PRIMARY SUCCESSION OF HAWAIIAN MONTANE RAIN-FOREST ON A CHRONOSEQUENCE OF 8 LAVA FLOWS

The primary-successional sere of a Hawaiian montane rain forest was in ferred from an age sequence of eight closely located 'a'($) over bar a flows (clinker type lava); 8, 50, 140, ca. 300, ca. 400, ca. 1400, ca . 3000 and ca. 9000 yr, on a windward slope of Mauna Loa, Hawaii. All study sites (0.2 ha each) were at 1120 - 1250 m a.s.l. with 4000 mm me an annual rainfall. The 400-yr, 1400-yr, and 9000-yr flows had younger volcanic ash deposits, while the others were pure lava. Comparisons o f tree size and foliar nutrients suggested that ash increased the avai lability of nitrogen, and subsequently standing biomass. An Unweighted Pair Group Cluster Analysis on the samples (flows) using quantitative vascular species composition revealed that clusters were correlated w ith age regardless of the substrate types (pure lava vs. ash), and an indirect ordination on the samples suggested that the sequence of samp le scores along axis 1 was perfectly correlated with the age sequence. Although ash deposits increased biomass, they did not affect the sequ ence of the successional sere. Both pubescent and glabrous varieties o f Metrosideros polymorpha (Myrtaceae) dominated upper canopy layers on all flows greater than or equal to 50 yr and less than or equal to 14 00 yr, but the pubescent variety was replaced by the glabrous on the f lows greater than or equal to 3000 yr. Lower layers were dominated ini tially by a matted fern, Dicranopteris linearis, up to 300 yr, and sub sequently by tree ferns, Cibotium spp., to 9000 yr. The cover of Cibot ium declined slightly after 3000 yr, while other native herb and shrub species increased. A 'climax' stage in the conventional sense was app arently not reached on the observed age gradient, because the sere cha nged continuously in biomass and species; this divergent successional phenomenon may be unique to Hawaii where the flora is naturally impove rished and disharmonic due to its geographic isolation in contrast to more diverse and harmonic floras in continents.