Changes in island biota - The Great Barrier Reef: An Environmental History - page 211

degradation of the eastern foreshore of that island - concluded that eradication
programmes, if well organised and conducted with sufficient resources, were an
appropriate means of managing the problem of overgrazing by goats . 26
The impacts of goats on the islands on which they were introduced have
been contested. Brennan (1988) argued that the degradation caused by goats
occurred primarily to grasses and that trees were comparatively unscathed; he
also argued that grass communities at several islands recovered quickly after the
eradication of goats was completed. However, Brennan (1988) considered only
continental islands, whereas oral history evidence suggests that the cays that
supported goat populations were severely degraded by overgrazin g. 27 I n addition,
the documentary evidence presented above suggests that, even at the continental
islands, substantial damage was inflicted by goats to many vegetation species,
including Pandanus and Pisonia trees. Furthermore, additional environmental
impacts that have been described above - including the import of ticks and
the disturbance of gull and bridled tern nesting sites at Lady Musgrave Island -
were also attributed to the goat populations. Together, those impacts probably
constitute a substantial modification of several island habitats.
Nonetheless, after the eradication of the goats, some recovery of the island
vegetation occurred. At Lady Musgrave Island, Curtis stated that when he
visited the island in 1966, significant re-growth of vegetation had occurred . 28
The recovery of vegetation at Lady Musgrave Island was described by A. B. Gibb
in 1975:
The removal of goats has led to a marked increase in ground cover plants.
Bare shingle edges and ridges of conglomerate exposed by guano mining had
been fairly conspicuous features of the cay during the 1969 visit but are now
mostly obscured by ground cover plants. There appears to have been a marked
increase in the area occupied by the two thickets of Caesalpinia bonduc . The
smaller patch is at present approx. 90 × 65 ft. and the larger approx. 330 ×
215 ft. During the 1969 visit nearly all aerial roots of Pandanus had their
apices damaged by goats and failed to reach the ground. Aerial roots are
now developing normally. Several groups of Casuarina seedlings were seen
whereas none were noted in 1969. Casuarina branches frequently sweep the
beach area whereas previously all were trimmed to the maximum height of
the goats' reach. In addition to species noted in 1969 the following native
or naturalised species were noted in 1975: Argemore ochroleuca , Boerhavia
repens , Euphorbia tannensis , Panicum spp. [and] Tournefortia argentea . 29
The consequences of the extensive, prolonged damage caused by goats at
Lady Musgrave Island are uncertain; no evidence was found to indicate whether
vulnerable or rare plant species recovered after the animals had been removed
from the cay. The destruction of vegetation by goats, however, may have caused
significant changes in the vegetation communities of several islands in the Great
Barrier Reef.