One Century of Treeline Change and Stability - Experiences from the Swedish Scandes

This paper elaborates and visualizes processes recorded in a recent regional and multi-site study of elevational
treeline dynamics during the period 1915 to 2007 in the Swedish Scandes. The purpose is to give a concrete face of
the landscape transformation which is associated with the recorded treeline shifts. The main focus is on stand-level
structure of past and present treelines and the advance zones, where climate change elicited responses by Betula pubescens
ssp. czerepanovii, Picea abies and Pinus sylvestris. All species shifted their treelines upslope by a maximum
of c. 200 m in elevation. Most sites, however, manifested changes of smaller magnitudes. This relates to topoclimatic
constraints which decouple treeline performance from the macroclimate. The general character of sites which
support large and small treeline shifts, respectively, are outlined. The spacing, age structure, growth rates of the tree
advance zones are accounted for each of the concerned species. In temporal and spatial detail, the different tree species
responded individualistically according to their specific ecologies. Current spread of young seedlings and saplings
to increasingly higher elevations in the alpine tundra is particularly highlighted as it may represent the forefront
of future treeline advance. It is argued that the current evolution of the treeline ecotone represents a fundamental,
although not necessarily entirely unique, reversal of the long-term (Holocene) trend of neoglacial treeline descent.