Adaptation of silver and white fir to the climate of lowlands in western Poland

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