Small tree from the neotropics invading disturbed areas and natural forests in the Society and Hawaiian Islands. It regenerates freely under canopy to eventually form monotypic stands. Many endemic species are being displaced and are thought to be at risk.
Small tree, up to 15 m tall, bearing large leaves (up to 1 m long) which are often green with three pale green nerves above and purple-blue below.
Trees with bicoloured leaves are restricted to Central America while the other form occurs in both Central and South America.
Small white and slightly fragrant flowers are borne in large panicles. Both allo- and autogamy occur, particularly in isolated individuals. Infructescences bear up to 500 blue-black fleshy berries (ca 0.6-0.7 cm in diameter) each containing around 140-230 seeds (size 0.7x0.5 mm). Flowering and fruiting may start within four years of germination. In Tahiti there are at least three peaks of flowering and fruiting per year. During the first fruiting season a young tree produces around 200,000 seeds on two infructescences and when older over 5 million seeds per year. Seed dispersal agents include gravity, wind, water, birds (mainly introduced species in the Society Islands) and small mammals, the latter two being the main agents. In Tahiti M. calvescens produces a large seed bank (up to 50,000 seeds m-2) where seeds are viable for more than two years and seeds germinate from fruits left in water for three months. Germination (rate up to 90%) is staggered and may take place under all light regimes including low light intensities (down to 0.02% of full sun light). Microsite requirements are varied and germination may even take place on rocks and the bark of trees.
Vegetative layering and resprouting occur.
Miconia is shade-tolerant but it regenerates freely and grows more rapidly in forest gaps and open areas. In its native range is commonly found in disturbed areas.
No information is available.
Introduced to European botanical gardens and commonly cultivated in greenhouses because it had "one of the best and most striking of all conservatory foliage objects". Currently sold as an ornamental plant in the tropics.
Natural distribution extends from southern Mexico (18o N) to southern Brazil (26o S). It is absent from most of the Amazon basin and the north coast of South America.
Its distribution suggests a wide climatic amplitude with a preference for tropical climates with distinct seasonality.
Generally found in old pastures, forest edges, river banks, trailsides, roadsides and disturbed areas and sometimes in natural forest from sea level to 1800 m.
This species is never common even in disturbed areas.
Introduced to Tahiti in a private botanic garden in 1937 and some years later planted at the Agriculture Research Station (Taravao). Introductions to the nearby islands of Moorea and Raiatea are thought to be the result of, respectively, wind-dispersal or hikers and contaminated soils (coffee and timber saplings).
In Tahiti, the spread of M. calvescens was not noticed until 44 years after its introduction, however by that stage the species was already widespread. In Hawaii M. calvescens began to spread as soon as the introduced trees started fruiting and this would suggest that in the Society Islands the observed time-lag is not an ecological phenomena but, rather, a human perception problem. In Hawaii the plant was detected twenty years after its introduction and only following warnings emanating from French Polynesia as to the threat posed by the species.
In the Society Islands M. calvescens has spread into disturbed areas (i.e. roadsides, abandoned pasture and forest edges) and into natural forests. In forests it regenerates under canopy, and became the dominant canopy tree over large areas of Tahiti particularly after hurricane-induced disturbance. The ability of M. calvescens to dominate oceanic island tropical rain forests is linked to the low stature of the trees found in these forests.
It dominates forests over 70% (ca 70,000 ha) of the island of Tahiti.
The climate of the Society Islands is tropical oceanic with two seasons, one warm and humid and the other, between March and November, is cooler and drier. Mean annual temperature is 26°C and rainfall varies greatly with an average of 1700 mm/yr. M. calvescens is found between 10 and 1300 m a.s.l. and in areas with more than 2000 mm of rainfall per year.
The Society Islands have 623 native species, of which 273 are endemics, and over 1500 species have been introduced. The original vegetation was dominated by forests.
Specific natural enemies have not been found.
M. calvescens has dramatically altered natural forests of the Society Islands. Native species are unable to tolerate the heavy shade cast by M. calvescens and are displaced. As a result, half of all endemic species are though to be at risk. The superficial and tentacular rooting system is thought to contribute to landslides.
No obvious negative effects besides altering the physiognomy of the forested landscape.
In the Society Islands and Hawaii major educational and control programmes have been initiated. Besides preventing the introduction of M. calvescens to other islands, eradication of the species from lightly infested islands has been attempted. Small individuals are uprooted while large one are cut and treated with herbicide (2,4-D) to prevent resprouting.
No native species appear to have life history characteristics (rapid growth (up to 1 m/yr), small seeds, profuse seed production, seed bank, shade tolerance etc.) similar to those of M. calvescens.
In the neotropics M. calvescens is not abundant and never dominates vegetation as it does in Pacific islands and this may result from the absence of natural enemies in the introduced range. The altitudinal range of the species is wide in both the native and introduced ranges.