Brown Bear Habitat Quality in Gorski Kotar, Croatia
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BROWNBEAR HABITATQUALITY IN GORSKIKOTAR, CROATIA JOSIP KUSAK,Biology Department, Veterinary Faculty of the Universityof Zagreb,Heinzelova 55, 10000 Zagreb,Croatia, email: [email protected] [email protected] DJUROHUBER, Biology Department, Veterinary Faculty of the Universityof Zagreb,Heinzelova 55, 10000Zagreb, Croatia, email: [email protected] Abstract: The brown bear (Ursus arctos) population in Croatia is a possible source of bears for reintroducingand augmenting disappearing Europeanbrown bear populations in western Europe. For successful reintroduction,knowledge about bear habitat quality of both source and target areas is necessary. We developed a habitat suitability index (HSI) model to assess Europeanbrown bear habitatquality in Gorski kotar, Croatia. Importanthabitat variables included seasonal foods, cover, roads, and fragmentation. Food sources were available year-round,whereas foraging and denning cover were more limited. Humaninfluence was manifestedthrough a relatively high density of roads (1.91 km/km2),which included forest roads. Habitatfragmentation did not occur within the study area, but a highway under constructionwas a possible threat. The overall HSI value of 0.42 for the entire area indicatedthat brown bear habitatin Gorski kotar is average. Brown bear habitatcould be improved with changes in managementpractices such as closing forest roads, seasonally avoiding logging in denning areas, and reducing reforestationof beech-fir (Fagus sp.-Abies sp.) areas to spruce (Picea abies). Ursus 10:281-291 Key words: Croatia,European brown bear, habitat quality, habitat suitability index, Ursus arctos. One of the largest remainingbrown bear populations This study was fundedby the CroatianMinistry of Sci- in Europe occurs in the Dinara, Sara, and Pindus moun- ence, Wildbiologische Geselschaft-Miinchen, John tains (approximately 60,000 km2) spanning Slovenia, Sheldon Bevins Memorial Foundation, and Stiftung Croatia, Bosnia and Herzegovina, Monte Negro, EuropaiischeNaturerbe (EURONATUR). We thank A. Macedonia (Huber and Frkovic 1993), Albania, and Frkovic, D. Majnaric,and B. Plese for logistic field sup- Greece (Servheen 1990). Within the Croatianportion of port. Special thanksare due to the reviewers and associ- this range, about 400 bears inhabit approximately9,800 ate editors for improving the style and quality of the km2(Huber and Frkovic 1993), and this numberhas been manuscript. stable since the early 1980s (Frkovicet al. 1987). Mitochondrial DNA testing has demonstrated that brown bears in the Dinara Mountains have greater ge- BROWNBEAR HABITAT SUITABILITY netic similaritiesto the small, isolated populationsin the INDEXMODEL Alps, Apennines, and Pyrenees than to other European populations(Taberlet and Bouvet 1994, Randiet al. 1994). HabitatUse Requirements Consequently,they may be the best source to reintroduce Food habits and habitatuse of brown bears in Croatia or to augment existing bear populationsin western Eu- were analyzed by Cicnjak (1991). In spring and early rope. Projectsto reintroducebears from the DinaraMoun- summer,bears were found at lower elevationswhere food tains to other countriesare in progress,with 3 (2 F, 1 M) was available. Main food sources includedbroad-leaved bears already translocatedto the AustrianAlps and an- garlic (Allium ursinum), lords and ladies (Arum other 3 (2 F, 1 M) to the FrenchPyrenees. maculatum),and carrionand corn at permanentfeeding Maintenance of suitable bear habitat is central to sites. Bears also visited meadows where they consumed the continued presence of the species in Europe grasses (Gramineaespp.), clovers (Trifolium spp.), and (Servheen 1990). Knowledge of brown bear habitat sorrels (Rumex spp.). During the summerwild angelica relationships is needed to enhance management of (Angelica silvestris) and stinking aposeris (Aposeris existing European brown bear populations and to im- foetida) were the main plant foods eaten, althoughbears prove chances for successful reintroduction efforts. occasionally fed in oat fields (Huber and Moric 1989). We developed a habitat suitability index (HSI) model By late summer,fruits ripened in meadows, abandoned for brown bears in southern Europe following the U.S. orchards,along fields and roads, and in the forest; the Fish and Wildlife Service's (1981) habitat evaluation most importantbear foods were raspberry(Rubus idaeus), procedures. We then used the HSI model to evaluate bramble (R. fruticosus), common buckthor (Rhamnus brown bear habitat in the Gorski kotar region of cathartica),and blueberry (Vacciniummyrtillus). Dur- Croatia; we recommend management changes based ing fall, bears spent the most time in forestedareas where on that analysis. beech nuts