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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   5
These days we have finally witnessed a long-expected change at the helm of the company Croatian Forests Ltd. The Croatian Forestry Association has on several occasions decidedly expressed its opinion and criticism of the work of the past Management, especially in this column, and has sought answers to various expert issues; however, there has never been any answer, let alone a professional debate. All we received was arrogant disregard and retaliation that went as far as to take the form of the cancellation of the subscription to this journal.
For every new beginning it is necessary to establish the factual state of affairs as a basis for a new working programme/plan. For this reason we would advise the new Management to facilitate its insight into the facts by consulting the answers to our questions, criticisms and suggestions (given particularly in the two texts in the column Challenges and Confrontations in No. 11-12/2016 and in the text by the MB of the Croatian Forestry Association entitled “How does the Croatian Forestry Association perceive Croatian forestry” in No. 11-12/2015).  Our well-meaning criticism and suggestions were intended to warn the public against inexpert operations in the forest and even more against what has regrettably not been done but should have been done, mostly because this would have conflicted with profit, the only goal of the Management regardless of the adverse consequences for the forest. We have also highlighted the need for a more rational use of all the benefits of forests and forestry, which was also sadly missing. We have advocated and will continue to advocate a decentralised form of management of forest wealth. We also expect managers of forest administrations, forest offices and even forest districts, who are experts in forest resources and their sustainable management, to be given much more power. A decentralized form of management will ensure general benefits for the owner/state, but also for the local community, which is something that has obviously been forgotten. Our attitudes towards the situation in forestry have never been of a declarative nature, but have always been based on facts. By advocating decentralized management, we rely on the data from the article “Forests and Forestry” by Academy members Slavko Matić and Igor Anić, contained in the brochure “Croatian National Treasure” published by the Croatian Academy of Science and Art. 
The complex nature of forest management in certain parts of Croatia, one of the most forested countries of Europe (half a hectare per person) and the employment of high quality forestry experts is reflected primarily in the forest vegetation composed of 102 forest communities with no less than about 260 woody species and 94 tree species. By endorsing treatments that are necessary to ensure sustainable forest management and an improved quality and value of Croatian forests, we again present data from the mentioned article, in which 5 % of the forests are of very good quality, 22 % are of good quality, 43 % are of medium quality and 29 % are of poor quality. Forty-five percent of the best quality lowland forests were estimated as very good. Investing in the improvement of the mentioned structure would result not only in a greater raw material base, something that was exclusively supported by the former Management, but also in other benefits of the forest and in particular in its non-market functions. 
When we raise questions related to delayed silvicultural treatments or even their omission and to the adverse effects of this on the future of stands, e.g. with regard to pedunculate oak, the most valuable Croatian tree species, and sessile oak (according to the above brochure, pedunculate oak accounts for14.83 % and sessile oak for 8.35 % of the area), we like to remind ourselves of what we learned about these tree species at the Faculty, but forget to apply this knowledge. Based on the texts from the monograph “Pedunculate oak in Croatia”, we list the following silvicultural stages: seedling stage, sapling stage (young and old), young forest (younger and older), young, middle-aged and mature stand. Thus, for example, the older sapling stage (15 - 20 years of age) experiences the culmination of height increment and maximal crown increment in the width. This is where future trees are singled out, which results in tree differentiation and selection into stories in the young stand. From a commercial standpoint there are: prop stage, pole stage, pile stage and finally sawmill roundwood stage, where thinning operations are applied in the pole stage and differentiation into height, diameter and value classes takes place. In a middle-aged stand, when the stand structure is already formed, the biological potential related to a response to stand tending (50 - 70 years of age) gradually decreases. The concluding question is: what kind of experts are we and how have we optimally made use of certain potentials of a forest habitat? This is what we have repeatedly stressed, because every developmental stage, not only the ones mentioned above, requires timely interventions. True, they come at a certain cost, but on the other hand they provide immeasurable benefits, especially for the future.
This concludes the current double issue. In the next issue we will focus on other topics of interest and we will accompany them with data. These topics include the forest as an infrastructural category, non-market forest functions, relations with wood processing, attitudes of the society and politics towards the forest and forestry, and similar.
<br>Editorial Board

