Clidemia hirta (L.) D. Don (Melastomataceae)

Neotropical bird-dispersed shrub introduced to many parts of the tropics. Considered a weed on many oceanic islands where it forms dense thickets and suppresses most ground vegetation. Even small stands are impossible to eradicate.


Species characteristics

Life form, size, lifespan

Densely-branched shrub up to 5 m tall but normally between 0.5 and 3 m.

Taxonomy, variation and plasticity

A taxonomically difficult genus and the plant has sometimes been misidentified. Varieties of C. hirta have been described. Var. hirta and var. elegans were introduced to Hawai'i and the Seychelles respectively.

Reproductive biology

Several white or pinkish flowers borne on axillary or terminal cymes. A mature plant can produce over 500 blue-black berries (6-9 mm long) per year each containing over 100 seeds (0.5-0.75 mm long). Seeds form a very large seedbank where they remain viable for up to 4 years. In Hawai'i, long distance dispersal is carried out by humans and seeds are locally-disseminated by birds and feral pigs which can also carry seeds in their fur. In Hawai'i flowering and fruiting occurs all year round where there is no dry season and rainfall exceeds 2500 mm.yr-1. In areas where a dry season occur flowering ceases.

Resilience and resistance

In windy areas the shrub is scrambling and is less than 1 m tall. Resistant to drought lasting up to 6 months although some shoot tips die back during the dry season. It does not appear to tolerate salt-spray. On the ground of rain forests detached leaves can root.

Environmental requirements and successional status

In the native range it is an early coloniser of disturbed areas and is rapidly replaced by vines. Tolerates full sun light as well as complete canopy cover.

Products and uses

Has no fodder value and no known uses.


Status in native range

Range and abundance

Widely distributed in Central and South America and the Caribbean islands where it is not a very common plant.

Climate

Broad climatic requirements ranging from dry to wet tropics.

Site requirements

It is an early colonizer of open areas, including slash-and-burn agricultural grounds, where it becomes dominant twelve months after disturbance before being smothered by vines. It is found in low densities in open forested areas, forest plantations, and roadsides. In Jamaica its altitudinal distribution ranges between 30 and 1200 m a.s.l.

Weediness

Not weedy but said to be common in Jamaica in moist pastures.

Pests and diseases

All plants show signs of heavy herbivory.


Status in invaded regions

History of introductions and intensity of invasions

C. hirta is a serious weed on many tropical oceanic islands (e.g. Fiji, Seychelles), southeast Asia, India and East Africa. The date of introduction to Hawaiian Islands is unknown and it was first recorded in 1941. It was grown in the Wahiawa Botanic Garden and was thought to be "very promising because it won't be spread by birds". It was first noted as escaping in 1949 on the island of O'ahu and by 1952 covered at least 100 ha. By the late 1990s it had invaded all suitable habitats covering over 100,000 ha. In the 1970s and 1980s it was accidentally introduced by humans to five other Hawaiian islands. On Fiji C. hirta was probably accidentally introduced prior to 1890 with coffee plants imported from British Guiana. It became a pest by 1920.

Patterns of invasion and time-lag

In Hawai'i all new spread occurs in disturbed areas such as roadsides and landslides and following disturbance by windstorm, pigs and fire. If seeds are present they germinate rapidly and within two years the disturbed area can become smothered. However, on the steep slopes of the Seychelles enough light reaches the ground for C. hirta regeneration to take place without forest canopy disturbance. Although this species is rarely recorded until it forms monotypic stands, the more recent Hawaiian introductions suggest that it starts to spread as soon as it is introduced to new suitable habitats subjected to regular disturbance.

Site and climate

C. hirta tolerates widely differing tropical climatic conditions including a wide range of rainfall (<1000 to > 2500 mm). On the Seychelles the shrub is absent from drier areas.

Floristic region and vegetation types

Most tropical island forest areas appear to be susceptible to C. hirta invasion regardless of their floristic composition as long as some form of disturbance affects them.

Pests and diseases

It is only affected by one insect introduced as a biocontrol agent.

Impact on ecosystem

Under heavy infestations of C. hirta most plant, including most mosses and liverworts normally found in shaded habitats and subcanopy species, are displaced. It is thought that the species has the potential of driving some species to extinction.

Impact on humans and related activities

In Hawai'i the plant is despised because of its dense growth. Its growth along trails and roadsides increases maintenance costs as well as reduce the aesthetic, educational and recreational value of forest lands. In Fiji it renders large areas of grazing land useless and interferes with the development of plantations (rubber, cocoa).

Control

Biological control, using the thrips Liothrips urichi, was initiated in Fiji in the early 1930s and much later in Hawai'i. The introduced insect seriously affect the growth of C. hirta in open sunny areas whereas in shaded areas (forest or frequent cloud cover) it is not effective. The only hope of controlling an invading population of C. hirta is to identify the problem at a very early stage and eradicate all seed-sources. In Hawai'i repeated efforts to control seedlings in expanding populations have failed.


Ecological differences

Existence of ecological equivalent species and competitive interactions in invaded regions

No ecological equivalent appears to exist.

Differences in status and ecology between invaded and native ranges

C. hirta suffers from heavier insect herbivory and subjected to strong competition from other Melastomataceae and vines in its native range. In the native range the species is purely an early successional species whereas in parts of its invaded range it can become established below forest canopy. In Hawai'i the shrub grows taller.


Selected references

* Gerlach, J. (1993) Invasive melastomataceae in Seychelles. Oryx 27, 23-26.
Gleason, H.A. (1939) The genus Clidemia in Mexico and Central America. Brittonia 3, 97-140.
* Markin, G.P., Lai, P.-Y. & Funasaki, G.Y. (1992) Status of biological control of weeds in Hawai'i and implications for managing native ecosystems. In Stone, C.P., Smith, C.W. & Tunison, J.T. (Eds) Alien plant invasions in native ecosystems of Hawai'i: management and research, pp. 466-482. University of Hawaii Press, Honolulu.
** Nakahara, L.M., Burkhart, R.M. & Funasaki, G.Y. (1992) Review and status of biological control of clidemia in Hawai'i. In Stone, C.P., Smith, C.W. & Tunison, J.T. (Eds) Alien plant invasions in native ecosystems of Hawai'i: management and research, pp. 452-465. University of Hawaii Press, Honolulu.
* Sheil, D. (1994) Naturalized and invasive plants in the evergreen forests of the East Usambara Mountains, Tanzania. Afr. J. Ecol. 32, 66-71.
**Smith, C.W. (1992) Distribution, status, phenology, rate of spread, and management of Clidemia in Hawai'i. In Stone, C.P., Smith, C.W. & Tunison, J.T. (Eds) Alien plant invasions in native ecosystems of Hawai'i: management and research, pp. 241-253. University of Hawaii Press, Honolulu.
* Wee, Y.C. & Corlett, R. (1986) The city and the forest. Singapore University Press, Singapore.
** Wester, L.L. & Wood, H.B. (1977) Koster's curse (Clidemia hirta), a weed pest in Hawaiian forests. Environ. Conserv. 4, 35-41.

Pierre Binggeli

May 1997