PATTERNS OF LOSS ACROSS ISLAND TAXA 317timber and fuel, the introduction of alien plants,
and clearance for cultivation, plantations, and pas-
ture (Cronk 1989). No native mammals occurred on
the island, as is typical of remote oceanic locations.
The Portuguese introduced goats, pigs, and cattle,
principally to supply homeward-bound carracks
from India, and also brought with them rabbits,
horses, donkeys, rats, and mice. Within 75 years of
their introduction, goats had formed vast herds,
devastating the vegetation.
The introduction of exotic plants began in earnest
in the nineteenth century by way of British colonial
botanic gardens, in part to provide a new plant
resource to replace the exhausted native cover.
Large numbers of herb and shrub species were
introduced, along with timber trees such as Pinus
pinasterandAcacia melanoxylon. By the time the first
reliable botanical records were made in the nine-
teenth century most of the destruction had already
occurred, but some documentary evidence, and the
relict occurrence of endemic plants in isolated
places such as cliffs, provide some indications of
the former cover. Of the 46 endemic plants known
from the island, 7 are considered extinct, the rest
threatened (Groombridge 1992; compare with
Table 11.8). Some species are restricted to only a few
individuals, and in the early 1980s Nesiota elliptica
andCommidendrum rotundifoliumwere reduced to
just single plants, the latter becoming extinct in the
wild in 1986 (Cronk 1989).
Goats have been particularly important in pre-
venting woodland regeneration by grazing and
barking saplings. So, as old trees were cut for fire-
wood, areas became converted to a mosaic of
anthropogenic formations, notably grassland and
Opuntiascrub. Erosion has been very rapid, and on
decadal timescales, isolated thunderstorms cause
sheet and gully erosion where the vegetation cover
has been removed by herbivores. After such ero-
sion little vegetation cover can re-establish. Goats
were nearly shot out in the early 1970s and all
domestic goats are kept penned by law; however,
sheep were still allowed to roam freely. Cronk
(1989) considers that a process of rehabilitation is
possible, based on trial plantings of native species,
but that initially, at least, plantings require protec-
tion by fencing.
Turning to one of the showcases of plant evolu-
tion, Wiles et al. (1996) provide estimates for Hawaii
of about 100 extinct taxa, 200 endangered or threat-
ened, and a further 150 recommended for listing;
however, 282 species appear on the list of federally
endangered plants (Cox and Enquist 2000), and yet
another estimate is given in Table 11.8. Although
different criteria generate different numbers, it is
clear that a disproportionate number of Hawaii’s
plant species are in trouble: for instance, the figure
of 282 contrasts with 486 on an equivalent list for
the mainland USA (Cox and Enquist 2000).
Numerous introduced plant species have become
naturalized on Hawaii, to the point at which the
exotic flora outnumbers the endemic flora. Several
have become serious pest species (Primack 1993).
In the Marianas (Micronesia) the forces involved
in the demise of native vegetation include loss of
forest to agriculture; war and development; the
introduction of alien animals, plants, and plant
pathogens; alterations to the fire regime; and
declines in animal pollinators and seed dispersers.
The impacts on several native plant species have
been severe. Serianthes nelsonii(Leguminosae) is
one of the largest native trees, and is endemic to
Rota and Guam. It formerly occurred on volcanic
soils but is now restricted to limestone substrates.
Wiles et al. (1996) reported that just 121 adult trees
survived on Rota, and 1 on Guam. The populations
were senescent, with little or no regeneration occur-
ring, and the main threats were from browsing by
introduced deer and pigs, plus infestations of her-
bivorous insects (Wiles et al. 1996). On Guam, sev-
eral plant species were found to be showing poor
regeneration for these same reasons, and in one
case at least, germination problems limit re-estab-
lishment. It appears that the seeds of Elaeocarpus
joganeed to pass through the gut of a bird, yet
native frugivores have been wiped out by the intro-
duced brown tree snake (Boiga irregularis)
(Box 11.3). Another species, Pisonia grandis, is rarely
seen with fruit, perhaps because of the loss of
native pollinators such as fruit bats or birds. In
addition to impacting on seed set and germination,
the loss of frugivorous birds and the reduction of
the one extant pteropid fruit bat species to a rem-
nant population of a few hundred animals have