    Uredništvo HŠD    
Ivan ANDRIĆ, Davorin KAJBA  UDK 630* 111.8 + 181.8 (001)
Narrow-leaved ash (Fraxinus angustifolia Vahl) is a fast growing and light demanding forest tree species. In Croatia, the largest complexes of this species can be found along the Sava River. The main objective of research was to determine the influence of environmental drivers on budburst dates. Research was carried out in the clonal seed orchard of Nova Gradiška through four vegetation seasons (2012, 2014, 2015 and 2016). In total, 42 clones were involved in this study. The target phase of phenology monitoring was the phase with distinct budburst and partial segregation of bud scales. Three environmental drivers were selected (temperature, precipitation and insolation) with three different summing dates (1st November, 1st December and 1st January). Statistical data processing included the following analyses: Spearman Rank Correlation, Linear Regression, Multiple Regression and Stepwise Multiple Regression. Among three tested environmental drivers in all of the analyses performed in the study, insolation proved to be the most important factor in the description of budburst dates in narrow-leaved ash.

Key words: climate change; temperature; insolation; precipitation; phenology

    ANDRIĆ, Ivan    ŠL
    KAJBA, Davorin      ŠL
Ivan BALENOVIĆ, Ante SELETKOVIĆ, Renata PERNAR  UDK 630* 587 (001)
Although the application of aerial stereo photogrammetry in forest inventory has a long tradition, in many countries including Croatia forest inventories are based on labour and time consuming field surveys. Therefore, the objective of this research was to evaluate the applicability of using the digital aerial images of high spatial resolution (ground sampling distance – GSD of 10 cm and 30 cm) for predicting forest stand attributes (basal-area weighted mean dbh – DBHg, Lorey’s mean height – HL, stand density – N, basal area – G, volume – V). This research continues the work of the previous research (Balenović et al. 2013, 2015a), where accuracy of photogrammetrically estimated arithmetic mean diameter and arithmetic mean height of forest stands were evaluated.
The research was conducted in the even-aged (sessile oak management class) and the multi-aged stands (European beech and common hornbeam management classes) of a privately owned forest in the management unit Donja Kupčina – Pisarovina, 25 km south of Zagreb, Croatia (Figure 1). Field data were collected during the spring and summer of 2009 as part of the regular forest inventory conducted according to the valid Regulation on Forest Management. A total of 183 circular plots with radii of 8 or 12 m were systematically set in
the 14 selected subcompartments. The positions of the sample plot centres were recorded with GPS receiver. Within each plot, the diameter at breast height (dbh) was measured and tree species was determined for all trees with dbh≥10 cm. The height of each tree was calculated by means of the constructed local height curves fitted with Michailloff’s function. The basal area (g) of each tree was calculated from the measured dbhs using standard equation, whereas the merchantable tree volume up to a diameter of 7 cm overbark (v) was calculated from field-measured dbh and estimated h using the Schumacher-Hall function and parameters from Croatian volume tables. The forest stand attributes were calculated by averaging data of all sampled tree within each stand (DBHg, HL) or summing the tree data and dividing it by the total area of all plots for each stand (N, G, V). Stand-level field data were used in the statistical analysis and comparison with photogrammetric data as a ground-truth reference data (Table 1).
The colour infrared (CIR) digital aerial images of GSD 30 cm and GSD 10 cm were acquired using a Microsoft UltraCamX digital large-format aerial camera during two aerial surveys in July 2009 (Figure 1, Table 2). The digital terrain data (breaklines, formlines, spot heights and mass points) for the digital terrain model (DTM) generation were collected by stereo-mapping of digital aerial images according to the rules of the Croatian State Geodetic Administration. The whole procedure of image acquisition, aerial triangulation, and collection of 3D data was conducted by Geofoto Ltd. (Zagreb, Croatia).
