Plant Diversity in a Chronosequence at Glacier Bay, Alaska

Eight sites of known age were sampled in Glacier Bay National Monument, Alaska, to examine the changes in plant diversity during primary succession in that region. Four strata–trees, tall shrubs, low shrubs—herbs, and bryoid—thalloids–were sampled independently. Data suggested a sequence of wave—like invasions on sites by strata, largely in order of increasing size. Bryoid—thalloids were exceptional in demonstrating a late peak in cover values. In general, diversity of a particular stratum declined during the period in which the stratum dominated the community in terms of foliar cover. Richness (species number) of communities increased rapidly in the first 100 years, then more gradually to reach a maximum in the muskeg steady state. Equitability (evenness of distribution of foliar cover among species) was erratic, but tended to increase with age. After initial rises, three diversity indices showed nearly flat curves with two exceptions: marked decreases in the 30— to 50—year period; and a rise to maximum levels in the final steady state. Total information per unit area calculated from diversity and foliar cover increased in a sigmoid manner with peak information in the final muskeg stage.