The age, size and morphology of trees, including crown dimensions, can influence crown defoliation. In Croatia, the selection management of silver fir (Abies alba Mill.) forests involves pure or ...mixed stands, either of which can be affected by various disturbances, resulting in unbalanced stand structures. The aim of this study was to estimate the probability of trees transitioning from one defoliation class to the next, examine the influence of tree attributes on that process and analyze the changes in survival over time. The study was conducted over a 18-year period (1990–2007) on two sites with contrasting stand structures: a uniform stand with a dominant share of silver fir (Site A) and an uneven-aged mixed beech–fir stand (Site B). Logistic regression was used to model tree transitions between defoliation classes. Uniform stand structure increased the likelihood of silver fir trees transitioning to a higher defoliation class, with limited dependence on the tree crown position. In contrast, suppressed and central trees in uneven-aged stands were more likely to transition to a higher defoliation due to greater competition between them. Diameter at breast height (DBH) was found to be a significant predictor of tree transition to higher defoliation classes, with a linear trend of increasing probability with increasing DBH. Crown position and crown length were also found to be significant predictors of changing defoliation class, with observed differences between sites occurring due to differences in stand structure. To ensure a balanced stand structure and enhance tree vitality, careful consideration of easily measurable tree elements such as DBH, crown length, and tree crown position is imperative when selecting trees for felling.
Background and Purpose: The aim of this article is to create a virtual forest stand based on the field measurement of spatially separated sample plots and to examine its credibility based on the ...deviation of the basic characteristics of the virtual stand as compared to the field measurements.
Material and Methods: Field measurements were made on 20 circular sample plots with a 20 m radius, set on a 100x100 m grid. By using the univariate Ripley’s K function the regularity of the spatial pattern of trees was analysed. The diameter distribution and the frequencies of height within individual diameter class were mathematically fitted and used for generating the virtual stand. The whole process of generating the virtual stand was done in the R software. Area of study are even-aged silver fir stands in the Croatian Dinarides.
Results: The main unit of the virtual stand is a tree, with the purpose that the virtual stand can then be used as a basis for forest stand growth simulators. The result of the research was a virtual stand of 3 ha whose characteristics only slightly differed from the field measured plots. Within the virtual stand, special emphasis has been put on tree heights, which were generated according to the variability of tree height for trees of the same diameter at breast height.
Conclusions: Considering the distribution of diameters at breast height, tree heights, the number of trees, basal area and volume, the virtual stand has minimal deviations from the situation in the field and it adequately shows variability measured in the field.
In recent decades, changes in stand structure in Central European fir-beech forests, such as accumulation of large-diameter firs, fir dieback, and poor regeneration, have been well documented. ...Besides environmental factors, light harvesting was suggested as one of the main drivers of the negative structural dynamics of these forests in Croatia. This study applied the MOSES 3.0 stand simulator on permanent sample plot data to reconstruct stand development over the past 20 years and simulate long-term projections of selection stand structure and regeneration with respect to theoretical values, using three management regimes differing by the applied harvesting intensity (traditionally applied, theoretical intensity, and no management). Sample plot data from three sets of detailed measurements (1992, 2002, and 2012) were used for validation of the simulator, and eleven 10-year cycles of management were then simulated under the above management scenarios. Results showed a positive influence of harvest intensity on stand regeneration and the achievement of a targeted selection structure in the long term. Two management scenarios predicted a decrease in stand volume (34% and 40%, respectively), an increase in the initial percentage (28%) of beech and maple (58% and 75%, respectively), and the achievement of optimal stand regeneration of 11-13 recruited trees per hectare annually (60% firs). No management scenario could achieve old-growth structure (accumulation of standing stock, large trees, and deadwood). The theoretical intensity scenario was evaluated as the better approach to be applied in this type of forest stands in Croatia.
