american samoa - University of Hawaii at Manoa

Scvcral other trees are characteristic of Alava ridge,
but arc more heliophytic (sun-loving) species that do
not do well in the shade of undisturbed montane
forest. 'The three most significant of these are
Me/ro.videros collina, Spiraeanlhemum samoense, and
Glochrdion cuspidatum, Metrosideros, which is
probably the same species that comprises most of the
native forests in Hawai'i, dominates the scrubby
vegetation found on the upper part of the steep slopes
of Alava Ridge, especially around the TV transmitter.
Spirueanthemum is also common there, and was found
to be the dominant species in one type of cloud forest
at I600 m elevation on Savai'i (Whistler 1978).
Glochidion cuspidatum is more of a secondary forest
tree closely related to Glochidion ram@orum, a tree
that typically occurs in disturbed forests of the
lowlands. Also common on these slopes are Neo-
nauclea forsteri (afa), which is a secondary forest
canopy species, and Syzygium samoense.
Some of the ridge top from the TV transmitter to
the beginning point of the old trail down to Vatia is
currently dominated by thickets of Hibiscus tiliaceus
(fau). This tree is common in many types of habitats,
especially disturbed ones, and its presence is probably
the result of previous cultivation along the stretch of
ridge. Most of the rest of the ridge in this area is open
montane forest consisting of scattered trees growing
out of a dense ground cover.
The distinction between the lower limit of the
montane forest and the upper limit of lowland forest is
not very clear, because there is a zone of variable
width where the characteristic species of the two
communities share dominance. In plot 11 (Appendix
B) at 350 m elevation, for example, the five dominant
trees were Calophyllum neo-ebudicum, Syzygium
inophylloides, and Buchanania merrillii, which are
lowland forest species, and Syzygium samoense and
I-lernandia moerenhoutiana, which are montane forest
species.
In undisturbed montane forest, the ground cover is
often dense, and is comprised of shade tolerant ferns.
The most characteristic and abundant species is
probably Lomagramma cordipinna (Fig. 24); other
common species include Asplenium nidus, Asplenium
polj~odon, Trichomanes spp., and Microsorium
.sy/vdicum.
Other plants present in the forest floor of montane
Sorest include Angiopteris evecta (king fern, nase),
Murallia smithii, and Cyathea vaupelii (olioli).
Angiopteris and Marattia are very similar to each
other-they have long thick fronds arising from a
thick base. Cyathea is a small tree fern. These
ferns are present in both undisturbed and dist-
urbed forest. Also common in these places are
Zingiber zerumbet (wild ginger, 'avapui), Helico-
nia laufao (laufao), and Cordyline fruticosa (ti).
Native grasses such as Centosteca lappacea (sefa),
Oplismenus compositus, and Cyrtococcum
oxyphyllum are also found in montane forest, most
often in clearings or along trails.
In the disturbed montane forest on Alava ridge,
the native, shade tolerant ferns are outcompeted in
the sunny conditions by introduced, weedy
heliophytic species, the most common of which
are Mikania micrantha (fue saina), Clidemia hirta,
and Paspalum conjugatum (vao lima). Mikania is
a vine that grows over low vegetation and even up
in the lower branches of trees. Clidemia is a
noxious shrub that is uncommon in lowland forest,
but very common in the summit scrub community
of Ta'u (although it apparently did not reach that
island until after 1976). Also common here are the
two Freycinetia species, which often form dense
tangles that are traversed only with difficulty.
The amount and variety of epiphytes is another
characteristic that serves to distinguish montane
forest from lowland forest. The difference is not
only in the amount or biomass of epiphytes, but
also in the number of species present. The
montane forest is the most floristically diverse on
Tutuila, not only for epiphytes, but also for trees
and ground cover species. Because of the cooler,
conditions in the montane forest, there is a pro-
fusion of epiphytes that are mostly absent from
lowland forest. By far the most important epi-
phytes are ferns and orchids. Only one epiphytic
vascular plant species reported here was neither a
fern (or fern ally) nor an orchid-Procris pedun-
culata, a member of the nettle family. It was not
very common, however.
Many of the trees on the less disturbed parts of
Alava Ridge are covered with epiphytes. The
most characteristic fern is probably Trichomanes
humile, a filmy fern that cannot exist in drier
forests. Also common are Hymenophyllum
imbricatum (another filmy fern), Hymenophyllum