An attempt was made to estimate critically the genetic gain in clonal seed orchards of Scots pine (Pinus sylvestris L.) in Finland. The selection differential of Scots pine and Norway spruce (Picea abies (L.) H. Karst.) is calculated on the basis of filed information on selected plus trees which has been kept by the genetic register at the Finnish Forest Research Institute. The differentials were computed as realized differences in height between plus-trees and normal stand characteristics on respectively site class and as a function of age.
The genetic gain in height growth of Pinus sylvestris was computed on the basis of information on selection differential and heritability. This genetic gain is between 2.6–4.4% provided there is no pollen contamination from unknown sources outside the seed orchard. The genetic gain of volume growth in Scots pine is about 7–15%, provided there is no pollen contamination in the seed orchard. However, according to investigations, there is invariably some pollen contamination in this kind of seed orchards. The contamination decreases to about 30–50% as the orchard matures and starts to produce endemic pollen. If the pollination would be entirely due to foreign pollen sources, the mathematically calculated genetic gain would be 3.5–7.5%.
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