Spatial variations in the growth rate of Hylocomium splendens and the thickness of the organic layer on a north-facing slope in Interior Alaska

Abstract

High-resolution data on spatial variations in the productivity of bryophytes and the mass of the organic layer are important components in geochemical models for northern forests. We investigated spatial variations in growth rates of the feather moss Hylocomium splendens and the thickness of the organic layer in relation to environmental factors on a north-facing slope in Interior Alaska. The forest floor on the 600 m × 600 m slope was classified into four types, i.e., Classes I–IV, characterized mainly by the dominance of leaf litter, H. splendens, Pleurozium schreberi, and Sphagnum spp., respectively. Spatial autocorrelation analyses showed clustering patterns for some tree and forest floor variables, which were associated with the distribution of the four classes on the slope. Mean growth (length) rates of H. splendens were high in Class II, while growth rates by weight were high in Class I due to a high weight-to-length ratio of shoots. The thickness of the organic layer in bryophyte patches ranged from 6.0 to 40.7 cm and was also controlled by slope orientation. The presence of large trees, particularly Betula neoalaskana, mediated the relationship between topography and forest floor characteristics.