Survival and early growth of silver fir and pioneer species on two sites in nurse crop regeneration systems in the Czech Republic

Silver fir used to be one of the most important tree species in the Czech forests until the 19th century. Large scale clearcuts, which nowadays occur after the salvage logging of Norway spruce due to wind of bark-beetle attacks are unfavourable for the artificial regeneration of a fir. Growth of silver fir and three pioneer species was studied during first three years in a nurse crop system established after forest disturbance events. Five-years-old containerized silver fir seedlings were planted in autumn 2014 with silver birch, alder or aspen with and without nurse crops (control plot) on two localities (Tornádo and Rakovec). The Tornádo site represents natural conditions of Central European forest (Fageta typica) type on a haplic cambisols and favourable soil water regime, while Rakovec site a Querco-Abietetum forest type on a haplic stagnosols, which was periodically waterlogged. Silver fir grew best in admixture with silver birch which significantly promoted the height increment of the firs on both localities and improved the fir survival rate at one of the sites. The lower mortality and faster growth of both silver fir and pioneers were observed on Tornádo site where 92% and 100% of the silver fir trees survived under the birch and aspen cover, respectively, while 93% of planted firs survived in the open area. Only 93% and 67% of silver firs survived on the Rakovec site with same two pioneer species, respectively and 73% in the open area. After three years the highest height increment of silver fir was observed under silver birch, where trees were by 20 cm and 11 cm taller at Tornádo and Rakovec sites, than on the control plots, respectively. Aspen and alder had no significant effect on the height increment of a silver fir at any of the study sites. The shelter of nurse crops had no effect on the air temperature. The artificial regeneration of a climax silver fir and a pioneer silver birch was beneficial on Tornádo sites. On the other hand, there should be a delay between the regeneration of silver birch and underplanting of fir on the waterlogged sites.