Raznodobne jelovo-bukove šume u Republici Hrvatskoj zauzimaju oko 157 000 ha. Tijekom povijesti njima se upravljalo različitim načinima gospodarenja, od jednodobnog do prebornog gospodarenja. Kao ...rezultat povijesne integracije hrvatskog šumarstva u njemačku šumarsku školu i uz jedinstvene ekološke značajke dinarskog područja, primarno se primjenjuje preborni način gospodarenja. U današnje vrijeme zbog različitih biotskih i abiotskih utjecaja, većina bukovo-jelovih šuma u Hrvatskoj ima prijelaznu strukturu između jednodobne i one preborne. Strukturu karakterizira velika drvna zaliha, mali prirast, loša vitalnost, slaba obnova jele i sve veći udio obične bukve. Takav ogledni primjer je i stalna pokusna ploha koja se nalazi u sjevernom dinarskom području Hrvatske i kojom gospodare “Hrvatske šume” d.o.o. Zagreb, a ujedno je i predmet ovog istraživanja. Cilj članka jest istražiti različite modele određivanja sječa koji će usmjeriti šumu u stabilniju prebornu strukturu s optimalanim prirastom i s odgovarajućim volumnim udjelom jele. Ulazni podaci dobiveni su sukcesivnim mjerenjima na stalnoj pokusnoj plohi u bukovo-jelovoj sastojini. Simulator šumskih stabala i sastojina, MOSES version 3.0, testiran je na primjenjivost u lokalnim uvjetima i korišten je za projekciju budućeg gospodarenja. Četiri scenarija temeljena na različitim modelima izračuna sječe korištena su za simulaciju mogućih smjerova budućeg gospodarenja s naglaskom na ciljani volumni udio jele, prirodnu obnovu jele, uspostavu i održavanje preborne strukture. Svi scenariji predviđaju smanjenje volumena jele praćeno agresivnom regeneracijom obične bukve te djelomično postizanje preborne strukture. Krajnje strukture šumskih sastojina (nakon 110 godina) uspoređene su i rangirane na temelju sastojinskih i ekonomskih pokazatelja. S gledišta ekološke, šumsko-gospodarske i ekonomske održivosti, model izračuna sječe koji je temeljen na trenutnoj drvnoj zalihi i desetogodišnjem prirastu pokazao se kao najbolji među istraženim scenarijima.
Uneven-aged beech-fir forests cover approximately 157 000 hectares in Republic of Croatia. During the history they have been managed according to different management systems, varying from even-aged to selection management. As a result of historical integration of Croatian forestry into the German forestry school, alongside with unique ecological characteristics of Dinaric area, selection management system has been practiced in Croatia’s forestry ever since. Today, due to various reasons majority of beech-fir forests in Croatia have transitional structure between even-aged and selection structure. It is characterized by large growing stock, small increment, low vitality, poor fir regeneration and increasing share of beech. Example of such case is permanent experimental plot situated in Croatia’s north Dinaric area and managed by “Croatian forests” Ltd., which is a subject of this research. The aim of this research is to explore different annual cut models which will in future direct forest into stabile and optimal growth rate in selection structure with adequate volume share of fir. Input data have been acquired from successive measurements on permanent experimental plot in beech-fir stand. Tree growth simulator MOSES version 3.0 was tested for applicability in local conditions and has been used for projecting future stand‘s growth. Four scenarios based on different cutting models have been used to simulate possible types of future management emphasizing fir natural regeneration, establishment and maintenance of selection structure with targeted volume share of fir versus beech, and also supporting valuable broad-leaved species. All scenarios represent fir volume reduction followed by aggressive beech regeneration and partially accomplishment of selection structure in long-term. Thus, obtained different future stand structures were compared and ranked based on stand attributes and economic indicators. Annual cut based on decennial volume increment and stocking has been found best scenario from aspects of ecological, management and economic sustainability.
Iako se šumarstvo smatra tradicionalnom strukom i područjem znanosti, njegova važnost i značenje u današnjim prilikama povećane svijesti o klimatskim promjena i dobrobiti održivog razvoja prirodnih ...ekosustava svakim danom sve više raste. Suvremeni i ažurirani studijski programi neophodni su uvjet za primjereno obrazovanje stručnjaka za gospodarenje šumskim ekosustavima i proizvodima.
