Modelling the distribution of palsas in Finnish Lapland with logistic regression and GIS

The location of palsas (peat mounds with a perennially frozen core) was mapped in an area of 3370 km 2 in Finnish Lapland by interpreting aerial digital photographs. Using environmental variables derived from digital land cover data and an elevation model, the distribution of palsas was modelled using geographic information system (GIS) techniques and multiple logistic regression. The relative roles of eight environmental variables potentially affecting the distribution of the palsas were studied in a spatial grid system with 3370 grid squares of 1.0 km 2 , of which 172 were found to contain palsas. The altitudes of the palsas varied from 180 m to 390 m. In the logistic regression model the probability of the presence of a palsa in a 1.0 km 2 square increased with 1) the area of mire, 2) the proportion of flat topography, 3) water cover and 4) elevation of the lowest point in the 1.0 km 2 analysis square. The palsa distribution model was validated by fitting it to an independent test area of 300 squares bordering on the main study area: the overall classification rate was 97.67%. The application of GIS data and techniques with logistic regression modelling has potential for wide use in studies on distribution patterns in periglacial processes and landforms.