摘要：Age structure, tree characteristics, and environmental data were used to analyze the status of the birch treeline in three regions along the Scandes Mountains from 62°10′N to 69°50′N. Aspect and estimated relative radiation explained most of the treeline altitude across studied regions, but not all variation. Main tree establishment occurred during the 1940s in the southern and northernmost regions, and during the 1960s in the middle region. Age distribution patterns at 2 m (tree size), however, showed stable or possibly progressive treelines in the southern and middle regions but recent recession in the north. Growth rates varied through time and between regions, with an apparent decrease in the north since the 1940s. Weak negative correlations between altitude and age in the south indicate recent changes favoring tree growth or increased turnover at higher, more exposed altitudes. Although Scandinavian treelines are expected to advance in response to climate warming, this was not evident as a general pattern for all regions. Seasonally different climate patterns, browsing, and abrasion are mechanisms involved in this. These regionally different patterns have to be taken into account in predictions of future responses to avoid overestimation of, e.g., ecosystem change, carbon uptake capacity, and feedbacks to climate systems.
