Impact of competition on survival, growth, and tree characteristics of young conifers

The thesis summarises results of four studies on the impact of competition on survival, growth and tree charcteristics of young conifers. The objective was to evaluate alternatives to dense initial spacing for producing high quality timber. By planting seedlings of different size, a size hierarchy was established in Scots pine (Pinus sylvestris) plantations. Size differentiation was accentuated 32-37 years after plantation. Diameter, annual ring width, and branch diameter among less dominant trees were reduced compared to dominant trees. Mortality was highest among smaller seedlings and increased with competition. Potential quality of residual trees after first thinning, carried out from above or below, was compared in two Scots pine stands. Differences between thinning types evened out due to extraction of strip road trees and damaged trees. Increment of individual trees in two Scots pine stands, originating from advance growth or planting was analysed. Advance growth responded to release from overstorey competition with increased growth. Height growth response was delayed, especially among saplings. Logging damage to advance growth may have reduced both quality and increment. Naturally regenerated seedlings had a similar height development as planted seedlings. Increment of smaller planted trees was reduced and potential timber quality was higher compared to more dominant trees. The stand originating from advance growth had lower volume production. Survival and increment of advance growth of Scots pine and Norway spruce (Picea abies) and supplementary planted lodgepole pine (Pinus contorta) and Norway spruce was analysed after selective logging in a mixed stand. Survival of advance growth decreased with increased logging intensity, while damage level among surviving advance growth increased. Six years after logging, advance growth had not fully recovered from suppression. Increased overstorey density had no negative effect on survival of planted seedlings. Height increment of planted seedlings was reduced when overstorey density was high. It is concluded that competition has a great impact on seedling increment and on potential timber quality. The studies indicate that with knowledge of the impact of competition on increment of individual seedlings, there are silvicultural alternatives to dense even-sized plantations that may give acceptable production and quality.