Ecology of Andreaea in western Norway

The ecology in western Norway of twelve taxa within the moss genus Andreaea has been investigated. Taxon abundances along environmental. gradients were recorded in 568 sample units. Numerical methods were used to estimate the realized niches of each taxon separately by regression analyses, and the realized niches for all the taxa simultaneously by constrained ordination. The genus Andreaea is restricted to hard rocks with a low calcium ‘concentration, although it can also grow on mildly basic rock types. In addition, lithosols and phyllite are alternative substrates at high altitudes. The main environmental factor differentiating between the niches of the Andreaea taxa is moisture, although the taxa are separated more along the altitudinal gradient. A general trend for Andreaea taxa is an interaction between moisture-controlling environmental factors; a low degree of flushing correlates with a high degree of shelter or cracks, or with low radiation. At high altitudes snow-persistence interacts with the moisture gradient. Taxa normally occurring in late snow-beds receive less water from sources other than snow-melt, whereas taxa occurring in sites free of snow early have a wider range of water sources. The second major environmental factor for niche differentiation is chemistry, namely soil pH. However, all taxa occur in sites with low values for soil pH. Other environmental factors mainly differentiate between pairs of taxa: hard rock — lithosols (A. rupestris var. rupestris — A. alpestris), degree of slope (A. rothii ssp. falcata — A. rothii ssp. rothii), and number of cracks (A. rothii s.1. — A. megistospora ssp. megistospora). All Andreaea taxa found within the study area are ecologically distinct in relation to one or more environmental factor. The ecological difference between A. rupestris var. rupestris and A. alpestris is, however, weak within the study area. In general, taxa with a wide morphological variability have a wide ecological tolerance and a wide geographical and altitudinal distribution. Explanation of distributional patterns at different spatial scales requires consideration of the dispersal strategies. Taxa that are regarded as pleisomorphous tend to occur in sites experiencing high humidity (A. nivalis, A. frigida), whereas there is a dominant trend towards a higher drought tolerance in apomorphous taxa (A. rothii s.1., A. megistospora ssp. megistospora, A. rupestris s.1.). A. blyttii is a special case, probably with an early departure from the other taxa in section Nerviae. It grows mainly in late or extremely late snow-beds. Within the section Andreaea, forms of A. obovata show some signs of ecological convergence towards pleisotypic ecology (flood-zone habitats), although A. obovata favours an intermediate humidity. A. alpina, a lowland taxon favouring high humidity, probably separated early from other taxa in this section.