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The paper presents the dendrochronological analysis of silver firs (Abies alba Mill.) growing in the canopy layer of the forest stands. We searched for the similarities in the rhythm of radial growth of studied trees and we analysed the response of these stands to the increment disturbances related to the occurrence of adverse climatic factors and the pressure from industrial pollution. The research material was collected in 30 pure and uneven−aged silver fir stands located in the Świetokrzyskie Mountains (central Poland). We investigated the effect of age of the stands and the conditions for their growth (location, forest habitat type) on an average tree−ring width. In order to detect similarities in the rhythm of radial growth of the surveyed stands, we grouped the raw chronologies by the means of the cluster analysis, using Ward's agglomeration procedure with 1−r distance (r – Pearson correlation coefficient). We assessed the incremental response of the investigated stands to the disturbances (situations of significantly reduced radial growth) using indicators of resistance, recovery and resilience proposed by Lloret et al. [2011]. We also studied the influence of the stand age and the forest habitat type on the response of analysed for stands to the detected disturbances. The shortest chronology consisted of 94 tree−rings, while the longest one of 137. Average length of the obtained silver fir chronologies was 119 years. Older fir stands characterised with narrower rings (r=–0.451, p=0.012). Neither the location, nor the forest habitat type are the factors determining the similarity of the rhythm of radial growth of silver firs from the Świętokrzyskie Mountains (p=0.243 and p=0.967 respectively). The extreme climatic conditions responsible for the majority of the short−term (one−year−long) incremental depressions are the factor of regional importance, which affects the growth of investigated trees. Older stands characterized with better possibilities of increment recovery after the disturbance than younger stands (p<0.001), which may be a result of the production of secondary crowns. No consistent differences in the indices of resistance and resilience were found among analysed stands.
The study analysed the causes of the annual variation of tree−ring widths of silver fir and white fir. The partial populations of both fir species has been growing for over 100 years in Rzepin (western Poland) in a fresh broadleaved forest site. We assumed that the year−to−year changes of the size of radial increment presents sensitivity of trees to local climate factor. The period from 1931 to 2015 was analysed. We found that the silver and white firs had high homogeneity of radial growth responses and sensitivity to year−to−year changes of weather conditions. Warm November of the previous year, short winter and high air temperature in August had positive influence on the size of their radial increment. Moreover, precipitation in February, April and July of the year of tree−ring formation contributed to wider tree−ring. The white fir was highly resistant to winter frost in contrast to the silver fir. In addition, this fir species preferred cold springs. Furthermore, the silver fir suffered from overabundant precipitation in August. The climate conditions of western lowland part of Poland were not a limiting factor for growth of both species because the studied populations achieved the highest site index class.
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