Controls on Decomposition Processes in Alpine Tundra

The snowpack gradient in the alpine generates a temperature and moisture gradient that largely controls organic matter decomposition. While low temperatures constrain decomposition and mineralization (chapter 12), moisture appears to be the strongest source of landscape variation in the alpine, with surface decay rates of plant materials highest in moist and wet meadow habitats. Despite a longer snow-free season and higher surface temperatures in dry meadows, decay in these areas is substantially lower than in moist meadows. Studies of decay rates of roots within the soil indicate that decay is uniformly low in all habitats and is limited by low temperatures and perhaps by the absence of certain groups of decomposer invertebrates. As in other ecosystems, substrate quality indices such as nitrogen and lignin content can be shown to be important factors influencing the rate of decay of specific substrates. Alpine ecosystems were overlooked during the flurry of activity associated with the extensive ecosystem science programs of the 1960s and 1970s. With the few exceptions to be discussed here, decomposition studies in cold regions were conducted in arctic tundra or northern temperate and boreal forests. The need for this information in conjunction with efforts to understand carbon cycling in the alpine stimulated a substantial research effort in the 1990s. Studies have included both the effects of landscape location on decay (O’Lear and Seastedt 1994; Bryant et al. 1998), information on the importance of substrate chemistry on decomposition processes (Bryant et al. 1998), and preliminary information on some of the decomposer organisms (O'Lear and Seastedt 1994; Addington and Seastedt 1999). Niwot Ridge researchers also participated in the Long-term Intersite Decomposition Experiment Team (LIDET) study, which involved placement of a dozen different litter types in the alpine and in 27 other sites from the tropics to the arctic tundra (Harmon 1995). All but one of the plant species used in the LIDET experiments were exotic to the alpine. Collectively these studies have provided sufficient information to represent the alpine in global decomposition modeling efforts.