Jurij Diaci

Regeneration dynamics in a Norway spruce plantation on a silver fir-beech forest site in the Slovenian Alps

Conversion of Norway spruce (Picea abies (L.) Karst.) plantations is a great challenge for silviculture in Europe today. While complex problems with these stands are widely recognised, methods to regenerate or convert them to mixed stands are not yet well established. The purpose of this study was to determine favourable combinations of site factors (diffuse solar radiation (DIFF) and direct solar radiation (DIR), forest ground vegetation cover, thickness of humus horizons, browsing) for development of tree regeneration within gaps of different size and age, located in a Norway spruce plantation on a silver fir (Abies alba Mill.) and common beech (Fagus silvatica L.) forest site. Fifteen fenced and fifteen unfenced gaps with nine plots each were placed on the north slope of Mount Krasica, in the mountain vegetation belt, on limestone parent material. From 1993 to 1998 woody seedlings and saplings were observed. A successful development of Norway spruce, sycamore (Acer pseudoplatanus L.) and other frequently seed-bearing broad leaves was determined for the first years. Further development of seedlings was hindered by dense forest ground vegetation and browsing impact. Beech and silver fir regeneration was insufficient due to a lack of seed-bearing trees. On the basis of direct and DIFF radiation four groups of microsites were separated. This satisfactorily explained the differences in regeneration patterns among tree species. Norway spruce seedlings were most frequent in the group with high levels of diffuse and low levels of DIR, while sycamore saplings were most frequent in the group with high levels of both radiation components. Results obtained suggest that natural regeneration success and composition can be successfully influenced by managing the incidence of radiation in context with gap geometry (shape, size and orientation).

A dendroecological reconstruction of disturbance in an old-growth Fagus-Abies forest in Slovenia

The scarcity of large old-growth forests has made it challenging to quantify disturbance regimes in Central Europe. The objective of this study was to reconstruct the history of disturbance in an old-growth Fagus-Abies forest reserve in Slovenia using a dendroecological approach. We extracted cores from canopy trees blown down during a recent windthrow event and identified growth releases in the tree-ring series using boundary-line release criteria to infer past disturbances. A total of 216 release events were identified from 88 trees. Between 1790 and 1990, moderate, asynchronous release events were present in nearly every decade of the disturbance chronology, suggesting a history of frequent, low severity disturbance. However, there were also peaks in the chronology corresponding to synchronous release events in a large proportion of the trees, suggesting that less frequent, intermediate severity disturbance events played an important role in forest development. These events are likely caused from wind damage associated with local thunderstorms, which seem to occur at intervals between 20–80 years on the study site. Thus, in addition to the small-scale gap phase processes operating in the forest, the results indicate that periodic intermediate severity disturbance events are an important component of the disturbance regime in mountain forests of Central Europe.RésuméLe faible nombre de forêts anciennes suffisamment étendues rend difficile la quantification des régimes de perturbation en Europe centrale. L’objectif de cette étude est de reconstituer l’histoire de ces perturbations dans une hêtraie-sapinière ancienne mise en réserve en Slovénie en utilisant une approche dendroécologique. Des carottes ont été extraites du tronc d’arbres dominants renversés lors d’un récent chablis. Les séries temporelles de cernes ont été analysées pour identifier des périodes de relâchement de contraintes de croissance et pour en déduire l’intensité des perturbations passées. Un total de 216 événements de relâchement de contrainte a été identifié pour 88 arbres. Entre 1790 et 1990, des événements d’intensité modérée et asynchrones ont été détectés dans les séries chronologiques au cours de pratiquement toutes les décennies. Cela suggère une fréquence élevée de perturbations de faible intensité. Cependant, des pics d’enregistrement d’événements synchrones ont été identifiés dans la chronologie dans une proportion importante d’arbres. Cela suggère que des perturbations de sévérité intermédiaire ont joué un rôle important dans le développement de la forêt, malgré leur plus faible fréquence. Ces événements ont probablement été causés par des chablis provoqués par des orages locaux violents, qui semblent se produire à des intervalles de 20 à 80 ans sur le site d’étude. Les résultats montrent ainsi qu’en sus de perturbations locales de faible intensité conduisant à la formation de petites trouées, les perturbations périodiques de sévérité intermédiaire constituent une composante importante du régime de perturbations dans les montagnes en Europe centrale.

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.

Gap dynamics and structure of two old-growth beech forest remnants in Slovenia.

