Zna~ajke prostorne distribucije su{aca u bukovo-jelovoj {umi

Features of Spatial Snag Distribution in a Beech-Fir Forest With the participation of about 65% in the total growing stock of conifers, silver fir is the most important andthe best represented conifer species in Croatia. The increasing share of sanitary felling in the annual felling plansdemands that special attention be paid to the health status of fir forests and the quantity of unplanned felling. Thisis the reason why dieback of silver fir in beech-fir forests in the Dinaric Alps is an acute and topical manage-ment-ecological problem. In the past 10 years, the share of total unplanned felling in the overall annual felling forfir has amounted to 57%. Such a high share of unplanned yield (mainly snags) has had a negative effect on sustain-able forest management. Determining the spatial distribution of damaged trees and snags, as well as their monitor-ing is one of the priorities of sustainable management. Hence, it is of utmost importance to detect less healthystands and apply timely measures for the purpose of maintaining their vitality and productivity at an optimal level.Due to the seriously disturbed stand stability caused by forced canopy opening, which in turn affects the healthcondition and natural regeneration of the stand, it is necessary not only to detect snags but also determine thecauses of dieback. According to the results of past research, increased tree dieback is associated with the impact ofdifferent site and stand characteristics (altitude, exposition, slope, soil, structure, etc.), as well as abiotic and bioticfactors (fir needle moth, mistletoe); however, the real causes are yet to be discovered. It is difficult to make efficientsnag inventories with standard field methods. For large areas, a remote sensing method (the application of CIR ae-rial photographs) is much more practical, more cost effective and more reliable. All research activities so far haveproved that, in terms of accuracy, this method is equal to field working methods, while in terms of speed and objec-tivity it is far more efficient. Snag inventories by means of CIR aerial photography interpretation and GIS enableefficient enumeration (detection) and spatial distribution (mapping) of snags. The proposed method is highly im-portant not only for the detection and monitoring of the occurrence, distribution and direction of dieback progress,but also for the detection of possible dieback causes, on the basis of which experts will prescribe adequate measuresand treatments. The objective of CIR aerial photography interpretation is to determine the current situation andacquire an objective picture of forest condition (database) in as short a period as possible, while mapping on a colorinfrared digital orthophoto (DOP) is intended to provide the spatial distribution of snags for the surveyed area. Anaerial survey of the Lika area with the CIR film (Forest Administration Gospi}) was conducted in strips (Fig. 3).The coordinates of the start and finish points of aerial photogrammetric series in the associated zones of theGauss-Krüger cartographic projection, as well as planned strip lengths, are given in the following survey (Table 1).A total of 88 aerial photographs were taken at an average scale of 1:6000 and longitudinal overlap of 60%, which al-lows for the interpretation of individual trees in the stereomodel. As the total length of all the three strips amounted Croat. j. for. eng. 32(2011)1325Zna~ajke prostorne distribucije su{aca u bukovo-jelovoj {umi (313–327)R. Pernar i dr.