Common Name: Velvet tree, MiconiaAuthor: Leni R. Darrow
Scientific Name: Miconia calvescens (aka: Cyanophyllum magnificum, Miconia magnifica Triana)
Classification :Phylum or Division: MagnoliophytaIdentification : Miconia calvescens is a highly invasive and ecologically damaging introduced plant which has caused tremendous ecological disruption in Tahiti and threatens the Hawaiian Islands. It begins life as a shrub but grows into a tree which reaches up to 12 - 15 meters (close to 50 feet) in height, with large, velvety leaves that can grow to over 1 meter in length. The leaves are dark green on top, with three pale green nerves, and purple-blue underneath. Trees can produce flowers and fruit at four to five years of age and above three to four meters in height. Full-sized trees produce 50 to 200+ clusters of flowers (inflorescences), each consisting of 1,000 - 3,000 pinkish-white flowers. The flowers are fragrant, and the tree bears dark purple, fleshy berries, each about 0.6 - 0.7 cm.(approximately 1/4 inch) in diameter. The berries are sweet tasting, and each one contains between 50 - 200 seeds. A tree can flower and fruit two to three times per year. Flowering/fruiting of mature trees seems to be synchronized and may be brought on by weather conditions of rain or drought. An event of flowering/fruiting can last for a prolonged period of time, and there are often all stages of immature and mature fruits on a single tree. Miconia calvescens can reproduce either sexually between two plants or from a single plant.
Class: Magnoliopsida (Dicotyledoneae)
Original Distribution: Miconia calvescens is native to the tropical forests of Central and parts of South America. The native range of Miconia calvescens extends from 20 degrees north parallel in Mexico, Guatemala, and Belize to 20 degrees south parallel in Brazil and Argentina. It is absent from most of the Amazon basin and the north coast of South America. It is found in lowland to montane forest areas and has been seen at elevations ranging from 45 meters to 1830 meters. The bi-color form appears in the native range only in Central America; otherwise in the native range the leaves are green on both sides. The species is found in tropical rain forests or wet forests with mean annual rainfall greater than 2,000 mm (approximately 80 inches) and mean annual temperature greater than 22 degrees centigrade. Miconia tolerates shade, but it grows more quickly in forest gaps and open areas. It is commonly found in old pastures, forest edges, river banks, trailsides, roadsides and disturbed areas, and more rarely in dense primary forest. The ability of the species to dominate oceanic island tropical rain forests is linked to the low stature of the trees which typically proliferate in those forests.
Current Distribution: Miconia calvescens is present in the following countries in its native range: Mexico, Guatemala, British Honduras, Nicaragua, Costa Rica, Panama, Colombia, Equador, Peru, Bolivia, Brazil, Paraguay, and Argentina. Other sites where the species has been introduced and appears to have become naturalized in modest numbers include various gardens and other locations in Australia, Grenada, Jamaica, New Caledonia, and Sri Lanka. Where naturalization has occurred, the plant has not been consistent in its tendency to invade. Miconia calvescens has invaded the Society Islands of French Polynesia, particularly Tahiti but also Moorea, Raiatea, Tahaa, Huahine, and Mehetia; Nuku Hiva and Fatu Iva of the Marquesas Islands of French Polynesia, and the Hawaiian Islands of O'ahu, Maui, Kaua'i, and Hawai'i. The only country outside of the native range in which the species is currently cultivated as an ornamental plant is the Philippines.
Early History: Miconia calvescens was originally discovered by Belgian botanical explorer Auguste Ghiesbrecht between 1850 and 1855 in "the wet and shady forests that surrounded the mysterious ruins of Palenque" in Chiapas, Mexico. He sent it to plant dealer Jules J. Linden in Luxembourg, who exhibited it in 1857 in London, the Paris Society of Horticulture exhibition, and the Horticultural Festival of Berlin. He named the species Cyanophyllum magnificum because of its large magnificent leaves with purple-blue undersides, and he described it as "a jewel of the plant kingdom." The first picture of the plant was published in 1859 in the French journal "Revue Horticole" which stated that it "aroused the admiration of all lovers of plant wonders." The plant was widely dispersed to botanical gardens and greenhouses throughout Europe and distributed to tropical gardens throughout the world. It was cultivated under the name Miconia magnifica Triana and sold under the common name "velvet tree" because of the small stellate hairs found on young stems and leaves. The "Cyclopedia of American Horticulture" in 1930 mentioned it as "one of the best and most striking of all conservatory foliage subjects ."
