Andrej Bončina

Long-term changes of structure and tree species composition in Dinaric uneven-aged forests: are red deer an important factor?

Uneven-aged silver fir-European beech forest stands were studied to (1) analyse the dynamics of diameter structure and tree species composition in the past two centuries and (2) determine the impact of red deer on the regeneration and recruitment of silver fir. The study used current data on forest stands, archival data from old forest management plans for the period 1789–2004, and red deer harvesting records for the period 1907–2006. During the observation period, the silver fir population aged and silver fir and European beech alternated in dominance. The study revealed a strong impact of red deer on the composition and recruitment of tree regeneration, especially on silver fir regeneration. The drastic changes in red deer density (from extermination up to 5.8 animals km−2) and past forest management practices were apparently the main factors driving the population dynamics of silver fir (regeneration, recruitment, and diameter structure) in the study area during the past two centuries.

Stand dynamics of Dinaric old‐growth forest in Slovenia: Are indirect human influences relevant?

Abstract Understanding forest stand structural change is crucial for forest ecosystem research and management. The aim of our research was to identify structural and compositional changes and possible natural and anthropogenic causes of these changes in an old‐growth silver fir‐beech forest in the Dinaric mountains of Slovenia. Data on stand structure of the Rajhenavski Rog (51.14 ha) forest reserve originated from traditional methods, including five successive full callipering (1957–2007), two regeneration inventories and analysis of developmental phases (1984, 2007). A drastic decrease in the silver fir proportion in the last 50 years was probably caused by two indirect anthropogenic factors: polluted air and heavy browsing damage of silver fir regeneration. Nevertheless, other factors including reciprocal replacement of fir and beech and climate change also influenced the species composition, as similar processes were documented in the past with less air pollution. Furthermore, the alternation of fir and beech often developed asynchronously, regardless of ungulate density. Although the vertical profile of the old‐growth forest was opened due to the loss of fir trees during past decades, the establishment of more light‐demanding species was uncommon, primarily because the growing stock and forest climate were sustained. The results suggest a high stability of mixed Dinaric old‐growth forest ecosystems.

Factors related to natural disturbances in mountain Norway spruce (Picea abies) forests in the Julian Alps.

Abstract: An analysis of natural disturbances in the Julian Alps was carried out in the Jelovica-Pokljuka region (9627 ha) for the period 1979–2006. Data from salvage cuttings were used to examine the occurrence of windthrow, snow break, and insect attack disturbances in relation to site and stand characteristics, previous disturbances, and forest management. Forest stands at the site were characterized by a high growing stock (400 m3·ha-1 on average) and a large proportion of Norway spruce (87%). Salvage cutting due to windthrow, snow break and insect attacks was strongly related to altitude, aspect, topographic position, diameter structure, developmental phase of the stands, and forest landscape heterogeneity. Pole stands were more susceptible to snow breakage and less susceptible to windthrow and insect attack. A more heterogeneous forest landscape increased the risk of windthrow and insect attack occurrence, while the severity of all natural disturbances was lower in more heterogeneous forest landscapes. Natural disturbances and previous cuttings also significantly influenced the likelihood of occurrence and the severity of subsequent disturbances. To improve stand resistance, forest management measures considering the silviculture system and thinning are discussed. Nomenclature: Pfeffer, 1995; Oberdorfer, 2001.

Conceptual Approaches to Integrate Nature Conservation into Forest Management: A Central European Perspective

SUMMARY There are two main approaches to nature conservation in forest management. In the segregation approach, nature conservation is one of the management objectives which is limited to protected forest areas, while the integration approach considers the economic, social, and ecological components of sustainable forest management at the same time and place. Nature-based (close-to-nature) silviculture and forest planning that conserve natural stand dynamics, respect the local site conditions, monitor forest ecosystems and their conservation status, and harmonise suitable measures addressed to management objectives and nature conservation standards are crucial for integrating nature conservation into forest management. The social, economic, and bio-geographical conditions of forests vary greatly; therefore, concepts of integrating nature conservation into forest management cannot be uniform. On a global scale, the segregation model is generally accepted as the most suitable approach, but the integration model could be a possible alternative in many cases.

