CHANGES OF THE MONITORING WINDFALLEN AREA ON THE BABIA GÓRA MOUNTAIN

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 2003, 2011, 2012 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.


INTRODUCTION
In the past several decades a progressing climate warming has been observed, accompanied with an increase in extreme phenomena.The third and fourth IPCC reports confirm the increase in the number of meteorological phenomena of extreme nature in Europe [Miętus 2005, Grabowska et al. 2007, Węgrzyn 2008, Kundzewicz 2011].In moderate latitudes one of them is strong winds [Dotzek 2003, Leckebusch andUlbrich 2004], which, depending on their speed, manner and place of occurrence are called gales, whirlwinds, hurricanes or foehn/halny [Rojan 2010, Pawlik 2012b, 2015].The occurrence of such violent phenomena poses serious hazards for forest stands, where falling trees lead to the formation of extensive areas covered with windfallen trees [Zachara 2006, Dąbrowska 2009, Pawlik 2012a, 2015, Dmytrenko et al. 2015].In the mountains the areas most susceptible to this phenomenon are forest areas with dominant homogeneous ageand species-wise tree stands [Gądek 1987].The ones considered most sensitive are coniferous species [Schaetzl et al. 1989, Philips et al. 2008], especially the spruce, whose shallow roots lead to its increased susceptibility to windfalls [Gądek 1987, Zachara 2006, Simon et al. 2011].
Fallen trees bring about significant changes in the functioning of a given section of the forest [Stephens 1956, Norman et al. 1995, Philips et al. 2008, Šamonil et al. 2010a, 2010b, Simon et al. 2011, Pawlik 2013].When a tree falls down, it creates a gap in the forest canopy, providing more access to sunlight, wind and rainfall, which accelerates soil falling off the exposed roots.This leads to the forming of post-windfall microrelief made up of tree holes and roots which in time form a post-windfall knoll.The decomposing leaves, needles, bark, branches and the wood of the fallen tree enrich the soil surface with organic matter, which is favorable to the development of nitrophilic plants [Masalska 1997].
An important factor contributing to the falling of trees is their soil substrate.This phenomenon occurs most frequently on shallow, marshy or strongly skeletal soils [Stocki 2003].Tree toppling, through uprooting, causes a local distortion of the soil profile, followed by shifting or blending of soil levels.This results in exposing lower, mineral soil levels, usually very poor in humus, or in the formation of places enriched with organic matter [Masalska 1997[Masalska , Šamonil et al. 2010a[Masalska , 2010b]].
The post-windfall holes constitute characteristic microhabitats which can, depending on the size of the surface of the windfallen area, form a considerable part of the general habitat structure of the forest [Sokołowski 1934, Grodzki and Starzyk 2004, Šamonil et. al. 2010a, 2010b;Simon et al. 2011, Pawlik 2012].The appearance of windfallen trees results in the changes in soil properties in this area and favors the forming of new microhabitats.The soil variability in such windfallen areas determines the formation of microhabitats which differ in the pace and range of plant colonization [Beatty and Stone 1986].
Due to its location, height and landform, the Babia Góra mountain range is exposed to violent meteorological phenomena connected with strong winds, including the very strong, blustery foehntype wind -the halny [Obrębska-Starkel 2004].Among the many effects of this in the Babia Góra mountain range are the areas covered with windfallen and windsnapped trees, the occurrence of which has clearly increased in recent years, which is also connected with the age and species composition of the existing tree stands [Chochół 2008].
The aim of the research was to establish the pace and range of the windfallen spruce area in Compartment 93 of the Babia Góra National Park (BGNP) in the past decade.