Site and Date of Introduction: In 1937, Harrison W. Smith planted Miconia calvescens in his private botanical garden (today called the "Harrison Smith Botanical Garden") in the Papeari district of Tahiti, on the wet side of the island close to the native forest. Some years later it was planted at the Agricultural Research Station in Taravao. The first specimen in the Hawaiian Islands was a single tree in Wahiawa Botanical Garden on Oahu which was donated by the naturalist Joseph Rock and planted there in 1961. The species had reached the island of Hawaii by 1964 and Maui by the late 1960s or early 1970s. It is thought to have reached Kauai by the early 1980s, based on the discovery in 1995 of a mature tree there over 10 meters high.
Mode(s) of Introduction: Once established in Tahiti, the species was distributed to the nearby island of Moorea by wind dispersal or hikers and to the other Society Islands through piles of soil originating in Tahiti that were used for construction or stuck on wheels of bulldozers, or in soil from plant pots. Likewise, the introduction in the Marquesas appears to coincide with the building of roads in 1996 using equipment from Tahiti. The method of invasion in Sri Lanka, Australia, New Caledonia and Grenada is unknown. In the Hawaiian Islands, only two progeny of the original planting at Wahiawa on Oahu are known to have escaped the grounds of the garden: one across the street from the arboretum and one in a housing area. The introduction of the species elsewhere on Oahu, Kauai, and Maui were also from plantings in gardens. The species was introduced on the island of Hawaii as an ornamental.
Reason(s) Why it has Become Established: In Tahiti, Miconia calvescens is overwhelmingly dominant, having taken over approximately 65 - 70% of the island's natural forest. There are a number of reasons why it has become so widespread, including the introduction of the plant without its natural enemies, the characteristics of the invaded ecological area, specific characteristics of the species, and certain abiotic factors which played a role in its invasive success. The species was not really recognized and acted upon as a threat until 44 years after it was introduced, by which time its invasion was of enormous proportions.
In the species' native range, there are a variety of insects, fungi, and other pathogens which keep it from spreading invasively. These include a leaf-spot fungus Coccostroma myconae, and insects including weevils, leaf beetles, and butterfly larvae. The larvae, which feed on its leaves, are the most common and damaging insects to the plant. These natural predators are not native to the Pacific island groups, however, and therefore cannot contribute to the natural control of the plant.
The islands' climate conditions are very similar to those of Miconia calvescens' natural range. Tahiti has two seasons, one warm and humid and the other, between March and November, cooler and drier. Rainfall is variable and averages 1,700 mm per year, and the mean temperature is 26 degrees centigrade. These conditions have contributed to the spread of the species. The species is found between 10 and 1300 meters above sea level and in areas with 1,800 - 2,000 mm (75 - 80 inches) or more of rain annually.
Miconia calvescens' specific characteristics, including rapid growth up to one meter per year, ability to reproduce alone, small seeds, profuse seed production, and shade tolerance, have enabled it to propagate profusely. A typical 10 meter tall tree will produce up to 3 million seeds, two to three times per year. The species produces a large seed bank where seeds are viable for more than two years, and perhaps up to eight years, and germinate from fruits left in water for three months. Germination takes place in up to 90% of seeds and in all light intensities down to 2% of full sunlight. The plant will germinate on a variety of sites, including rocks and the bark of trees. Over time, the soil located under areas of dense growth accumulate a tremendous amount of seeds. In one set of greenhouse trials in Tahiti, a square meter of the top 2 cm. of soil from a dense Miconia calvescens stand produced 17,808 seedlings in six months.
In the Hawaiian Islands, Miconia calvescens began to spread as soon as the introduced trees began fruiting. Data from Maui suggests that the trees' seed banks lie largely dormant in the shade but become viable when the overhead canopy is opened up. One abiotic factor which contributed significantly to the rate of spread of the species in Tahiti were the six hurricanes which hit between December 1982 and April 1983. Although miconia calvescens had already gained widespread foothold in the undergrowth of the forest areas, the hurricanes suppressed the natural canopy by breaking the tops of trees and by defoliating emergent native trees. This enabled more light to get through to the invasive species, allowing for faster growth and flowering/fruiting.
The establishment process has been aided by gravity, wind, and water. Animals have also been a significant factor. In particular, the seeds are dispersed by birds, especially silvereye and red-vented bulbul in the Society Islands and, in Hawaii, the Japanese white-eye, common myrnah, and perhaps northern cardinal. Mammals, such as rodents, cattle, or wild pigs, also contribute to the spread of seeds. In addition, the species' seeds are easily transported on the boots or clothes of hikers, hunters, or anyone else who has been in the affected area.
