资源环境科技发展态势分析平台

Mountain birch Betula pubescens ssp. tortuosa is the main treeline species in northern Europe, and the recent increase in treeline elevation in Fennoscandia due to climate change and land use has made mountain birch an important bioindicator. Birch seedlings from 10 populations were therefore transplanted to 3 northern Fennoscandian sites (1 oceanic, 1 continental mountain and 1 Arctic coastal site). Annual measurements were carried out on growth parameters and phenology (date of budbreak) from 1992 onwards. At the coastal site, measurements covered the whole period 1993 to 2010, while at the 2 other sites measurements covered only the period 1993 to 1997 (mountain site) and 2010 to 2014 (both sites). During the last period (2010 to 2014), measurements were made on a new set of seedlings, transplanted in 2002. The plants suffered a temporary transplantation stress because of root damage. In general, budburst occurred earlier in populations from northern and continental sites than from southern and coastal sites. Survival rates were dependent on climate and were generally higher at the oceanic than at the mountain site, due to more autumn frost and insect damage at the latter. At the mountain site, survival rates were lowest in oceanic and southern populations; at the Arctic site, survival rates were lowest in continental populations; while at the oceanic site, only small differences were found between populations. The present results seem to indicate that climate is an important driver of change at the mountain birch treeline, although land-use changes may be more important in the short term. In the future, when a warmer climate is predicted, plants that are adapted to a coastal climate may expand their range, and increased winter temperatures are expected to favour insect-resistant polycormic birch inbreeding with dwarf birch Betula nana.