american samoa - University of Hawaii at Manoa

APPENDIX E. PLANTS AS INDICATORS OF PAST LAND USE
Prior to the arrival of the first Polynesian settlers,
most of the surface area of the Samoan archipelago
was covered with native rainforest vegetation. The
only areas with vegetation not classified as rain-
I'orcst were littoral communities, summit vegetation
(montane scrub and summit scrub communities),
recent lava flows and ash deposits, and disturbed
vegetation. Nowadays over half of the vegetation of
the islands is classified as disturbed or secondary (as
opposed to primary), a figure that has been rising in
recent years because of the expansion of agriculture
to meet the needs of an expanding population and
because of a forestry industry that has devastated the
lowlands of the archipelago (particularly in Western
Samoa). Prior to human settlement, all the disturbed
vegetation was natural, caused mostly by hurricanes
and landslips, and possibly by occasional forest
fires. Nowadays, however, most of the disturbed
vegetation is the result of human activities such as
agriculture and the development of villages. The
disturbed communities recognized in the present
report are managed land vegetation, secondary
scrub, and secondary forest.
It is sometimes useful to know the past uses of an
area of land. In order to set lease prices within the
park, there is a need to determine which areas are
currently or were historically used for agriculture.
This was done mainly by the use of aerial photo-
graphs and the maps of Cole et al. (1988). More
accurate studies involve the structure and floristic
composition of the vegetation. Native Samoan plant
species require certain environmental conditions for
germination and growth, and it is often possible to
determine the recent historic uses of the area by
analyzing the species composition, community
structure, and population dynamics of an area of
vegetation. This is most easily done by looking for
indicator species, plants that are indicative of a
certain type of human activity or climatic event.
The most obvious sign of recent disturbance is the
dominance of herbaceous vegetation. The only kind
of natural vegetation in Samoa that is herbaceous is
in littoral areas (herbaceous strand) and montane
scrub (which is characterized by ferns and climbers
dominating the ground between scattered trees and
shrubs). The most common species in the recently
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disturbed areas, most of which are abandoned taro
or banana plantations, are Mikania micrantha
(mile-a-minute vine, fue saina), Bidens alba
(beggar's-tick), Paspalum conjugatum (T-grass, vao
ha), and Nephrolepis hirsutula (sword fern, vao
tuaniu), but over 250 species that fit into this
category (weeds) have been recorded from Tutuila
(see Appendix A).
Several other species planted as ornamentals
sometimes remain significant long after cultivation
has ended. One such species, the mint Pogostemon
cablin (patchouli, patiale), sometimes forms dense
patches by vegetative means; it has not been
recorded from the Tutuila park, however. Other
weedy species are typical of forest trails. Axonopus
fissifolius and Eleusine indica (ta'ata'a) are often
found in lowland plantations and along trails in
lowland forest. Two other grasses, Oplismenus
compositus and Oplismenus hirtellus, are often
found in secondary forest and thus can be indicative
of past disturbance. Another two grasses, Cento-
steca lappacea (sefa) and Cyrtococcum oxyphyllum,
occur in primary vegetation, and are thus less
valuable as indicator species.
One species of fern, Dicranopteris linearis (false
staghorn fern, asaua), is a natural dominant species
in montane scrub (which is usually on trachyte soil),
but its presence in other places, such as ridges, is an
indication of past disturbance. There are only a few
areas (outside of montane scrub) on Tutuila that are
reported to be dominated by this fern. These are
probably areas of former plantations or villages on
ridges, from a period when the bulk of the Samoan
population lived inland (for protection from
marauders and enemies). The soil has been so
over-utilized and the soil minerals so depleted that
the native vegetation (mostly ridge lowland forest)
has never been able to recover. Similar vegetation is
found on 'Upolu, and is attributed to the same cause
(Wright 1963).
When managed land is left alone for long enough,
the herbaceous vegetation is shaded out by a number
of characteristic woody shrubs and trees. The most
typical of these are Pipturus argenteus (soga),
Omalanthus nutans (fogamamala), Macaranga