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HR  EN   



Scientific-technical and professional journal
of Croatia Forestry Society
                         Issued continously since 1877.
       First issue of this web edition start with number 1-2/2008.
   ISSN No.: 1846-9140              UDC 630*https://doi.org/10.31298/sl

Portal of scientific
journals of Croatia
   Issued by: Croatian Forestry Society

   Address: Trg Mažuranića 11, HR-10000 Zagreb, Croatia
   Phone/fax: ++385 1 4828477
   e-mail: urednistvo@sumari.hr
   Editor in Chief: Josip Margaletić

Uredništvo   513
What does the Glasgow Conference bring us?      
The major UN climate conference COP26 recently ended with the adoption of the global “Glasgow Climate Pact” agreement. At the same time, all unresolved elements in the mechanisms for the implementation of the 2015 Paris Agreement on Climate Change were acknowledged and the transparency of the procedures in its application was agreed upon. As part of the signed Declaration on Forests and Land Use, which has so far been supported by over 140 countries in which more than 90 % of world’s forests are located, the leaders pledged to work together to “halt and reverse forest loss and land degradation” by 2030.
The first objective of the conference was to limit the increase in global average temperature to a level significantly lower than 2 °C above the level in the pre-industrial period, as well as to invest efforts in limiting it to 1.5 °C. The second objective was to adapt to the effects of climate change and align financial flows with climate-resilient development. To this end, it is planned to mobilise 100 billion US dollars by 2025. As a leader in the fight against climate change, the EU has committed itself to reducing greenhouse gas emissions by at least 55 % by 2030 compared to 1990.
The general conclusion is that forests will be vital in achieving the goals of fighting against global warming. According to research by the World Resources Institute (WRI), forests absorb 30 per cent of carbon dioxide emissions. Although the forest is a natural climate buffer in the fight against global warming, the fact is that the world’s forest area continues to decline rapidly.
The Conference was also attended by the Croatian Prime Minister, Mr Andrej Plenković. He announced the cessation of electricity production from coal by 2033 at the latest and an increase in the share of renewable energy sources in overall consumption to more than two thirds. He spoke highly of Croatian forestry and its century-old tradition, which is otherwise rarely heard from our politicians. One of the activities that Croatia is planning in the next period is the planting of one million additional trees per year by 2030. This means an increase in the planting from the current nine million trees to ten million in order to annul the greenhouse gas emissions generated by tourist vehicles ­arriving in Croatia.
The Prime Minister’s announcement raised a number of questions in the public, such as what the current condition of our forests is, whether they are being rapidly cut down, whether the company Croatian Forests Ltd can meet such an ambitious plan, and others. All these issues once again showed a lack of understanding and ignorance of forests and forestry. First of all, cutting down forests is prohibited in Croatian forestry, except in prescribed cases, as evidenced by the increase in forest areas. The public associate afforestation, that is, planting seedlings, only with forest regeneration. Throughout the century-long tradition of Croatian forestry, forest regeneration has been based on natural regeneration, while bare, unforested and non-forested areas are afforested, including those forest areas affected by fires and other disasters where natural regeneration is not possible or has failed for any other reason. Regrettably, the “Brussels bureaucrats” do not know this either, otherwise they would not, as was the case with ice-break in Croatia in 2014, have recognized and financially valorised only the planting of trees as a recovery measure. Among other things, by doing this we are returning the pioneer species to forest areas improved by climatogenic species, thus making a “step backwards”.
The next danger lies in limiting felling, (read: managing forests). As much as it makes sense to stop cutting down forests, in Croatia and countries with developed forestry it may have negative consequences. Restricting forestry operations through passive protection of forests, preferring “old forests”, etc. will have a negative effect on their condition and stop the process of their regeneration. It is well known that young forests increment the most and thus absorb the highest amounts of CO2.
Another question is how we dispose of the felled wood mass. Are we finalizing it sufficiently, are we cascading wood, are we recycling it, or are we replacing it all with the need for new quantities? Let us also ask ourselves in what way and in what amounts we use wood as the most environmentally friendly energy source. The fact is that we have not yet systematically mastered the extraction of biomass from our forests, while wood pellets, the production of which we have raised to an enviable level thanks to cheap raw material, end up mostly in other countries, reducing their greenhouse gas pollution.
Editorial Board

