Current state and the structural analysis of the mixed even-aged pedunculate oak and common hornbeam forests in Croatia

Background and Purpose: Mixed forests of pedunculate oak and common hornbeamare among the most important and most recognizable forest ecosystems in Croatiawith exceptional ecological, economical and sociological significance. Stand structure of these forests can be very complex, and their development highly dynamic due to the relationships between the add-mixed tree species aswell as vertical and horizontal stand structural elements. In the contemporary management of oak-hornbeam forests in Croatia growth and yield tables of domestic authors are used. Aimof this research is to give an overview of the current state of mixed forest stands of pedunculate oak and common hornbeam in Croatia through the analysis of available information on the area extent and basic stand structural features. Furthermore, the information obtained in the research are compared with the data from the growth and yield tables of domestic authors. Materials andMethods:Database used in this research is maintained by the state-owned forest management company Croatian Forests Ltd., and is comprised of the data collected within the regular forest management. In total, 5,060 forest stands (sub-compartments) with total area of 75,948.76 ha from whole area extent of pedunculate oak in Croatia were included in the analysis. Record for each stand included: phytocoenological community, forest area, stand age and age class. Width of the age classes is 20 years. Analyzed stand structural attributes were grouped for each stand by tree species (pedunculate oak, common hornbeam and other species) and as a whole, and included: stand density, basal area, volume, quadratic mean diameter and height. Finally, the shares of pedunculate oak and common hornbeam in the total basal area of each stand were calculated. Results and discussion: Total area of mixed pedunculate oak and common hornbeam forests in Croatia, according to the results of this research, amounts to 98,364.43 ha. Age structure of these forests is irregular, both by area, and by the number of forest stands with stands older than 80 years (5th age class and older) dominate in the total area. Most of the stands (> 68%) grow on 1st site class, i.e. the best site class. Structural elements of forest stands on 1st site class, show a large variation of the analyzed structural elements throughout the development of the stands (2nd to 8th age class). Highest variation is established in the shares of tree species in the total basal area of the stand. These values are under the direct influence of the growth and development of diameters at breast heights of trees of different species and of the corresponding diameter distributions. Basal area shares are also highly influenced by the silvicultural measures applied during the life-time of each particular stand. Comparison of actual stand structural attributes with the values indicated as optimal in the growth and yield tables of domestic authors revealed a high degree of discrepancy. Conclusion: As a general conclusion, it can be said that the currently used growth and yield tables only very rarely correspond with the actual state of forest stands in the field. New and improved methods of forest management planning are highly desirable at this moment in Croatian forestry

MODELING OF THE STAND BASAL AREA WITH STANDARD GROWTH EQUATIONS?

Temeljnica sastojine jedan je od osnovnih elemenata koji čine strukturu sastojine. U ovom radu prikazani su modeli razvoja sastojinske temeljnice, mješovitih sastojina hrasta lužnjaka i običnoga graba, pomoću standardnih funkcija rasta, koje se najčešće potrebljavaju u praksi, a razvoj zavisne varijable opisuju pomoću samo jedne nezavisne varijable (starosti). Realizacija postavljenog cilja ovog istraživanja provedena je kroz dvije faze rada: • Izrada modela razvoja temeljnice na razini gospodarskih sastojina. • Usporedba razvoja temeljnice sa prirasno-prihodnim tablicama. Istraživanje prve faze provedeno je na uzorku od 5060 odjela/odsjeka gospodarskih lužnjakovo-grabovih sastojina u Republici Hrvatskoj, ukupne površine od 75948,76 hektara. U drugoj fazi istraživanja napravljena je grafička usporedba razvoja sastojinske temeljnice, dobivenog u prvoj fazi istraživanja, s razvojem sastojinske temeljnice u prirasno-prihodnim tablicama domaćih autora. Dobiveni rezultati pokazuju kako razvoj sastojinske temeljnice mješovitih gospodarskih sastojina hrasta lužnjaka i običnoga graba, od početka do kraja ophodnje, karakterizira velika varijabilnost podataka, a modeli njezina razvoja, dobiveni odabranim standardnim funkcijama rasta, imaju sličan oblik i slične vrijednosti. Iz dobivenih rezultata razvidno je kako modeliranje razvoja temeljnice na razini sastojine standardnim funkcijama rasta previše statično i jednostavno prikazuje njezin razvoj, zbog vrlo malo informacija koje bi opisale dinamiku i zakonitosti razvoja promatranog elementa strukture u današnjem vremenu promijenjenih klimatskih uvjeta te sve naglašenijega antropogenog utjecaja na okolinu.Stand basal area is one of the fundamental stand structural elements. In this contribution we present growth models of the stand basal area in mixed pedunculate oak and common hornbeam forests developed with four standard growth functions. These functions prevail in practiacal use in forestry, and they describe development of basal are with only one independent variable: stand age. Research was conducted through two work stages: • Development of the stand basal area models based on data from managed forest stands. • Comparison of the stand basal area development with values tabulated in growth and yield tables. For the first phase of the research, we utilized the sample of 5,060 stands, or subcompartments of managed oak-hornbeam forests in Republic of Croatia, with total area of 75,948.76 ha. In the second phase we compare development trends of the stand basal area as achieved in the first research phase, with the development of the stand basal area tabulated in the growth and yield tables of domestic authors. Results of the research clearly show high variability of the stand basal area development with stand age, from the beginning to the end of the stand rotation in the mixed oak and hornbeam forests. Four models of the stand basal area development over age obtained in this research are very similar, both in the curve shape as well as in the model values over stand age. It is quite obvious, based on the results of this research, that modeling of the stand basal area development with univariate growth equations oversimplifies the multitude of the basal area growth trajectories that can occur in various forest stands, i.e. this type of models are to static to properly account for the stand basal area variability over stand age

