| Popis: |
During history of Earth, before the runaway impact of global warming, the alternations of solar activity were major factors of modification of the global climate. The alternations of solar activities could affect the dynamics of biotic and abiotic factors which provides various impacts on natural ecosystems as forests. In general, there are two main stressors which are responsible for decline of forests: changes in hydrologic conditions i.e. droughts and outbreaks of various pests. Natural hazards as droughts comprise clear cyclical pattern in some regions across EU gradient. During the last century (1901-1999) extreme droughts, as classified by the PDSI (The Palmer Drought Severity Index), occurred with greater frequency over continental eastern Europe. On the other hand, droughts were rarer along the north west European seaboard, the Mediterranean seaboard, and the Alps. The same results confirm that drying tendencies exist in central eastern Europe and western Russia which is in accordance with the IPCC findings. Drought, especially in the Mediterranean area, is a reccurring phenomenon i.e. its behaviour comprises a cyclical periodic pattern. One of the most significant forest pest is Gypsy moth (Limantria dispar L.), a polyphagus herbivore and defoliator which caused significant damages to forests, especially on pedunculate oak (Quercus robur L.), the most valuable tree species in Europe. In this research the cyclical pattern of droughts and population of gypsy moth was analyzed to discover specific relations of their dynamic with solar activity cycle. The cyclical patterns of 11 years were discovered in both forest stressors what proves that synchrony between analyzed time series and population dynamics exists. Increased solar activity cause the periodic occurrence of drought episodes (1991-1993 ; 2000-2003) and also increase of gypsy moth outbreaks. There are also evidences of synchronization of droughts and outbreaks i.e. outbreaks are taking place at the end of episodes of drought with a lag in respect to solar cycle. The results of established relationship can help in future prediction of respective stressors with aim of reduction of potential damages on forests in the region. |
