Suitability of tree biomass harvesting systems in spruce forest culture

Istraživanje je provedeno s ciljem utvrđivanja pogodnosti primjene djelomično mehaniziranih i mehaniziranih sustava pridobivanja drvne biomase u uvjetima neprorjeđivane smrekove šumske kulture. Kao preduvjet za interpretaciju razultata istraživanja sustava pridobivanja drvne biomase istražen je potencijal iznačajke nadzemne biomase stabala obične smreke, koje ju definiraju u smislu ulazne sirovine u proizvodni sustav. Izrađeni su matematički modeli za izračun količina i strukture nadzemne biomase te udjela vode u pojedinim segmentima stabla. Provedena istraživanja rezultirala su dinamičkim modelom za komparativnu analizu učinkovitosti rada istim sredstvima, a različitim metodama rada, odnosno usporedivim metodama, a različitim sredstvima rada.Terenski je dio istraživanja proveden na pokusnoj plohi (4437' N, 1519' E; n.v.573 m) na području gospodarske jedinice Žitnik kojom gospodari Šumarija Perušić Uprave šuma Podružnice Gospić trgovačkoga društva Hrvatske šume .Istraživana smrekova šumska kultura starosti 42 godine osnovana je sadnjomsadnica u redove s razmakom sadnje 2 × 2 m. Stablima nisu orezivane grane, aprva je proreda provedena tijekom ovoga istraživanja.Sukladno ciljevima istraživanja formirana su četiri sustava pridobivanja drva.Djelomično mehaniziranim sustavima pridobivanja drva (sortimentnom i stablovnom metodom) sječa i izrada stabala obavljena je ručno-strojno motornompilom, a privlačenje skiderom. Mehaniziranim sustavima pridobivanja drva(sortimentnom metodom i metodom utovarnih duljina) sječa i izrada obavljena je strojno harvesterom, a izvoženje forvarderom. Sustavi su upotpunjeni iveračem za izradu drvne sječke na pomoćnom stovarištu.Utvrđeno je da je jedinični trošak sječe, izrade i primarnoga transporta po stablunajmanji primjenom sortimentne metode mehaniziranim sustavom, slijediprimjena metode utovarnih duljina mehaniziranim sustavom i primjena stablovnemetode djelomično mehaniziranim sustavom, a trošak primjene sortimentnemetode djelomično mehaniziranim sustavom dvostruko je veći. Za proizvodnjukonačnog šumskog proizvoda (dr vne sječke), troškovima stablovne i metodeutovarnih duljina treba pridodati još i odnosne troškove iveranja, no unatoč tomenjihova je primjena još uvijek troškovno pogodnija od primjene sortimentnemetode djelomično mehaniziranim sustavom. Mehanizirani sustav pridobivanjazbog neusporedivo veće proizvodnosti, u troškovnom pogledu, nema alternativepri provođenju prorede u istraživanoj šumskoj kulturi. Uporaba djelomičnomehaniziranog sustava pridobivanja može biti opravdana samo u slučaju nužnostiprovođenja geometrijske prorede sječom jednostrukih redova, a prednost mu je imanje oštećivanje preostalih dubećih stabala (pri sječi dvostrukih redova).The research was conducted to determine the suitability of the application ofpartially mechanized and mechanized biomass harvesting systems in conditionsof non thinned spruce forest culture. As a prerequisite for the interpretation of theresearch results of biomass harvesting systems the potential and characteristics ofaboveground biomass of spruce trees, that define it in terms of feedstock in theproduction system were explored. Mathematical models were constructed tocalculate the amount and structure of aboveground biomass and the water contentin individual segments the tree. The studies carried out have resulted in adynamic model for comparative analysis of the efficiency of the the same meansof work in different methods of work, or comparable methods of work anddifferent means of work.The field part of this research was conducted at the experimental plot (4437' N,1519' E; altitude 573 m) in the area of management unit "Žitnik" managed by theForest office Perušić, Forest administration Gospić of "Croatian Forests" Ltd.Studied spruce forest culture was established by planting seedlings in rowsspaced 2 × 2 m 42 years ago. Tree branches were not pruned, and first thinningwas conducted during this study.In accordance with the goals of the research four harvesting systems wereformed. In partially mechanized harvesting systems (by assortment and full treemethod) felling and processing of trees was done motor-manually by a chainsawand skidder was used for extraction, In mechanized harvesting systems (byassortment and load-length method) felling and procesing was done by aharvester and extraction was performed by a forwarder. Systems werecomplemented with a chipper to produce wood chips at the landing.It was found that the unit cost per tree of felling, processing and extraction wasthe smallest when assortment method with mechanized system was applied,followed by the application of the load-length method of mechanized system andthe full tree method of partially mechanized system. The cost of application ofassortment method with partially mechanized system is twice as high. For thefinal production of forest products (wood chips), costs of full tree and load-lengthmethod have to be increased with the relative costs of chipping. But despite that,their application is still more cost efficient than the application of assortmentmethod with the partially mechanized system. Mechanized harvesting system,due to much greater productivity, in terms of cost has no alternative inconducting thinning in the studied forest culture. Using partially mechanizedharvesting systems can be justified only in the case of necessity of geometricthinning with felling of single rows, and it has the advantage of causing lessdamage to the remaining standing trees (when cutting duplicate rows)