Pointer Years in Tree-Ring Width of European Ash with Different Crown Condition and Their Relationships with Climatic Factors in Latvia

The effect of climatic factors on tree-ring width (TRW) of European ash (Fraxinus excelsior L.) with healthy and damaged crowns growing in the central and eastern part of Latvia was assessed by dendrochronological techniques. Pointer year indices were calculated to assess the variability of TRW. Positive pointer years were more frequent than negative, similarly for damaged and healthy trees, suggesting similar limiting factors. The relationships between TRW and climatic factors differed regionally and locally. In the eastern part of Latvia, TRW was affected by temperature in spring of current and preceding years. In the central part of Latvia, weather conditions in current and preceding summer mainly affected TRW; temperature and precipitation had positive effect suggesting occurrence of water deficit, but the daily range of temperature had a negative effect. Hence, regional diversification of radial growth patterns might be expected. Some differences in sensitivity to climate were observed between the damaged and healthy trees. In the central part of Latvia, the damaged trees appeared additionally sensitive to temperature in summer. In the eastern part of Latvia, damaged trees were additionally sensitive to temperature in May. Nevertheless, some additional factors were significant for the healthy trees.