The photogrammetric stereo measurements and the visual interpretation of tree attributes were performed on digital aerial images of 30 cm GSD and 10 cm GSD using PHOTOMOD 5.24 digital photogrammetric system according to procedures described in Balenović et al. 2013, 2015a. The photogrammetric plots were overlaid upon the aerial images based on the spatial coordinates (x, y) of the field plot centres recorded by the GPS receiver. The determination of tree species and crown tops as well as the delineation of crown areas was performed manually for each tree whose top fell inside the plot. The height of each tree was calculated as the difference between the tree top elevations and the corresponding tree bottom elevations determined from the DTM. A raster DTM of 1 m grid size was generated through linear interpolation of a triangular irregular network (TIN) which was previously created from the digital terrain data. The dbh of each tree on the plot was calculated using local regression models with tree height and crown diameter as inputs (Balenović et al. 2012). Crown diameter was calculated from delineated crown area by applying the equation for circle surface area. Further calculations of photogrammetric tree (g, v) and stand variables (DBHg, HL, N, G, V) were identical to previously described calculations of field data.
The accuracy of the photogrammetrically estimated stand attributes was evaluated by calculating differences (D), mean differences (MD) and RMSE between photogrammetric- and field-estimates. The relative values of D%, MD%, RMSE% were calculated according to the mean of the field reference values. The D and D% were calculated for each subcompartment, whereas MD, MD%, RMSE and RMSE% were calculated for the whole study area.
The results in Table 3 show that photogrammetric measurements of the aerial images of 30 cm GSD (PM30) and 10 cm GSD (PM10) produced reasonable accurate estimates for HL, G, V with relative RMSEs ranging from 3.65% to 5.36%. Similar accuracy was obtained for DBHg estimated by PM10 (RMSE=4.94%), while lower accuracy was obtained for N estimated by PM10 (RMSE=7.71%) and DBHg estimated by PM30 (RMSE=9.460%). The lowest accuracy was obtained for N estimated by PM30 (RMSE=15.90%). Both photogrammetric measurements (PM10 and PM30) estimated HL and G with similar level of accuracy, whereas V was estimated with slightly higher accuracy by PM10 then by PM30. For estimation of DBHg and V, PM10 produced considerably better results, i.e. estimates of approximately twice higher accuracy then PM30. Figure 2 shows relations between D% and field estimates of corresponding attributes for each subcompartment. As can be seen, photogrammetrically estimated HL and V varied between overestimation and underestimation (HL: from -13.6% to 2.8% for PM10, from -12.8% to 3.7% for PM30; V: from -7.0% to 2.2% for PM10, from -10.2% to 8.2% for PM30), but with a slight tendency to underestimate field estimates. Photogrammetrically estimated G also varied between overestimation and underestimation (from -6.2% to 12.9% for PM10, from -5.0% to 10.2% for PM30), but with a slight tendency to overestimate field estimates. DBHg was overestimated for all subcompartments by both photogrammetric measurements (from 1.1 to 9.5% for PM10; from 3.0% to 16.5% for PM30). On the contrary, both photogrammetric measurements underestimated N throughout all subcompartments (from -2.6% to -10.6% for PM10; from -5.1% to -24.4% for PM30). For both DBHg and N, PM30 produced estimates of lower accuracy than PM10. This is a consequence of lesser visibility of details (e.g. crown boundaries) on images of lower spatial resolution (GSD 30 cm) and decreased ability to detect individual trees, especially in the part of stands with greater proportion of younger trees. According to Figure 3, the notable underestimation of N by PM30 was found in the lowest dbh size class (10.0-14.9 cm).
The results of this research showed that HL, G and V can be accurately estimated by manual measurements of digital aerial images of high spatial resolution. The use of images of high spatial resolution, along with the
use of local dbh models, led to improved accuracy regarding individual tree detection and dbh estimation. Moreover, the errors of N underestimation and DBH overestimation have been mutually abolished, which in the end resulted with reasonably accurate estimates of G and V at stand level. Since the errors of N underestimation and DBH overestimation with PM30 were both proportionally (twice) greater than with PM10, G and V were estimated on both 10 cm and 30 cm GSD images with similar level of accuracy. Although PM10 overall produced the more accurate results than PM30, it should be noted that the price of 10 cm images is several time higher than of 30 cm images. Therefore, a potential user should decide which images to use depending on desired accuracy and available funds.

