Plant Succession on Volcanoes in Papua
stands of this forest have a well-developed dominant layer, a very sparse second tree layer at 7 m. and a dense ground layer 2-3 m. in height. Up to 80 per cent of the trees of the dominant layer are Octomeles sumatrana but many other species occur. Species recorded are: Casuarina papuana; Neonauclea sp., 'kaforna' (On); '4lbizia falcata, Dysoxylztm sp., 'jomo' (Or);Alstonia sp., 'ibuga' (Or); Vitex cofassus Reinw. and Ficus sp., 'mumbura' (Or). The dense ground layer consists of Saccharum spontaneum, Saccharum sp., 'ohogo' (Or),Imperata cylindrica and many species of ferns. The transition between this forest community and the woodland communities is gradual and consists of a gradual-reduction in height and an increase in importance of Casuarina papztana. The boundary with the surrounding climax rainforest is exceedingly sharp, due to the nature of the eruption, and this transition area is marked by an abundance of climbing palms, Calamus spp., in the Octomeles sumatrana forest.
MT. VICTORY Mt. Victory is an 1800 m. high volcano situated 40 km. due north of Waiowa Vol- cano. The date of the last eruption of this volcano is not known, but the tentative date of 1870 is suggested. European settlement did not come to this area until the present century, but in the closing years of the nineteenth century the smoke from Mt. Victory was used as a landmark by mariners and the explosion is still fresh in the legends of the native peoples.
The eruption is presumed to be very similar to the explosion of Mt. Lamington in 1951, with the main devastation being due to a glowing cloud of hot ash covering an area of 400km2. Lava flows from this last eruption are absent, but there are extensive lahar deposits consisting predominantly of sand and gravel, often of considerable depth. Nothing is known of the pre-eruption vegetation, but presumably at lower levels this was similar to the tall tropical rainforest now growing just outside the blast area. This forest is 35-45 m. in height and is of very mixed floristic composition and rich in species; the most frequent are Syzygium sp., 'dara' (Or), Tristiropsis subangula, Pometia pinnata, Terminalia sp., 'kowuja' (Or), Anisoptera polyandra B1. and Cedrela toona Roxb.
At present the major changes in the vegetation are associa ed with differences in elevation. Three zones are recognized; a lowland zone generally below 700 m. elevation, a lower montane zone 700-900 m. in elevation and a montane zone above 900 m. Due to the limited time available only the lowland zone was investigated in any detail.
Lowland zone. Variations in composition and structure within this zone are as- sociated with edaphic conditions. The greater part of the area is covered by a mature soil of considerable age. The topsoil consists of a dark brown loam or clay loam, 20-40 cm. deep, and this overlies a yellow to yellow-brown subsoil ranging in texture from clay loam to loamy sand. This mature soil is generally free of recent ash but is occasionally covered to a depth of 30 cm. The remainder of the lowland zone is covered by lahar deposits.
On the mature soils the vegetation is a high rainforest with three tree layers, the
uppermost this layer,
layer frequently exceeding 50 m. in height. Octomeles sumatrana and Albizia falcata.
Two species predominate in Other common species are
E n d o s ~ e r m u sp., 'poporga' (Or),Artocarpus incisa L.,Elaeocarpus Tetrameles nudiflora, Canarium spp. and Ficus spp. Another fifty