Applicability of Vertex telemeter in measuring the structure of montane beech stand using variable probability sampling

Uporabljivost ultrazvučnog visinomjera/daljinomjera Vertex pri izmjeri strukture brdske bukove sastojine primjenom uzoraka promjenjive vjerojatnosti selekcije ocijenjena je na temelju rezultata procjene strukturnih elemenata i vremena, odnosno novčanih sredstava utrošenih za izmjeru. Istraživanje je provedeno u čistoj bukovoj sastojini na području Uprave šuma Podružnice Karlovac, Šumariji Slunj u gospodarskoj jedinici Mašvina. Na kvadratnoj mreži 100x100 metara postavljeno je 25 stajališta na kojima je provedena izmjera prsnih promjera Bitterlichovom metodom (PPS). Za odabir stabala korišten je Bitterlichov štapić (faktor temeljnice 1) i Bitterlichov zrcalni relaskop (faktori temeljnice 1, 2 i 4). Provjera udaljenosti rubnih stabala provodila se Vertexom, a uz faktore temeljnice 2 i 4 i mjernom vrpcom. Kao referentna metoda postavljena je kružna ploha radijusa 20 m. Na temelju izmjera različitim metodama izračunate su vrijednosti strukturnih elemenata (broj stabala, temeljnica i volumen) za pojedine plohe i sastojinu u cjelini. Analizom varijance ponovljenih mjerenja nije utvrđena statistički značajna razlika u prosječnim vrijednostima strukturnih elemenata između različitih metoda izmjere uz razinu značajnosti 0,05. Za odabrane PPS metode provedena je studija vremena i procjena troškova inventure. Uz veće faktore temeljnice znatno se smanjuje vrijeme i trošak inventure (i do 71 %). Ukupno vrijeme i troškovi inventure primjenom faktora temeljnice 2 uz korištenje Vertexa su 20 % manji, a kod faktora temeljnice 4 su 12 % manji nego kada se udaljenost rubnih stabala provjerava mjernom vrpcom. Ovim istraživanjem potvrđeno je da se troškovi izmjere PPS metodama mogu smanjiti primjenom Vertexa, a jednako tako i primjenom odgovarajućih faktora temeljnice, kao i organizacijom rada (prijevoz ekipa).Applicability of ultrasonic telemeter Vertex in inventory of montane beech stand was estimated. Evaluation was based on estimates of structure elements from Bitterlich variable plot sampling, time consumption and costs. Research was carried out in pure beech stand located near Slunj, in management unit "Mašvina", Forest administration Karlovac, Croatia. Systematic sample of 25 plots was laid on a grid 100 x 100 m. Breast height diameters (DBH) and heights of trees over 10 cm DBH were measured using Variable plot sampling with different metric basal area factors (BAF). Sample trees were selected by Bitterlich stick (BAF 1) and Spiegelrelaskop (BAFs 1, 2 and 4). Distance of borderline trees was checked by Vertex telemeter and measurement tape (BAF 2 and 4). In total, seven combinations of Bitterlich plots (methods) were carried out (Table 1), and circular 20 m radius plots on the same standpoints were set as a reference method. Diameter distributions estimated from BAFs 1, 2, and 4 were compared to distribution from 20 m radius plots by chi-square test, difference of 0.05 being considered statistically significant. Distributions from BAF 2 and 4 were found to be statistically different (Table 2), with difference mostly coming from number of trees DBHs 10 to 20 cm (Fig. 2). Number of stems, basal area and volume were calculated for each method per each plot and whole stand (Table 4). All estimates were compared by repeated measures ANOVA with significance level 0,05. No statistically significant differences were found between estimates of N, G and V coming from different methods (Table 5). Time study and estimation of costs were carried out for measurement methods. Bigger BAFs were found to considerably decrease time (Figure 4) and costs (Table 6), even up to 71 % (BAF 4 vs. BAF 1). Using Vertex instead of measurement tape for checking borderline trees reduced time and costs by 12 % (BAF 4) and 20 % (BAF 2). By economically organizing transport of field crews (two crews using the same vehicle) time and costs were reduced by 8 %. This research confirmed that cost of forest stand inventory using variable plot sampling can be reduced by use of Vertex telemeter, as well as by choice of appropriate BAFs and economical transport of the field crews

Analysing the duration of studyng on undergraduate studies et the Faculty of forestry, University of Zagreb

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)

Modeling Bark Thickness of Silver Fir Trees (Abies alba Mill.)