DISTRIBUTION OF ALEPPO PINE (Pinus halepensis Mill.) AND ITS EFFECT ON VEGETATION AND LANDSCAPE STRUCTURE OF WIDER AREA OF ŠIBENIK

Primorski krš Hrvatske je već više od stotinu godina pod utjecajem intenzivnog pošumljavanja u najvećoj mjeri alepskim borom, čime su stvoreni uvjeti za njegovo širenje u prostoru. Istraživanje provedeno na širem području Šibenika uz pomoć geografskog informacijskog sustava donosi realnu sliku stanja rasprostranjenosti alepskog bora, koji se danas prirodnim putem uvelike proširio izvan prostora pošumljavanja. Posebna dinamika širenja alepskog bora, koja često podrazumijeva pojavu požara, postala je ključni čimbenik dinamike vegetacije ovog prostora, što pak dovodi do izravnih promjena u strukturi pejzaža, a alepski bor svrstava u kategoriju invazivnih vrsta. Pošumljavanje vođeno vizijom obnove autohtonih šuma hrasta crnike do danas nije polučilo značanije rezultate, ukazujući na potrebu za promjenom pristupa u pošumljavanju, kao i znatnijem ulaganju rada i kapitala.The landscape dynamics in coastal areas of Croatian karst is under heavy influence of reforestation in which the use of Aleppo pine (Pinus halepensis Mill.) was predominant. This prevailance of Aleppo pine in reforestation has led to its vast spatial expansion which in turn has resulted in the direct consequences on the whole environment. The purpose of this research paper is to examine the real distribution of Aleppo pine in the wider area of Šibenik and its impacts on other vegetation, both of which reflect on the landscape structure. The main source of data were sattelite images obtained from the State Geodetical Administration of the Republic of Croatia and data from CORINE Land Cover database and Hrvatske šume d.o.o. Supported by the field research where needed, a map of spatial distribution of Aleppo pine was created using ArcMap 10.0. which categorizes the appearance of Aleppo pine in 3 categories. The areas where Aleppo pine has the complete dominance comprise 13 % of research area, while larger clusters of Aleppo pine trees appear in 19 % of area. These areas are mainly found on islands, coastal areas or in the vicinity of larger settelments. Sporadic appearance of Aleppo pine trees is noticed on further 33 % of research area, meaning that, from the late 19th century when Aleppo pine was present only on 30 ha of island Krapanj to the present times, its growth area has expanded by 31.750 ha or 600 % per year. Out of that area 15.680 ha is heavily forested by Aleppo pine which would imply its invasive character, which is also supported by the studies indicating negative effects of Aleppo pine on biodiversity of the area where it grows. The expanding stands of Aleppo pine are inducing the regrowth of autochthonous holm oak (Quercus ilex L.) but the results are not satisfying and call for the increased investments in silviculture