Occurrence of frost episodes and their dynamics in height gradient above the ground in the Jizerské hory Mts.

We have verified whether the temperatures in the zone of terminal leaders of saplings (+100 cm) were less extreme than the temperatures in the zone of terminal leaders of common-sized planting stock (+30 cm). In May and June of 2011 and 2012 we investigated the occurrence of late frosts at different levels above the ground. The number of days and amount of hourly frost records were counted and the sum of sub-zero temperatures was calculated. Our study confirmed that sub-zero temperatures mostly occur at levels near the ground. Therefore, on the sites exposed to late frosts, such as mountain frost hollows, in addition to common-sized planting stock we recommend to consider also the use of large-sized transplants (saplings), since their terminal buds are mostly above the zone near the ground most endangered by frost.