were abundant. Similar patternswere found 282 Ursus 10:1998 in Cantabrian Mountains, Spain (Clevenger et al. can increasetraffic mortality of bears. Crossing sites on 1992a,b). Beech treesstart producing nuts at 40-50 years. roadsand railroadswere recognizedas importantparts of Maximumcrop production(x = 1.38 kg/tree) can be ex- migratingcorridors (Huber et al. 1998). Telemetrystud- pected every 7th to 12th year; in other years production ies in Slovenia (Kaczenskyet al. 1996) showed thathigh- is 0.11 kg/tree. The cycle of beech productivityis differ- ways are a physical barrierfor movements of females, ent in differentparts of the forest (Regent 1980). Depre- whereas males occasionally cross during the mating dation on domestic animalsin Croatiawas lower than in season. other Europeancountries because of the availability of natural and supplementalfood (Cicnjak 1991). While HSIModel Applicability feeding on naturalfood, the average distance of bears to This model describeshabitat suitability in Gorskikotar, settlementsand roads was not statisticallydifferent from Croatia(Fig. 1). It can be appliedto similarmountainous randomlydistributed points (Cicnjak1991). Brown bear areas in Europe, such as the Alps, Pyrenees, Apenines, distributionand abundancehas not been associatedwith and Carpathians. It is designed to produce HSI values water availabilityin Croatia(Cicnjak 1991). for year-roundhabitat needs of the brown bear. We as- Europeanbrown bears do not rely on protectivecover sumed that carryingcapacity is restrictedby food avail- to access food; they have developedcrepuscular and noc- ability and that a weak compensatoryrelationship exists turnal activity patterns when protection cover is poor for food availability among seasons. To stress impor- (Roth and Huber 1986). The closest distance to which tance of fall food, we weighted it by a factor of 2. The man can cautiously approacha Europeanbrown bear is model can be appliedon areaswhere beech, mixed beech- about 30 m (pers. observ.). Bears that are approached fir, and spruce forests prevail. The average home range closely may abandonsome feeding places, but this may size for both sexes of bears during foraging season not be of great importance in habitat with good food was 28 km2 (range = 1-102 km2) (Huber and Roth sources elsewhere. Protective cover may be more im- 1993). Therefore, the model requires a minimum habi- portantfor selection of suitabledaybeds or dens. Resting tat area of 30 km2. sites (day beds) had the shortesthorizontal visibility (x = The model was developed based on our knowledge of 8.4 m, range = 3-46 m), followed by denning sites (x = bear biology, expert opinion (A. Frkovic, CroatianFor- 12 m, range = 1-18 m) and feeding sites (x = 36, range = ests, Delnice, Croatia,pers. commun., 1993) and a thor- 6-186 m) (Cicnjak 1991). ough comparison with other models (Aste 1993; Van Bearsin Croatiaden in forestedareas at elevationsfrom Manen and Pelton 1993, 1995; Clevenger et al. 1995); 450 m to 1370 m (x = 863 m, N = 28). The average however, it has not been tested underfield conditions. distancefrom dens to the nearestroad was 486 m (range = 39-1500 m) and from dens to the nearest settlement Components was 1435 m (range = 200-4000 m) (Huber and Roth A habitatsuitability index (HSI) is a numericalindex 1995). Feeding on energeticallyrich beech nuts, which that representsthe ability of a given habitatto supporta were the most importantfood source for bearsin Croatia specific species. An index of 0.0 representsunsuitable in autumn(Cicnjak 1991), could be of great importance habitat,whereas an index of 1.0 representsoptimal habi- for successful winteringand giving birth(Schooley et al. tat. For HSI to be between 0.00 and 1.00, an assumed 1994). linear relationshipbetween chosen habitat components In Croatia,habitat types reflect differences in eleva- and carryingcapacity must be met (U.S. Fish and Wild- tion, geology, and other ecological factors. Seasonal life Service 1981). movements of bears reflect changes of food availability We defined food, cover, andhuman impact as the main in differenthabitat types. In the contiguoushabitat found bearhabitat components (Fig. 2). Van Manenand Pelton in Gorskikotar, average home rangesize of bearsfor both (1993) defined ecological, physical, and culturalhabitat sexes did not vary between spring,summer, and fall (x = componentsfor Americanblack bear (Ursus americanus). 28 km2,range = 1-102 km2,n = 32), althoughwinter range Aste (1993) listed the following bearhabitat components of was significantlysmaller (x = 4 km2,range = 0-18 km2,n for Austria: food type, food availability,availability factors. = 5) (Huberand Roth 1993). remote and safe places, and effect of limiting in Cantabrian Forest management in the mountains of Croatia in- Clevengeret al. (1992a)