Growth and mortality in underplanted tree seedlings in response to variations in canopy closure of Norway spruce stands

Abstract

Six broadleaved tree species and Picea abies (L.) Karst. were planted under spruce plantations of varying densities, in Sweden. Treatments included control (994 stems ha−1), dense (538 stems ha−1), sparse (294 stems ha−1) and gap (0 stems ha−1) overstory treatments. There was an increase in height and diameter growth from control to sparse overstory treatment of all underplanted tree species except for ash (Fraxinus excelsior L.) and Norway maple (Acer platanoides L.). Site conditions may have hampered the growth of these species, as well as wild cherry (Prunus avium L.). Both oak (Quercus robur L.) and spruce had greater growth in the gap treatment, relative to the other treatments. Insecticide application did not influence seedling growth or survival. The performance of beech (Fagus sylvatica L.), lime (Tilia cordata Mill.), spruce and oak was consistent with shade tolerance ranking. Beech and lime had a very high survival rate, even under the densest canopy. The growth and mortality of ash, maple and wild cherry differed significantly from what was expected. This experiment demonstrated significant variation in interspecific growth and mortality between seven planted tree species in relation to canopy density. Correct site and species selection is crucial when underplanting in shelterwood systems.