Temeljni cilj istraživanja bio je načiniti modele koji objašnjavaju debljinu kore obične jele u dinarskim bukovo-jelovim šumama Hrvatske, kao funkciju stanišnih (ekoloških) čimbenika i značajki pojedinih stabala. Od stanišnih čimbenika pri modeliranju korištena je nadmorska visina, nagib te orijentacija terena, a od značajki pojedinih stabala korišteni su prsni promjer, visina te starost stabla. Uzorkom je obuhvaćeno 531 stablo obične jele, kojemu je osim navedenih parametara izmjerena debljina kore na izvrtku dobivenom Presslerovim svrdlom u prsnoj visini. Istraživanje je provedeno u dinarskom dijelu areala obične jele u Republici Hrvatskoj (Uprave šuma Podružnice: Delnice, Gospić, Ogulin i Senj). Pri modeliranju debljine kore obične jele, u provedenoj parcijalnoj linearnoj korelaciji statistički značajnim varijablama pokazali su se: prsni promjer, visina stabla, starost stabla, i nadmorska visina. Bonitet sastojine u radu uzet je kao kategorijska varijabla. U statističkoj obradi korištene su varijable u izvornom i logaritamskom (ln) obliku. Koeficijenti determinacije dobiveni modeliranjem nalaze se u rasponu od 62,5 % do 70,4 %. Modeli s varijablama u logaritamskom obliku daju oko 4 % veće koeficijente determinacije u odnosu na modele s izvornim varijablama. Složeniji modeli sa svim značajnim varijablama ukupno povećavaju objašnjenu varijabilnost sa svega 3–4 %, pa se preporučuje uporaba jednostavnijeg modela s prsnim promjerom kao jedinom nezavisnom varijablom te korištenje logaritamske funkcije. Pokazalo se da bonitet sastojine značajno utječe na debljinu kore, te je kora deblja što je bonitet lošiji. U radu je istražen i utjecaj gospodarenja ovim sastojinama u prošlosti na debljinu kore. Rezultati ovih istraživanja ukazuju na manju debljinu kore u sastojinama kojima se intenzivno gospodarilo u odnosu na ekstenzivno gospodarene ili negospodarene sastojine, iako se iz rezultata ne može razlučiti koji dio te razlike je posljedica intenziteta gospodarenja, a koji nešto boljeg srednjeg boniteta intenzivno gospodarenih sastojina.Basic aim of research was to make correlation models that explain bark thickness of silver fir in dinaric beech – fir forests as a function of ecological and stand factors. Modeling was made by using spatial variables (altitude, terrain slope and orientation) and individual tree characteristics (diameter at breast height, tree height and age). Sample was taken by measuring given parameters of 531 fir trees in dinaric region of Republic of Croatia (Forest Administrations: Delnice, Gospić, Ogulin i Senj). Bark thickness was measured on increment cores taken at breast height by using Pressler’s increment bore. Calculating was made by MS Excel application, and modeling bark thickness by Statistica 7.1 software. Diameter at breast height (DBH), tree height, tree age and altitude were variables with highest correlation coefficients to bark thickness that proved to be statistically significant, and were therefore used in model building. Models were made using partial linear correlation method, with variables calculated both in original and logarithmic form, considering p = 0,05 as a limit of statistical significance. Determination coefficients of 8 models ranged from 62,5 % to 70,4 %, with logarithmic form variables showing on average 4 % higher values. Diameter at breast height proved to be basic variable for models, with determination coefficient of 63 %, while additional variables increased it at most to 70 %. Therefore it is suggested to use simple model for predicting bark thickness, with DBH in logarithmic form as the only independent variable. Impact of site quality on bark thickness was also studied, emphasizing that trees in lower quality stands have thicker bark. Models obtained by this research give lower values of bark thickness compared to former studies of Bojanin (1966a, 1966b) and Klepac (1972). Calculating percentage in tree dimensions, according to our model 1.2, bark make 4,1 % (diameter class 97,5 cm) to 8,1 % (diameter class 12,5 cm) of tree diameter, which is about 2,3 % lower to 1,7 % higher compared to their research. According to this study silviculture and management proved to influence bark thickness: trees in intensively managed stands have thinner bark. However this may be the result of difference in site quality of intensively managed and non-managed stands. Bark increment can also be predicted based on obtained models. According to model 1.2, bark contributes from 2,8 % (diameter class 92,5 cm). to 5,6 % (diameter class 12,5 cm) in tree diameter increment

