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ABSTRACT
Scots pine (Pinus sylvestris L.) stands are regenerated by planting, and only small portion (c.a. 13%) by self-seeding in Latvia. Seeds for plant production are collected only in seed orchards - thus represent the results of tree breeding. Aim of our study was to assess the growth and damages as determined by forest type and genetics in Scots pine stands at the age of first commercial thinning. Tree parameters were measured in Scots pine open-pollinated progeny trials on mineral soils, differing by fertility (poor Cladinoso- callunosa and rich Hylocomiosa), including 35 families in 4 replications in each trial, at the age of 40 years. There were statistically significant differences among the forest types in parameters characterizing tree growth (diameters, height), however, the values of best performing families in poor growing conditions exceeded the values of worst performing in better growing conditions. Genotype x environment interaction effect on tree growth was significant, however, it could not be practically used - establishment of separate seed orchards for different forest types would be too costly. Therefore selection of best performing genotypes across range of conditions is proposed. Selection differential is similar on both studied forest types, with selection intensity of 10% leading to increase of 6.3-8% in height and diameter of the trees.
Keywords: genetic gain; selection differentia; breeding effect; Pinus sylvestris
INTRODUCTION
Scots pine is one of the most abundant tree species in Latvia. Type of final felling is usually clear-cuts in these stands. Natural regeneration is practiced mostly on poor peat soils. However, in other forest types are regenerated primarily by planting. Most common soil scarification method is disc trenching, but also spot mounding, ensuring improved height growth on wet soils and not increasing the time spent (and costs) of tending is practiced increasingly more often during recent years [3]. Growth of planted trees is affected by formation of lammas shoots, especially at the first years after establishment: a study had found significantly increased height at age 8 years for Scots pine with lammas shoots ate the age of 4 years [8]. Occurrence of lammas shoots is affected both by environment (improved growth conditions, including reduced competition, appropriate moisture regime) and genetics. It has no long-lasting negative impact to the stem quality, like occurrence...