In addition, the establishment of the species was aided by inaction. Although scientists and naturalists recognized the potential threat of Miconia calvescens as early as the 1970s, no action was taken by the local authorities in Tahiti to combat the problem. It wasn't until 1988 that the Miconia Research Program was begun there. By that time, the species had run rampant.
Ecological Role: Miconia calvescens has had a tremendous impact on the natural ecology of areas which it invades. The species creates a heavy shade canopy which native plants are unable to tolerate, thereby displacing them. No native species appear to have characteristics similar to those of Miconia calvescens.
Threat(s): Miconia calvescens is considered to be the most highly invasive and damaging of alien plant species in the wet forest areas of the Pacific islands. As a result of Miconia calvescens' invasion of Tahiti and the Society Islands, French Polynesian ecologists estimate that between one quarter to one half of all endemic species are at risk of extinction. The plant forms dense thickets that take nutrients from the soil and block sunlight from reaching the forest floor, so that few plants under its canopy can survive. It thereby deprives native birds of the plants they need to survive. In addition, the species root system is superficial and tentacular, which is believed to contribute to landslides. Tahitians call Miconia calvescens the "Green Cancer," and in Hawaii it is referred to as the "Purple Plague." Miconia calvescens was declared a noxious weed in the State of Hawaii in 1992.
Benefit(s): Ornamental and horticultural value only.
Control Level Diagnosis: Highest Priority. Miconia calvescens poses an extremely high threat to natural species in those areas which it invades.
Control Method:Tremendous efforts have been made in the Hawaiian Islands to control Miconia calvescens. Each affected island has an Invasive Species Committee made up of representatives from each of the appropriate agencies and organizations on that island. Plants less than about 3 meters tall are routinely removed by hand uprooting by government workers and groups of volunteers. Larger plants that cannot be removed in this fashion are cut down and the stump is treated with herbicide or it will resprout. In certain cases, helicopter herbicidal spraying of the trees has been undertaken. In both the Society and Hawaiian Islands, major public education programs urging the cutting down and treating of plants, and thorough cleaning of hands, shoes, equipment, and anything that could come into contact with seeds have been undertaken.
Efforts were undertaken in the 1990's to try to find biological control for the species. The Hawaii Department of Agriculture, in cooperation with the Cooperative National Park Resources Unit and the U.S. Forest Service/Institute of Pacific Islands Forestry, attempted to import natural insect predators and pathogens of the plant from its native habitat. Unfortunately, the tests did not prove particularly successful. Although there were more than 25 different species included, the numbers of each sample were low and the range of territory covered by the trials was small. In the current habitat of the plant In both the Society Islands and the Hawaiian Islands, the Chinese rose beetle (Adoretus sinicus) is frequently observed eating the leaves, but this has not been seen to kill any trees.
A plan by the Haleakala National Park in Maui to institute entrance fees at the Park to be used for Miconia calvescens eradication has been stopped by the U.S. Interior Department. The Honolulu Advertiser reported on February 5, 2002 that the Government ruled in December 2001 that money collected at the Park can only be used for projects within the boundaries of the Park, and not for environmental control outside of the Park proper. Recent heavy rainfall has caused a profusion of flowering on the trees, and the refusal by the Government is expected to set back the Park's contribution to the Miconia eradication project by at least six months.
http://mobot.mobot.org/cgi-bin/search_vast?name=Miconia%20calvescens"Epidemiology of the Invasion by Miconia calvescens and Reasons for a Spectacular Success," Jean-Yves Meyer, Proceedings of the First Regional Conference on Miconia Control (August 26-29, 1997)
"Control of Infestations Originating from Single Miconia calvescens Plants on O'ahu and Kaua'i, Hawaii," Patrick Conant and Guy Naga, Proceedings of the First Regional Conference on Miconia Control (August 26-29, 1997)
HNIS Report for Miconia calvescens, a product of the Hawaiian Ecosystems at Risk Project: http://www.hear.org/hnis/reports/HNIS-MicCal.pdf
Minutes, Maui Invasive Species Committee, Friday, November 9, 2001
"Park's Miconia war chest vanishes in technicality," by Timothy Hurley, Honolulu Advertiser, page B1, posted on Tuesday, February 5, 2002
Maui Invasive Species Committee, 2002 Action Plan