Bolji uvid u studentsku socioekonomsku pozadinu i motivaciju za studij mogu poslužiti za unapređenje studijskih programa, kao i pomoć studentima u postizanju boljih rezultata. Provedeno je istraživanje radi usporedbe trajanja preddiplomskog studija i postignute prosječne ocjene s analizom čimbenika koji bi mogli na to utjecati. Proveden je upitnik među studentima (N=185) diplomskih studija Šumarskog fakulteta Sveučilišta u Zagrebu akademske godine 2016/2017. Analizom varijance testirane su razlike između prosječnih ocjena studija i trajanja studija. Za procjenu utjecaja čimbenika na trajanje studija provedena je višestruka linearna regresija.
Približno trećina studenata dolazi iz Zagreba. Više od dvije trećine studenata na šumarskom odsjeku je završilo gimnaziju, dok su na drvnotehnološkom odsjeku dvije trećine studenata završile srednje strukovne škole. Prosječne ocjene i trajanje studija ne razlikuju se statistički značajno po studijskim programima ni po spolu. Prosječna ocjena studija i trajanje studija statistički su značajno negativno korelirani za sva tri studijska programa. Statistički značajni prediktor trajanja studija za sva tri studijska programa je prosječna ocjena studija. Za studij Šumarstvo dodatni prediktori za kraće studiranje su stipendija i osobna motivacija, dok su za studij drvne tehnologije spol (M), stipendija i završena srednja škola (gimnazija).
Although forestry is often considered as a traditional field of applied science, it resumes its importance in context of increased awareness of climate change and benefits coming from natural ecosystems. Updated and contemporary study programmes are needed to ensure an adequate education on managing forest ecosystems and its products.
A better insight in student background and their motivation for studies are welcome to improve the study programmes and also to find the ways how to help students achieve better results. A case study research was carried out to measure success of studies by duration of studies and average grades achieved, with possible causes. Three undergraduate study programmes on Zagreb Faculty of Forestry were analyzed (Forestry N=94, Urban forestry N=54 and Wood Technology N=39), with data acquired from a questionnaire among forestry graduate students on the same faculty academic year 2016/2017. A Factorial ANOVA was performed to test differences between the studies, and a multivariate linear regression for the influence of predictor variables on the duration of study.
Although this profession is associated with people from rural areas, about one third of all students comes from the capital city (Figure 1). Students of Wood Technology (DT) are mostly coming from vocational schools (70%) while Forestry (ŠO) and Urban Forestry (UŠ) students are mostly from gymnasiums (67% and 83%). For about 91% of students main motivation was a personal sake rather than a family interest (9%). Average scores and the duration of study on three study programmes have not been proven significantly different between the studies, nor between male and female students (Table 5). A longer time of study is proven to negatively correlated with the average grades on all study programmes: ŠO (r = -0,56), UŠ (r = -0,55) and DT (r = -0,38) (Table 4.). Statistically significant predictor for duration (with logarithmic transformation) on all study programmes in regression analysis was the average grade, with negative sign, thus leading to a shorter study time. Additional statistically significant predictors for ŠO were obtained grant and personal motivation (negative sign), and for DT were sex, obtained grant, and type of high school (Table 6).
Većina privatnih šumoposjednika u Hrvatskoj ima šumoposjed manji od 1 ha, što predstavlja značajan ograničavajući čimbenik u gospodarenju šumama. Cilj ovoga rada je ispitati povezanost ...sociodemografskih značajki šumoposjednika i obilježja šumoposjeda s razinom zainteresiranosti šumoposjednika za kupnju, zamjenu ili prodaju čestica pod šumom, u svrhu okrupnjavanja i povećanja suvislosti posjeda. Neposrednim anketiranjem ispitano je 500 šumoposjednika na području kontinentalne Hrvatske. Za dobivene podatke napravljena je statistička deskriptivna obrada, te izračunate mjere korelacije i testiranje razlika pojedinih kategorija. Rezultati ukazuju na jasnu povezanost sociodemografski, regionalnih i drugih obilježja šumoposjednika s razinom zainteresiranosti za okrupnjavanje šumoposjeda. Tipičan šumoposjednik zainteresiran za povećanje šumoposjeda je muškarac mlađi od 50 godina, sa završenom srednjom školom ili fakultetom, iz središnje Hrvatske koji je svoj posjed stekao kupnjom i već je aktivan bilo u udrugama šumoposjednika, bilo da koristi savjetodavne usluge Ministarstva poljoprivrede. Premali udio šumoposjednika zainteresiranih za prodaju šumoposjeda (18,9%) onemogućava daljnje okrupnjavanje. Prema tomu, mjere regulatora treba usmjeriti na proces nasljeđivanja, oprezivanje negospodarenja šumoposjedom i daljnje subvencioniranje aktivnog i disperziranog gospodarenja šumama (biomasa, nedrvni šumski proizvodi, općekorisne funkcije šuma, naknade za pohranu ugljika, naknade za ciljane vrste).
