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Povzetek: Tree heights are one of the most important aspects of forest mensuration, but data are often unavailable due to costly and time-consuming field measurements. Therefore, various types of models have been developed for the imputation of tree heights for unmeasured trees, with mixed-effects models being one of the most commonly applied approaches. The disadvantage here is the need of sufficient sample size per tree species for each plot, which is often not met, especially in mixed forests. To avoid this limitation, we used principal component analysis (PCA) for the grouping of similar plots based on the most relevant site descriptors. Next, we compared mixed-effects models with height-diameter models based on artificial neural networks (ANN). In terms of root mean square error (RMSE), mixed-effects models provided the most accurate tree height predictions at the plot level, especially for tree species with a smaller number of tree height measurements. When plots were grouped using the PCA and the number of observations per category increased, ANN predictions improved and became more accurate than those provided by mixed-effects models. The performance of ANN also increased when the competition index was included as an additional explanatory variable. Our results show that in the pursuit of the most accurate modelling approach for tree height predictions, ANN should be seriously considered, especially when the number of tree measurements and their distribution is sufficient.
Ključne besede: height-diameter models, national forest inventory, permanent sample plot, mixed forests, model comparison, principal component analysis
Objavljeno v DiRROS: 08.06.2022; Ogledov: 576; Prenosov: 248
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Povzetek: Legislation and policy makers have recognized private forest owners cooperation in machinery ring as an instrument to support wood mobilization through efficient use of machinery. The study analyzes private forest owner’s cooperation in the machinery ring in Slovenia and determines whether this cooperation contributes to wood mobilization from small-scale private forests. The research was conducted in two phases. In the first phase, the survey was conducted among the members of machinery rings at their annual general meetings (24 machinery rings participated in the survey, representing 64.9% of the total number of machinery rings). The questionnaire was distributed to all members present at the annual general meetings (n=529) and only those who were private forest owner or provided services within machinery rings were eligible to complete the questionnaire (n=438). In the second phase, data on the amount of service provided by machinery ring members were compared with the amount of felling in private forests for 2019 to gain insight into the extend of forestry work (timber harvesting) carried out in a private forest under neighbourhood assistance.The results show that machinery rings members are predominantly male, on average 50 years old, mainly with high school education and occupation in agriculture, owning on average 15.2 ha of forest. Regardless of forest management activities, machinery ring members perform forest management activities in their forest by themselves or with the help of family members. Only a small proportion of members use neighbourhood assistance to carry out the work. This most often occurs in the transport of timber. A very small proportion of members provide forest services through the machinery ring, but their scope of services is not insignificant. In 2019, machinery ring members most often performed harvesting activities with the chain saw, followed by timber skidding as a service. Equipment with machinery for providing services is good among members – about three quarters of them have a chainsaw and an adapted agricultural tractor, but this machinery is quite old, showing that machinery is insufficiently used for forestry operations. The results show that machinery rings are nowadays an essential part of strategic (operational) management in Slovenian agriculture and forestry, and provide important insights into the possibilities to improve forestry operations and the future development cooperation between private forest owners in machinery rings to support wood mobilization from small-scale private forests.
Ključne besede: private forest management, harvesting intensity, cooperation, machinery cooperation, neighbourhood assistance
Objavljeno v DiRROS: 25.04.2022; Ogledov: 613; Prenosov: 441
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Povzetek: The European spruce bark beetle (Ips typographus L.) is an eruptive forest pest that has caused a great deal of damage in the last decades because of increasing climatic extremes. In order to effectively manage outbreaks of this pest, it is important to predict where they will occur in the future. In this study we developed a predictive model of the sanitary felling of Norway spruce (Picea abies (L.) H. Karst.) because of bark beetles. We used a time series of sanitary felling because of bark beetles from 1996 to 2020 in Slovenia. For the explanatory variables, we used soil, site, climate, geographic, and tree damage data from the previous year. The model showed that sanitary felling is negatively correlated with slope, soil depth, soil cation exchange capacity, and Standard Precipitation Index (less sanitary felling in wet years). On the other hand, soil base saturation percentage, temperature, sanitary felling because of bark beetles from the previous year, sanitary felling because of other abiotic factors from the previous year, and the amount of spruce were positively correlated with the sanitary felling of Norway spruce due to bark beetles. The model had an R2 of 0.38. A prediction was performed for 2021 combining an occurrence model and a quantitative model. The model can be used to predict the amount of sanitary felling of Norway spruce due to bark beetles and to refine the risk map for the next year, which can be used for forest management planning and economic loss predictions.
Ključne besede: sanitary felling, prediction, Ips typographus, Picea abies, Slovenia, forecasting, insect outbreak forest pest
Objavljeno v DiRROS: 21.02.2022; Ogledov: 709; Prenosov: 596
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Povzetek: It is expected that climate change as well as abiotic and anthropogenic disturbances will strongly influence temperate forests. Besides changes in the main climate variables, various disturbance factors may significantly worsen conditions for mesic Slovenian forests (SE Europe) dominated by European beech (Fagus sylvatica), Norway spruce (Picea abies) and European silver fir (Abies alba). In Slovenia, the climate has warmed in recent decades, with an average annual rate of increase of about 0.4°C per decade or even more than 0.5°C per decade in summer. In addition, disturbances have caused considerable damage to trees in the most extensive forest types in Slovenia, starting with a widespread ice storm in 2014, followed by bark beetle outbreaks, windthrows and salvage logging interventions. After 2014, salvage logging increased from about one third to two thirds of the total annual felling. Over the last two decades, we have observed a decline in Norway spruce growing stock, with the highest rate of decrease in areas below 500 m a.s.l., and an increasing trend for European beech. Overall, the three dominant species (beech, spruce, silver fir), which together account for more than 70% of the total growing stock, have shown a declining trend over the last 20 years. The patterns observed are broadly consistent with earlier predictions developed for different climate change scenarios and with those reported in many other European countries. Adaptive forest management, which implements close-to-nature silviculture, has been traditionally practised in the region under study and has the potential to play an important role in reducing the risks associated with the impacts of climate change and disturbances in the future.
Ključne besede: climate warming, disturbance factors, ice storm, bark beetle outbreaks, spruce decline, salvage logging, tree species composition, temperate forest, Slovenia
Objavljeno v DiRROS: 03.01.2022; Ogledov: 822; Prenosov: 660
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Ključne besede: karst hydrogeology, global environmental changes, large-scale forest disturbances, aquifer recharge, water monitoring
Objavljeno v DiRROS: 03.12.2021; Ogledov: 1191; Prenosov: 727
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