•We compared silver fir and beech in managed Dinaric karst forests during three years.•Quantum yield was studied in same four light microsites and three different gaps.•Response of species within ...same microsites was different between gaps.•With gap size quantum yield increased for beech and decreased for silver fir.•Gaps with low direct light or extended towards the southern gap edge favour fir.
Montane forests of silver fir (Abies alba Mill.) and European beech (Fagus sylvatica L.) in the Dinaric region are the largest continuous forest area in Central Europe, where silver fir’s regression is one of the region’s major concerns. Designing appropriate sized canopy gap spatio-temporal dynamics is the main silvicultural tool for indirect promotion of silver fir. Within gap microsites, categories based on shares of direct and diffuse radiation proved to be an interesting conceptual model for explaining microsite variation and seedling success induced by light and general climate variability.
In order to evaluate the response of beech and fir in different gap microsites, different light regimes were evaluated based on the proportion between direct and diffuse radiation in three different sizes of forest gap in managed forests. The photosynthesis response to different light conditions (max. photosynthetic rate – Amax and quantum yield – Φ) in beech and silver fir was compared on all microsites during three consecutive g periods (2009, 2010, and 2011) under controlled environmental conditions.
A different response between species in microsite light categories was shown between different gap sizes. In all microsite categories of both species, quantum yield appeared at lower light intensities with increasing gap size, with the exception of beech with a predominant direct light component, in which yield significantly increased. In order to favour fir, gaps with low direct light levels should be created, while existing gaps should be extended towards the southern gap edge. Our conclusions emphasize the importance of gaps, relatively smaller in size (0.03–0.11ha) but significant in contributing to increasing the competitive advantage of fir in mountainous, mixed-species Dinaric forests.
Rationalization and optimization of work is becoming increasingly important in the European forestry sector. In this study a tool for modeling three different precommercial thinning approaches in ...young beech mountain stands was developed based on several field studies. The simulation examines three primary types of precommercial thinning: selective thinning and two types of situational thinning. We studied the impact of the number of candidates/crop trees and the impact of harvesting intensity on the structure and consumption of productive time. We found that in terms of costs situational precommercial thinning is more rational than selective precommercial thinning, that harvesting intensity has a significant impact on time consumption and that the number of candidates or crop trees has a significant impact on time consumption as well as on the relationships between main and auxiliary productive time. The modeling has shown that situational thinning is an alternative to selective thinning and that, in addition to requiring smaller and more efficient harvesting machines, it offers a cost-effective and ergonomic option (more walking, less chainsaw operation) for the pre-commercial thinning of young forest.
Studies of old-growth forests are becoming increasingly important for the improvement of silviculture and for understanding environmental changes. However, in Europe such forests are rare, fragmented ...and influenced by millennia of human activity. Comparative studies of old-growth forests across Europe are needed to improve knowledge on how direct and indirect anthropogenic factors influence their structure. We analysed structural dynamics in 15 silver fir-beech-Norway spruce old-growth forests in Slovenia, Croatia, Slovakia and Bosnia-Herzegovina. Changes in diameter distributions, stand parameters and regeneration were analysed at intervals of 6-116 years. Most diameter growth at breast height (d.b.h.) distributions approximated a rotated sigmoid shape, which could be explained by differences in growth and mortality rates with respect to d.b.h. class and by disturbance history. Our results suggest that different disturbance types are likely to cause different changes in d.b.h. distributions. For example, overbrowsing, canopy dieback of silver fir and windthrow decreased the density of small, intermediate and large-diameter silver fir, respectively. The slopes of the fitted diameter distribution curves were steeper for beech than for silver fir, which could be explained by their different life strategies. Despite disturbances, growing stocks remained stable over the long term. A synchronous silver fir decline was confirmed. It was more pronounced in Slovenia and Slovakia, both of which experienced more SO2 pollution and had higher ungulate densities. The silver fir sapling stage was often totally absent in both countries. Our results suggest that anthropogenic disturbances, especially air pollution and overbrowsing (resulting from human-induced increases in deer density), significantly influenced the coexistence of silver fir and beech; asynchronous, patchy changes in species mixture have been replaced by large-scale synchronous changes.
Overview of resistance spot welding control Podržaj, P.; Polajnar, I.; Diaci, J. ...
Science and technology of welding and joining,
04/2008, Letnik:
13, Številka:
3
Journal Article
Recenzirano
This paper presents an overview of resistance spot welding control. The presentation of the physical background of the resistance welding process is followed by the description of the main problems ...concerning the appurtenant control theory. Solutions to these problems are presented primarily according to the measured signals used and to the type of control strategies.
