Forest dynamics study using aerial photos and satellite images with very high spatial resolution

The paper presents an integrated database created using as input information ground-based and remote sensing data which was used to study forest changes and identify forestation stages. Using remote sensing methods and GIS technologies make it possible to accomplish an objective monitoring of forest areas using various aerospace data for different temporal stages. The purpose of the presented paper was to study the forest dynamics in the drainage basin of the West Lake, located in the territory of Sofia Municipality, Bulgaria, and to create an inventory map of the felling of the study area over 68-year period of time (1940- 2008). Satellite images with very high spatial resolution from QuickBird and archive and modern aerial photos were used to this end. The territory chosen for the purpose has been seriously affected by anthropogenic activity during the last decades and it also holds a natural landmark, called Kutina Pyramids. The structural scheme of the study included the following working stages: 1. Preliminary examination of the study area; 2. Assessment of the input information and choosing appropriate years to study the forest dynamics; 3. Creation of integrated geodatabase for objective monitoring of the forest; 4. Conductance of computer-aided visual interpretation and deciphering of the aerial photos and panchromatic satellite images; 5. Conductance of supervised land use classification using multispectral satellite images from QuickBird and accuracy assessment of the classification results; 6. Conductance of several field checks of the classification and deciphering results; 7. Assessment of the forest dynamics and creation of forest change maps; 8. Creation of an inventory map of the forestations and felling using the results from deciphering, visual interpretation and classification in combination with ground-based data from the State Forestry, Sofia. The study of the forest dynamics and forestations was carried out for different years, depending on the available information for the study region and the beginning of the anthropogenic activity. The study started with an archive aerial photograph from 1940, which represents the period before intensive anthropogenic activity began. A satellite image from QuickBird acquired on 31.05.2008 was used to define the forests' current state. The supervised classification uses the USGS land cover/land use classification system adopted for the purpose. The LCLU classification includes two levels, where level II represents the differentiation of forest land into 3 classes - deciduous, coniferous and mixed forests. Computer-aided visual deciphering and interpretation of the high spatial resolution aerial photographs and supervised classification of the satellite images for the aforementioned years were carried out. Based on the created thematic database, a number of thematic cartographic models, tables, and graphs of the forest change were produced. A large scale map of the forest change was created. As a result of the area's investigation it was found that in 1940 the territory was occupied by insignificant percentage of forest (less than 5%), which was represented only by natural deciduous forests. Nowadays, the study area is characterized by widely distributed forest areas (almost 50%) - coniferous and deciduous, whereas the vast majority of them are artificial and are not typical species for this elevation zone. The situation is similar in the area of the Kutina Pyramids natural landmark, where forest land has increased from 30% deciduous forest to 75 % deciduous forest and 4% of the territory of the protected area has been afforested with coniferous species. The inventory map of the felling is created using ground-based data. The created geodatabase and the obtained results can be used by the forestry for inventory of the carried out forestations and felling and further planning of the forestation and clear felling procedures.