Spring and autumn frost tolerance was measured using material from a range-wide (50Á678 N, 38Á1588 E) provenance trial of four Russian larch species (Larix sukaczewii Dyl., L. sibirica Ledeb., L. gmelinii Rupr. and L. cajanderi Mayr.) growing in northern Sweden. Shoots were collected in early May and late September and frozen at (8, (12, (16 and (208C. Cambial damage was assessed visually after development under ideal conditions for 2 weeks. Differences in frost damage among provenances were highly significant in both spring and autumn. Autumn frost damage was significantly correlated with provenance latitude and longitude and spring frost damage was significantly correlated with provenance longitude but not latitude. Frost damage was not correlated with provenance elevation. North-western provenances showed the least damage and far-eastern provenances the greatest damage in both spring and autumn. A possible explanation for less spring frost damage to north-western provenances is adaptation to maritime conditions in proximity to the Barents Sea, which is often ice free in late winter. This would counteract early loss of frost tolerance and bud flushing if warm spells occurred in late winter. North-eastern Siberian provenances did not show similar adaptation and may exhibit increased spring frost damage if global warming eventually results in the Arctic Ocean north of Siberia becoming ice free in late winter.

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The influence of pine iwist rust (Melampsora pinitorqua) on growth and development ol Seots pine wa.s studied during three consecutive years. Tbe e.xperimcntal material included three provenances from natural stands and one open pollinated seed orchard progeny, l fftd b i tit t bd Trees affected trees tands and one open pollinated seed orchard progeny. s severely affected by pine twist rust reacbed an avorai;e of 3S % lower height than did nonted trees, while mildly affected trees grew somewhat better, on tbe average, dian did non-alfeeted . Pine twist rust caused ihe greatest loss of height incrcinent in the seed orchard progeny.

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Four Russian larch species; (Larix sukaczewii Dyl., L. sibirica Ledeb., L. gmelinii Rupr. and L. cajanderi Mayr.) were tested in combined provenance-progeny tests on three sites in Sweden. 29 provenances, two seed orchards and four seed stands-material were assessed for juvenile height growth and survival after five growing seasons in the field. Genetic parameters were also determined on the family level. The results show that provenances of L. sukaczewii originating from western Russia have the highest survival. Compared to the closely related L. sibirica, L. sukaczewii show better adaptation, a pattern that has also been observed in Finland and Iceland. Provenances of L. gmelinii from the Russian Far East demonstrate best juvenile height growth on all three sites. L. cajanderi from northern interior Siberia failed on all three sites. Both climatic and geographical variables showed strong correlation with survival and height. At this early evaluation it seems like provenances of L. sukaczewii can be transferred northward with satisfactory survival whereas southern transfer or transfer from strongly continental areas in Russia to the semi maritime climate in Sweden results in poor growth. CVA values suggested relatively high genetic variation in height for L. sukaczewii and L. sibirica. The heritabilities for height growth and survival were at this early evaluation generally low (h2 < 0.10) and often non-significant.