The paper presents the analysis of the influence of various factors on the accuracy of the Digital Terrain Model (DTM) generated under forest conditions in pine stands. DTMs with 0.5, 1, 2, 3, 4, 5 and 10 meter pixel sizes have been evaluated. The accuracy assessment has been performed for 4 age classes (developmental stages) in flat terrain and on slopes. Additionally, the analysis of differences between values obtained from single pixels and from 3x3 pixels moving window for various DTM pixel size has been performed. The General Linear Model for repeated measures has been applied for the analyses. Only the overstocked young stands show different patterns of relationships between the DTM accuracy and resolution. On average, model error for slopes was 3 times larger than for the flat terrain. The height obtained from DTM created using direct pixel values of height, is slightly more accurate than those obtained using values smoothed by 3x3 pixel windows, the difference, however, is not statistically significant. The use of percentiles is much more appropriate than mean-based measures, especially for not normally distributed and skewed data.

Key words: Digital Terrain Model, Airborne Laser Scanning, Repeated Measures ANOVA, error analysis, percentile, earth surface, Scots pine, slope, survey.