The Impact of Overstory Species and Soil Properties on the Growth of Planted Silver Fir Abies alba in the Karkonosze Mountains, Poland

ABSTRACT Silver fir Abies alba was once an abundant tree species in the Karkonosze Mts. in Poland but its population has decreased. The aim of our study was to assess 1) the impact of canopy trees on the growth dynamics of silver fir saplings and 2) the relationship between the growth rate of silver fir saplings and the soil properties, with special regard to the soil enzyme activity. The study was conducted in the Karkonoski National Park on five experimental plots. Silver fir seedlings were planted in Scots pine, European larch, Norway spruce, silver birch and European beech stands in 1999. In 2016, we measured the diameter at breast height (DBH) and height of the canopy trees and the height, DBH, height increments, needle width and length of 100 silver fir saplings. The dehydrogenase, urease, phosphatase and asparaginase activity was analysed in organic and humus soil horizons. The height, diameter and needle dimensions of young silver fir trees were significantly different under different canopies. The urease and asparaginase activity was the highest under the larch and spruce canopy in both soil horizons. Phosphatase activity was also the highest under larch canopy but only in organic soil horizon. Young silver fir (thicket) has grown under the canopy of all tested tree species but found best growth conditions under larch and pine canopies. The relative growth of silver fir is therefore a function of both stand canopy and soil properties.