Recent height and diameter growth variation in Scots pine (Pinus sylvestris L.) along the Arctic margin: the importance of growing season versus non-growing season climate factors

Background: High-latitude forests are controlled by climate and as temperature increases, a northward extension in distribution and more vigorous tree growth are expected. The replacement of tundra by forest involves changes in carbon sequestration, land-atmosphere energy balance and ecosystems. The understanding of climate-related height and diameter growth patterns across geographical regions is therefore important. Aim: To analyse recent within- and between-region variations in climate-growth relationships for Scots pine at the forest-tundra ecotone (northern Norway, Kola Peninsula). Methods: Six pine (Pinus sylvestris) woodland sites, representing different climate regions along the forest-tundra zone, were sampled for annual height growth (saplings) and diameter growth (adult trees) and the analyses were related to local climate data. Results: Height growth was strongly similar among all sites and climate regions, but not diameter growth. Although summer temperature was the most important factor, non-growing season climate showed significant importance for both diameter and height growth across regions. Conclusions: The results highlight the importance of factors that are often overlooked, specifically, non-growing season factors for tree growth at high latitudes, and the role of short-term climate variation. Future climate scenarios predict moister and milder winters for large areas of high-latitude regions. Thus, detailed analyses of region-specific climate-growth relations that focus on growing season vs. non-growing season effects are essential in the evaluation of future forest cover response to climate change.