The objectives of the proposed research are to (1) determine the relative importance of competition and facilitation as mechanisms influencing primary succession in a nutrient- impoverished environment, (2) dissect these mechanisms into their component biological processes, and (3) compare experimental, observational, and historical (retrospective) approaches to the study of succession. The research will be conducted at Glacier Bay, "the" classical example of facilitation. Although most experimental work has shown facilitation to be unimportant in terrestrial ecosystems, this work has been largely restricted to secondary succession where soils are well developed, whereas the concept of facilitation originated mainly from observations in primary succession, where plants confront a more severe environment. The central hypothesis to be tested is that life history traits explain the basic pattern of succession, but that the rate of succession is influenced by both facilitative and competitive interactions among species. Life history traits to be measured in the field are seed rain, growth rate, age of first reproduction, and longevity. Possible inhibitory effects of established vegetation upon seed germination and initial establishment will be tested by sowing spruce and alder seeds into each of four successional stages (uncolonized, Dryas, alder, and spruce) in presence and absence of forest floor. Competitive or facilitative effects of established vegetation upon seedling growth will be tested by planting alder and spruce seedlings into each successional stage. The record of past competition and facilitation will be derived from studies of tree cores and stand age structure.
