Soil Acidity, Content of Carbonates, and Available Phosphorus Are the Soil Factors Best Correlated with Alpine Vegetation: Evidence from Troms, North Norway

We investigate which bedrock-derived soil nutrients are most important for the floristic composition and diversity of alpine, exposed, rocky habitats in North Norway, and whether the widely used pH parameter is a good estimate of soil chemical conditions in the middle alpine belt. Vegetation at 17 sites was recorded using the grid frequency method. Differences in the diversity of vascular plants, bryophytes, and lichens on the different substrates were compared using Shannon’s diversity index. Local soil consisted of weathered material from one of five bedrock categories: carbonate rocks, calcareous mica schist, noncalcareous mica schist, mafic rocks, and felsic rocks. Particle size, loss on ignition, pH, and levels of calcium, magnesium, potassium, phosphorus, and nitrogen were measured in soil samples. Canonical Correspondence Analysis showed that soil pH and bedrock derived phosphorus in the soil influence the floristic composition. Randomization tests further indicated that the floristic variation explained by bedrock derived phosphorus was not correlated with soil pH. Thus, the pH measure should be used with caution for the characterization of soil conditions. Vegetation growing directly in soil derived from carbonate rocks is distinct from communities on other calcareous soils. Species at such sites should be referred to as carbonate specialists rather than lime demanding.