David Mijoč, Nikola Perković, Mario Šporčić, Matija Landekić, Matija Bakarić, Andreja Đuka, Tomislav Poršinsky  UDK 630*360 +761
Evaluation of the method of calculating the planned price of timber harvesting operations      
The paper presents the method of calculating planned prices of timber harvesting operations, which are the subject of public tenders in the forest management company Hercegbosanske šume Ltd. Kupres and the analysis of deviations of the planned from the contracted (realised) prices for timber harvesting operations in 97 groups of compartments, which were the subject of public tenders in 2019 and 2020. Descriptive and correlation statistical analysis also included stand and terrain indicators in groups of compartments in public tenders: area, net volume of marked trees, harvesting density, number of marked trees per hectare, volume of medium marked tree, slope, average timber extraction distance, terrain stoniness and parameter of uphill timber extraction. The test of dependent data pairs indicated that there is a statistically significant difference between planned and contracted prices of timber harvesting operations (t = 7,78, p < 0.001), and the results of correlation analysis confirmed the connection of influential factors of forest operations with the contracted and planned timber harvesting prices. Due to the statistically significant (p < 0.05) and very strong correlation with the contracted and the planned price of the timber harvesting operations calculated by the presented method, the dependence was equalized by a linear regression model with a coefficient of determination of 0.667. In conclusion, the method of calculating the planned price of timber harvesting operations is a good predictor of what can be contracted prices in public tenders thus showing its suitability in future calculations. Weak and negative correlation (p < 0.05, r = -0.22) of the difference between the contracted and planned price of the timber harvesting operations on the volume of the medium marked tree, indicated future monitoring to determine its causes, which could be: 1) mutual competition between timber harvesting operations providers with a larger volume of medium marked tree or 2) overestimation of the volume of medium marked tree in the presented model. Guidelines for increasing the accuracy of determining input parameters (average timber extraction distance, slope, terrain stoniness, and parameter of uphill timber extraction) are also presented. Given that the calculation is related to the average planned price at the level of forest management, which is determined by the management of the company, it is necessary to constantly monitor the market in order to react in time if major oscillations occur.

Key words: timber harvesting; planned price; contracted price; market

    David Mijoč  
    PERKOVIĆ, Nikola    ŠL
    ŠPORČIĆ, Mario      ŠL
    Matija Landekić  
    BAKARIĆ, Matija    ŠL
    Andreja Đuka  
    PORŠINSKY, Tomislav      ŠL
T. Gomerčić, I. Topličanec, V. Slijepčević, S. Blašković, I. Selanec, I. Budinski, J. Tomaić, J. Kusak, Gj. Ivanov, M. Sindičić  UDK 630* 152 + 146 (001)
Distribution and minimum population size of Eurasian lynx (Lynx lynx) in Croatia in the period 2018–2020      
Scientific data on distribution and abundance of endangered species are the foundation for their effective conservation and management. In this paper, we present results of the first scientifically – based estimation of lynx population size in Croatia. The goal of the study was to determine the area of lynx distribution and to estimate the minimum size of lynx population in Croatia in the period 2018 - 2020. To determine lynx distribution, 902 signs of lynx presence were collected in the period from the beginning of May 2018 until the end of April 2020. Out of those, 92.8% of lynx observations were categorized as C1, 2.8% as C2 and 4.4% as C3. Permanent lynx presence was confirmed in Primorsko – Goranska and Ličko – Senjska county, in southern part of Karlovac county and north-eastern part of Zadar county on the total surface of 7200 km2. For the minimum population size estimation, 804 camera trap photographs led to identification of 89 – 108 adult lynxes. Among 108 identified individuals there were 29 females, 22 males, while for 7 animals the sex was not determined. During the two reproductive seasons, we photographed 44 cubs in 25 litters. Future important steps in lynx population monitoring are correcting the deficiencies identified in this study and implementation of methodology that will allow us to use spatial capture recapture models for estimation of lynx abundance in Croatia.