Key words: forest inventory; stereo measurement; visual interpretation; digital aerial images; digital photogrammetric workstation

    BALENOVIĆ, Ivan    ŠL
    SELETKOVIĆ, Ante      ŠL
    PERNAR, Renata      ŠL
Nedim TUNO, Admir MULAHUSIĆ, Jusuf TOPOLJAK, Alma ELEZOVIĆ  UDK 630* 582 (001)
Knowledge about positional accuracy of forest geospatial information, obtained by interpretation of satellite imagery, is of great significance. The consequences of the decisions that are based on data with insufficient or unknown quality could be very negative. This paper investigates the accuracy of closed linear shapes that represented boundaries of forest cover. Forest areas are effectively extracted from Landsat image by implementing the process of multiresolution image segmentation (figure 4), using all bands. Multispectral classification of defined segments was performed by special rules. The results of object-oriented classification showed that an overall accuracy from 99 reference points was better than 90 % (table 1), which can be considered as a very good result. The number of forest polygons, obtained by satellite imagery classification, was reduced by 37 times by cartographic aggregation (figure 5). The Polynomial Approximation with Exponential Kernel (PAEK) method was used for cartographic smoothing of the forest polygons, which smoothes lines in relation to a softening tolerance (tolerances from 30 m to 180 m were used in this research) (figure 6). The positional accuracy assessment of the boundary of forest areas, based on procedure of comparing a tested lines to a reference lines, showed that the best results were obtained by PAEK smoothing with 150 m and 180 m tolerances (CMAS = 49 m, according to STANAG 2215) (tables 2 and 3, figure 8).
The findings of this empirical research showed that cartographic generalization contributes to improvement of the forest boundaries accuracy, as well as the appropriate processing of the medium spatial resolution remotely sensed data can result in satisfactory quality of vector data.

Key words: Landsat; object-oriented forest classification; cartographic generalization; positional accuracy

    Nedim TUNO  
    Admir MULAHUSIĆ  
    Jusuf TOPOLJAK  
    Alma ELEZOVIĆ  
Adrienne ORTMANN-AJKAI, Gábor CSICSEK, Márió LUKÁCS, Ferenc HORVÁTH  UDK 630* 239 + 226 (001)
Insufficient natural regeneration of pedunculate oak (Quercus robur L.) in alluvial hardwood forests is a serious problem both for close-to-nature silviculture and nature conservation, as it may lead to in-depth changes of forest structure. Natural regeneration processes in pedunculated oak forests are especially difficult to study due to the lack of strict forest reserves, where natural processes would be able to manifest. No-intervention (passive) conservation of closed floodplain pedunculate oak forests is often regarded as a failure not only of economic, but also of conservational point of view.
Our observations on spontaneous stand development of a floodplain pedunculate oak forest, including all woody species, were carried out in a strict forest reserve in Southern Hungary. Data on the current structure of a 120-years old stand, unmanaged for 17 years were sampled with the three-layer protocol of the Hungarian Forest Reserve Program, and analysed with PCA. Stand structure change was described by comparing current results with those of Braun-Blanquet releves from 1995-96. We presented a detailed case study of an unmanaged floodplain oak forest, and demonstrated that instead of regeneration of the closed Quercus robur-dominated high forest, forest-like stands of Crataegus monogyna developed. No-intervention conservation allowed natural processes to manifest, but not preserved local conservational values, and apparently did not sustain present, economically very valuable oak stands. Our results on the consequences of 17 years of passive conservation provide information useful for conservational decision-making.

