No abstract

In this paper, changes in the duration of the meteorological vegetation period in Poland were analyzed for the three decade period: 1981-2010 as compared to the 1971-2000 period. The meteorological data regarding the monthly mean air temperature values from 53 weather stations distributed evenly across Poland were used. It was proved that the meteorological vegetation period in the years 1981-2010 increased by four days on average, as compared to the 1971-2000 period.

The article presents the changes in the values of average air temperature and its spatial diversity in the four seasons of the year (spring, summer, autumn, winter) in the years 1981-2010 compared with the 1971-2000 period. In the 1981-2010 period (the new climate normal currently in force) the largest increase in air temperature expressed in the average area value occurred in summer and reached 0.5°C. In spring and autumn the increase in average air temperature was smaller and was 0.4°C and 0.3°C respectively; in winter average temperature did not change compared with the previous climate normal.

The conducted research aimed at establishing the pace and range of the formation of spruce windfall in Compartment 93 of the Babia Góra National Park, where in 2005 by the decision of the Park's Director, with the approval of the Scientific Council of the Park, a monitoring area was created. During field work the range of the existing windfall area was mapped through determining its outermost points and their stabilization by means of the GPS. During the research an analysis of the aerial photographs made available by the Babia Góra National Park was carried out, in order to determine the changes in the range of the area deprived of trees. The analyzed photographs covered the area of 5 ha in Compartment 93 of the Park. The evaluation of changes in the tree layer was based on the graticule reproducing the 10 x 10 m area of the real land. The "lack of trees" was stated when the areas were exposed in at least 75%. The comparative analysis of the images from aerial photographs of Compartment 93 in 2003Compartment 93 in , 2011Compartment 93 in , 2012Compartment 93 in and 2014 showed distinct changes in the range and size of the gaps made by fallen trees. The share of the gaps in the forest stand in the whole analyzed area increased from 2% in 2003 to over 52% in 2014. Therefore, the progression of the size of the changes is considerable and the disintegration of the tree layer is growing, especially comparing the 2003-2011 and the twice shorter 2011-2014 periods. In the analyzed periods, the increase in the gap area was similar (ca. 26%), yet the pace of the phenomenon was twice faster. The obtained results were an argument in favor of increasing the monitoring area from 0.28 ha to 1.55 ha.