Browsing by Author "Takala, Terhi"

The biodiversity in Finland is dependant on the vast forest areas in Russia and Karelian Isthmus acts as an important ecological corridor which connects these forests together. However, Karelian Isthmus is also important for the forest industry and increasing forest use has caused concerns of the effects forest cuts have on the biodiversity of the area. The purpose of this study was to examine how the forests in the Karelian Isthmus have changed in the past 20 years. Special attention was given to the changes of the landscape structure and regional differences. The study was based on the data from a field survey and Landsat satellite images. After image registration the satellite images were normalized using linear regression method. This was done in order to calibrate the radiometric differences in the images. The interpretation of the images was done using supervised classification. The training areas used in classification were based on the ground truthing data collected during the field work. Two classifications were done to each image and four forest types were used: spruce, pine, mixed and deciduous forest. In the more detailed classification the forest types were further divided into young and old forests. The accuracy of the classification was assessed using reference data and contingency tables. The detailed classification was clearly less accurate and only the simple classification without the age classes was used in the following analyses. For estimating the changes in the forest structure at the landscape level, landscape metrics were calculated from the classified images. Five landscape indices were used in this study: class area (forest type area), number of patches, mean patch size, edge density and mean nearest neighbour. According to the interpretation of the satellite images the total forest area in the Karelian Isthmus has increased 4 %. Forest area of the mixed forest and especially deciduous forest had increased. Spruce forests had decreased 34 % and pine forests 25 % but these meant only 4 % change in proportion to the total land area. Regional variation also existed. In some areas changes in the forest structure were significant, particularly concerning spruce forests. The most notable changes occurred in the central areas of the Karelian Isthmus. In these areas the fragmentation of the spruce forests was significant. The number of patches had increased and the mean patch size decreased in the same areas where the total spruce forest cover had decreased. Also the edge density and the mean distance to the nearest neighbour had increased. In the case of pine forests the changes varied within different areas and although the total area had diminished, fragmentation was not clearly observed. Deciduous forests had increased in all places whereas mixed forests had increased especially in the areas where spruce forests had decreased. The increase of the deciduous and mixed forests was probably a result of regeration in harvested areas. Forest cuttings in the coniferous forests and natural regeneration after clear cuts have changed the forest type composition and the landscape structure in the Karelian Isthmus. However, changes have been fairly moderate in proportion to the total forest area. In number and also in connectivity, all of the forest types classified in this study existed broadly. Based on the results of this study it can be estimated that the ecological consequences of changes occurred in the past 20 years have not been exceptionally substantial and Karelian Isthmus is able to keep supporting forests species rich in biodiversity.