Mountain vegetation in the Faroe Islands in a climate change perspective

Sammanfattning: This thesis is a study of the mountain vegetation in the Faroe Islands based on five altitudinal transects sampled during the period 1999-2001. The vegetation was studied on the basis of plant communities, life-forms and biodiversity of vascular plant species and is discussed in a climate change perspective. The boundary between arctic and temperate vegetation is established and the tolerance of character species was tested according to different temperature parameters. The aim has been to assess how the vegetation might be affected by climate change. Three significantly different altitudinal vegetation zones were defined, a temperate zone (upper limit at 200 m a.s.l.), a low alpine zone (200-400 m a.s.l.) and an alpine zone (above 400 m a.s.l). The shift in vegetation zones is also seen in the change of biodiversity of vascular plant species where two maxima in biodiversity are found, one at 250 m a.s.l, the other at 500 m a.s.l. These maxima might indicate transition areas between the zones, more or less overlaps with the low alpine vegetation zone. The study on Raunkiær’s life-forms also showed that the ratio between hemicryptophytes/chamaephytes was at its maximum in this zone. In earlier studies, the boundary between the low alpine and the alpine zone is found at a higher altitude. This could indicate that a lowering in the alpine zone has occurred within the last fifty years as a result of a cooling by about 0.25°C. The responses of changing summer and winter (soil) temperature on twelve plant species, in a cooling or warming scenario, shows that the species most threatened by a warming scenario are those that are found with a limited distribution restricted to the uppermost parts of the mountains, especially Salix herbacea, Racomitrium fasciculare, and Bistorta vivipara. For species found at lower altitudes, the effect will mainly be a general upward migration. The most sensitive species are those with a low tolerance, especially Calluna vulgaris, and also Empetrum nigrum, and Nardus stricta. If the climate in the Faroe Islands should become colder, the most vulnerable species are those at low altitudes, especially Vaccinium myrtillus and Galium saxatilis. Species like Empetrum nigrum, Nardus stricta, and Calluna vulgaris may also be threatened. In any case, these species can be expected to migrate downwards.