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ŠUMARSKI LIST 3-4/2018 str. 30     <-- 30 -->        PDF

1). Furthermore, the sum of temperature could interact with the other environmental variables.
Statistically significant differences were obtained for all variables (GDD, precipitation, day of year and insolation) and for variable differences between years over the course of the study period. The results are consistent with the observations of significant leaf unfolding variability between years (Morin et al. 2010). The experimental warming and reduced precipitation for several populations of three European oak species (Quercus robur, Q. pubescens, Q. ilex) in this study caused a longer growing season and higher mortality. The leaf unfolding date was not significantly affected by variations in water quantity, but the date varied significantly by year. Certain genotypes may respond to a higher amount of precipitation, which ultimately means that they need a longer time and many more hours of insolation to facilitate leaf unfolding.
Temperature, which is the prime environmental factor regulating the leaf unfolding process, in addition to other environmental cues, such as photoperiod, may modulate the leaf unfolding process, especially for the late flushing species (Basler and Körner 2012, Caffarra et al. 2011, Heide 1993, Körner and Basler 2010). Several experiments have tested the effects of increasing temperature, and the leaf unfolding date was often advanced by higher temperatures (Repo at al. 1996, Guak et al. 1998, Arft et al. 1999, Hollister et al. 2005, Kilpelainen et al. 2006, Cannel et al. 1999, Menzel et al. 2001). Certain results confirm that continued and intense warming may not result in further advances in the date of leaf unfolding in the late successional species of oak and beech if the warming exceeds a certain threshold that leads to insufficient chilling temperatures for dormancy release (Fu et al. 2012b, 2013). The leaf unfolding of sessile oaks was 2.3 times more sensitive to temperatures over an elevation gradient than that of beech trees (Dantec et al. 2014). The timing of leaf unfolding in deciduous forest trees is genetically determined with respect to temperature changes (Derory et al. 2006, Vitasse et al. 2010), and temperature requirements are under strong genetic control (Rousi and Pusenius 2005, Sanz-Perez et al. 2009). The leaf unfolding date has been shown to be strongly genetically controlled