Key words: Quercus robur; spontaneous dynamics; Crataegus monogyna community; strict forest reserve; passive conservation

    Adrienne ORTMANN-AJKAI  
    Gábor CSICSEK  
    Márió LUKÁCS  
    Ferenc HORVÁTH  
Gonca Ece ÖZCAN  UDK 630* 453 (001)
one of the most important factors of natural balance in the forests are insects, which are a part of ecological diversity. Being in a constant change, forest ecosystems are affected by bark beetles in low level or wide ranged ratios. The pressure of Ips sexdentatus, one of the most important pests of conifer forests and principal species of Turkey, can be at a sensible level from time to time. In this study, it was determined that the beetles carry out two flights in the region, first flight starts around the beginning of May, this period continues until mid-June, second flight starts around mid-June and continues until the beginning of September. The number of beetles captured by the traps in the first and second flight period were statistically different and, also the average number of beetles in first period were more than second period. When the results of pheromone trap capturing were evaluated monthly, it was seen that the averages of June, July and August were not statistically different, meanwhile May average was statistically different from other months. No significant difference were found between the averages of I. sexdentatus captured by the pheromone traps in sunny and shaded aspect. No dying due to beetle damage was found on the trees in the study area after the flight of beetles, however, the damage ratio of the beetle was identified as 16.38% in a hectare. A statistically significant difference was found between the specified diameter classes in terms of beetle damage.

Key words: bark beetle; Ips sexdentatus; damage; pheromone trap; population density

    Gonca Ece ÖZCAN  
Alen BERTA, Vladimir KUŠAN, Josip KRIŽAN, Denis STOJSAVLJEVIĆ, Dalibor HATIĆ  UDK 630* 923
Private owned forests occupy 22 % of the total forest and forest land area i.e. approximately 600,000 ha, according to Forest Management Plan for the area of the Republic of Croatia. Some of the private owned forest characteristics are as follows: small cadastral plots and estates, large number of landlords for the same area and great discrepancy of cadastral data. In this research, analyzed data about cadastral plots and landlords are taken from 319 cadastral municipalities (CM) distributed in 5 regions of the Republic of Croatia as well in 53 private owned forest management units. The sample represents 8.74 % of the Croatian area i.e. 15.69 % of the private owned forest area, according to the Forest Management Plan for the area of the Republic of Croatia. In addition to the statistical characteristic of the cadastral plots regarding regions, two cluster analyses are performed for better characterization of the regions. The first cluster analysis refers to the possession variables: average area of the cadastral plots inside CMs included in private-owned forest management plans (P-FMP), average area of the estates inside CMs included in P-FMP and average amount of the landlords in possession sheets by CMs included in P-FMP. Second cluster analysis refers to spatial variables: total area of the CMs, ratio of the forested areas by private-owned forests and ratio of the „non-forest” land according to cadastral land use data included in P-FMP.
This research gave us an insight about the most pronounced characteristic of each region and about unique relation of the observed characteristics for each region.
This research defines that regions Istria and Kvarner, Slavonija and central Croatia are more differentiated from the other regions in terms of possession variables, whilst the regions of Gorski kotar, Lika and Dalmatia are better explained with spatial variables as differentiation factor from other regions. Few principles are also confirmed as the results of the cluster analysis, for example the relation between the size of the cadastral plots and number of the landlords as well as relation regarding private owned forests ratio and ratio of the „non-forest“ land included in P-FMP.

Key words: private owned forests; cadastral plots; estate; forest landlords; cluster analysis

    Alen BERTA  
    KUŠAN, Vladimir    ŠL
    Josip KRIŽAN  
    HATIĆ, Dalibor    ŠL