Key words: distribution; abundance; Lynx lynx; minimum population size; Croatia

    Tomislav Gomerčić  
    Ira Topličanec  
    Vedran Slijepčević  
    Silvia Blašković  
    Ivana Selanec  
    Ivan Budinski  
    Josip Tomaić  
    Josip Kusak  
    Gjorge Ivanov  
    Magda Sindičić  
Lovre Panđa, Ante Šiljeg, Ivan Marić, Fran Domazetović, Silvija Šiljeg, Rina Milošević  UDK 630*174.7
Comparison of GEOBIA classification algorithms based on Worldview-3 imagery in the extraction of coastal coniferous forest      
With their ecological, economic, aesthetic, and social function, coniferous forests represent an important part of European forest communities. The main objective of this paper is to compare the most used GEOBIA (Geographic Object-Based Image Analysis) classification algorithms (Random Trees - RT, Maximum Likelihood - ML, Support Vector Machine - SVM) for the purposes of the coastal coniferous forest detection on a high-resolution WorldView-3 (WV-3) imagery on the topographic basin of the Split settlement (Figure 1). The methodological framework (Figure 2) includes: (1)
derivation of a sharpened multispectral image (WV-3MS) (Figure 3); (2) testing of the user-defined parameters in segmentation process (Figure 4); (3) marking of test samples (signatures); (4) classification of a segmented model; (5) accuracy assessment of the classification algorithms, and (6) accuracy assessment of the final model. The developed ACP tool (Automated Classification Process) (Supplement figure 5) for speeding up the entire classification process, enabled the simultaneous generation of output results for three selected classification algorithms (RT, ML and SVM) (Figure 6). Metric indicators (correctness - COR, completeness - COM, and overall quality - OQ) have shown that RT is the most accurate classification algorithm for the coastal coniferous forest detection (Table 1; Figure 7). The iterative setting of segmentation parameters enabled the detection of the most optimal values &8203;&8203;for generating a segmentation model. It is found that shadows can cause significant problems if classification is done on high-resolution images (Figure 8). The solution may be to collect a larger number of samples in different areas for the purpose of more detailed class differentiation. The modified Cohen’s kappa coefficient (K) indicator shown the accuracy of the final model of 87.38% (Table 2; Figure 9). WV-3MS can be considered as very good data for the detection of coniferous forests using the GEOBIA method (Figure 10). According to this research, 31.36% of the Split topographic basin is covered by highly and extremely flammable vegetation.

Key words: GEOBIA; WorldView-3; Coniferous Forest; Random Trees; Maximum Likelihood; Support Vector Machine.

    Lovre Panđa  
    Ante Šiljeg  
    Ivan Marić  
    Fran Domazetović  
    Silvija Šiljeg  
    Rina Milošević  
Marina Milović, Verica Vasić, Milan Drekić, Branislav Kovačević, Saša Pekeč, Zoran Galić, Saša Orlović  UDK 630* 181.3 + 164 (001)
Diversity of ectomycorrhizal fungi associated with Quercus petraea in the national park Fruška gora in the Republic of Serbia      
Although sessile oak is one of the most important deciduous forest tree species in Europe, data on the diversity of ectomycorrhizal (ECM) fungi on sessile oaks in the Republic of Serbia are scarce. The aim of this study was to provide the first insight into the diversity of ECM fungi on sessile oak in Serbia. Two sites Info center and Brankovac, located in National Park Fruška gora were chosen. ECM fungi were identified combining morphological and anatomical characterization with molecular analysis of nuclear rDNA internal transcribed spacer (ITS) region. All vital ECM root tips were counted, diversity indices were calculated, and ECM fungi were classified into the exploration types. The granulometric and chemical composition of soil were analyzed as well. At both sites, 26 different ECM fungal taxa were recorded in total, 17 taxa were observed at the site Info center and 12 taxa at Brankovac. ECM communities consisted of a few abundant taxa and a larger number of rare taxa. Lactarius quietus, Cenococcum geophilum, and Tomentella sublilacina were recorded at both sites. High abundance of contact and short-distance exploration types recorded in studied stands suggests that soils are sufficiently rich in total nitrogen and organic matter. Values of diversity indices recorded in studied sessile oak stands from Fruška gora were lower in comparison to those obtained in stands of different oak species across Europe which is likely induced by drought. To get a more thorough insight into the diversity of ECM fungi on sessile oak, research should be continued at more sites and seasonal dynamics should be included.

