| Abstract (croatian) | Istraživanje o strukturi nadzemne biomase obične bukve provedeno je na tri različite lokacije unutar šumskogospodarskog područja Republike Hrvatske, a cilj je bio utvrditi pogodnost uporabe alometrijskih funkcija za izračun biomase obične bukve u različitim sastojinskim uvjetima. Alometrijske funkcije konstruirane su na temelju podataka prikupljenih neposredno in situ destruktivnom metodom. Prema uzgojnom obliku sastojine A i C su visokog uzgojnog oblika, dok je sastojina B panjača. Sastojine A i B su brdske bukove šume kojima se gospodari regularno, a sastojina C je preborna jelovo-bukova šuma. Na svakom lokalitetu posječen je i izmjeren određen broj stabala, pri čemu se posebna pozornost posvetila na reprezentativnost uzorka (prsni promjer) s obzirom na distribuciju doznačenih stabala. Svakom posječenom stablu izmjereni su prsni promjer i visina (duljina). Obujam krupnoga drva promjera >7 cm utvrđen je metodom sekcioniranja. Grane promjera od 3 cm do 7 cm s korom izmjerene su, odnosno sekcionirane kao i krupno drvo, a ostalom dijelu sitne granjevine tanjem od 3 cm određena je masa u svježem stanju. Oblikovanje izračuna biomase triju sastavnica, kao i ukupne nadzemne biomase, izvršeno je prema tri različita modela. Za ocjenu modela korištena su dva parametra, koeficijent determinacije (R2) te drugi korijen prosječne kvadratne pogreške (RMSE). Na osnovi navedenih parametra, za ocjenu modela najbolji model za procjenu svih triju sastavnica te ukupne nadzemne biomase je model 2 – eksponencijalna jednadžba s dvije nezavisne varijable (d, h) i tri koeficijenta. Od preostala dva ispitivana modela, najbolji se pokazao model 1 i to u 9 slučajeva, što je bilo pomalo neočekivano, jer model 3, koji kao nezavisnu varijablu koristi obujam stabala iz lokalnih tarifa propisanih osnovom gospodarenja, već obuhvaća informacije o promjeru i visini stabala. Najveći prinos biomase očekivano je u sastojinama viših boniteta. Povećanjem prsnog promjera stabla povećava se postotni udio biomase krupnog drva promjera >7 cm u ukupnoj nadzemnoj biomasi stabla, a to povećanje najizrazitije je u regularnoj sastojini II boniteta. Udio biomase granjevine promjera 3–7 cm gotovo je konstantan promjenom prsnog promjera stabla, dok se biomasa treće sastavnice (granjevina <3 cm) u postotnom udjelu smanjuje povećanjem prsnog promjera, što je uočljivije u regularnim sastojinama. Ovdje predloženi modeli mogu predstavljati podlogu za daljnja istraživanja u cilju poboljšanja planiranja procesa proizvodnje te naknadne analize izvršenih sječa. Poseban potencijal predstavlja sastavnica drvne biomase promjera manjeg od 7 cm, čiji udio u određenim sastojinskim uvjetima može doseći i preko 10 % ukupne nadzemne biomase kod stabala većih prsnih promjera (uključujući i lisnu biomasu), a preko 20 % kod stabala manjih prsnih promjera. |
| Abstract (english) | The study was conducted at three different locations (three sub-compartments of different management units) within the forest management area of the Republic of Croatia (Figure 1) with the aim of determining the suitability of using allometric equations for calculation of the common beech biomass in different stand conditions, constructed on the basis of input data collected directly by in situ destructive method. Two locations were situated in high forests (stand A in regular managed beech forest and stand C in selective managed fir-beech forest) and one location, stand C was a coppice forest (Tables 1 and 2). Durring the investigation, a preparatory felling was conducted in the stand A, a tninning was conducted in the stand B, and a selection cut was conducted in the stand C. At each site a number of trees was cut down and measured; 15 at the felling site A, 14 at the felling site B and 17 model trees at the felling site C. In doing so, attention was given to the representativeness of the sample (dbh) given the distribution of marked trees. For each cut tree dbh and height (length) were measured. Volume of wood >7 cm was determined by the sectioning method. Branches with a diameter of 3 cm to 7 cm with bark was measured (sectioned) and for the rest of the brushwood, thinner than 3 cm, fresh mass was determined. In felling sites A and B research was conducted in the dormant season, and in the felling site C research was conducted during the growing season. Therefore, the amount of brushwood thinner diameter than 3 cm biomass included foliar biomass. Modeling of three components of biomass, and total aboveground biomass was carried out according to equations 1, 2 and 3, Equation 1 uses dbh as input with two coefficients (a i b), in Equation 2 an additional independent variable (tree height) was included in order to improve the model and it contains three coefficients (a, b and c). When planning harvesting operations, under the felling plan based on dbh of the marked trees (which are directly measured) with the help of prescribed tariffs planned gross volume of a tree in a specified dbh class is calculated. For this reason (availability of data) in equation 3 volume of tree from tariffs is included as the independent variable with two coefficients a and b. For the evaluation of the models two parameterswere used, the coefficient of determination (R2) and root mean square error (RMSE). Based on these parameters the best model for the calculation of all three abovegaround biomass components and for the total aboveground biomass is model 2, the exponential equation with two independent variables (d, h), and three coefficients (Table 4). In 11 of the 12 cases this model gives the best results. After the model 2, from the other two models tested, the best model has proven to be the model 1 (in 9 cases). This is somewhat unexpected because the remaining model 3, which uses the volume of tree calculated on the basis of local tariffs prescribed by the management plan as an independent parameter, already includes information on the diameter and height of trees. Therefore, it was expected that this model will be better than model 1, but that was not determined in this study. Mentioned model 3 proved to be better in just 3 cases. Determining the amount of two categories of aboveground biomass wita a diameter less than 7 cm is particularly important because in the traditional wood harvesting this part of the forest residue usually remains unused, and in the production of wood chips is a usable income potential of our forests. When comparing the features of marked and cut trees from three different felling areas, the highest yield of biomass is in the stands of higher site index, as expected. By increasing the dbh of trees the percentage of the biomass of wood >7 cm in total aboveground tree biomass increases, and this increase was most pronounced in the regular stand of the site index II. The share of brushwood 3–7 cm biomass is almost constant when dbh increases, while the share of the third component of biomass (branches <3 cm) reduces by increasing the dbh, which is more noticeable in regular stands. Models proposed in this paper can represent the basis for further research in order to improve the planning of the production process and the subsequent analysis of felling results. Biomass of a diameter less than 7 cm represents a special potential, which share in certain stand conditions can reach over 10% of the total aboveground biomass of trees with larger dbh (including foliar biomass), and over 20% of the total aboveground biomass of trees with the smaller dbh (Figure 5). |