Most forest owners in Croatia have forest holdings smaller than 1 ha, while less than 1% have holdings larger than 10 ha. Parcelization of forest holdings in addition to small size presents significant limitation for forest management. Therefore, important aim of forest policy is to stimulate enlargement and consolidation of forest holdings. First step in that process is to recognize the characteristics of forest owners interested in enlargement of their holdings and active forest management.
The aim of this research is to relate the sociodemographic attributes of private forest owners and characteristics of their forest holdings with their interest for selling and/or buying forest estates for enlargement and consolidation of forestland area.
Direct survey questionnaire covered 500 private forest owners in continental part of Croatia. Respondents are classified by sex, education, employment, location of forest holding, activities in forest associations and means of acquisition of forest estate. Answers included level of interest for activities in enlargement and management of forest holdings. Statistical analysis included descriptive statistics (arithmetic mean, median, and standard error), testing between groups (Mann Whitney and Kruskal Wallis test), and Spearman rank correlation.
The results indicate correlation of sociodemographic, regional and other characteristics of forest owners with their interest in enlargement of forest holding. According to these results most interested in enlargement of forest holding are younger male owners from the central Croatia who purchased forest and are already active in forest associations (tables 1 and 2). Non-employed and self-employed owners are also more interested in enlargement of forest area to increase their incomes (table 1). However significant share of owners (35%) are not interested in increase nor in selling their forest (Figure 1) which is an impediment in consolidation of forest areas.
The results of this study are useful for future forest policies aimed at small scale forestry, although these actions are subject to large scale restrictions due to increase of protected areas and limitations to forest management resulting from reducing carbon emissions. Therefore, state regulatory measures should aim at subsidizing active and diversified forest management (forest biomass, non-wood forest products, amenity values, credits for carbon sequestration, aimed species, biodiversity). On the other hand, law measures should improve the process of inheritance and penalize the abandonment of forest areas (sources of pests and diseases, invasive species, forest fires).
The study focuses on the development of stand growth models for more intensive management of black walnut (Juglans nigra L.) plantations in Croatia. In total, 48 plots were sampled (ages between 3 ...and 91 years) and, on average, 28.3 trees (between 17 and 43 trees) were measured diameter at breast height (dbh), total height, two crown diameters, increment core on each plot. Management scenarios with rotations of 50, 60, 70 and 80 years were developed under three different management regimes: conservative (CAS), high individual tree growth (HTGS) and high stand growth (HSGS). Indicators of competition (current annual increment in dbh, basal area and crown area) were used for scheduling thinning and the intensity of interventions for the intensive scenarios. Depending on the management options and rotation, final stand densities varied between 105 and 210 trees ha
−1
, mean dbh between 30.4 and 46.1 cm, and total heights between 25.9 and 29.5 m. The mean annual increment in total volume varied between 7.1 and 11.0 m
3
ha
−1
per year under different rotations and management options, yielding in total accumulated volume of 529-666 m
3
ha
−1
. The CAS yielded the lowest and the HSGS the highest total volume, and HTGS yielded the highest mean dbh.
Background and Purpose: Beech-fir forests cover about 13% of forest land in Croatia, thus being a significant forest resource that is dominantly managed by uneven-aged selection management system. ...Continuous and successful regeneration is an essential prerequisite for this kind of forest management. Therefore updated and sound information on the present state of regeneration is important, especially in the context of climate change and the actual structure of beech and fir forests. The aim of this paper is to present and analyse current state of regeneration in beech and silver fir forests of Gorski kotar region, with regard to forest ownership (management model), forest communities and habitat characteristics.
