Monika Dobosz

One of the most widespread land cover change processes in European countries is the increase in forest cover. Forest expansion on abandoned agricultural land has played a major role in marginal mountain areas since World War II, and especially affected the post-socialist countries in Central and Eastern Europe. This study aimed at mapping forest cover change and forest succession in one of the communes of the Polish Carpathians ( Budzów ) over two time periods : 1977 – 1997 and 1997 – 2009. We identified rates of agricultural land abandonment and forest succession and assessed the dynamics of the process using aerial photographs, orthophotomaps as well as cadastral and census data. The results showed that Budzów commune experienced an expansion of forest cover from 40% in 1977 to almost 45% in 2009, and a significant increase in forest succession from 1% in 1997 to 10% in 2009, at the expense of agricultural land area ( 54% in 1977 and 40% in 2009 ). If the trend is widespread over the Polish Carpathians, the real forest cover may be much higher than follows from statistical data.

Though the State Forests in Poland maintain an accurate spatial database covering roughly 80% of the forest area in Poland, the remaining 20% of forests, mostly private, are not mapped with similar accuracy. Several national mapping projects have been carried out in Poland recently, yet it is not trivial to integrate their results in  the context of forest cover estimation, due to inconsistencies of incorporated forest definitions. For instance, some datasets exclude areas which are legally forest, but temporarily devoid of trees due to damage by wind or pests. Moreover, the unknown extent of secondary forest succession on abandoned agricultural land  introduces much uncertainty in assessing the actual forest area. Our work proposes therefore a semi-automatic algorithm that integrates spatial data on contemporary forest cover from various sources, and eliminates their mutual inconsistencies. The study was conducted in the Polish Carpathians, where, due to a high share of  private forests, reliable forest cover estimates are particularly difficult. The approach combines forest cover information from the national topographic data, both past (1970s) and current (2010s) and from the State Forests spatial databases. Contrary to the current national topographic data, the produced map presents forests in coherence with the Polish forest definition and is comparable to the earlier topographic maps. Our results suggest that various databases underestimate forest cover in the Polish Carpathians, and that the expert knowledge- based fusion of the datasets may provide complete and reliable information on the actual current forest cover in the region.