Choice of adaptive forest management model based on long-term projection in dinaric fir-beech stands

SažetakRaznodobne 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.SummaryUneven-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

Influence of a measurer and measurement errors on measurement of a tree diameter

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

Generating Virtual Even-Aged Silver Fir Stand Structure Based on the Measured Sample Plots

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

Precision of Structure Elements’ Estimation in a Beech – Fir Stand Depending on Circular Sample Plot Size

Osnovni elementi strukture sastojine (broj stabala, temeljnica i volumen) procjenjuju se na temelju uzorka primjernih ploha. Cilj ovog istraži vanja je usporediti rezultate procjene strukturnih elemenata sastojine dobive ne na primjernim plohama različite veličine, te posredno ocijeniti učinkovitost iz mjere glede veličine ploha. Mjerenja su provedena u bukovo-jelovoj sastojini Nastavno-pokusnoga šumskog objekta “Zalesina” na području prebornih šuma Gorskoga kotara u Hrvatskoj. Na sistematskom uzorku 17 koncentričnih kruž nih primjernih ploha izmjereni su prsni promjeri stabala te njihov položaj (azi mut i udaljenost) u odnosu na središte plohe. Pri tome su stabla iznad 10 cm promjera mjerena na krugovima radijusa 13 m, stabla iznad 30 cm promjera na krugovima radijusa 19 m, te samo stabla deblja od 50 cm na krugovima radi jusa 26 m. Načinjen je računalni program za izračun strukturnih elemenata sa­stojine te njihovu simulaciju i obračun po plohama radijusa različitih od onih izmjerenih. Uspoređeno je osam veličina kružnih ploha – osim mjerenih ploha (radijusi 13, 19 i 26 m) uzete su plohe radijusa korištenih u uređajnoj inventuri (7,98 m; 12,62 m; 5 i 12 m), nacionalnoj inventuri (7, 13 i 20 m)i nekoliko po kus nih veličina krugova (9,77 m; 11,28 m te 7 i 13 m). Na svim stajalištima su za svaku veličinu plohe izračunate prosječne vrijednosti broja stabala, temelj nice i volumena po hektaru. Razlike u procjeni strukturnih elemenata na ra zini sastojine između ploha različitih veličina nisu statistički značajne, uz ra zinu značajnosti 0,05. Za rezultate procjene izračunata je preciznost procje ne uz 95 % pouzdanosti koja izravno ovisi o odabranoj veličini ploha. Bolja preciznost procjene strukturnih elemenata dobivena je na većim plohama, gdje je zbog većeg broja uključenih stabala dobivena manja prostorna varija bilnost. Primjenom koncentričnih krugova posebice je kod procjene broja sta bala zbog manje mjerenih stabala povećana varijabilnost i pogreška uzorka. Preciznost procjene temeljnice i volumena na koncentričnim krugovima nije znatno pogoršana, što upućuje na opravdanost njihove primjene zbog moguće uštede pri izmjeri. Dobiveni rezultati omogućuju odabir željene veličine ploha uzorka na temelju omjera broja mjerenih stabala na plohama i kakvoće (pre ciz nosti) procjene strukturnih elemenata. Prije praktične primjene potrebno je istraživanje provesti na većem uzorku ploha u više sastojina različitog pro stornog rasporeda stabala te analizirati razdiobe broja stabala, temeljnice i volumena po debljinskim razredima. Mjerenje vremena potrebnog za izmjeru ploha omogućilo bi točniji izračun učinkovitost izmjere na plohama različite veličine.Stand structure estimate is based on data from sample plots. The aim of this research was to compare the stand structure estimates based on sample of circular plots with different radii. Through this influence of plot size on structure estimate and efficiency of stand measurement was also indi rectly assessed. Measurements were made in beech-fir selection stand in the Educational and experimental forest site “Zalesina” in Gorski kotar region, Croatia. Stand size is 20,63 ha, it is situated from 790 to 850 m above sea level, and belongs to site class II. Stand exposition is south to east, terrain slope is 5–10°. Tree breast height diameters (DBH) were measured on syste matic sample of 17 concentric circular sample plots. Tree location from plot centre was recorded by azimuth and distance. All trees of DBH 10 cm or more were measured on 13 meter radius plot, trees of DBH 30 cm and more were measured on 19 m radius plot and trees of DBH 50 cm and more on 26 m ra dius plot. Computer programme CirCon for calculation of stand parameters based on measured plots and simulated plots, with radii different from measu red ones, has been developed. Plots based on real measurements were simula ted according to