Potential for Timberline Advance in Northern Finland, as Revealed by Monitoring during 1983-99

Seedling density, tree density and basal area of Scots pine ( Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst) were monitored and compared in the timberline areas of northern Finland during the period 1983-99. Rows of 9-12 circular plots were established at 13 localities in four regions: pine-dominated northern and southern regions and spruce-dominated western and eastern regions. Temporal changes were monitored in three altitudinal zones: in the forest, at the coniferous timbe rline (where forest canopy closure ceases), and at the tree line (where coniferous trees higher than 2 m cease). Pine seedling densit ies decreased abruptly in the southern region, especially at the timberline, but increased slightly in the northern region. The zone·region·change interaction was significant. The change in spruce seedling densities was small in the forest and timberline zones, but the densities more than doubled at the tree line. Tree density and basal area increased in all the zones and regions . New regeneration and tree establishment during the study period indicate a potential for the tree line to advance. However, there w as great heterogeneity in regeneration and seedling establishment among the localities.