Materials and Methods: Field measurement has been done on 313 plots in the beech and fir forests of Gorski kotar region, Croatia. The assessment of regeneration was based on measurement of trees ranging from 0 to 10 cm dbh (species, number of trees, average height) and also the estimation of seedlings up to 1.30 m high (regenerated area in 10% classes, the share of tree species, the origin of stand establishment, regeneration quality).
Results: Attributes like the success of regeneration, the structure of seedlings by species and the recruitment of saplings were analysed with regards to ownership, forest communities and the aim of forest management. The results indicate poor incidence of regeneration especially of silver fir (more than 50% percent of field plots with no regeneration). Silver fir saplings (height>1.3 m, dbh ≤10 cm) are registered on 9% of plots, average number being only 165 per ha (all species together 2044 per ha). The estimated average share of the regenerated area is 16.3% of total forest area, contributed by 5.2% of conifers and 3.8% silver fir. A total of 14 tree species were recorded on regenerated areas, clearly dominated by broadleaves, especially beech (over 50%).
Conclusions: Significant differences in regeneration attributes were proven by ANOVA between ownership categories, forest communities and habitat characteristics. In order to get better insight on the structure of regeneration, it is recommended to improve future assessment by establishing special sub-plots for measurement of seedlings by species.
U radu je prikazan utjecaj mjeritelja i pogrešaka mjerenja na izmjeru prsnog promjera stabla. Istraživanje je provedeno na nastavno-pokusnom šumskom objektu Zagreb: u nizinskoj sastojini hrasta ...lužnjaka i običnog graba te u sastojini obične jele i bukve (na nagnutom terenu). Pokušalo se obuhvatiti najčešće pogreške pri izmjeri prsnog promjera te su tri mjeritelja mjerila unakrsne prsne promjere stabala na samoodređenoj i označenoj prsnoj visini. Također, mjeren je promjer na način da je promjerka pozicionirana deset centimetara ispod i iznad stvarne prsne visine, zatim sa krakovima promjerke odmaknutim od debla, s normalnim i jačim pritiskom na krakove te izmjera promjera stabla sa krakovima promjerke okrenutim prema gore radi lakšeg očitanja vrijednosti. Rezultati su pokazali da je razlika između dva unakrsna promjera (eliptičnost stabla) veća nego pogreška izmjere promjera pri subjektivnoj procjeni prsne visine. Također, izmjera provedena ispod i iznad stvarne prsne visine daje statistički značajnu pozitivnu odnosno negativnu vrijednost prsnog promjera u odnosu na stvarnu. Kod krakova odmaknutih od debla dobivene su očekivane niže vrijednosti prsnog promjera kao i kod izmjere sa krakovima okrenutim prema gore. Utvrđene su i razlike u izmjeri promjera između samih mjeritelja. Obzirom da je prsni promjer stabla osnova za procjenu volumena pojedinačnog stabla i sastojine, iz svega spomenutog jasno je da pogreške pri izmjeri prsnog promjera, bile one uzrokovane nepažnjom mjeritelja ili metodološke, mogu imati značajan utjecaj na dobivene rezultate.
A tree diameter at breast height (dbh) is a basic variable measured in forest inventory. Generally, it is measured with calipers whose arms have to be perpendicular to the beam. Therefore, caliper has to be rectified before measurement. Measurement should be performed in the way that caliper itself is perpendicular to the tree stem with arms and beam touching the tree without applying too much pressure to caliper arms. Measurer mistakes and failing to follow standard measurement procedures lead to errors that reflect in all inventory results (basal area, stand volume). Experience gathered while working with students and colleagues in practice, showed that measurement procedures sometimes significantly depart from required. Therefore, the aim of this research was to quantify and analyze known and observed dbh measurement errors.
For that purpose two sites in Zagreb Training and Forest research center were selected: one site in area of lowland oak and hornbeam forest stand and another in mountain area with mixed fir and beech forest. Total 282 trees (74 Pedunculate oak, 56 Common hornbeam, 76 Silver fir and 76 Common beech) in wide diameter range were measured. (Table 1). All selected trees were marked with a number before measurement.
