Plant Succession on Volcanoes in Papua
The Trema sp. associes occurs on the steeper slopes where all the topsoil has been removed by erosion. It is a woodland community dominated by Trema sp., 'siha'
(Or). Other tree species are rare. Those recorded are Ficus spp., 'topu', 'ahorni' and 'sombahu' (Or), and PiPturus sp. 3348. The ground layer may be sparse to
dense and consists predominantly of Imperata cylindrica.
The Saccharum sporttaneum -Lycopodium cernuum associes occurs on the steeper slopes of the old crater where erosion has been most severe and the lower layers of the subsoil are exposed. The associes ranges from an almost continuous stand of tussocks of Saccharum spontaneum separated by a dense mat of moss or Lycopodium cernuum L. to almost bare ground with a scattered cover of moss and Lycopodium cernuum. In small gullies on the old crater walls occur small societies dominated by the trailing herb Gunnera macrophylla B1. 3327. These societies frequently have 100 per cent ground cover and receive additional water by drainage from the surrounding slopes.
There are many active steam vents arising from the dome of Mt. Lamington, but no trace of sulphur was found. With one exception these vents are devoid of vegeta- tion. The exception is the lowest vent at 1000 m. elevation. Immediately around this vent is a relatively lush growth consisting of many mosses, grasses, ten species of ferns and one dicotyledon seedling, probably Octomeles sumatrana. This com- munity drew the greater part of its water supply from steam which could be seen condensing on leaves and rocks. Surrounding the steam vent community was the usual desert of scattered moss plants typical of the upper part of Avalanche Valley.
As a result of the deposition of volcanic material from streams draining from Mt. Lamington, large areas of forest have been destroyed and a fresh sequence of sera1 communities formed outside the blast area. These are very similar to communities on riverine deposits elsewhere in the region and consist of scattered tussocks of Saccharum spontaneum or stands of small trees in the upper reaches where the deposits are coarse. In the lower reaches, where the deposits are finer and flooding more frequent, the community is dominated by a dense tall stand of Saccharum spontaneum or Phragmites sp. or by a dense mass of numerous water-loving her- baceous species.
Waiowa Volcano is situated near the junction of a piedmont plain with the foothills of the Goropu mountains, 20 km. south-west of the coastal village of Uiaku. The plain at this point is at 270 m. elevation and the small cone of the volcano is another 100 m. higher.
The history of the eruption has been reported by Baker (1949). Volcanic activity had not been reported from this area before December 1943, but during the next six months there were three major eruptions and long-continued ejection of gas, steam and ash and a flow of blocky lava. The eruptions were of the Perret type and a glowing cloud of hot ash devastated an area of 40 km." mostly on the piedmont plain. The plain surrounding Waiowa Volcano is virtually uninhabited and outside the blast area it is covered by a mature tropical rainforest of very mixed floristic composition. Some of the more frequent species in this forest are Pometia pinnata Forst., Tetrameles nudi$ora R. Br., Syzygium spp., Dysoxylum spp., TristiroPsis subangula K. Sch., Alstonia scholaris R. Br., Pterocarpus indicus Willd. and Pala- quim sp.