Context Due to a long history of intensive forest exploitation, few European beech (Fagus sylvatica L.) old-growth forests have been preserved in Europe. Material and Methods We studied two beech forest reserves in southern Slovenia. We examined the structural characteristics of the two forest reserves based on data from sample plots and complete inventory obtained from four previous forest management plans. To gain a better understanding of disturbance dynamics, we used aerial imagery to study the characteristics of canopy gaps over an 11-year period in the Kopa forest reserve and a 20-year period in the Gorjanci forest reserve. Results The results suggest that these forests are structurally heterogeneous over small spatial scales. Gap size analysis showed that gaps smaller than 500 m2 are the dominant driving force of stand development. The percentage of forest area in canopy gaps ranged from 3.2 to 4.5% in the Kopa forest reserve and from 9.1 to 10.6% in the Gorjanci forest reserve. These forests exhibit relatively high annual rates of coverage by newly established (0.15 and 0.25%) and closed (0.08 and 0.16%) canopy gaps. New gap formation is dependant on senescent trees located throughout the reserve. Conclusion We conclude that these stands are not even-sized, but rather unevenly structured. This is due to the fact that the disturbance regime is characterized by low intensity, small-scale disturbances.

Comparing close-to-naturesilviculture with processes in pristine forests: lessons from Central Europe

The specific goals of this paper are the following: 1. To determine, using beech-dominated pristine forests as anexample,themaindrivingforcesofgenerationrenewal intermsoflifecycledurationandspatialrenewalpatterns; 2. Toillustratecontrastinglightrequirementsduringrenewal by comparing pristine oak and beech forests; 3. To elucidate the lower limits of stocking and canopy openness for silvicultural renewal in small clusters based on pristine forest research; 4. Topresentanapproachforimplementingthesefindingsin a liberal and versatile forest management

Response of Quercus robur L. seedlings to north-south asymmetry of light within gaps in floodplain forests of Slovenia

To examine Quercus robur establishment and growth in low to intermediate light levels, we analysed regeneration in different microsites created by light asymmetry within gaps in two main floodplain forest regions of Slovenia: Dolinsko and Krakovo. Four years after a mast year in 1995, we installed systematic grids of 1×1 m plots in 11 gaps (0.03–0.40 ha) on wet and dry site variants. In 256 plots, seedling species, cover, density, height, height increment, browsing damage, tree architecture, understory vegetation species and cover, and direct and diffuse light were measured. The average seedling density in all gaps was 15/m2, but the highest densities were found in gap positions with low diffuse light levels (10–20%). Competing understory vegetation was more abundant in positions with high diffuse light. In gaps on dry site variants a combination of low diffuse and high direct light was favourable for regeneration. The results indicated that Q. robur can successfully establish in gaps. Here, both light components were sources of within gap resource heterogeneity, therefore knowledge of light asymmetry can improve regeneration success.RésuméPour examiner l’installation et la croissance de Quercus robur, sous des niveaux d’éclairement faibles à moyens, nous avons analysé la régénération dans différents microsites affectés par l’asymétrie da la lumière dans des trouées en forêts inondables en Slovénie : Dolinsko et Krakovo. Quatre années après une forte glandée en 1995, nous avons installé des placettes d’observation suivant une grille de 1×1 m dans 11 trouées (0.03–0.40 ha) de stations sèches et humides. Les paramètres suivants ont été mesurés sur 256 emplacements : l’espèce des semis, l’abondance relative, la densité, la hauteur l’accroissement en hauteur, les dommages d’abroutissement, l’architecture des arbres, les espèces du sous-bois, l’éclairement direct et diffus. La densité moyenne des semis de toutes les trouées était de 15/m2, mais les plus fortes densités ont été trouvées dans les trouées aux expositions caractérisées par des faibles niveaux d’éclairement diffus (10–20%). La végétation compétitrice du sous-bois était plus abondante dans les situations à niveau élevé de lumière diffuse. Dans les variantes sèches des trouées, une combinaison de faible niveau de lumière diffuse et de fort éclairement direct était favorable à la régénération. Les résultats indiquent que Quercus robur peut s’installer avec succès dans les trouées. Ici, les deux composantes de l’éclairement ont été sources d’hétérogénéité dans les ressources des trouées, par conséquent la connaissance de l’asymétrie de l’éclairement peut améliorer le succès de la régénération.

