Abstract: The aim of the present research is to show the possibilities of applying computer technology in ecosystem investigations. The object of the research is the chestnut forests located on the Northern slopes of Belasitsa mountain (Southwest Bulgaria). Three study areas are determined for detailed investigation of structural and functional parameters (indicators) of chestnut ecosystems. These areas are located in forests with different ages (45-120 years old), different forestry management and different state. Ecosystem indicators are modeled on the base of field investigation and available published data, and the assessment of the forest state is done by spatial interpolation (inverse distance weighted) in geographic information system (GIS) environment (ArcGIS). Resulting model values are verified and validated by field investigations. An output layer showing the state of the chestnut forest in the investigated region is generated on the base of the raster surfaces, result of the interpolation and application of map algebra. Also, weight coefficients to the assessment values of the different indicators are used which makes the spatial analysis more correct. Created mapping model shows significant matching areas of forests in poor condition and forests in good conditions compared to the relevant determined on the base of forest management plan. The research confirms the advantages of GIS technology in processing large and varied data for assessing the impact of many factors on forest vegetation.