MATERIALS AND METHODS
The research was carried out in the windfallen spruce area formed in November 2004, whose area is growing due to the continual falling of trees.The area is situated on the south-eastern slope in the ecotone zone of the lower and upper sections of the Babia Góra mountain range (Compartment 93 of the BGNP, Fig. 1).In 2005 by the decision of the BGNP Director with the approval of the Scientific Council of the Park, a monitoring area was created there.
The research included field work and studies.During the field work the range of the existing windfall area was mapped through determining its outermost points and their stabilization by means of the GPS technology -in 2005 using GPSmap 60CSx (Garmin) and in 2015 using Spectra Precision (Ashtech) MobileMaper 10 with Esri Ar-cPad 10.0 R4.The obtained measurements were used to make maps of the range of the growing area in the Esri ArcMap 10.2.2.program (the license owned by the BGNP with the main office in Zawoja) (Figure 1).
Additionally, in 2005, in order to establish the range of the changes in the soil cover of the windfallen area, preliminary measurements were carried out of the elements of windfall microrelief.The measurements were made not only in the examined area but also in the adjacent windfall area formed at the same time.
The studies involved determining the changes in the range of the area deprived of the dense forest canopy as a result of successive tree falls.During the research an analysis was carried out of the aerial photographs made available by the Babia Góra National Park, from the Małopolska Province Marshal Office, the Province Centre for Geodetic and Cartographic Documentation (2003) and from the BGNP Territorial Information System (2011, 2012 and 2014).The analyzed photographs covered the area of 5 ha in Compartment 93 of the BGNP.The evaluation of the range was carried out by analyzing the photographs of that area as regarded the density of the forest canopy, based on the graticule reproducing the 10×10 m area of the real land.The "lack of trees" was stated when the areas were exposed in at least 75%.

RESULTS AND DISCUSSION
The post-windfall tree throws constitute characteristic microhabitats, which can, depending on the size of the windfallen area, be a significant part of the general forest structure.The inventory of the tree holes in two windfallen areas formed in November 2004 in Compartment 93 of the BGNP showed significant changes in the soil cover.In the first, 40-are area the tree holes occupied 5.09 ares and knolls 4.31 ares, which altogether was 9.40 ares, i. e. 23.5% of the whole windfallen area.In the second, 70-are area, the holes occupied 7.26 ares and knolls 5.34 ares, which altogether was 12.60 ares, i.e. 18.0% of the whole area.
The analysis of the available aerial photographs of the fragment of Compartment 93 from 2003 (Fig. 2), 2011 (Fig. 3), 2012 (Fig. 4) and 2014 (Fig. 5) showed distinct changes in the range and size of the gaps formed as a result of tree toppling.
The share of the area deprived of trees in the whole analyzed area increased from 2% in 2003 to over 52% in 2014 (Fig. 6).The progression of the size of the changes is therefore significant, and the phenomenon of the tree stratum disintegration has been growing, especially when considering the periods: 2003-2011 and the twice shorter 2011-2014.In those periods the increase in the gapped area was similar (ca.26%), however the pace of the phenomenon was twice faster.The characteristic microrelief formed as a result of the windfalls, with its distinct tree throws and torn out roots, considerably affects the prop-  3. The formation of a windfallen area plays a significant role in shaping the microrelief of the land and soil cover, particularly in mountainous areas.

The functioning of the monitoring area in
Compartment 93 of the BGNP has a significant impact on the accuracy and precision of long-term observation of changes taking place in the formed windfallen area, not only within the tree stand itself but also other elements of the environment.
The violent hurricane-force winds which result in the appearance of large windfallen areas are a considerable hazard to the forests in Poland [Stocki 2003, Grodzki and Starzyk 2004, Zachara 2006, Dąbrowska 2009, Pawlik 2012b, Franczak 2013, Dmytrenko 2015].The research carried out as part of the monitoring of the windfallen area in Compartment 93 of the BGNP confirmed a major influence of violent winds on the tree stands there.The windfallen areas formed as a result of the winds are continually growing on account of successive weather phenomena.The size and pace of those changes is varied, with a distinct upward trend in the past years.The increase in this phenomenon results in the growing interest of the local community [Franczak 2011-2012, Fujak 2011-2012].It is a serious hazard for the Babia Góra forest stands dominated by the spruce.Tree toppling and dead wood lying on the ground may cause an increase in the number of forest pests and impact the potential hazard of gradations, whose presence contributes to the weakening of the still standing trees [Gądek 1987].The infected and weakened trees are even more susceptible to falling.In consequence, the windfallen areas are growing larger and the natural conditions there are undergoing significant changes.