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iForest -Biogeosciences and Forestry
IntroductionAnnual tree-rings provide a valuable source of environmental information and have been widely used throughout the world to document past forest conditions (Martin-Benito et al. 2011). Parameters related to the annual stem increment are extremely reliable indicators of general forest health and stability (Cook & Kairiukstis 1990). Tree rings provide unique possibilities for the retrospective assessment of growth rates over an extended period of time . Modern tree-ring analysis methods were developed at the beginning of the 1980s, when forest damage was recognized as a serious and widespread regional problem (Eckstein 1985, Cook 1987a, 1987b, Innes & Cook 1989, Schulze 1989. However, a few years later an apparently opposite view on Europe's forest conditions was presented by Spiecker et al. (1996), based on 22 growth studies from 12 countries. The results revealed a considerable increase in forest growth over central Europe (Solberg et al. 2009).Many potential causes for the increase in net primary productivity have been proposed, even though forest health was simultaneously deteriorating. The relative importance of different factors has been difficult to assess because of a multitude of interacting stresses affecting trees throughout their lifetimes (Makinen et al. 2001). Despite this, the main factors for the enhanced growth rates were attributed to increases in the photosynthetic rate, the length of the growing season and the leaf area index (Hyvonen et al. 2007, Boisvenue & Running 2006. Meteorological variation had a major response to these changes (Becker 1989, Innes 1994, Spiecker et al. 1996, Raitio 2000.Our earlier investigations revealed that acidifying pollutants mainly resulted in changes in the rate of tree crown defoliation vs. tree stem increment when the effect of crown defoliation on increment was considered (Augustaitis & Bytnerowicz 2008).In this study, we attempted to detect the effects of acidifying pollutants on stem increment after taking into account the effect of meteorological parameters. Therefore, this study aimed to analyse recent changes in meteorological variables, air pollution, and acid deposition to identify the cause of changes in the stem annual increment of over-mature, pre-dominant healthy pine trees.
Material and methodsIn 2010 we assessed tree conditions within national parks (NP) in different regions of Lithuania: Curonian Spit, Zemaitija and Aukštaitija NPs. These three parks are located at a seaside site, in western and northeastern Lithuania, respectively (Fig. 1). A hundred of predominant pine trees were selected matching the following characteristics: age exceeding 120 years, diameter at breast height larger than 50 cm, upper crown taller than the general level of the canopy, no visible crown or stem damage, healthy status (defoliation 0-15 %). Moreover, trees were selected within permanent observation plots already monitored by different methodologies: in Curonian Spit NP plots were established based on UN ECE Forest ...
