permettant de prendre en compte des paramètres forestiers importants, comme le DBH et les essences présentes, et de cartographier la position des arbres. Cela aiderait les gestionnaires des récoltes et les arpenteurs forestiers à passer d'une optique purement opérationnelle à une optique sylvicole, en prenant en compte des paramètres tels que l'espacement, le recrutement et les tiges d'avenir lors de la planification des opérations d'abattage. L'absence de ce type de planification parmi les sociétés forestières est principalement due au fait que les modèles d'exploitation forestière en milieu tropical sont généralement basés sur des paramètres de zonage (modèles à l'échelle des peuplements ou selon les classes de dimension) qui ne sont pertinents que par rapport aux besoins de la planification à grande échelle. Ces modèles n'intègrent généralement pas les données spatiales générées par la planification, ils nécessitent des données beaucoup plus nombreuses et différentes de celles utilisées pour planifier les opérations d'abattage et ne produisent pas de résultats utiles à la planification opérationnelle des récoltes. Il est plus utile de se servir de modèles par arbre qui intègrent des données spatiales et produisent des résultats pertinents au plan opérationnel, comme les diamètres, les essences et la position des arbres. Cet article rappelle les contraintes opérationnelles de l'exploitation forestière à impact faible ou réduit, et préconise des approches pour la modélisation des rendements compatibles avec ces systèmes.

Predicting future diameter of sugar maple in uneven-aged stands of west-central New Brunswick and New York

We used data from uneven-aged research plots in west-central New Brunswick to validate a sugar maple (Acer saccharum Marsh.) diameter growth model initially developed from remeasured trees in single-tree selection system stands at two New York State locations. We also refitted the coefficients to fit the New Brunswick data and added variables to account for variation across locations and treatments among the New Brunswick plots. The original equation predicted future diameter for New Brunswick trees reasonably well, but a version with coefficients specific to New Brunswick proved more accurate. Adding variables that account for unique features of the New Brunswick data reinforced the notion that growth rates differ across locations, and also that post-cutting diameter growth varies with the intensity of release. Although the New York model and the general model with refitted coefficients unique to New Brunswick indicated that rates of growth do not change throughout a cutting cycle, equations having a variable to account for location of the New Brunswick research sites showed that growth decreased with time. Test results are presented.

Effect of canopy gap size and ecological factors on species diversity and beech seedlings in managed beech stands in Hyrcanian forests

We studied the species diversity of the herb layer and eco- logical factors in harvest-created gaps in beech stands under a single-tree selection system in Northern Iran. To determine diversity, the number of beech seedlings, and other ecological factors, 16 gaps were selected and subplots of 5 m 2 were positioned at the centre and at the cardinal points of each gap. Species richness and Simpson diversity index increased with increasing gap area as did numbers of seedlings. With increasing humus layer thickness, species richness declined but the Hill evenness index increased. Species richness increased with increasing light availability. There was no relationship between crown radii of beech trees and diver- sity indices. Correlations between environmental factors and numbers of individuals of some species in the herb layer were not significant except in a few cases. The results help explain the effects of man-made gaps on the dynamics of managed beech stands and this benefits evaluation of silvicultural operating plans.