Management Information
Preventative measures: A Risk assessment of Clidemia hirta for the Pacific region was prepared by Pacific Island Ecosystems at Risk (PIER) using the Australian risk assessment system (Pheloung, 1995). The result is a score of 27 and a recommendation of: reject the plant for import (Australia) or species likely to be a pest (Pacific).
Physical: Manual weeding may be effective for small populations. In healthy ecosystems Clidemia hirta's dominance is a temporary phenomenon with forest trees overshading it within 7 years.
Ground disturbance created by feral pigs (Sus scrofa) plays a major role in the establishment of C. hirta and other populations of alien species in Hawaii (Smith 1993, Stone et al. 1993, in Peters 2001). These pigs are native to North Africa and Eurasia, including Malaysia, but are currently found on many oceanic islands and all continents except Antarctica (Lever 1985, in Peters 2001). They are omnivorous and obtain a substantial portion of their food by grubbing for roots, bulbs, fungi, invertebrates, and other belowground material (Aplet et al. 1991, Fensham 1993, Kotanen 1995, in Peters 2001). Severely grubbed areas may extend for more than a hectare, but are typically composed of many small (ca 1 m2) patches of ground disturbance. Through trampling, rooting, and preferential feeding, feral pigs in Hawaii have disturbed natural plant communities dramatically (Aplet et al. 1991, Stone 1993, in Peters 2001). Wild pigs may also act as agents of dispersal for introduced species including C. hirta(Stone and Loope 1987, in Peters 2001). Because of this link the possibility exists of controlling C. hirta by managing pig populations, especially at places where the link between soil disturbance and invasive plant spread has been established, such as at the Pasoh Forest Reserve (Malaysian peninsula).
Disturbance is a key element in the establishment and invasion of C. hirta. Wildfires, landslides, windstorms and other forms of soil disturbance (such as pig rooting) accelerate the dominance of this weed (Smith Undated; Peters 2001). In its native environment plants are confined to open areas and only become dominant about twelve months after disturbance, such as in slash-and-burn agricultural areas (Burkhart Pers. Comm, in Smith Undated). All new range extensions in Hawaii begin along the open edges of trails or other disturbed areas. In order to keep the weed out of an area the primary management objective should be to minimise and prevent disturbance (Smith Undated).
All efforts to eradicate newly established populations of C. hirta in Hawaii failed when they were not initiated before first fruit set (Smith Undated). There have been many well-meaning attempts by volunteer groups to control the spread of C. hirta through pulling it by hand, unfortunately the effort is likely to fail. The seed bank produced by these plants is colossal over a very short period of time (Smith Undated). In order to effectively control an infested area by mechanical means eradication efforts must be conducted at least once a year for up to 10 years. Only two instances of successful control, Kamakou (Moloka'i) and Pu'u Kukui trail (Maui) are known (Smith Undated). Clidemia is susceptible to a number of herbicides but will regenerate unless further applications are made. Chemical control does not appear to be practical in Hawaii's native ecosystems, particularly those difficult to access (Smith Undated).
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Location Specific Management InformationEast Usambaras (Tanzania, United Republic of)
Both Pyrostegia venusta and Selaginella species appear to spread purely vegetatively and become dominant, respectively, at ground and canopy level. To date the dispersal agent of all East Usambara invasives have been bird-dispersed and to a lesser extent wind-dispersed. Maybe with the exception of Clidemia hirta, all invaders of the natural forest have been associated with natural disturbance (treefall gaps) and/or human disturbance (pit-sawing gaps or industrial logging) whereas Pyrostegia venusta and Selaginella sp. spread regardless of the presence or absence of gaps and light intensity.
Probably the main issue relating to invasives in the East Usambaras concerns the Amani Botanic Gardens. They contain mainly exotic species many of which are spreading or could potentially spread into the surrounding natural forest which is rich in endemic species. In view of past and current experiences it is highly unlikely that a large collection of exotics can be maintained in harmony with rare endemics. Thus, swift action is required to remove many of these introduced species and also prevent the introduction of new ones, otherwise the nature reserve will ultimately become a heaven for the garden's exotics. Fiji
Climedia hirta was declared a noxious weed in Fiji in 1920. A biological control effort was begun in 1930 using a thrip, Liothrips urichi. Hawaii (United States (USA))
The only significant insect pest is a thrip Liothrips urichi (Thysanoptera: Phlaeothripidae), an introduced biocontrol agent). Plants are now found in forested areas and open situations where rainfall is high and cloud cover frequent. In open areas with high isolation Liothrips debilitates the weed sufficiently to control it. In shaded areas it is not so effective.
All efforts to eradicate newly established populations of C. hirta in Hawaii failed when they were not initiated before first fruit set (Smith Undated). There have been many well-meaning attempts by volunteer groups to control the spread of C. hirta through pulling it by hand, unfortunately the effort is likely to fail. The seed bank produced by these plants is colossal over a very short period of time (Smith Undated). In order to effectively control an infested area by mechanical means eradication efforts must be conducted at least once a year for up to 10 years. Only two instances of successful control, Kamakou (Moloka'i) and Pu'u Kukui trail (Maui) are known (Smith Undated).
