Height and Purity of Beech Tree Trunks According to the Type of Felling and the Percentage of Technical Roundwood in the Trunks and Tree Tops in Relation to Applied Standard

Abstract

Istraživana je čistoća i visina debla bukovih stabala, kao i postotni udio tehničke oblovine u deblima i krošnjama stabala s obzirom na prsni promjer, vrstu sijeka i primijenjenu normu za razvrstavanje tehničke oblovine. Čistoća debla definirana je kao dužina debla od perca do prve žive ili urasle grane, te ostalih grešaka koje nisu površinske naravi, a veće su od 15 % prsnog promjera. Visina debla definirana je kao dužina debla od perca do mjesta gdje se gubi jednostruka uzdužna os stabla, ili kao dužina debla od perca do prve deblje žive grane koja suvislo tvori krošnju. Prikrajanje i razvrstavanje (klasiranje) drvnih sortimenata tehničke oblovine izvršili smo prema Hrvatskim normama proizvoda iskorištavanja šuma od 1995. godine (HRN) i hrvatskim normama HRN-EN 1316-1:1997. Na čistoću debla, pojavnost grešaka ima važan utjecaj. Pojavnost grešaka slučajnog je karaktera i nije u korelaciji ni sa jednim mjerljivim parametrom stabla. Iz tog razloga nismo uspjeli utvrditi čvršću vezu između čistoće debla i prsnog promjera stabla. Srednje vrijednosti visine debla po debljinskim stupnjevima rastu od proreda prema dovršnim sjekovima. Raspored srednjih visina debla po debljinskim stupnjevima i vrsti sijeka nije posljedica slučajnosti. Visina debla stabala u sastojini uvjetovana je nizom čimbenika. Raspored srednjih visina debla u sječinama određene vrste sijeka u velikoj je mjeri posljedica naših odluka kojima se rukovodimo prilikom odabira stabala za sječu pojedine vrsti sijeka. Postotni je udio tehničke oblovine u neto obujmu stabla kod primjene HRN-EN veći za stabla svih debljinskih stupnjeva. Utvrđena je razlika između udjela tehnike u deblu stabla kod proreda i pripremnog sijeka s jedne strane te naplodnih i dovršnih sjekova s druge strane. Udio tehničke oblovine debla raste od proreda prema pripremnim sjekovima. Srednje vrijednosti tehničke oblovine debla za cijeli uzorak primjernih stabala pokazuju linearnu ovisnost o debljinskim stupnjevima i padajući trend, koji je posljedica povećanja obujma tehničke oblovine izrađene iz krošnji s porastom prsnoga promjera stabala. Veće vrijednosti postotnih udjela tehničke oblovine u deblima stabala kod primjene HRN mogu se protumačiti većom količinom izrađene tehničke oblovine iz krošnji stabala pri primjeni HRN-EN.The subject of research were purity and height of beech trees, as well as the participation of technical roundwood in trunks and tree tops in relation to breast diameter and the type of felling. Research was carried out in the economic unit „Bjelovarska Bilogora“ of Forest Office Bjelovar, Forest Administration Bjelovar. Data gathering, i.e. measurement of exemplary beech trees was carried out in 36 areas on 46 occasions (fellings). All the areas belong to ecological-economical type II-D-11 and structural class BEECH, with the rotation of 100 years, which participates in the area of the economic unit with 76.1 %, and with 80.6 % in its timber stock. Measurements of exemplary trees were made in relation to diameter class and the type of felling. Trunk purity was measured on 693 exemplary trees, of which 237 mere measured in the felling areas of preparatory felling, 139 in the areas of thinning felling, while 317 were measured in the areas of final felling. Trunk height was measured on samples including 787 trees in the areas of thinning felling, 788 trees in the areas of preparatory felling, 467 trees in the areas of seeding felling and 266 trees in the areas of final felling – a total of 2,308 trees. Altogether, the research included 3,001 exemplary trees. Trunk purity is defined as the length of trunk from the butt-end to the first live or ingrown branch, and other flaws which are not superficial, and take up more than 15 % of the breast diameter. Trunk height is defined as the length of trunk from the butt-end to the place where the single longitudinal axis of the tree disappears, or as the length of trunk from the butt-end to the first thicker live branch which coherently forms the top of the tree. Bucking and sorting (classification) of timber assortment of technical roundwood was carried out according to two standards: Croatian Standards of Forest Exploitation Products from 1995 (HRN), and European Standards EN 1316-1:1997 (HRN-EN). Occurrence of flaws has crucial influence on trunk purity. Occurrence of faults is random in character and isn’t in correlation with any measurable tree parameter. For that reason we couldn’t establish a closer connection between trunk purity and breast diameter of tree. Average values of trunk height according to diameter class increase from thinning felling towards final felling. Thinning felling has an extremely falling (almost linear) trend of trunk height average with the increase of diameter class. The average values of trunk height of final felling show the highest values of all the diameter classes. Such distribution of average trunk height according to diameter class and the type of felling is not accidental. Trunk height of trees in the stand depends on a range of factors, from hereditary (genetic) predisposition of trees, over conditions of growth, to the position of trees in the stand. The distribution of average trunk heights in the felling areas of a certain type of felling is to a great extend a consequence of the decisions that we make during the selection of trees for felling in a particular type of felling. Because of their poor technical, (but not evolutionary) quality, forked trees are the first choice for assignation in thinning felling and preparatory felling. According to the European Standards, the participation of technical roundwood in the net tree volume is greater for trees of all diameter classes. The difference decreases with the increase of breast diameter of tree, and it ranges from over 20 % for the thinnest diameter classes to almost 5% in the thickest diameter classes. Upon implementation of the two standards (HRN and HRN-EN), a difference was established between the participation of technical roundwood in the tree trunk in thinning and preparatory felling on one side, and seeding and final felling on the other side. Trend lines of average values of technical roundwood in the tree trunk of the thinning and preparatory felling have a falling and convex form, while the trend line form of the seeding and final felling is concave. Furthermore, we can conclude that the participation of technical roundwood of trunk increases from thinning felling towards preparatory felling. Average values of participation of technical roundwood of trunk of the whole sample of exemplary trees show a linear dependence on diameter class and the falling trend which is a consequence of the increased quantity of technical roundwood produced from the tree tops with the increase of the breast diameter. Higher participation of technical roundwood in tree trunks according to the Croatian Standards can be interpreted by larger amount of technical roundwood produced from tree tops according to the European Standards. This is the result of smaller minimal dimensions and higher tolerance of flaws for D quality class of technical roundwood according to the European Standards