Effects of selective thinning on growth and development of beech (Fagus sylvatica L.) forest stands in south-eastern Slovenia

We studied the effects of two types of selective thinning on beech stands formed by a shelterwood cut in 1910 — with lower number of crop trees and higher thinning intensity (T1) and higher number of crop trees with lower thinning intensity (T2). The stands were thinned in 1980, 1991 and 2001. Despite a lower stand density after thinning, the annual basal area increments of thinned stands in both thinning periods (1980–1991 and 1991–2002) were around 20% higher compared to those of the control (unthinned) stands. The mean annual basal area increment of dominant trees was 30–56% larger in the thinned plots compared to the control plots. Of 176 initial crop trees in the T1, 72% were chosen again during the last thinning. In the T2, 258 crop trees were chosen in the first thinning, and only 62% of these trees were chosen again during the last thinning. Only crown suppression and diameter classes of crop trees significantly influenced their basal area increment when diameter classes, crown size, crown suppression, and social status were tested. In the thinned stands, the dominant trees are more uniformly distributed if compared to the dominant trees in the control plots. Finally, the herbaceous cover and the species diversity were higher in the thinned plots.RésuméNous avons effectué des recherches sur les effets de deux sortes d’éclaircies sélectives entreprises sur des peuplements de hêtres formés par la coupe d’abri de 1910 : l’une avec un faible nombre d’arbres de place et une grande intensité d’éclaircie (T1), l’autre avec un nombre élevé d’arbres de place et une intensité faible. Ces peuplements ont été éclaircis en 1980, 1991 et 2001. Bien que la surface terrière de ces peuplements ait été réduite, l’accroissement en surface terrière des peuplements éclaircis a été supérieur de 20 % approximativement aux cours des deux périodes séparant les éclaircies (1980–1991 et 1991–2002) à celui des peuplements non éclaircis. L’accroissement moyen en surface terrière des arbres dominants a été de 20 à 56 % supérieur dans les peuplements éclaircis. Soixante-douze % des 176 arbres de place initiaux de la parcelle expérimentale T1, ont de nouveau été désignés lors de la dernière éclaircie. Sur T2, il y avait 258 arbres de place lors de la première éclaircie, et seulement 62 % d’entre eux ont été de nouveau désignés au cours de la dernière éclaircie. Une analyse parallèle de l’influence des classes de diamètre, de la taille et du couvert des houppiers, et du statut social des arbres montre que le couvert et les classes de diamètre des arbres de place exercent une influence marquée sur l’accroissement de leur surface terrière. Dans les peuplements éclaircis, la répartition spatiale des arbres dominants est plus régulière que dans les peuplements non éclaircis. Le couvert de la strate herbacée et la diversité des espèces sont plus importants dans les peuplements éclaircis.

Comparison of forest stand structure and management of silver fir–European beech forests in the Central Apennines, Italy and in the Dinaric Mountains, Slovenia

In this study, silver fir – European beech forest types were examined in their structure and tree species composition. Two study areas, one in the Molise Region in Italy (Abeti Soprani) and one in the Dinaric Mountains in Slovenia (Leskova dolina), were compared in their dynamics and present structure. The aim of the study was to assess if a standardized field survey protocol can supply indicators related to forest structure and composition, and deadwood amount in two different Natura 2000 sites. The present structure and composition were evaluated on a 1-ha plot in each area. All live trees, standing and downed dead trees, snags, stumps, and lying coarse woody debris were censed. For each individual tree, the position within the plot, the species, diameter at breast height, height or length, crown structure and height, and decay level (only for deadwood) were recorded. The forest structure was influenced by past management, modifying the tree density, the amount of deadwood and the growth trends. The spatial distribution of trees and their vertical stratification show pluristratified stands with a mainly horizontal random pattern. The assessment of forest parameters in large plots could be an opportunity to evaluate the best choices for a nature-based silvicultural approach.

