Application and Comparison of Different Models for Regeneration Planning of Pedunculate Oak Stands (Quercus roburL.) – a Management Unit “Josip Kozarac” Case Study

U odnosu na planiranje intenziteta obnove na razini šume, složeniji i zahtjevniji dio planiranja odnosi se na odabir odgovarajućih sastojina za obnovu. To je posebno izraženo u uvjetima narušene strukture šume i sastojina, pri čemu se rangiranje sastojina prema prioritetu obnove treba zasnivati na objektivnim kriterijima. U radu je korišten model razlike prosječnog potencijalnog prihoda (rente) kao posljedica odluke o provedbi ili odgodi obnove potencijalno zrele lužnjakove sastojine, za rangiranje prema prioritetu obnove. Na primjeru uređajnog razreda hrasta lužnjaka u gospodarskoj jedinici “Josip Kozarac”, prema propisanom 10-godišnjem etatu glavnog prihoda od 265 ha, odabrane su sastojine dobi iznad 100 godina rangiranjem na temelju razlike u renti i dobi kao kriterija. Rangiranje je pokazalo da sastojine loše strukture dobi manje od 120 godina i prosječno manje površine imaju najveći prioritet, dok sastojine kvalitetne strukture, dobi iznad 135 godina i prosječno veće površine imaju najmanji prioritet obnove. Obnovom 21 najstarije i strukturno najkvalitetnije sastojine ostvario bi se najveći ukupni prihod od 73 mil. kuna, ali i najveći posredni i dugoročni gubitci. Ukupnim prihodom od 47 mil. kuna i najmanjim dugoročnim i posrednim gubitcima bi rezultirao pristup temeljen na modelu razlike u renti. Postojeći pristupi planiranja obnove lužnjakovih sastojina dijelom uzimaju u obzir zahtjeve dugoročne održivosti gospodarenja, a primjena i razvoj modela odlučivanja vodio bi intenzivnijem i učinkovitijem gospodarenju.Continuous stand regeneration is one of the most important prerequisites of sustainable forest management. In relation to the planning of regeneration intensity at the forest level, a more complex and challenging part of planning is the selection of appropriate stands for regeneration. This is particularly expressed in conditions of undesired and spatially heterogeneous structure of the forest and stands, the large number of potentially mature stands for regeneration and the multi objective approach of forest management, where ranking of stands according to regeneration priority should be based on objective criteria. The planning of appropriate regeneration dynamics and selection stands for regeneration is particularly (emphasized) stressed in lowland pedunculate oak forest management planning, where tree dieback is a significant ecological and management problem. In such circumstances stand age and its relation to rotation are not sufficient criteria for stand selection. In the study a previously obtained model of rent difference (Eq. 1, Table 1) as a consequence of the decision of regeneration (prompt or adjournment) of a potentially mature pedunculate oak stand (Figure 2, Figure 3),was used for stand ranking according to regeneration priority. Based on the obtained results and analysis, the aim was to compare and discuss qualitative and quantitative characteristics of stands planned for regeneration, according to three different models (E_DEL_REN, E_DOB, E_OG), define the influence on sustainable forest management and to indicate limitations and possible future improvements of pedunculate oak forest management planning. The forest research site was the management class of pedunculate oak within the management unit “Josip Kozarac”. Total area of the oak forest (3,690.8 ha) is divided into 321 p. oak stands (11.5 ha average area). Mostly old stands, and a few young and middle aged stands, with intensive regeneration during the last 20 years are the characteristics of age class distribution (Figure 1). Based on the model of rent difference (Eq. 1, Table 1), potentially mature oak stands (older than 100 years) were classified in six categories of regeneration priority (Table 2, Figure 4, Map 2). Stands to be regenerated in the next 10-year period (265 ha planned regeneration area) were selected on the basis of the rent difference model and stand age model in relation to forest management plan and spatial distribution (Map 3, Map 4), and the structural-qualitative characteristics of the selected stands (Table 3) were compared. Results showed that under stocked stands, younger than 120 years and on average smaller areas, have greatest priority, while stands with high-quality structure, older than 135 years and larger average areas, have least regeneration priority. Regeneration of 21 of the oldest and structural highest quality stands would lead to the highest yield of 73 million kuna, but also to the highest indirect and long term losses. On the other hand, yield of 47 million kunas and at least long term and indirect losses would the result of an approach based on the rent difference model, while actual planning partly considers the demands of long term sustainable management. The characteristics of the situation and management in the studied forest site represent similarities which exist (on a wider scale ) in the entire pedunculate oak forest area in Croatia. With regard to planning and management, due to the large share of mature stands with unfavorable structure and quality, comprehensive and complex demands of stand regeneration are necessary on the one hand, in order to ensure gradual and long term improvement of the forests, and, on the other hand, to ensure essential income for current management. Although, there are considerations of long term sustainability on the operative level of stand regeneration planning, open questions should be answered: what is the minimal level of achieving long term forest management demands, and to what extent the level is obtainable and sustainable, as well as what the projections are for future management periods. New information on mature pedunculate oak stands obtained from the rent difference model could be applied as supplement and support for the current approach of stand regeneration planning. Further development of the complex and dynamic spatial-temporal projection model would provide abundant information describing the current state of forest resources and management, relations between influencing factors, limitations and demands of management, as well as possible future developments. Application of the system would improve planning and management efficiency, as prerequisites of sustainable forest management, within the framework of a wider, strategic, level of decision making and its appropriate transfer to the operative levels of forest management