X hits on this document





57 / 61



recorded as present in this layer and probably many more species occur but were not recorded. The two most abundant species have very large open crowns and as a result the second tree layer is well developed.

Species found in the second tree layer can be classed into three groups. The largest group consists of species already present in the dominant layer, but Octomeles sumatrana and Albizia falcata are very rare. Seedlings of these two species have been observed elsewhere in the Northern Division to be light-demanding and do not normally regenerate in their own shade. The second group consists of species which have reached their maximum height and this group includes many species of Myristi- caceae, two species of Pandanus, several Palmae, Macaranga spp., Ficus spp. and

  • -

    Litsea sp., 'wowrae' (On). The third group is smallest in number of individuals but


rich in species and includes young individuals of species absent or very rare in the dominant layer but characteristically found in-the dominant layer of climax rain- forest outside the blast area. Tlie more important of these species are Pometia pinnata, Tristiropsis subangula, Chisocheton sp., Dysoxylum spp., Alstonia scholaris and Palaquium sp. The lowest tree layer is made up of species present in the second layer and of species commonly found in forest openings or in young regrowth on abandoned native gardens.

Because of the large number of species involved, no two stands have the same composition, even if only the dominant layer is considered. Over the greater part of this area the variations seem mainly dependent on chance, but in the south-east portion near the edge of the blast area Octomeles sumatrana and Albizia falcata are rare and the predominant species in the dominant layer are Pometia pinnata and Tristiropsis subangula; otherwise the communities are very similar. As is usual for the blast area of Mt. Victory there is a sharp change between this section and .the surrounding climax forest, but the change to a community dominated by 0.samatrana and A . falcata is gradual. The eruption was probably less severe in this small section and permitted the rapid regeneration of some species of the climax forest. Elsewherein the Northern Division Pometia pinnata and TristiroPsis subangula have been noted to regenerate rapidly when forest is cleared but not burnt.

On the lahar deposits the vegetation ranges from 10-40 m. in height, varying with the texture and depth of the deposits. These communities are closely related floristically to communities on mature soils 'but have only one or two tree layers.

Lower montane and montane zone. Only one day was available to investigate the higher sections of the blast area and during this day a track was cut to an eleva- tion of 1400 m. The great majority of species encountered were new to the author as well as to the local natives who accompanied him. As a result, notes are confined mainly to the structure of the communities encountered and these notes may be applicable only to the ridge on the northern slope where the ascent was made.

At approximately 700 m. elevation the vegetation changes sharply from the typical lowland community to a two tree layered sub-montane rainforest 30-35 m. in height. The two most common specieshave been provisionally identified as a Dipterocarpacea and Syzygium sp. This forest is the equivalent of the sub-montane rainforest of Beard (1944) but would be included in tropical rainforest by Richards (1952).

At the top of a particularly steep section of the ridge at 900 m. elevation the vegetation changes to montane thicket as described by'Beard (1955). This type is intermediate between the mid-mountain forest and mossy forest as described by Lane-Poole (1925) and Richards (1952). The community ranges from 6-13 m. in

Document info
Document views142
Page views142
Page last viewedFri Dec 02 20:07:43 UTC 2016