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Experience in use of colour infrared (CIR) aerial imagery in forest decline assessment in the Republic of Croatia

The CIR aerial photographs have been used in Croatia for operational forest decline assessment since the year 1988. The tree crown damage was classified according to the scale used in European Union, slightly modified, and the stand damage according to our own established scale. The forest decline inventories have been carried out in two ways: (1) the whole area of the beech and fir forests in southwest Croatia (ca 240000 ha) was covered by sample photostrips (ca 296 km). The sampling method similar to the methodology used in European Union was performed, designed according to a preliminary investigation. (2) The severe damaged fir forests "Brloško" & "Bitoraj" and of the National park "Risnjak" in southwest Croatia were photographed with full coverage (about 10.000 ha). In lowland pedunculate oak forests in slavonian Sava valley sample strips have been taken (69 km long). The photographed forest area was divided into strata in which a number of single crowns equally distributed in the area, proportional to the area size were interpreted. The maps of decline distribution were made using graphical methods (radial triangulation and radial line intersection) and the topographic base map at scale 1:5000. Some of the inventory results were incorporated in organised GIS models. For the Educational and Research Forest "Opeke" photoplan was made by proportional transformation of scanned aerial photographs using ARC/INFO Grid module.

CIR aerial photographs; forest decline inventories; the beech and fir forests in southwest Croatia; pedunculate oak forests in slavonian Sava valley; GIS

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