Invasive alien species

Q&A

Invasive alien species Frangula alnus
Description

F. alnus is a deciduous shrub or small tree usually 4-5 m in height (Tutin et al., 1968), but may grow to 7 m (Gleason, 1963). It develops an erect, slender habit with branches somewhat irregular in alternate pairs, ascending at an acute angle to the main stem (Godwin, 1943). Young twigs are green but turn grey-brown with age and develop red-brown to dark violet tips. Lenticels may be evident as white dots and stripes. Lemon-yellow inner-bark tissues are exposed when the outer-bark is damaged and the young wood is dark brown. Old bark is smooth, except in very old specimens, and readily peels off dead wood. Spines are absent from F. alnus. Leaves are petiolate, obovate in shape, 2-7 cm in length and usually little more than half as wide. They are cuspidate to acuminate in shape, typically ending with a short pointed tip. Leaf margins are entire but wavy, although in seedlings leaves may be serrated. The lower surface of young leaves is pubescent, being covered with dense brownish hairs which are later shed so that older leaves are glabrous and shiny green in colour. Sun leaves are relatively broader and more shiny than shade leaves. The leaves turn yellow, then red in the autumn. Lateral veins are conspicuous on the upper surface of the leaves with 6-12 (commonly 7) pairs running more or less parallel to each other.
F. alnus develops sessile umbels in the leaf axils on young wood with 2-8 flowers borne on stout, unequal, glabrous pedicels 3-10 mm long;occasionally single flowers develop. Individual flowers are greenish-white, about 3 mm in diameter and bisexual. The flowers are 5-merous with broadly obovate petals 1-1.4 mm long and cleft at the tip (Gleason, 1963). Fruits are 6-10 mm in diameter, and change from green to red, then to violet-black on ripening;flowering and fruit development are rather asynchronous, hence all stages of ripening may be present. Each drupe usually contains 2, but occasionally 3, pyrenes or stones which are broadly obovoid in shape, about 5 mm long and 2 mm thick;they have a faint ridge running down the inner face and a deep furrow at the base. Young and Young (1992) report 52 seeds/g for F. alnus. Germination is hypogeal (Godwin, 1943).

Impact

F. alnus was introduced to North America from Europe more than 100 years ago. Once established it maintains itself due to prolific seed production, vigorous growth over an extended growing season and its ability to regenerate following burning and cutting. These characteristics make it difficult to eradicate. Repeated cutting and application of herbicides required to eliminate F. alnus is laborious and expensive. Consequently, most restoration work has been conducted in natural ecosystems of special interest. Its adverse effect on native species arises because F. alnus shades out understorey plants. Its aggressive character, especially in wetlands, is widely noted (Catling and Porebski, 1994).

Hosts

F. alnus is a problem species in native communities because it establishes in dense stands which shade out other understorey species. Possessky et al. (2000) reported a reduction in composition and abundance of the herbaceous cover in riparian habitats in the northern Allegheny Plateau (of Pennsylvania, New York and Ohio, USA) following invasion by F. alnus. Similarly, Reinartz (1997) described how an undisturbed bog community in Wisconsin was invaded by F. alnus in 1955 with a dense tall shrub canopy dominating the site within 12 years. The species is listed as an invasive weed in Tennessee and Wisconsin, USA (Southeast Exotic Pest Plant Council, 1996;Hoffman and Kearns, 1997). F. alnus was recently rated as one of the six principal invasive aliens of wetlands in Canada, and one of four principal invasive aliens in Canadian uplands. In a national survey it was rated second to purple loosestrife (Lythrum salicaria) with respect to the extent to which it is spreading in natural habitats and its severity of impact in Canada (White et al., 1993).
F. alnus is associated with crown rust (Puccinia coronata) which infects several cool season turfgrasses, native grasses and cereals. The uredia, telia and basidiospores are produced on the graminoid hosts, the aecia and pycnia are produced on F. alnus (and Rhamnus cathartica;Partridge, 1998). Alfalfa mosaic virus, which infects a wide variety of plants, including crops, and is vectored by aphids, has also been isolated from young leaves and root cuttings of F. alnus in Italy (Marani and Giunchedi, 2002).


