LANDSCAPE PATTERNS OF LITTER DECOMPOSITION IN ALPINE TUNDRA

A two-year study of the decomposition of alpine avens (Acomastylis ros sii) foliage in alpine tundra of the Front Range of Colorado demonstra ted a strong landscape-mediated effect on decay rates. Litter on sites with intermediate amounts of snowpack decayed more rapidly than Litte r on sites with larger or smaller amounts of snow. Annual decay consta nts (k-values) of this foliage ranged from -0.33 in dry tundra to -0.5 2 in moist tundra to -0.47 in the wettest habitat. No site differences in mass loss of litter were detected until late winter-early spring o f the first year of decomposition, when significantly faster decomposi tion was observed for litter beneath the snowpack. In spite of obvious landscape-related patterns in rates of litter decomposition, total mi croarthropod densities in the top 5 cm of soil did not differ among ha bitats. However, the relative abundance of the oribatid and prostigmat id mites did vary significantly across the landscape in relation to th e moisture gradient. Oribatid mites comprised a greater proportion of total mites in wetter areas. Microarthropod densities and composition, as well as patterns of decomposition, were compared with previous alp ine, as well as arctic tundra, studies. The effects of soil invertebra tes on decomposition rates in the alpine were evaluated with a mushroo m litterbag decomposition experiment. Naphthalene was used to exclude fauna from a subset of litterbags placed in mesic and xeric habitats. Mushrooms without naphthalene additions decayed significantly faster i n the me sic sites. Densities of invertebrates were also greater on mu shrooms in these mesic sites. Mushrooms placed in xeric sites generall y lacked fauna. Thus, both the activities and the composition of the d etritus-based food web appear to change substantially across the moist ure gradient found in alpine tundra.