Modelling drainage fluxes in managed and natural forests in the Dinaric karst: a model comparison study

Two models for calculating the forest water balance were applied to different development stages of managed and non-managed forests in the Dinaric Karst for two hydrologically contrasting growing seasons. A simple model WATBAL, which calculates water balance on a monthly basis, and the BROOK90 model, which calculates water balance on daily basis, were used. Differences between calculated drainage fluxes between the models were less pronounced in the drier growing season and were lower in the forest stands compared to forest gaps. Average calculated drainage fluxes of the two growing seasons were highest in the gaps and lowest in the stand in the virgin forest remnant, followed by the mature stand in the managed forest. According to model fitting, testing the calibration robustness and sensitivity analysis the BROOK90 model was considered best at simulating the water balance of the various research sites. The difference in model behaviour is considered to be mainly the result of the difference in model time step and the inclusion of macropore flow in BROOK90. The greater complexity of the BROOK90 model meant it could be parameterized to describe more fully the complexity of the horizontal and vertical structure of forest stand and soil properties. A disadvantage of the BROOK90 model is the greater need of input data. WATBAL, however, was useful for obtaining rougher estimates of the water balance components and can be applied to areas where there is less data available. Choice of model is therefore determined by data availability.

Variation in irradiance, soil features and regeneration patterns in experimental forest canopy gaps

Key messageNatural regeneration of beech, maple and fir was investigated in relation to irradiance, ground vegetation and soil features. Seedling establishment may be favoured by creating small and irregular gaps and by successive extension of gaps along the sun-exposed gap edge.ContextTo successfully manage natural regeneration, it is important to understand the interactions of forest gap micro-climates and soil features.AimThe aim of this study was to identify conditions for successful natural regeneration of European beech, sycamore maple and silver fir in mixed forests.MethodsSeedling growth and survival were recorded within and around two artificial gaps, and the relationships to irradiance, ground vegetation and soil features were examined. A simple conceptual model was applied to identify optimal micro-sites for regeneration.ResultsGround vegetation hindered the establishment of natural regeneration in the centre of the gaps. Small seedlings of maple and beech were more abundant within the small gap and along gap edges; beech had the highest density on sun-exposed edges and maple on shaded gap edges. Tall beech and maple seedlings were more abundant along sun-exposed gap edges. Greater variability of irradiance in the larger gap contributed to greater micro-site heterogeneity relative to the small gap.ConclusionsSeedling establishment may be favoured by creating small and irregular gaps and by successive extension of gaps along the sun-exposed gap edge. Circular gaps with diameters greater than stand height contribute to increased ground vegetation coverage and hinder tree regeneration, including semi-shade tolerant maple and spruce.

Functional analysis of vegetation on alpine treeline ecotone in the Julian and Kamnik-Savinja Alps in Slovenia

Our study focused on the functional aspects of plant species and vegetation at the transition from larch (Larix decidua Mill.) forest to mountain pine (Pinus mugo Turra) stands on the alpine treeline ecotone. With increasing elevation, living conditions grow harsher, which is reflected in the plant species and functional trait composition of plant communities. At four different localities in the Slovenian Alps, relevés along an altitudinal gradient and according to vegetation type were made (European larch forests, larch trees-mountain pine shrubs, mountain pine shrubs), using standard Central European phytocoenological method. In the upper mountain pine belt, few differential species were found, since most species represented in mountain pine stands also occurred in the lower two vegetation belts, while there were many differential species in the lower forest belt. Species with considerable competitive ability and moderate stress tolerance dominated the upper treeline ecotone, whereas ruderality is poorly expressed. The importance of stress tolerance in plant strategies increased slightly in the mountain pine belt. Changes in the representation of some functional traits attributes were detected by vegetation belts, but complete species turnover did not occur. Changes in dominant life form involved greater cover of chamaephytes and nanophanerophytes in the upper mountain pine belt. Species with evergreen leaves dominated mountain pine stands and deciduous forest stands. The share of species with scleromorphic leaves increased in the direction of the mountain pine belt while the share of species with mesomorphic and hygromorphic leaves declined. Mountain pine stands create good conditions for the regeneration of tree species and colonisation by ecologically more demanding forest species while species of alpine grasslands withdraw on open areas. Since today’s treeline is lowered due to past human activity, an upward shift is expected. Also, considering the great importance of competition strategy, current conditions in mountain pine stands are favourable for future forest succession.

Culture and Silviculture: Origins and Evolution of Silviculture in Southeast Europe

SUMMARY Silvicultural practices are generally developed to meet societal objectives given the constraints of the site. This simple premise is a foundation of modern silviculture. However, silviculture may vary for other reasons related to cultural factors. This paper reviews the differences in silviculture in the twelve countries that comprise southeastern Europe, an area that includes a variety of cultures, and a complex history. The silviculture generally follows three models: coppice systems that are largely unregulated, even-aged stands that include former coppice stands and other reforested sites, and systems to develop and maintain complex stand structures. Plantation management is not common. Cultural and historic drivers have affected the development of silviculture in this region. Additional drivers include forest access, the importance of wood for fuel, and proximity to central Europe. It is anticipated that European Union membership of countries in the region will lead to greater regional and international exchange and cooperation in the future.