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Habitat changes on the most important areas for birds in Croatia during 1990-2000 period

Authors researched the habitat changes on specific habitat types on area previously assessed as the most important areas in Croatia for the protection of endangered bird fauna during 1990-2000 year period. The areas used in the analysis were four areas in continental part of the Croatia (Danube and Drava River alluvium, Pokupsko depression, Sava River basin, Upper Drava River basin) and four areas in the Mediterranean part (Neretva River estuary, NW part of the North Dalmatia, Paško field, Lake Vrana). For the analysis of changes in classified habitat types Corine Land Cover Databases for 1990 and 2000 years were used. We used to assessment of the ornithological of the whole territory of Croatia according known distributions of endangered birds (Radović et al. 2003). Using software package ArcView (Version 9.1, Copyright © 2006 ESRI) we abstracted the polygons with detected change in habitat class from period 1990 – 2000, further analysis was performed with SAS [JMP] software (Version 7) of the SAS system (SAS Institute Inc.). Almost no changes in habitat were detected on the Mediterranean part of the country, for example the greatest change was detected on Vrana lake (less than 2% of total area as degradation of forest) while on other areas even less than 1%. The four areas are in the Pannonian part of Croatia are Pokupsko depression, Sava River basin, upper part of the Drava River basin and Danube and Drava River floodplains (Fig 1). Both, total area and percent change detected was much greater on areas in Pannonian part (Fig 4) and that is the reason why all other results and discussion will be focused on them. At Danube and Drava River floodplains habitat changes were detected on more than 8% of total area (Fig 3.) and more than 5% was changed in Sava River basin but with greatest absolute amount. We are totally aware that this kind of analysis is not optimal for the assessment of changes in habitat quality for small area extents. Altogether 57 possible groups (directions) have been identified (Fig 5). In total, the greatest change during 1990 – 2000 year was identified on forest habitats (Fig 5). Almost all changes were detected on broad-leaved forests with extremely small portion of mixed forests. All the changes were those between forest stands transforming to transitional woodland and scrub and vice-versa with notably greater extent of forest degradation compared with maturation of forest stands. This process is detected on two areas: Sava River basin and Pokupsko depression (Fig 5) with total amount of change more evident along Sava River basin. Authors discussed the possible impact on several bird species listed in Red Data Book of Birds of Croatia for what the detected changes should have the greatest impact on populations. Because of inadequate country-wide monitoring schemes for the most of the bird species listed in Red Data Book of endangered birds in Croatia the discussion presented below should be seen only as rough indicator of assumed impact on regarded bird species according species-specific research and monitoring programs conducted elsewhere.

bird; habitat; Reda Data Book

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