Climatic factors affecting radial growth of Betula ermanii and Betula platypylla in Kamchatka

Radial growth responses to climate were studied in two species of birch broadly distributed across Kamchatka Peninsula. Wood cores were obtained in different locations and environments, from upper to lower treelines, and from wet maritime sites at the Pacific to the subcontinental interior of the peninsula. Response functions were calculated using the four longest meteorological records (1920s–2000) in Kamchatka. In Betula ermanii Cham., the dominant species in mountains and maritime woodlands, ring width in high-elevation (500–600 m) trees increased with warm and less rainy June and July and decreased with rainy/snowy cool weather during the prior September and October. Radial growth in B. ermanii low-elevation trees increased with higher winter precipitation, suggesting that water from melting snow prevents water stress and possibly desiccation in low-elevation trees. In Betula platyphylla Sukaczev, a common taiga species in interior Kamchatka, low summer temperatures limited growth at its upper distributional limit (300–350 m) and in cool, wet sites dominated by Picea ajanensis Lindl. et Gord. On drier sites dominated by Larix cajanderii Mayr., growth was limited by warm April and dry June weather. Variable responses along elevation–continentality gradients reinforce the necessity of a site-dependent differentiation for the assessment of impacts of climate change on species performance and geographic range shifts.