The State of Hawai'i should intensify its public awareness campaign to prevent the dissemination of C. hirta and other weeds into new locations. Conservationists should coordinate their programs and reach out to other organisations to reinstill pride in Hawai'ian ecosystems, improve the quality of life and conteract the dominance of economic considerations as the only criterion in development and politics. Conservationists, scientists and hikers should record all alien species observed during excursions and report them in newsletters and other publications of local environmental interest groups. Hawaii (United States (USA))
Sierra Club trips to control this weed have been unsuccessful to date. DeWalt Denslow and Ickes (2004) planted C. hirta into understory and open habitats where it is native (Costa Rica) and where it has been introduced (Hawaii) and applied pesticides to examine the effects of fungal pathogen and insect herbivore exclusion. In understory sites in Costa Rica, C. hirta survival increased by 12% if sprayed with insecticide, 19% with fungicide, and 41% with both insecticide and fungicide compared to control plants sprayed only with water. Exclusion of natural enemies had no effect on survival in open sites in Costa Rica or in either habitat in Hawaii. Fungicide application promoted relative growth rates of plants that survived to the end of the experiment in both habitats of Costa Rica but not in Hawaii, suggesting that fungal pathogens only limit growth of C. hirta where it is native. Galls, stem borers, weevils, and leaf rollers were prevalent in Costa Rica but absent in Hawaii. In addition, the standing percentage of leaf area missing on plants in the control (water only) treatment was five times greater on plants in Costa Rica than in Hawaii and did not differ between habitats. The results from this study suggest that significant effects of herbivores and fungal pathogens may be limited to particular habitats. For C. hirta, its absence from forest understory in its native range likely results in part from the strong pressures of natural enemies. Its invasion into Hawaiian forests is apparently aided by a release from these herbivores and pathogens. Kaua`i Is. (United States (USA))
The Hawaii Division of Forestry has been sending crews to eradicate C. hirta on Mt Kahili (where it is fairly common) and another small population found recently along the Nounou Forest Reserve tree plantation trail. They have met little success so far. Moloka`i (Molokai) Is. (United States (USA))
Participants of the Sierra Club service trips began removing the plants along the trail in the spring of 1974. Oahu Is. (United States (USA))
The introduction of an effective biological control agent, should one be found, will require very careful evaluation prior to release as infestations of C. hirta are so heavy in some areas that the sudden loss of this weed could result in serious consequences. The loss of ground cover could cause erosion to become a serious problem. Alternatively the exposure of so much bare ground could provide a good seed bed for a number of other serious weeds, particularly the grasses Hilo grass (Paspalum conjugatum), broomsedge (Andropogon virginicus) and strawberry guava (Psidium cattleianum). Grasses would significantly increase the fuel load increasing the risk of bush fires. Strawberry guava would form an impenetrable thicket preventing the reestablishment of native species.
Wester and Wood (1977) recorded the domination of an area on O'ahu by clidemia within two years after a fire. Similar responses have been seen elsewhere on O'ahu after fire. Two years after Hurricane Iwa in 1981 (which disturbed much of the area along the Contour Trail in the Wai'anae Mountains on O'ahu) there was an almost impenetrable thicket of clidemia 3 m or more tall. Palau
It is recommended that C. hirta be evaluated to detect the extent of its distribution and to determine the possibility of its eradication. This species has not yet been targeted for control or eradication due to limited resources. Future work includes the development of management plans for each invasive plant species. Pasoh Forest Reserve (Malaysia)
Current land conversions at Pasoh are inconsistent with the expressed desire to maintain the ecological integrity of this site. Reunion (La Réunion) 
Two control methods are practiced in Reunion. The first is chemical control using Round-up ©. The result is relatively successful. The second method is physical control using machetes, but its impact on the plant seems to be very limited in the medium term. Shoots and seedlings re-emerge (Hivert, 2003). Seychelles
The management of an effective buffer zone should focus on large openings that may function as step stones for invasions (‘nascent foci’ sensu Moody and Mack 1988). An example is the opening around the former cinnamon distillery where problematic invasives such as Vielle fille (Lantana camara) or Faux vatouk (Clidemia hirta) build up propagule pressure.
Management Resources/Links
2. Hivert, J. 2003. Plantes exotiques envahissantes - Etat des méthodes de lutte mise en oeuvre par l'Office National des Forêts à La Réunion. ONF Réunion.
Summary: Synthèse des méthodes de lutte employées par l'ONF à la Réunion contre une vingtaine de plantes exotiques envahissantes. 3. Julien, M. H. (ed.) 1992. Biological control of weeds: a world catalogue of agents and their target weeds (3rd edition). CAB International, Wallingford, UK. 28pp. 4. Kueffer, C. and Mauremootoo, J., 2004. Case Studies on the Status of Invasive Woody Plant Species in the Western Indian Ocean. 3. Mauritius (Islands of Mauritius and Rodrigues). Forest Health & Biosecurity Working Papers FBS/4-3E. Forestry Department, Food and Agriculture Organization of the United Nations, Rome, Italy. 6. Peters, H.A. 2001. Clidemia hirta Invasion at the Pasoh Forest Reserve: An Unexpected Plant Invasion in an Undisturbed Tropical Forest, Biotropica 33(1): 60 - 68. 10. Wilson, Colin, Wildlife Management Officer, Department of Infrastructure, Planning and Environment, Parks & Wildlife Service, Northern Territory, Australia.
Summary: Compilor of original GISD profile of Chromoleana odorata. Results Page: 1
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