Potential Range and Corridors for Brown Bears
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POTENTIALRANGE AND CORRIDORSFOR BROWNBEARS INTHE EASTERN ALPS, ITALY LUIGIBOITANI, Department of Animaland HumanBiology, Viale Universita 32,00185-Roma, Italy,email: boitani @ pan.bio.uniromal .it PAOLOCIUCCI, Department of Animaland HumanBiology, Viale Universita 32,00185-Roma, Italy,email: ciucci@ pan.bio.uniromal .it FABIOCORSI, Istituto Ecologia Applicata, Via Spallanzani 32,00161 -Roma,Italy, email: corsi @ pan.bio.uniromal .it EUGENIODUPRE', Istituto Nazionale Fauna Selvatica, Via Ca Fornacetta,40064-Ozzano Emilia, Italy, email: infseuge@ iperbole.bologna.it Abstract: Although several techniqueshave been used to explore the spatialfeatures of brownbear (Ursus arctos) range (e.g., potentialdistribution ranges,linkages between isolated sub-populations, and analyses of habitatsuitability), quality and quantity of datahave often constrainedthe usefulness of the results.We used 12 environmentalvariables to identifypotentially suitable areas for bears in the Italianpart of the EasternAlps. We usedMahalanobis distancestatistic as a relativeindex of the environmentalquality of the studyarea by calculatingfor eachpixel (250 meters)the distancefrom the centroid of the environmentalconditions of 100 locationsrandomly selected within known bear ranges. We used differentlevels of this suitabilityindex to identify potentialoptimal and sub-optimal areas and their interconnecting corridors. The model identified4 majorareas of potentialbear presence having a total size of about 10,850 km2.Assuming functionalconnectivity among the areasand mean density for west Europeancountries, the EasternAlps could support108-325 bears.Potential ranges were also comparedwith existingprotected areas to evaluategaps betweenbear range with adequateprotection andrange needing protection. Only 31%of existingprotected areas was foundsuitable for bears.We suggestthat bear conservation will dependmore on establishingand managing effective corridorsthan other protected areas. Ursus 11:123-130 Key words: Alps, brownbear, geographic information system, GIS, habitatsuitability, Italy, Mahalanobis statistic, potential distribution, Ursus arctos Brownbear populations in Europeancountries are dras- and Hackman 1995). Because spatial requirementsare tically reducedfrom earliersizes, with populationsrang- evaluatedin terms of availability,localization, and con- ing as low as 4-5 up to 80-100 bears (InstitutRoyal des figurationof suitableareas with respectto a humandomi- Sciences Naturelles de Belgique [IRSNB] 1992). Al- nated land matrix, it is unlikely that available remnants thoughsome of these are still in contactwith sourcepopu- of wilderness are large enough to accommodateviable lations (e.g., Pindusand Rhodope populations in Greece), bear populations.Rather, a networkof protected(or ap- the majority appear highly isolated (e.g., in the propriatelymanaged) areas has been viewed as an alter- Cantabrian Mountains, Trentino, Abruzzo, and the native solution to meet viability requirementsfor large Pyrenees) and in need of conservation.Small propagules carnivores(Noss and Harris1986). Such a system should of expanding populations, which are of paramountim- be centeredon criticalareas of suitableenvironments con- portance for naturalrecolonizations (e.g., the Tarvisian nected throughcorridors and should be integratedinto a populationin northeasternItaly), also need promptcon- human-dominated matrix which includes transitional servationmeasures to ensure their protectionand to fos- areas (i.e., buffer zones) devoted to sustainableuse. Fur- ter their growth. Bears in the EasternAlps survive in 2 thermore, any local conservation measure (e.g., estab- small, isolated populations: 3-4 individuals in the lishing a protected area) or management intervention Adamello-BrentaNatural Park, considered a relict popu- (e.g., incentives for fruit tree plantationsor alternative lation unable to reproducesince 1989 (Osti 1994), and a livestock husbandry),to be effectively implementedand small Tarvisianpopulation probably composed of bears monitoredat the administrativelevel, needs to be planned immigratingfrom Slovenia (H. Roth, Abruzzo National within a broaderland-use policy articulatedthrough geo- Park,Pescasseroli, Italy, personal communication, 1996). graphically explicit guidelines. Development of such a Both populationsare valuablefor the survivalof bears in land-use matrix requires a broad-scale approach; this the ItalianAlps and have been the focus of several con- planning can be greatly enhanced by geographic infor- servationinitiatives. The effective conservationof these mation system (GIS) methodology which incorporates 2 populations,however, remainsquestionable as conser- estimates of environmentalquality into