Source: cabi.org
Invasive alien species Senna spectabilis, Yellows Short, Long
Description


Tree to 10 or more metres high, the branchlets usually tomentose when young. Leaves moderately large, an average leaf about 20-foliolate;petiole short, pubescent, eglandular;rachis usually about 2 dm. long, eglandular and otherwise like the petiole;leaflets several to many pairs, lanceolate, 3-8 cm. long and usually about 2 cm. wide, acute apically, obtuse basally, pubescent below, especially along the veins, puberulent to subglabrous above and less dull than below, opposite on the rachis, with 10 or more pairs of prominent lateral veins;petiolules 2-3 mm. long, pubescent. Inflorescence of several terminal or subterminal several-flowered racemes;bracts lanceolate, a few mm. long, caducous. Flowers yellow;sepals 5, obovate-orbicular, markedly unequal, up to 1 cm. long and broad, glabrous to lightly puberulent;petals 5, mostly obovate, markedly unequal, up to 2.5 cm. long and 1.5 cm. broad, subglabrous, venose, short-clawed;stamens 10, 3-morphic;the 3 lowermost the largest, their anthers oblong, about 7 mm. long, short-rostrate apically and dehiscent by terminal pores, the loculi somewhat converging terminally;anthers of 4 median stamens 5-6 mm. long, similar to the 3 lowermost except the rostrum reflexed and the loculi divergent terminally;3 uppermost stamens markedly dissimilar, more or less rudimentary, the anthers distinctly bilobed, each lobe reniform and dehiscent the length of its outer margin;ovary linear, glabrous. Legume linear, turgid-quadrangular, up to 2 dm. long and 1 cm. wide, transversely multiseptate, tardily dehiscent along one margin (Missouri Botanical Garden, 2014).

Impact

S. spectabilis is a medium to large tree from tropical America, listed in the Global Compendium of Weeds as an ‘environmental weed’, ‘garden thug’, and ‘naturalised weed’ (Randall, 2012). The species is extremely fast-growing, flowers and sets seed profusely, and re-sprouts readily when cut (Mungatana and Ahimbisibwe, 2010). In Australia it is considered naturalized, has been recorded as a weed of the natural environment and an escape from cultivation, and is labelled an invasive species, indicating its high negative impact on the environment due to its ability to spread rapidly and often create monocultures (Randall, 2007). In Uganda, the species is considered an invasive alien species with high risk to the native flora (Mungatana and Ahimbisibwe, 2010). In Singapore S. spectabilis has been identified as a casual, spontaneous exotic species that survives outside cultivation but does not form self-replacing populations, and relies on repeated introductions or limited asexual reproduction for persistence (Chong et al., 2009). The species is a cultivation escape in Trinidad and Tobago (Irwin and Barneby, 1982) and is considered an invasive species in Cuba (Oviedo-Prieto et al., 2012).

Hosts


Agroforestry experiments in Kenya showed that while S. spectabilis is useful as hedges for cropping systems, if grown in semi-arid conditions S. spectabilis will out-compete crops for water uptake and suppress crop yields;in the cases recorded, grain yields of maize grown with S. spectabilis or Leucaena leucocephala were reduced by between 39% and 95% (Noordwijk et al., 2004).


Source: cabi.org
Invasive alien species Pinus elliottii
Description

P. elliottii var. densa differs in a number of ways from var. elliottii (Little and Dorman, 1954);it is characterized by a grass-like, almost stemless stage that lasts for 2 to 6 years. It has a restricted range, a less desirable tree form than var. elliottii, and is more difficult to regenerate. As a result, almost all information available relates to var. elliottii.

Impact

Pinus elliottii var. elliottii, commonly known as slash pine, is an important timber tree species native to the lower coastal plain within the southeastern USA. Trees grow up to 36 m in height and 0.9 m in diameter, producing a long, clear bole. Because of its rapid early growth and production of highly valuable wood products, it has been widely introduced into other countries. As an exotic, it is used in Africa, especially southern Africa, and in Australia and South America for various products, ranging from lumber to pulpwood. In Brazil, P. elliottii makes an important contribution to the resin production industry. Where it has been planted outside its native range it has escaped from cultivation and become naturalized, and in some areas become an aggressive invasive weed, threatening native species and ecosystems. Trees can form dense stands that shade out other plant species.

Hosts

P. elliottii can form dense stands that shade out other plant species. In Australia it is particularly common in eucalypt woodland areas. In Hawaii, Poa mannii, a federally listed endangered endemic grass growing only on the island of Kauai, is threatened by competition from P. elliottii and other alien invasive plant species (US Fish and Wildlife Service, 2010).


Source: cabi.org

Non-indigenous species, subspecies or lower taxa whose establishment and spread threaten ecosystems, habitats or species with economic or environmental harm.