had a predictably marked effect on seed dispersal
on Guam (Rainey et al. 1995). Thus, while habitat
removal is again a key driving force of plant reduc-
tions and extinctions, a broad array of factors and
their synergistic interactions is at work.
In illustration of how differing factors have pri-
macy in different situations, we can turn to Tahiti,
where the overriding threat to endemic plants cur-
rently takes the form of another plant species. Tahiti
is in the Society Islands (Polynesia), and is a large
(1045 km^2 ), high (2241 m) island, of diverse habi-
tats, with a native flora of 467 species, 45% of which
are endemic (Meyer and Florence 1996). Some 70%
of the endemic plants occur in the montane cloud
and subalpine forests, which are some of the
largest, finest, and most intact to be found through-
out the Pacific. The Polynesians colonized Tahiti
perhaps 2000 years ago, bringing with them about
30 domestic and 50 other accidental plant introduc-
tions. European arrival in the AD1760s led to mas-
sive resource overuse, and habitat loss, as well as a
great flood of exotic plant species—in excess of
1500 now being known for the Society Islands.
Many of these have become naturalized, and some
have become problem plants. The lowlands and
coastal zones were totally transformed by people,
and such native forests as remain on Tahiti are
endangered by pressures such as housing, agricul-
ture, forestry (e.g. based on exotic Pinus caribbea),
feral animals, and hydroelectricity schemes.
Yet, the highlands of Tahiti remained essentially
intact until the arrival of what has become the
worst of all exotic ecosystem transformers, Miconia
calvescens, a small tree species introduced to the
ornamental gardens in 1937. In less than 50 years it
had spread to all the mesic habitats between 10 and
1300 mASL, including the montane cloud forest,
often forming pure stands. It now covers over two-
thirds of the island of Tahiti, and has spread to the
nearby islands of Moorea and Raiatea. It is a poten-
tial problem for other islands in the region, and is
already recognized as one of the 86 plant pests of
Hawaii, having been introduced there by horticul-
turalists as recently as the early 1970s. It is an effec-
tive invader thanks to traits such as: tolerance to a
wide range of germination conditions, tolerance of
low light levels, fast growth, early reproductive
maturity, prolific year-round seed production, and
efficient dispersal by small introduced passerines
such as the silvereye (Zosterops lateralis). In Tahiti
alone, 40–50 endemic plant species are considered
to be threatened directly, including 8 species of
Cyrtandra, 6 Psychotria, and 2 Fitchia.
What can be done to halt this decorative invader?
One approach is to dig it out. In 3 years (1992, 1993,
and 1995), nearly half a million plants were
uprooted by hand, and Miconiawas cleared out of
its bridgehead sites on the island of Raiatea. In addi-
tion to such plain labour, Meyer and Florence (1996)
promote the need for a systematic assessment and
inventory of alien and endangered native species,
for research, monitoring, and control programmes,
and for ex situconservation in the botanic gardens—
which still remains only an ornamental garden. Part
and parcel of such an integrated approach to con-
servation, as commonly advocated in other similar
studies, is a sustained educational programme.
The problem posed by invasive exotic plants may
be first and foremost for native plant species but, if
on sufficient scale, can also present a problem for
native fauna (Cronk and Fuller 1995). For instance,
the now pantropical shrub Lantana camaraforms
dense impenetrable stands in parts of the
Galápagos, threatening both some endemic plant
species and the breeding habitat of an endangered
bird, the dark-rumped petrel (Pterodroma phaeopy-
gia) (Trillmich 1992). Invasive plants may alter the
environment in other, more subtle ways (Cronk and
Fuller 1995). The shrub Myrica faya, native to
Macaronesia, was introduced to Hawaii in the late
nineteenth century, and has since been spread
within the National Park, especially by an exotic
passerine, the white-eye (Zosterops japonica), and by
feral pigs. It has a highly effective nitrogen-fixing
symbiont, which in part accounts for its ability to
out-compete the native flora. By increasing nitro-
gen inputs relative to native species by 400%, it
alters the nutritional balance of the Hawaiian soils.
It poses considerable management problems and is
predicted to have additional long-term conse-
quences because the altered soil nutrient status is
likely to facilitate the spread of other alien species
(Vitousek et al. 1987b; Cuddihy and Stone 1990;
Vitousek 1990). For further details see Box 11.4.318 ANTHROPOGENIC LOSSES AND THREATS TO ISLAND ECOSYSTEMS