Forest planning across Europe: the spatial scale, tools, andinter-sectoral integration in land-use planning

New approaches to forest planning are needed to support the transition of European forests to sustainable management. The aim of this study is to review forest planning systems already in place throughout Europe by exploring a set of case-study countries reflecting the main silvicultural schools of Western Europe, including Belgium, Finland, France, Italy, Portugal, and Slovenia. A literature review and case-study data were used to assess the scale factors (vertical logic) as well as the relationships between forest planning and other environmental/land-use planning sectors (horizontal logic). The influence of EU policy on the development of forest planning is also discussed. As assessed using the vertical logic, the multi-scale and multi-topic planning approaches adopted in the countries studied here are highly heterogeneous. The horizontal logic shows that despite the importance of an inter-sectoral and harmonic relational framework between forest planning and the planning efforts of other sectors such as landscape and urban planning, the various plans are barely consistent with each other across the European countries studied here. Although interest is growing in the multi-functionality of forests, their sustainable management calls for the development of better integrated planning approaches across Europe.

Ensuring the validity of private forest owner typologies by controlling for response style bias and the robustness of statistical methods

In survey-based segmentation of forest owners, two threats to the validity of results have largely been ignored: (1) response style bias and (2) the robustness of the statistical methods. This study demonstrates response style bias detection, presents an approach for correcting for acquiescence – the systematic tendency to agree with survey items, and explores the sensitivity of a probabilistic clustering algorithm to requirements for the validity of the typology. Structural equation modeling and Monte Carlo data generation techniques were employed to detect acquiescence and estimate its effect on construct validity. A survey of the relevance of management information for private forest owners (N = 364) was used as an example. Although acquiescence was confirmed, it had minor effect on the results and no effect on the substantive construct. Uncertainty about the number of forest owner types and membership can be reduced by using probabilistic clustering and observing the number of clusters while changing the requirements for the validity of clusters. The expectation maximization algorithm proved to be robust even to stringent requirements for the validity of clusters. By controlling for response style and the robustness of statistical methods, the validity of private forest owner typologies can be better ensured.

Importance of Priority Areas for Multi-Objective Forest Planning: A Central European Perspective

SUMMARY In the framework of multi-objective forest management, ‘priority areas’ which are relatively more important for the selected management objectives are commonly designated. Using a comparative analysis of guided interviews, we examined the use and importance of priority areas in forest planning in nine Central European countries. In all countries, priority areas have been widely used, forest function areas and protected areas being the most common. According to management objectives, more than 20 types of priority areas were recognised, with priority areas for protection against natural hazards, nature conservation, recreation, welfare, and production being the most prevalent. Criteria for the designation differ among the countries; however, site conditions and infrastructure facilities are most often used. The scale of designation ranges from 1:10 000–1:50 000, and the size of priority areas varies from 0.1 ha to several hundreds of ha. The level of participation of stakeholders involved in the designation of priority areas differs among and within the countries. The effectiveness of priority areas for forest management can be improved by transparent designation criteria, objective oriented management measures, and efficient financial instruments.

Ecology and silviculture of silver fir (Abies alba Mill.): a review

ABSTRACT Silver fir (Abies alba Mill.) is one of the most valuable conifer trees in Europe for historical and economic reasons. Growing interest in the species, along with the recognition that silver fir was subjected to inappropriate silvicultural measures during the 20th century due a lack of understanding of its ecology, have spurred recent studies from various disciplines which have yielded new insights into the gene ecology, history, ecology, structure and dynamics of fir populations. In this paper, we provide a multidisciplinary, synoptical review discussing the prospects for silver fir forestry in the 21st century. We describe the main characteristics of the history and ecology of silver fir, with a particular emphasis on gene ecology and the structure and dynamics of fir populations with respect to mixed stands and fir management. Fir is a fundamental species for maintaining high biodiversity in forested ecosystems because of its shade tolerance, plasticity to environmental conditions and ability to coexist with many tree species. Silver fir ecotypes show remarkable variation in features such as frost hardiness, drought resilience and shade tolerance. Fir can create stands of heterogeneous stand structure, from one-storied through to multi-storied structure and finally to selection structure. Natural regeneration of fir will be scarce if fir stands are managed inappropriately through the application of clear cutting, a short regeneration period and abrupt removal of shelter trees. Climate change is expected to reduce the abundance and distribution range of silver fir. Improvements in forest management treatments are recommended to improve silver fir conservation.