Tristan da Cunha Is. (sub-Antarctic) (Saint Helena)
棲地改變: One of the most intrusive plant invaders is Phormium tenax, a large, long-lived species that has the potential to transform the vegetation over large parts of the islands, which could negatively impact on seabird nesting sites (Ryan et al. 2007a).
威脅瀕危物種: The global population of the 'Critically Endangered (CR)' Elaphoglossum dimorphum, is smaller than 50 mature individuals, comprising two subpopulations in Diana’s Peak National Park (St Helena). The main threat to the species is encroachment of invasive exotics such as Phormium tenax (Eastwood 2004). The 'Endangered (EN)' small bellflower (see Wahlenbergia angustifolia ) and the 'Critically Endangered (CR)' large bellflower (see W. linifolia) are unique endemics of Saint Helena flora. A continuing decline in both species is predicted if over-crowding by other species such as Olea africana and P. tenax and declining quality of habitat continue. W. linifolia is facing an extremely high risk of extinction in the wild in the immediate future, as the population is estimated to number less than 50 mature individuals. At High Peak P. tenax continues to invade and out compete the small subpopulations of W. linifolia . The rampant spread of flax and fuchsia which are able to colonise ledges and gaps in the tree ferns are considered to be the principal causes for the decline of the large bellflower (Cairns-Wicks 2003a; 2003b). The 'Vulnerable 'VU' endemic Tristan bunting (see Nesospiza acunhae ) and the 'Vulnerable 'VU' endemic grosbeak bunting (see Nesospiza wilkinsi ) are also negatively impacted by flax and permanently at risk from the accidental introduction of mammalian predators which could prey on eggs, chicks and nesting birds (BirdLife International 2008a).
棲地改變: The 'Critically Endangered (CR)' endemic She cabbage tree (see Lachanodes arborea ) has a high probability of becoming extinct in the wild within the next 10 years. Its former habitat range cleared for pasture and New Zealand flax plantation (Cairns-Wicks 2003g).
競爭: The 'Endangered (EN)' dogwood (see Nesohedyotis arborea ) (Cairns-Wicks 2003c) and the 'Critically Endangered (CR)' He cabbage tree (see Pladaroxylon leucadendron ), with a patchy distribution across Diana’s Peak National Park and at High Peak (Cairns-Wicks 2003d).
The 'Vulnerable (VU)' endemic black cabbage tree (see Melanodendron integrifolium ) faces threats due to its small distribution and the threat of competition with P. tenax. M. integrifolium is dependent upon the maintenance of consistent alien plant control and conservation management (Cairns-Wicks 2003e).
The 'Critically Endangered (CR)' endemic false gumwood (see Commidendrum spurium ) is known from just two isolated subpopulations with a total wild population of eight plants. Previous habitat loss occurred through land clearance making way for pasture and New Zealand flax P. tenax plantations (Cairns-Wicks 2003f).
Inaccessible Is. (sub-Antarctic) (Saint Helena)
棲地改變: Some 23 introduced plants occur on the island including New Zealand Flax Phormium tenax. P. tenax, a large, long-lived species has the potential to transform the vegetation over large parts of the islands, which could negatively impact on seabird nesting sites (Ryan & Glass 2001; Ryan et al. 2004; Ryan et al. 2007a).
Another threat is the invasion of the introduced New Zealand flax into areas of Phylica arborea resulting in the possible degradation of its habitat. Its preferred Phylica woodland habitat regenerates rapidly and is subject to storm damage. A further potential threat is the introduction of alien invertebrates or pathogens which could change food sources or reduce the seed set of Phylica (BirdLife International 2008b).
降低本地生物多樣性: The 'Vulnerable 'VU' grosbeak bunting (see Nesospiza wilkinsi in IUCN Red List of Threatened Species) is an endemic bird threatened by habitat degradation due in part to the introduction and spread of invasive species. It is permanently at risk from the accidental introduction of mammalian predators which could prey on eggs, chicks and nesting birds.
Nightingale Is. (sub-Antarctic) (Saint Helena)
棲地改變: Both Inaccessible and Nightingale Islands have a number of introduced plant species, of these, Phormium tenax has the potential to alter the structure and function of vegetation communities of the islands (Ryan & Glass 2001, in Ryan et al. 2007b). Transformation of vegetation over large parts of the islands, could negatively impact on seabird nesting sites (Ryan et al. 2007a).
降低本地生物多樣性: Although less abundant than on Inaccessible, New Zealand flax is spreading into surrounding vegetation, including among dense Spartina tussock and under Phylica woodland. These ponds offer breeding habitat for large numbers of 'Endangered (EN)' endemic Atlantic Yellow-nosed Albatrosses (see Thalassarche chlororhynchos in IUCN Red List of Threatened Species), whereas the Phylica trees are essential habitats for the 'Vulnerable (VU)' endemic Grosbeak Bunting (see Nesospiza wilkinsi in IUCN Red List of Threatened Species) (Ryan et al. 2007b).