Bud break and intra-annual height growth dynamics of saplings and pole-stage trees of Scots pine: case study for a boreal forest in northern Finland

The timing of phenophases of trees has increasingly been used as a bio-indicator for climate change. Many studies, however, did not sufficiently consider an influence of tree age. According to our exploratory study, the phenophases at the tops of saplings and of pole-stage trees of Scots pine growing in an open canopy boreal forest coincided with each other in a given year but differed between years (2008 and 2009). In 2008, bud break and the onset and end of height growth of saplings/pole stage trees occur at the same time, viz. at the end of May, beginning of June, and mid-July, respectively. In 2009, bud break and onset of height growth occured mid-May and end of May, respectively, whereas the end of height growth was the same as in 2008 (mid-July). This finding indicates the possibility of transferring observations made on easily accessible saplings to hardly accessible adult trees. This transferability may open up new ways to better understand growth processes of adult trees.