Silver birch (Betula pendula Roth) is productive on abandoned agriculture land, and thus might be considered as an option for profitable plantation forestry. Application of the most productive genotypes is essential. However, information about genetic gains in low-density plantations is still lacking. A 40-year-old low-density (400 trees ha −1 ) plantation of 22 grafted silver birch plus-tree clones growing on former agricultural land in the central Latvia was studied. Although grafted plantations are not common in commercial forestry, the trial provided an opportunity to assess genetic parameters of middle-aged birch. The plantation that had reached the target diameter for final harvest (DBH (diameter at breast height) = 27.7 ± 5.5 cm) had an 85% survival rate, and stemwood productivity was 5.25 m 3 ha −1 year −1 . Still, rootstock × scion interaction and cyclophysis might have caused some biases. Broad-sense heritability (H 2 ) ranged from 0.02 for probability of spike knots to 0.40 for branch angle. Estimated H 2 for monetary value of stemwood was 0.16. In general, the correlations between growth and stem quality traits were weak, implying independent genetic control, though branchiness strongly correlated with diameter at breast height. The monetary value of stemwood strongly correlated with productivity traits. The observed correlations suggested that productivity and stem quality of birch might be improved simultaneously by genetic selection.

In Europe, numerous Norway spruce (Picea abies L. Karst.) provenance trials have been established and evaluated at a juvenile age. Still, information about the adaptation potential and long-term fitness of transferred seedlots in the Baltic Sea region is lacking. The aim of the study was to evaluate the adaptation capacity of provenances and assess the patterns of their long-term reaction to environmental transfer. We examined a 32-year-old provenance trial in the mild Baltic Sea coastal climate of Western Latvia. Significant differences in height and stem volume were observed among provenances. Growth superiority for certain local and Carpathian provenances was maintained over more than one-third of the rotation period. The best predictor of climate transfer functions was minimum temperature of the coldest month at the place of origin, explaining 28% variation in tree height. Populations from sites with more frost days and a colder mean annual temperature, minimum temperature, and lower annual heat-moisture index than the planting site were generally taller.

Stem cracks are damaging for timber quality and can reduce the monetary value of a tree both directly and indirectly: serving as gateway for fungal infections. Aim of the study was to assess the influence of tree dimensions and seed origin on the frequency of stem crack for Norway spruce. The study was carried out in two contiguous provenance trials (material from 12 countries), established in 1972 and 1975 in Western Latvia. Stem cracking was assessed using five-score scale. Most of the affected trees (90%) had very light or light damage. There was no relation of diameter at breast height to incidence of stem cracks. Analysis revealed a significant provenance effect on occurrence of stem cracks. Russian provenances tended to have lower risk of stem cracking and relatively narrow variation within the region, while Baltic and Ukrainian origins had wide range of stem cracking, having best as well as worst provenances in terms of cracking. Overall it is possible to select fast growing provenances with relatively low incidence of stem cracks.

Genetic parameters of growth and stem quality traits were estimated for open-pollinated silver birch Roth progenies in Latvia at the age of 10 and 14 years. Tree height and stem volume were found to be under strong genetic control at both inventories (narrow-sense heritabilities varied from 0.41 to 0.66). Mainly low heritabilities were found for stem defects, yet genetic control of branch diameter, stem straightness and overall stem quality varied from low to high depending on study site. High additive genetic coefficient of variation was found for stem volume (25.3–32.5%). Genetic correlations among growth traits were strong and positive (0.90–0.99). Mainly weak genetic correlations between growth and quality traits implied simultaneous improvement. Still, strong negative correlations between branch angle and stem straightness might result in enlarged knot size for straighter logs. The genetic age-age correlations were strong. Weak genotype by environment interaction and stability of best genotypes over different sites was indicated by strong genetic correlations between trials. Each growth or quality trait alone showed substantial improvement in terms of estimated genetic gain (up to 62% over trial mean for stem volume). Therefore, selection index combining both growth and stem quality may be developed.Betula pendula

Five-year-old Norway spruce and four-year-old Scots pine seedlings of various origin were inoculated with Heterobasidion annosum s.s. and H. parviporum to estimate whether the susceptibility of seedlings to Heterobasidion was affected by origin of seeds. In total, 520 spruce and 538 pine seedlings from different seed sources and provenance regions of Latvia were tested. Four months after inoculation the fungal growth was measured. The results highlight differences between development of H. annosum and H. parviporum in spruce and pine seedlings. We did not find any seed source that was more resistant than others.