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

Abstract

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.