CR prepress abstract  -  doi: 10.3354/cr01457

Bioclimatic effects on different mountain birch populations in Fennoscandia

Oddvar Skre*, Bogdan Wertz, Frans E. Wielgolaski, Paulina Szydlowska, Stein-Rune Karlsen

*Email: oddvar@nmvskre.no

ABSTRACT: 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 changed climate and land use has made mountain birch an important bioindicator. Birch seedlings from 10 populations were therefore transplanted to three northern Fennoscandian sites (one oceanic, one continental mountain site, and one 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 1993-2010, while at the two other sites measurements only covered the period 1993-97 (mountain site) and 2010-14 (both sites). During the last period (2010-14) 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 damages at the latter site. 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 at short terms. 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 with inbreeding with dwarf birch (Betula nana).