ones used in forest management practice (singular and concentric circle plots). We simulated 8 methods: K7,98 (7.98 m radius plots), K9,77 (9.77 m radius plots), K11,28 (11.28 m radius plots), K12,62 (12.62 m radius plots); K5-12 (concentric circle plots with radii 5 and 12 m), K7-13 (concentric plots with radii 7 and 13 m), K7-13-20 (concentric plots with radii 7, 13 and 20 m) and K13-19-26 (three concentric circles of 13, 19 and 26 m radius). Calculated estimates for number of trees, basal area and volume on the same standing points differed between methods depending on spatial tree distribution and size of plots. Descriptive statistics (arithmetic mean, stan dard deviation, standard error) was made for each variable (number of trees, basal area and volume) on stand level. Sample error with 95 % confidence (SE/mean*t0.05,) was also calculated to express the precision of estimates. Different estimates by methods depending on plot size were compared by repeated measures ANOVA, due to lack of independence between methods (plot sizes) on the same standpoints. Estimates of number of trees by methods (Figure 2) ranged between 275.4 and 303.5 per hectare, although differences were not statistically significant at 0.05 confidence level (Repeated measures ANOVA: F = 0.6027, df = 7, p = 0.7526). Precision expressed by relative sample error varied from 13.58 % (K13-19-26) to 28.34 % (K5-12). Better results (lesser sample error) were ob tained on bigger plots, though concentric circles (K5-12, K7-13 and K7-13-20) have considerably greater sample error due to fewer trees per plot. Basal area estimates by methods ranged from 34.80 to 37.76 m2per hec tare (Figure 3), making no statistically significant differences (Repeated mea sures ANOVA: F = 0.2948, df = 7, p = 0.9547). Relative precision ranged from 10.13 % (K13-19-26) to 26.96 % on smallest plots (K7,98). Sample error of basal area estimate on concentric circles was just slightly bigger in spite of fewer trees per plot. Reason for that is stability of basal area on plots regardless to fewer trees: concentric circles include fewer trees but have great share of bigger ones that contribute to basal area more than smaller ones. Estimate of stand volume by methods ranged from 457.93 to 496.47 m3per hectare (Figure 4). There was no statistical difference in volume estimates bet­ween analysed methods (Repeated measures ANOVA: F = 0.2650, df = 7, p = 0.9661). Relative precision ranged between 10.14 % (K7-13-20) and 30.36%(K7,98). Better precision was obtained with bigger plots, due to more trees per plot. Concentric circles produce just slight increase in sample error while lowering the cost of measurement by reducing the number of trees per plot. Number of measured trees per plot was computed as an indicator of plot ef ficiency. Differences in number of trees per plot between plot sizes were stati­stically significant at 0.05 level (Repeated measures ANOVA: F = 187.621, df = 7, p = 0.0000), except for: K7,98 and K5-12; K7-13 and K9,77; K7-13-20 and K12,62 (Fisher LSD Post-hoc test). Evident increasing trend of number of trees per plot by increasing of plot size is the main cause of better precision. Although concentric circles reduce number of trees per plot, loss of precision for basal area and volume are mini mal (Figure 5). Therefore plots K5-12 are acceptable for use in this kind of stands, with remark that they require well trained staff and modern instru ments. Plots K7-13 do not improve precision while increasing number of trees per plot (9), therefore are not recommended. Triple concentric circles K7-13-20 reduce sample error almost by 10 %, although by significant increase of mea sured trees per plot. Plots K11,28 reduce number of trees per plot with minimal increase in sample error compared to K12,62 plots. That fact makes them acceptable choice for gain in efficiency. However, K11,28 sample should be adjusted with more plots to satisfy required sampling intensity (5 % of stand), which would increase costs. In order to simplify the sampling plan, legislation does not re quire precision rather sampling intensity (5 % of stand area), which restricts opportunity to optimize sample size. The choice of plot size is based on inventory goals and should depend on cost of measurements and expected precision. This kind of research can pro vide useful base for determining plot size by costs and precision of data. Exact ratio of cost and precision could be computed by including time measurement per plots of different sizes

