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Ponikve pripadaju među najznačajnije krške oblike koji se stoga smatraju i dijagnostičkim oblicima krša. Njihov prostorni raspored i gustoća važan su pokazatelj stupnja okršenosti nekog prostora, ali i njegova cjelokupnoga geomorfološkog razvoja. Cilj ovoga rada je utvrditi prostorni raspored i gustoću ponikava te analizirati utjecaj geološke građe i morfometrijskih karakteristika terena (hipsometrija, nagib padina, vertikalna raščlanjenost) na prostorni raspored ponikava na području jugoistočnog Velebita. Prvi je put na području krša Hrvatske uspoređen prostorni raspored ponikava s prostornim rasporedom ulaza u speleološke objekte i to samo na dijelu jugoistočnog Velebita – Crnopcu. Podaci o položaju ponikava preuzeti su s topografskih karata 1:25 000. Svi podaci su digitalizirani i računalno analizirani s pomoću ArcGIS 10.1 programskog paketa u GIS laboratoriju GO PMF-a u Zagrebu. Istraživanjem je ustanovljen snažan utjecaj morfometrijskih parametara reljefa na gustoću ponikava. Najznačajnija pojava ponikava vezana je za područja nadmorskih visina 1000 – 1200 m, nagiba padina manjeg od 2° i vertikalne raščlanjenosti reljefa 100 – 200 m/km2. Također, najveća gustoća ponikava zabilježena je u karbonatnim naslagama jurske starosti te je utvrđeno da zone glavnih rasjeda nemaju značajniji utjecaj na povećanje gustoće ponikava. Usporedbom prostornog rasporeda i gustoće ponikava i ulaza u speleološke objekte utvrđen je njihov visok stupanj korelacije., Dolines are considered to be among the most prominent karst formations, which is why they can serve as diagnostic forms of karst. Their spatial distribution and density are important indicators of an area’s degree of karstification, as well as of an overall geomorphological development. The aim of this paper is to determine the spatial distribution and the density of dolines, and also to analyse the influence of geological structure and morphometric features of the terrain (hypsometry, slope inclination, relative relief) on the spatial distribution of dolines in the area of southeastern Velebit. Moreover, for the first time with regards to the Croatian karst, the spatial distribution of dolines was compared with the spatial distribution of entrances into caves in the southeastern Velebit’s area of Crnopac. The data on the dolines’ position were adopted from 1:25,000 scaled topographic maps. All data were digitalised and analysed with ArcGIS 10.1 software in the GIS laboratory of the Geographic Department of the Faculty of Science in Zagreb. The research showed a strong influence of morphometric parameters of the relief on dolines’ density. The most prominent occurrence of dolines is linked with the areas ranging from 1000 to 1200 meters of altitude, slope inclination lower than 2° and the relative relief of 100 – 200 m per km2. Furthermore, the highest density of dolines was recorded in the Jurassic carbonate layers, while it was determined that the zones of main faults do not have a significant influence on the increase of dolines’ density. A high degree of correlation was determined by comparing spatial distributions and density of dolines and entrances into caves.

Cilj je ovog rada utvrditi prostornu gustoću ponikava na području krša Hrvatske i provesti korelaciju izračunatih vrijednosti gustoće ponikava s pojedinim geomorfološkim i geološkim čimbenicima njihova nastanka i razvoja. Kako bi se to postiglo, potrebno je izračunati prostornu gustoću ponikava temeljem jedinstvenih GIS metoda prikupljanja i analize podataka unutar čitavoga istraživanog područja. Gustoća ponikava unutar jedinične površne izračunata je na temelju kartiranih dna ponikava. Za potrebe određivanja dna ponikava upotrijebljene su digitalne kartografske podloge u mjerilu 1 : 25.000. Na temelju dobivenih podataka izračunata je prostorna gustoća ponikava jednostavnom kernel metodom unutar površine od 1 km2. Provedenom analizom prostornih razlika u intenzitetu gustoće ponikava, uočene su pojedine veze između njihova razvoja i morfometrijskih parametara reljefa, te litoloških i strukturnih obilježja terena., This paper deals with the spatial density of dolines in the Croatian territory covered by karst. The purpose of this paper is to calculate the spatial density of dolines and show a correlation between calculated doline density values and certain geomorphological and geological factors of their origin and development. Therefore, it has been necessary to calculate the spatial density of dolines applying unique GIS methods of data collection and analysis to the entire study area. Doline density per unit area has been calculated based on the mapped doline bottom. 1:25,000 scale digital cartographic models have been used to determine the doline bottom. The given data have been used to calculate the spatial density of dolines applying a simple kernel method to an area of one square kilometre. The analysis of spatial differences in doline density has revealed that certain connections exist between doline development and relief morphometric parameters as well as lithological and structural terrain features.