Key words: ectomycorrhiza; Quercus petraea; morpho-anatomical characterization; molecular identification; exploration types

    Marina Milović  
    Verica Vasić  
    Milan Drekić  
    Branislav Kovačević  
    Saša Pekeč  
    Zoran Galić  
    Saša Orlović  
Zafer Yücesan, Derya Bayram  UDK 630* 232.3 (001)
Effects of pretreatment, sowing time, sowing environment and climate factors on germination in Acer pseudoplatanus L.      
In this study, the effects of different sowing environment (greenhouse and nursery), pretreatment (cold moist stratification), different sowing time (autumn, spring and summer) and some climate factors (air temperature, relative air humidity, soil temperature and soil moisture) on the germination of Acer pseudoplatanus L. seeds were studied. Seeds were harvested from the tree located in the Karadeniz Technical University campus. Three different germination trials were carried out; (1) direct sowing in autumn after seed collection (Control), (2) sowing stratified seeds in spring (Stratification-1) and (3) sowing stratified seeds in summer (Stratification-2). During the germination trial processes, air temperature, relative air humidity, soil temperature and soil moisture were measured periodicaly. Thus, the germination percentage changes in different sowing environments have been established on the basis of some climate factors. Higher germination percentages were obtained in the autumn (Control) compared to the spring (Stratification-1) and summer (Stratification-2) sowings. The highest percentages of germination were ­determined in the control trials (70% in greenhouse and 58% in nursery). Obtained germination results based on different sowing times revealed secondary dormancy in Acer pseudoplatanus L. seeds. It has been determined that the mean germination time in the greenhouse (12 days) was shorter than the mean germination time in the nursery (18 days). In addition, the obtained results showed that stratification and sowing time have a positive effect on the mean germination time in the greenhouse. Because of getting the best germination rates, keeping some climate ­factors constant (21.0-24.9 °C air temperature; 17.0-19.9 °C soil temperature; 63.0-68.9% relative air humidity; 60.0-67.9% soil moisture) during the vegetative propagation practices in the greenhouse, should affect mass ­seedling production in Acer pseudoplatanus L.

Key words: cold-moist stratification; sowing time; seed storage; greenhouse; nursery

    Zafer Yücesan  
    Derya Bayram  
Ivan Balenović, Luka Jurjević, Krunoslav Indir, Ante Seletković  UDK 630* 587 + 622
Photogrammetric estimates of stand volume in pedunculate oak stands of the Pokupsko basin      
The application of digital aerial photogrammetry in forest inventory has been in the focus of a number of studies during the last decade (White et al. 2016, Goodbody et al. 2019). The results were tested and evaluated mostly on plot-level, and less often on stand-level (Bohlin et al. 2012, Rahlf et al. 2014, Gobakken et al. 2015, Pitt et al. 2015, Stepper et al. 2015, Puliti et al. 2016, Balenović et al. 2017, Iqbal et al. 2019). In almost all studies, a classic Area-Based Approach (ABA) which includes modelling at plot-level and ‘wall-to-wall’ mapping to estimate forest variables at stand-level were applied. A somewhat different ABA approach which implies direct modelling and estimation at stand-level were proposed by Balenović et al. (2017). This new approach, hereinafter referred to as Stand-Based Approach (SBA), is based on existing and easily available photogrammetric materials and data (aerial images from regular national topographic surveys, official national digital terrain data) as well as on data from existing forest management plans. The main precondition for the SBA method application is the approximate time coincidence between the time of aerial images acquisition and the time of the field data collection for the forest management plan generation. Similar to classical ABA, SBA also requires models (equations) for forest variable estimations. However, in SBA case, models are developed on the certain number of stands (subcompartments) of similar structural characteristics (e.g. forest management classes). In SBA, independent variables are metric stand-level data obtained from aerial images and its product (normalized point clouds or canopy height models), while reference (modelling or validation) data are obtained from regular forest management plans. Compared to classical ABA, SBA does not require additional field measurements, and therefore presents a fast and cost-effective alternative to ABA. An additional assumption is that models developed for the certain area can be applied for other forest areas with similar forest characteristics.
This work presents the continuation of previous study (Balenović i dr. 2017) with the aim to additionally test the effectiveness and accuracy of SBA method. More precisely, SBA method and existing models of stand volume estimation originally developed for lowland pedunculate oak (Quercus robur L.) of Spačva basin forest complex (Eastern Croatia) were tested in pedunculated oak forest of Pokupsko basin forest complex (Central Croatia).
A total of 87 even-aged pedunculate oak forest stands of Jastrebarski lugovi management unit were included in this study (Figure 1, Table 1). Photogrammetric data (aerial images, digital terrain data) were provided by the Croatian State Geodetic Administration, and were used to generate Digital Surface Model (DSM) and Digital Terrain Model (DTM). A raster Canopy Height Model (CHM) of 5 m resolution was generated by subtracting DTM from DSM (Figure 2). Metrics extracted from CHM for each stand and used for stand-level volume estimation are presented in Table 2. Equations (1) and (2) present photogrammetric models for stand-level volume estimation. A more detailed description of the models can be found in Table 3. SB-1 and SB-2 models consist of independent variables and parameters (regression constant and coefficients) originally developed for the Spačva basin area (Table 4). PB-1 and PB-2 models consisted of the same variables as SB-1 and SB-2 models, but their parameters were developed for the present study area (Pokupsko basin) (Table 4). All models were validated using the reference stand volume from the forest management plan. SB-1 and SB-2 models were validated using the entire dataset (87 stands), whereas PB-1 and PB-2 models were validated using the randomly selected 29 stands (other 58 stands were used for parameters estimation).
According to validation results (Table 2, Figure 3), PB models showed considerably greater performance than SB-models. Compared to SB-1 model, PB-1 model achieved 11% higher R2adj values, for 3,92% MD% values (absolute), and for 6,44% higher RMSE% values. Also, the results showed that the inclusion of stand age (SA) as an additional predictor in SB-2 and PB-2 models did not contribute
significantly on model performance. All models showed a similar trend (Figure 3), i.e. volume in stands with lover volume values were overestimated, while in stands with higher volume values were underestimated. However, overestimations (&8776; 8,5%) using SB models were considerably greater than underestimations (&8776; -4%) using PB models. Differences in SB and PB models performance are probably due to differences in stand and site characteristics between two forest areas (Spačva basin and Pokupsko basin). The obtained results suggest that the model with independent variables (Equation 1) originally developed for Spačva basin area can be used for Pokupsko basin and other areas with similar forest characteristics, but local model parameters have to be estimated in order to increase estimation accuracy. It has to be emphasized that the photogrammetric method tested in this paper can not replace the conventional field methods in regular forest inventory. However, its application is based on existing and easily available data (aerial images from regular topographic surveys, official DTM, forest management plan) and does not require additional field measurements and therefore present effective and low-cost solution when in a very short period large areas have to be inventoried. Further research should be focused on other important forest variables (e.g. mean stand height, mean stand diameter, basal area, stand density, biomass, etc.) and different forest types.

