Monday, September 9, 2013

Miconia "Sound the Alarm!"

                                                  Clearing Miconia stand in Tahiti

Miconia calvescens, is a tree from 35 to 50 feet tall with large leaves up to 3 feet in length. Although attractive with its beautiful leaves, green on top and purple on the bottom foliage, it is perhaps the most invasive and damaging, alien plant species to the wet forest lands of the Pacific Islands. These trees will form a large, thick canopy which can produce 100% shade, killing out or inhibiting the growth of all native species below. Miconia plants are a threat to completely take over moist and wet forests.

Miconia was introduced to Hawaii as an ornamental in the 1960s and now poses a threat to completely take over forests receiving 75-80 inches or more of annual rainfall. If left uncontrolled, it is estimated that miconia could invade up to 121,000 acres on Oahu. On Maui 37,000 acres could potentially contain miconia.  Presently, the Big Island has large infestations on the windward side, particularly on the Hamakua Coast and smaller populations on the leeward side.

A single mature tree has the potential of producing 3 million seeds, two or three times a year. These seeds can remain viable in the soil for 10 years or more. The seeds are spread by man, through the mud on his boots and other equipment including bulldozers. Seed is also dispersal by birds; in Hawaii, dispersal is presumably by the Japanese white-eye, the common mynah and perhaps the northern cardinal. In trials in Tahiti, a square yard of the top 2 cm. of soil from a dense Miconia stand, produced over 17,000 miconia seedlings in six months.

Miconia was introduced to Tahiti in 1937 and has since destroyed nearly 70% of the native forests and is directly responsible for threatening 25% of their native forest species with extinction. Miconia also causes serious landslides due to its shallow root system.

Hawaii residents: For many years the Big Island Invasive Species Committee (BIISC) has worked to maintain a miconia-free buffer zone and to stop miconia from spreading to upper-elevation, pristine watershed forests. Funding is now inadequate to continue this focus. For more information, you may contact them at (808) 430-3090 or email at pageeles@hawaii.edu.

Today, the strategy for control is to implement a serious of biological control measures: to introduce natural enemies from Miconia’s origin in Brazil. The approach is to use a variety of agents including weevils which bore out the stems, caterpillars which feed on the leaves, and other larvae which feed on flowers and seeds. The list of biological control agents also includes a fungus which attacks the leaves and causing premature leaf drop.  There is a BIISC Hotline to report new infestations, (808) 961-3299.