Mankind influences the vegetation in the northern permafrost areas of Eurasia by its activities, such as mining, forest clearing and pollution. However man is not the only factor inducing changes in Siberian boreal conifer forests, forest fires and other natural processes, e.g. climate change, also have impacts on the vegetation. In an area besides the Russian river Viluy in Central Yakutia those changes are eminently evident. The combination the local vegetation and the expansion of the cropped area are the mainly influencing factors. For this area, which is mainly covered by larch forests and geomorphological and hydrological very dynamic thermokarst depressions (alases) that are often filled with water, some approaches to quantify these processes are sampled in this work to extract tendencies for the whole circumpolar boreal forest belt. Therefore it has been worked with Landsat-remote-sensing-data and with climate data that were recorded at a weather station in the study area, which have been analysed thoroughly. The presented results show the exploration of the extent and possible reasons for the change of the forest cover.