spatiallyexplicit vation efforts have been plannedmostly on a local scale models. andhave not consideredspatially explicit models of habi- As a first step towardthis end, our aim was to develop tat suitability and sustainabledevelopment (Ciucci and a GIS-basedmodel to assess location and configuration Boitani 1996). of potentialranges for the brownbear in the EasternAlps Bears live at low densities andhave largehome ranges, of Italy.Our model, developed for the entireEastern Alps thus any conservationstrategy should have a broad-scale region, was essentially aimed at: (1) producingan index approachto accommodateviability requirements (Paquet of environmentalquality for bears using available data 124 Ursus 11:1999 for environmentalvariables; (2) incorporatingvarious Province of Trento, the Adamello-BrentaNatural Park humanland uses in the assessmentof environmentalqual- and its surroundingareas, and in the northeasternpart ity for bears;(3) producingspatially explicit results;and of the Province of Udine near the Slovenia border.Four (4) finding connectivity among areas of potential bear areas of known bear presence were identified from presence based on the environmentalquality index. radiotrackingdata and other evidence of presence(tracks, The model, althoughseverely limited in its currentap- hair,droppings, and denning activities). Two large areas plication by the paucity of data on habitatuse and selec- were located in the Province of Udine, and 2 smaller tion by bears in the Alps region, representsa useful tool areas were located in the Province of Trento. The total to assess bear conservationoptions in the EasternAlps areaof bearpresence was 963 km2,with 816 km2located in terms of population viability. It also facilitates the in the Province of Udine and the rest in Trento.A ran- evaluationof existing protectedareas and sets the ground dom sample of 100 points was selected within these 4 for an internationalapproach to bear conservation. areas and representedbear locations (RBL) in the subse- quentanalyses. One hundredRBLs were consideredsuf- ficient to representhabitat variability within the relatively STUDYAREA small range of bear presence. This model was developed for the Centraland Eastern To account for bears' awareness of the surrounding Alps of Italy. The 41,129 km2study area was defined to environment,each variablewas processed using a mov- the north and east by the Italianborder. Although obvi- ing window of 30 km2;a function of all the pixel values ously not an ecological limit for the bear,this borderwas includedin thatwindow was assigned to the centralpixel adoptedfor practicalreasons of data availabilityand ho- (Tomlin 1990). The size of the window was equal to the mogeneity-the major concerns for the final quality of averagehome-range of individualbears in the area(Roth the model. The southernboundary was the interpolated and Osti 1979). 100-metercontour line: in fact, at lower elevations hu- We overlaid the 100 RBLs onto the raster coverage mandensities and an almosttotal absenceof forests make and calculatedboth the vector of the means and the vari- the environment inadequate for the brown bear. Lake ance-covariance matrix. These were used to calculate Maggiorewas chosen as the westernboundary as it geo- the Mahalanobisecological distance (Clarket al. 1993, graphicallylimits bear movements. The area is mostly Knick and Dyer 1997) of each pixel of the study area mountainouswith extensive forests and relatively little from the environmentalconditions as measured at the human disturbance. RBLs. The resulting layer was a rastercoverage whose val- ues representedthe ecological distance (D) from the av- METHODS erage conditions as defined by the RBLs. The lower the The environmentalvariables selected for the model distance, the more similar the conditions were to those were greatly influenced by the paucity of digital data. observed in the areas of known bear presence and the Based on data availabilityand quality and on the known higher the environmentalquality for the bear. The re- ecological needs of brown bears, we selected 12 vari- sulting distance, which ranges from 0 to infinity,has no ables (Table 1). Seven variableswere obtainedfrom the absolutevalue but shouldbe interpretedin a relativeway. land cover map to accountfor basic environmentalqual- Lower values are an index of higherenvironmental qual- ity; 2 variableswere used as indicatorsof humandistur- ity. bance (human density and road density), and the Based on the ecological distanceraster, we divided the remaining3 variableswere selected to describetopogra- study area in 4 suitabilityclasses: optimal, sub-optimal, phy (elevation, slope, and aspect). We converted vari- connecting area, and area essentially avoided by bears. ables into co-registeredraster with a pixel size of 250 x The