Characteristics of private forest owners in relation to their activities in enlargement of forest holdings

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)

Ecophysiological Response of Sun-Exposed Common Beech (Fagus Sylvatica L.) Seedlings under Different Fertilization Levels

Sušenje obične jele (Abies alba Mill.) većih razmjera, prisutno u Hrvatskoj u zadnjih dvadesetak godina, dovelo je do netipičnih stanišnih uvjeta za rast podmlatka obične bukve (Fagus sylvatica L.) na područjima bu kovo-jelovih šuma. Ovakav razvoj događaja u kontradikciji je s prihvaćenom šumarskom praksom i poznatim ekološkim zahtjevima bukve (skiofilnost, osje tljivost na sušu). Da bismo odredili osnovne parametre ekofiziološkog odziva klijanaca bukve na uvjete punog osvjetljenja, postavljen je rasadnički pokus s tri razine gnojidbe (2, 4 i 6 g Osmocote Exact kompleksnog mineralnog gnojiva po litri uzgojnog supstrata), s ciljem oponašanja različitih uvjeta plodnosti tla (niska, optimalna i visoka dostupnost hraniva). Za svako tretiranje utvrđena je ukupna biomasa klijanaca (lišće, stabljika, korijen) a biljni materijal analiziran je na sadržaj biogenih elemenata (du šika, fosfora, kalija, kalcija i magnezija). Izmjerena je visina i promjer korije novog vrata biljaka, a morfologija korijena analizirana je pomoću WinRhizo softverskog paketa. Za mjerenja fotosintetskog kapaciteta, krivulje svjetlo snog zasićenja (0, 50, 250, 600 i 1200 µmol/m2s) i A-Ci krivulje (0, 100, 400, 700 i 1000 µmol CO2/l) dobivene su pomoću Li-Cor LI-6400 u kontroliranom okruženju. Visina, promjer i biomasa sadnica povećavala se s dozom gnojiva. Kon centracije N, P i K rasle su s dozom gnojiva, dok su koncentracije Ca i Mg po kazivale negativni učinak prekomjerne gnojidbe pri najvišoj dozi gnojiva. Duljina korijena, površina korijena i broj vrhova bili su najveći u srednjem tretiranju, a korijen se najslabije razvijao pri najvećoj dozi gnojidbe. U svim tretiranjima asimilacijska sposobnost bila je povezana s masom lišća (r2=0,59), koncentracijom N u lišću (r2=0,44) i korijenu (r2=0,58) kao i koncentracijom P u lišću (r2=0,45).The large-scale dieback of Silver fir (Abies alba Mill.), pre sent in Croatia in the past two decades, has led to atypical growth conditions for young Common beech (Fagus sylvatica L.) trees on beech-fir sites. This is in contradiction with recent forestry practice and ecological requirements of beech (skiophytic, drought sensitive). The aim of this study was to improve the fundamental understanding of the influence of light and nutrient availability in early stages of the development of beech seedlings. To determine the ecophysiological response of beech see dlings to full sunlight conditions, a nursery experiment was established with three fertilization treatments (2, 4 and 6g of Osmocote Exact per 1 liter of sub strate) to simulate various soil fertility conditions (low, optimal and high avai lability of nutrients). For every treatment, total biomass of seedlings (foliage, stem, roots) and the elemental concentrations of nitrogen, phosphorous, potassium, calcium and magnesium in the plant material determined by chemical analysis. Height and root-collar diameter have been measured and roots morphologi cally analyzed (WinRhizo software package). Light saturation curves (0, 50, 250, 600 in 1200 µmol/m2s) and A-Ci curves (0, 100, 400, 700 in 1000 µmol CO2/l) have been measured (Li-Cor LI-6400) in a controlled environment. Height, diameter and biomass of seedlings increased with fertilizer dose. Concentrations of N, P and K were growing with fertilizer dose, while Ca and Mg concentrations showed negative effects of overfertilization at the highest fertilizer dose. Root length, surface area and number of root tips were highest in the intermediate treatment while roots were least developed at the highest fertilizer dose. In all cases assimilation rates of seedlings corresponded well with leaf mass (r2 = 0,59), leaf (r2 = 0,44) and root total nitrogen (r2 = 0,58) and total leaf phosphorus (r2 = 0,45). Regardless of the conditions of full sunlight and an irregular water supply to seedlings while growing in the nursery, they showed a standard ecophysio logical response to fertilization treatments, indicating that despite the chan ged site conditions in beech and fir stands, the seedlings may keep the capacity to adapt to the environment. The most successful development of see dlings can be expected on nutrient-rich sites

