%0 Research article
%T Late termination of freezer storage increases the risk of autumn frost damage to Norway spruce seedlings
%A Hänninen, Heikki
%A Luoranen, Jaana
%A Rikala, Risto
%A Smolander, Heikki
%D 2009
%J Silva Fennica
%V 43
%N 5
%R doi:10.14214/sf.175
%U https://silvafennica.fi/article/175
%X Over the last few years it has become increasingly common in artificial  forest regeneration to extend the planting period by using  freezer-stored seedlings for early summer plantings. Developmentally,  however, planted freezer-stored seedlings lag behind seedlings planted  earlier in the spring. As freezer-stored seedlings also start hardening  later, they are more susceptible to early autumn frosts, especially in  years when the thermal growing season ends and the first autumn frosts  come earlier than usual. By means of computer simulations with a simple  temperature sum model and long-term air-temperature data from three  locations in Finland, we examined the effect of the freezer-storage  termination date on the risk of autumn frost damage to the seedlings.  The long-term simulations revealed a drastic effect of year-to-year  variation in the thermal conditions during the growing season on the  occurrence of autumn frost damage. Such results provide crucial  information complementary to those obtained in field experiments, which  are always restricted to a relatively short time period. Together with  earlier field data, the present results suggest that at an average  regeneration site in central Finland, the planting of seedlings whose  storage has terminated on 15 June and 22 June involve autumn frost  damage every tenth and every fifth year, respectively. The sensitivity  analysis revealed that the temperature sum requirement of maturation has  a great effect on the risk of autumn frost damage, thus pinpointing the  need for experimental studies addressing this ecophysiological trait of  the seedlings.