The practice of salvage logging dead and damaged timber following large high severity disturbances has raised much controversy, partly because of the negative ecological effects that such practices ...have on forest ecosystems. Many of the studies on salvage logging effects, however, have been done on sites damaged by large, severe disturbances. Less is known about the ecological consequences of salvage logging following intermediate severity disturbances that cause partial canopy damage at smaller scales. We examined the response of the herbaceous layer and tree regeneration to salvaged and non-salvaged treatments following small-scale intermediate severity disturbances in eight mixed beech (Fagus sylvatica L.) dominated forest stands in Slovenia. The cover and diversity of herbaceous vegetation, as well as the density and diversity of tree regeneration were similar between treatments across the study sites. The only notable differences between the treatments were that salvaged sites had a larger proportion of shade intolerant tree species in the regeneration layer, while non-salvaged sites tended to have a more well-developed regeneration layer in taller height classes. The results suggest that salvage logging following small-scale intermediate severity disturbances may not hinder forest recovery in mixed beech dominated forests.
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.
Protection forests play an important role in mitigating the influence of natural hazards. Despite the growing need for protective functions due to aging forests and increased risk of natural ...disturbances, active forest management has become increasingly uncommon across the Alps. Active management of protection forests can be facilitated by state subsidies. This requires an objective delineation of forests with a direct protection function and the development of silvicultural techniques that mitigate natural hazards. A study of protection efficiency of beech-dominated forests in the Soteska gorge in NW Slovenia, where a main state road and railway are at risk from debris flows and rockfall, was performed. We assessed the starting points of debris-flow hazard based on a small-scale geological survey of the terrain characteristics and a local debris flow susceptibility map. We applied the TopRunDF model for determination of the run-out zones. Forest structure data were obtained from 26 sample plots. A detailed description and delineation of forest stands was performed. The results showed that these forests play an important role in the protection of infrastructure. Forest protection efficiency can be improved by stand thinning for stability and careful planning of regeneration patches over time and space. In areas where silvicultural measures cannot provide sufficient protection, technical measures are needed. Since these forests have not been managed for several decades, natural disturbances (windthrow) are frequent. Research findings suggest that regular assessment and management of these beech-dominated protection forests are necessary, contrary to the current practice of non-management in protection forests in Slovenia.
The aim of the study reported here is the development of a new method which allows rapid and accurate in-vitro measurements of three-dimensional (3D) shape of laser ablated craters in hard dental ...tissues and the determination of crater volume, ablation rate and speed. The method is based on the optical triangulation principle. A laser sheet projector illuminates the surface of a tooth, mounted on a linear translation stage. As the tooth is moved by the translation stage a fast digital video camera captures series of images of the illuminated surface. The images are analyzed to determine a 3D model of the surface. Custom software is employed to analyze the 3D model and to determine the volume of the ablated craters. Key characteristics of the method are discussed as well as some practical aspects pertinent to its use. The method has been employed in an in-vitro study to examine the ablation rates and speeds of the two main laser types currently employed in dentistry, Er:YAG and Er,Cr:YSGG. Ten samples of extracted human molar teeth were irradiated with laser pulse energies from 80 mJ to the maximum available energy (970
mJ with the Er:YAG, and 260
mJ with the Er,Cr:YSGG). About 2000 images of each ablated tooth surface have been acquired along a translation range of 10
mm, taking about 10
s and providing close to 1 million surface measurement points. Volumes of 170 ablated craters (half of them in dentine and the other half in enamel) were determined from this data and used to examine the ablated volume per pulse energy and ablation speed. The results show that, under the same conditions, the ablated volume per pulse energy achieved by the Er:YAG laser exceeds that of the Er,Cr:YSGG laser in almost all regimes for dentine and enamel. The maximum Er:YAG laser ablation speeds (1.2
mm
3/s in dentine and 0.7
mm
3/s in enamel) exceed those obtained by the Er,Cr:YSGG laser (0.39
mm
3/s in dentine and 0.12
mm
3/s in enamel). Since the presented method proves to be easy to use and allows quite rapid measurements it may become a valuable tool to study the influence of various laser parameters on the outcome of laser ablation of dental tissues.
A long history of human presence in the Alps has made studies of natural forest structure, composition, and disturbance processes difficult. In the Slovenian Alps, we identified a mixed European ...beech (
Fagus sylvatica L.)-silver fir (
Abies alba Mill.)-Norway spruce (
Picea abies (L.) Karst.) stand with old-growth characteristics that escaped past cutting. We reconstructed the dynamics of the stand using a combination of stand and age structure analyses, dendroecological evidence of past canopy disturbance, and historical evidence of past human activities. The disturbance reconstruction revealed a stand-scale disturbance in the 1850s. Based on the presence of pit-and-mound topography throughout much of the stand and the absence of logging activities found in historical records, we assume this event was caused by strong winds. The current structure and composition of the stand are largely a result of this event. Post-disturbance forest development was dominated by the release of shade tolerant regeneration, especially
F. sylvatica. The windthrow also created appropriate conditions (i.e. increased light and exposed mineral soil) for recruitment of less shade tolerant species, including larch (
Larix decidua Mill.) and maple (
Acer pseudoplatanus L.). The results suggest that periodic, intermediate severity wind disturbances, similar to the event documented here, may have had an important influence on pre-settlement forest dynamics in mixed mountain forests of the Alps, and add to the limited available information regarding the historic range of natural variability of disturbance processes. This information may be useful for forest management that attempts to emulate natural processes.
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