Efficiency of Inventory in Uneven-Aged Forests on Sample Plots with Different Radii

Učinkovitost izmjere šuma na jednostrukim kružnim plohama različite veličine u prebornim jelovo-bukovim sastojinama u Gorskom kotaru ocijenjena je na temelju preciznosti procjene i utrošenoga vremena za izmjeru. Na 103 primjerne plohe radijusa 20 m izmjereni su prsni promjer, visina i položaj stabala. Računalnim programom CirCon napravljen je obra- čun strukturnih elemenata (broja stabala, temeljnice i volumena) za plohe u rasponu radijusa od 4 do 20 m s pripadajućom preciznosti procjene. Prosječne vrijednosti strukturnih elemenata na plohama različitih veličina uspoređene su analizom varijance ponovljenih mjerenja te Fisherovim post hoc testom. Na poduzorku 24 stajališta izmjereno je vrijeme potrebno za terensko mjerenje na plohama različite veličine te je za sve veličine ploha procijenjeno vrijeme izmjere u ovisnosti o površini plohe. Postignuta učinkovitost ocijenjena je kao umnožak kvadrata pogreške uzorka i utrošenoga vremena. Učinkovitost uz zadani intenzitet izmjere od 5%površine za različite veličine i broj ploha procijenjena je pomoću očekivane preciznosti i potrebnoga vremena. Procjena broja stabala na plohamamanjim od 7mradijusa statistički je značajno podcijenjena u odnosu na plohe radijusa 20 m, što nije potvrđeno za temeljnicu i volumen. Preciznost procjene bitno je poboljšana povećanjem ploha do radijusa 13 m, a prosječne vrijednosti ustaljuju se na približno 10 m radijusa. Uz isti broj ploha učinkovitost je znatno poboljšana povećanjem površine ploha do radijusa 10 m te podjednaka za plohe radijusa iznad 13 m. Za broj ploha prilagođen zadanoj ukupnoj površini uzorka utrošak vremena jednoznačno se smanjuje primjenom manjega broja većih ploha u odnosu na veći broj manjih ploha, uz male razlike u preciznosti procjene. Plohe površine 500m2 potvrdile su se prihvatljivima, s tim da bi uz istu veličinu uzorka veće plohe poboljšale preciznost procjene i učinkovitost. Prilagodbom veličine i broja ploha propisanom intenzitetu ove plohe također su se pokazale prikladnima uzmoguću uštedu vremena na plohama većega radijusa.For the purpose of forest management planning in Croatia, forest inventory is performed on sample plots of permanent sizes, generally from 500 to 1,000 m². Such plots have been accepted in practice on the basis of experience. Thus, the plot size has only partially been adjusted to different forest types. Although methods of sample selection are regulated by Forest Management Regulations and are limited to plots of permanent sizes, the Regulations still allow plot sizes to be adjusted to specific stand conditions. This article compares the results of forest measurement on differently sized plots in order to estimate their efficiency in selection fir and beech stands. Research was carried out in Gorski Kotar, where the stand structure was recorded using a sample of experimental plots. Systematic sampling with a random start was used to establish 103 sample plots in the management units of »Delnice« and »RavnaGora«. Breast height diameters over 10 cm and tree heightsweremeasured on circular plots of 20mradius, set up across a 100 x 100 m square grid, and their positions in the space (azimuth and distance from the centre) were recorded. The values of structural elements (number of trees, basal area and volume) were calculated from the obtained data bymeans of a specially constructed computer programme CirCon for the plots and stands. The precision of estimates was expressed as a relative sample error with 95% confidence. Thanks to spatial data for all the trees, a calculation was made of the structure for sample plots in the radius range from 4 to 20 m. The precision of structural elements estimate (sample error) was calculated for each plot size. The average values in differently sized plots were compared with repeated measurement analysis of variance (RM ANOVA) with significance level of 0.05. The results of different plot sizes were subsequently tested by means of the Fisher’s LSD \u27post hoc\u27 test. On a sub-sample of 24 standpoints, the time needed for field measurements on differently sized plots was later measured in order to estimate the efficiency of differently sized plots. From these data measurement time (t) for all plot sizes was assessed in dependence on plot area (P) using the equation t=a*PČb. Walking time and distance between the plots were measured, from