ABSTRACT

Kullman, L. 2003. Förändringar i fjällens växtvärld – effekter av varmare klimat. [Changes in alpine plant cover – effects of climate warming.] – Svensk Bot. Tidskr. 97: 210–221. Uppsala. ISSN 0039-646X.

Elevational limits of some vascular plants in the southern Swedish Scandes have risen significantly in response to slightly less than 1°C climate warming over the past century and, in particular, warmer winters since 1988. Present-day elevational limits are compared with historical records from the 1950s. The reality of the advance is confirmed by the juvenile character of the outlier specimens, as evidenced by annual ring counts (tree species) and documented by photographs.
The tree-limits have advanced maximally by 100–150 m since the early 20th century, while the upper range limits of these tree species are on average 200–250 m higher than in the 1950s. Over the latter period, some shrubs, dwarf-shrubs and herbs have shifted upslope by 100–175 m, whereas other species have not changed at all. Thus, species-specific response patterns to a certain climatic event are empirically sustained.
As a consequence of vanishing late-lying snow patches, grasses have expanded to form a virtual “grass steppe” over wide areas previously dominated by low-growing snow-bed species.
Conceivably for the first time since the early Holocene, the thermophilic (nemoral) tree species Acer platanoides and Ulmus glabra have become established in subalpine birch forest. This seems to be part of a general biogeographical shift in northern Sweden, implying altitudinal and latitudinal expansions of such plant (and animal) species.
As often surmised, climate warming has also been associated with the spread of exotic tree species, e.g. Pinus contorta and P. cembra, into undisturbed subalpine vegetation.
These changes may be ephemeral, but demonstrate that the alpine plant cover is more dynamic than previously realized. In case of a sustained warming, many plant species will obviously not be subjected to dispersal limitation.