Windstorms and forest disturbances in the Czech Lands: 1801-2015

The long-term relationship between windstorms and forest disturbances in the Czech Lands is analysed in this paper, covering a very long period of 215 years (1801-2015). Based on documentary evidence and instrumental records, long-term series of severe windstorms in the summer half-year (April-September) and in the winter half-year (October-March) are compiled. Severe windstorms were more frequent in the 1820s-1840s, 1900s-1930s, and 1960s-2000s, less so in the latter half of the 19th century and in the 1940s-1950s. Their long-term variability is revealed with three differently-created series of forest damage for the periods of 1801-1900, 1900-1980 and 1963-2015. Based on these comparisons, 14 windstorms that did outstanding damage to forests are selected: 12 occurred in the winter half-year and two in July. They are further investigated with respect to their meteorological character and the damage done. In this sample, the high-impact winter half-year windstorms are typically related to very distinct (>45 hPa) pressure gradients between low pressure systems over the North/Norwegian Sea and high pressure systems south-west of the Iberian Peninsula, which exhibits an eastward-shifted and tilted NAO pattern, inducing the passage of frontal waves across the Czech Lands. High temperatures arising from south-westerly airflow and wet ground before windstorms provided conditions conducive to extensive windthrow in forests, sometimes with damage exacerbated by subsequent bark-beetle calamities. The increase in windstorms with outstanding forest damage after 1950 may be attributed in part to the negative consequences of forest management that prioritises high, short-term profits over ecological well-being.