The Influence of Abiotic and Biotic Factors on the Condition of Birch Species in Lithuania.

During recent decades the birch stands, occupying more than one fifth of all forest stands in Lithuania, gaining higher economic value and more significance in the Baltic region. The aim of this study was to analyse the condition of two native birch species in Lithuania -- silver (Betula pendula Roth.) and downy birch (B. pubescens Ehrh.) -- in relation to the main environmental factors. The results showed that the mean defoliation of the birch species ranged between 16.2 and 23.0% in 1989-2011-year period. There were no clear dynamics of the number of birch trees damaged by abiotic and biotic factors. The significant peaks were registered in 1993-1995 and 2003-2004 because of storms or pest outbreaks. By 20% higher mean defoliation was recorded for the trees that were damaged by biotic than abiotic factors. The number of trees damaged by wind varied a lot: from no wind damages (in 1992-1993; 2005-2007) up to 87-100% (in 2001-2004) from all abiotic factors. The number of birch trees damaged by insects showed significantly decrease starting from 1991. [ABSTRACT FROM AUTHOR]