which the travel speed in the field was calculated. The efficiency of plots of a particular size was evaluated by the precision of estimate and the time needed for measurements. The achieved efficiency index was evaluated as the product of squared sample error and total time expressed in relation to the efficiency of 20mradius plots. The efficiency for differently sized plotswas also assessed by means of the expected accuracy at given sampling intensity of 5% area (5% cruise), as set down in the Forest Management Regulations. The results show the differences in the estimate of structural elements in dependence on plot sizes, especially for tree number. The differences were confirmed as statistically significant (RMANOVA: F = 2.31, df = 102, p < 0.0001). Subsequent testing revealed that on the plots with radii less than 7 m the estimate of tree number was statistically significantly lower than in the larger plots. Asimilar trend did not prove to be statistically significant either for the basal area (ANOVA PM: F = 0.72, df = 102, p =0.8772) or for the volume (ANOVA PM: F = 0.78 df = 102, p = 0.8124). Expectedly a more precise estimate was obtained with an increase in plot size. Considerable improvement in the precision was observed up to plot radii of about 13 m. The trend was slowed down with further increase: consequently, in terms of precision, plots with at least the above radii are recommended. The assessment accuracy of tree numbers in the smallest plots was better by 10% than that of the basal area; however, this difference decreases as the plot size increases, to become equal at plots with radii of about 12 m. The difference in the assessment accuracy of the basal area and volume ranges from about 2%in the smallest plots to less than 1%in the largest plots with 20m radius. In the case of smaller plots, apart from poorer precision of estimates, there were also bigger deviations from the average obtained on larger plots. With regard to the average assessment value of tree number, the basal area and volume, plots with radii greater than 10 m would be acceptable in the study area. The average measurement time increases almost linearly with an increase in plot size. In terms of the achieved efficiency index at the same number of plots, the smallest plots proved to be the least efficient, while the efficiency increases considerably up to 9 m radius, and levels from radii larger than 13 m. Along with the number of plots adjusted to the given sample size intensity of 5%, plots with radii between 8 and 15 m proved to be more precise than smaller and bigger plots. Time expenditure uniformly decreases with the application of a smaller number of bigger plots in relation to a larger number of smaller plots with an equal total area. Hence, the use of bigger plots is more practical since differences in precision are negligible. In terms of the number of measured trees per plot as a practical criterion that affects the quality of the results and of field work, plots with radii between 12mand 15mare recommended, which contain between 20 and 30 trees on average. This research confirmed the assumption that the reliability of estimates depends on plot size. Specific numerical relationships were obtained for the investigated selection stands. Plots of 500 m2, common in forest management practice, proved to be adequate for the investigated stands. Nevertheless, larger plots could significantly contribute to better precision of estimates at identical sample size. In terms of efficiency, these plots are definitely acceptable, taking into account the fact that even larger plots could also be efficient at identical sample size. By adjusting the size and number of plots to the prescribed intensity, standard plot sizes proved to be adequate. Still, plots of larger radii would possibly save the measurement time. Additional research involving a larger sample and broader range of stand conditions would give a clearer insight into the effect of plot size on precision of estimates. It would also enable better adjustment of plot sizes to individual stands for the purpose of forest inventory rationalization. For similar beech-fir selection stands, a comparison of nested plots (concentric circles) that are adjusted to the diameter structure should definitely be made. By doing so, the efficiency of assessment reliability and measurement efficiency could be improved, which is neglected by the present regulations