On both research plots three measurers performed following diameter measurements using Haglof Mantax caliper: crosswise diameters at self-estimated breast height with (1a, 1b), crosswise diameters at marked breast height (2a, 2b), 10 cm above (3a) and 10 cm under the marked breast height (3b), at marked breast height point with caliper beam held apart from tree and normal pressure on the caliper arms (4a) and higher pressure on the caliper arms (4b) and caliper beam on marked point with caliper tips facing up (5a). Measurement group consisted of two measurers. One measurer preformed measurement and other was writing the data. Since measurers height can affect the placement of the calipers on the tree, so position of breast height of 1,3m was determined using measuring tape before beginning of measurement for each measurer. Marking of breast height point on the tree was made after measurement with self-estimated breast height. Collected data were analyzed using t-test and ANOVA with 0,05 significance level.
Results show that average differences between two crosswise diameter measurements at self estimated breast height are statistically significant for hornbeam (average difference 1 cm) and beech (average 1,7 cm). Fir and oak had less differences (up to 0,7cm) that were not proven statistically significant. (Table 2).
At marked breast height differences of crosswise measurements are as well statistically significant for hornbeam and beech. (Table 3). Comparison between average diameter difference at self-estimated
and marked breast height show statistically significant difference for oak and beech. Negative average values for all measured species suggest that measurers usually slightly overestimated breast height (Table 4). According to Figure 1 it is visible that crosswise diameter differences are mostly within ±2-3 cm (50% difference). Certain trees show difference up to 15 cm in crosswise diameters. At the same time, diameter differences between self-estimated and marked breast height are smaller than crosswise diameter difference. Figure 2 shows that there is almost no trees which are not elliptical with fir having the smallest values.
Diameter measured 10 cm under marked breast height expectedly resulted in statistically significant higher values for all tree species with 0,49 cm on average (Figure 4), and diameters measured 10 cm above marked breast height resulted in lower values being statistically significant for oak, beech and fir (Figure 5). The biggest difference is for oak trees.
When caliper beam was held apart from tree and normal pressure on caliper arms applied, results were -0,12 to -0,26 cm lower and statistically significant compared to readings at correct position (caliper beam on the tree). The similar results were achieved with stronger pressure on the arms but with higher negative values, as expected.
Measurement with arm tips facing up resulted with statistically significant lower average diameter reading for all measured tree species (Table 9). Moreover, Figure 4 shows that in comparison to diameter measured on marked breast height readings on the caliper scale were in range between -1,5 to +0,5cm with extremes ranging from -4 to +2cm respectively.
Differences between measurers were observed on self-estimated breast height and for crosswise diameters on marked breast height. Table 10 and Figure 5 show that diameter differences between measurer 1 and other two measurers have proven to be statistically significant for self-estimated breast height of fir and beech trees (forest stand on sloping ground) where measurer 1 in average measured smaller diameters. Further, with diameters measured on marked breast height, differences were significant between measurer 3 and other two measurers in the way that measurer 3 on average measured larger diameters (Table 11 and Figure 6)
Diameter measurement is the basis for volume estimation of individual trees and stand as well. Therefore, measurement errors have impact on volume estimation, so measurement is subjected to control and sometimes allowable measurement departures are prescribed. Omule (1980) mentions that in Columbia Forest Service allowable errors of 1% for dbh is allowed and Melson et al. (2002) states that allowable dbh errors are ±0,25 cm for trees from 12,5 to 50 cm, ±0,5 cm for trees from 50-100 cm and 0,75 cm for treesfrom 100-150 cm dbh. Measurer responsibility is to perform the measurement according to the rules and with highest possible precision.
As the results show, differences in diameters can be a result of eliptical trees (Table 2, 3 and Figure 1). On tree level, differences sometimes reach 30% of tree diameter (Figure 1). With increase of tree diameter the difference between two crosswise diameters increases as well (Figure 3). Also, measurement under or above actual beast height results in statistically significant positive or negative diameter values.
Results based on measured sample trees show that hornbeam and beech breast height measurement gives a significant difference in crosswise diameters as a result of sloping ground and geographic orientation. Turning the caliper beam towards the plot center can cancel out these measurement errors assuming an adequate sample size. Furthermore, on trees that are to be cut, the breast height should be marked (on the upper side of the slope). In this way measurement error for a single tree level would be reduced. Finally, this research points out the importance of following correct procedures while tree diameter measurement in order to minimize measurement errors which can affect accuracy of measured data.
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