Clidemia has very broad environmental tolerances (Wester and Wood 1977). It is found in areas ranging from mesic (1,270 mm of rainfall per year) to very wet (7,600 mm/year), as well as in exposed habitats or sites with 100% canopy cover. It grows well under native forest trees as well as under introduced trees.
Clidemia can invade both disturbed and undisturbed areas in Hawaii (Smith in press). Population levels usually remain low in undisturbed sites. It spreads rapidly and achieves high densities after disturbances such as storms, feral pigs (Sus scrofa), landslides and fire, all of which open the subcanopy (Wester and Wood 1977, Smith in press). Disturbance is also the key to its intensification and spread in its native range (Smith in press). It can develop dense monotypic stands, shading out understory plants below its canopy, even bryophyte ground cover (Wester and Wood 1977, Smith in press). However, uluhe in exposed areas appears to be capable of excluding clidemia (Wester and Wood 1977). In moist, shaded habitats clidemia can reach 5 m, entering the subcanopy of Hawaiian forests. In exposed areas, it typically grows less than 1 m tall.
Vegetative growth and sexual reproduction typically occur throughout the year in rain forest habitats with no dry season, but in drier and seasonal habitats, dry periods reduce flowering and fruiting (Smith in press).
Clidemia reproduces by seed which are spread by alien birds (Hosaka and Thistle 1954, Smith 1985). Humans, mongooses (Herpestes auropunctatus), and feral pigs (Sus Scrofa) are also responsibe for localized dissemination (Wester and Wood 1977, Smith in press). Humans are undoubtedly responsible for frequent, inadvertent, long-distance dispersal. Hunters, hikers, marijuana (Cannabis sativa) growers, and vehicles are the main vectors. The seeds are thought to be viable in the soil for up to four years.
Its success as a weed may be due in part to prolific seed production, rapid recruitment from the seed bank, fast growth and maturation, and availability of dispersal vectors. A fruit contains over 100 seeds, and mature plants produce over 500 fruits per year. Growth is rapid after germination. Gill (pers. comm.) have observed that seedlings grow into fruiting plants in 10 months. Harada (pers. comm.), from his attempts to control clidemia, found that some plants grew from seedling stage to fruiting in six months.
Comments: Smith (1985) ranks clidemia as one of the 86 most disruptive alien plant species in Hawaii, principally because of its broad ecological tolerances, very rapid spread in Hawaii, capacity for long-distance dispersal, and tendency to form monospecific subcanopy stands. He characterizes its effects as devastating (Smith in press). Clidemia is established in Kamakou Preserve and nearby Wailau and Pelekunu Valleys, and is intensifying in these areas (Misaki pers. comm.). It is also established in Koolau Gap below the current boundaries of Waikamoi Preserve. Projected distributional limits of clidemia suggest that it will be confined to sites below 1,500 m (Smith pers. comm.), the lower boundary of Waikamoi. However, its upper elevational limit may not have been tested yet in Hawaii, and clidemia may reach higher elevations than expected from its distribution on Oahu and in central America.