Key words: aerial images; digital photogrammetry; canopy height model (CHM); stand volume; forest inventory

    BALENOVIĆ, Ivan    ŠL
    Luka Jurjević  
    INDIR, Krunoslav    ŠL
    SELETKOVIĆ, Ante      ŠL
Branislav Drašković, Marko Gutalj, Stefan Stjepanović, Boban Miletić  UDK 630* 233
Estimating recent forest losses in Bosnia and Herzegovina by using the Copernicus and Corine land cover databases      
The analysis of data from the first two decades of the 21st century shows that the area under forests in Bosnia and Herzegovina is gradually decreasing. In order to gain a detailed insight into this process, the paper will analyse the forest databases of the European satellite monitoring program Copernicus. This program, among other things, monitors the condition of forests in 39 European countries by using the High Resolution Layer (HRL). The HRL Forests database consists of 3 types of (status) products, and additional change products. The status products are available for the reference years 2012, 2015, and 2018. The status layers provide information on the Dominant Leaf Type and the Tree Cover Density at pixel level for the reference year 2018 in 10 m resolution. The Forest Type layer largely follows the Food and Agriculture Organization (FAO) forest definition.
Also, the paper will use the data on forests from the CORINE Land Cover project for 2000, 2006, 2012 and 2018. The time-series includes a land change layer, highlighting changes in land cover and land use. The CLC Changes database will be analysed separately for three periods: 2000-2006, 2006-2012 and 2012-2018, due to more accurate data on forest losses.
The results of the research show that forests in Bosnia and Herzegovina were reduced by 2.95%, in the period 2012-2018, where 2.55% of them were coniferous. Forests are primarily endangered by the process of conversion to transitional forest / shrub and fires.

Key words: forest; losses; BiH; Copernicus; database; changes

    Branislav Drašković  
    Marko Gutalj  
    Stefan Stjepanović  
    Boban Miletić