Feral Animals, Herbicides, Mikania, Pollution.
Lantau faces a number of human and environmental issues. Mikania is a non-native species that is damaging to native trees.
Though there are over 250 species in the genus Mikania, two species have drawn public attention to themselves. Mikania micranthia and M. cordata are invasive tree-climbers which have spread wildly across the Americas, Australia, India, most of southeast Asia, and extensive parts of China. The micranthia and cordata variations are so similar as to be almost indistinguishable from each other; but in the eyes of the taxonomist and botanist they are individual species.
Mikania is named after Joseph Gottfried Mikan, an early 19th century Bohemian botanist, and professor at Prague. His original studies of the genus focused on the South American species, particulary Brazil. Mikania, however, was long used throughout parts of Central and South America as a medicinal plant and some species are commercially valuable as crops for the medical and herbal market. Common uses of the plant are as digestive aids, fever remedies, a potent snake bite antidote, and as a headache cure. The plant is usally processed as either a tea or poultice, depending on the use intended.
The problem is with M. micranthia and M. cordata which have been recorded as growing as much as 3 cm in a day. This has earned them the common name of “mile-a-minute” in North America and Australia. The prodigious rate of growth, coupled with its creeping/twining nature, allow the climber to quickly cover large areas of land, smothering competing species and cutting them off from water and sunlight. It also releases an arsenal of compounds and chemicals into the soil and air that work to retard the growth of other competing plants in the area. Mikania can withstand a tremendous range of light and shade, moisture, and temperature, making it hardy and available to spread to a variety of regions.
It was mikania’s agressive nature that prompted it use agriculturaly as a smother crop to curb the spread of other competing weeds. Tea plantations in India, rubber plantations in Sri Lanka and Malaysia, coconut orchards in Samoa, and countless other breadfruit, oil palm, banana, and cacao ventures all introduced mikania to suppress rampant weeds and low-level brush which decrease productivity. It has been used selectively on rice paddies in parts of mainland Asia to hold back encroaching growth. The British Royal Airforce popularized the use of mikania as a natural camouflage for air bases and runways in the 1940s. It has also been used as a filler in cattle feed and many areas in Australia and South America have seen mikania spread through undigested seed and stem fragments.
The introduction of mikania was painfuly short-sighted, however. Mikania has recently been classified as the second largest weed threat to Australia, and figures prominently on the Departments of Agriculture invasive weed list of numerous countries. Mikania has become the number one weed affecting tea production in China and India, costing each country millions of dollars every year. It is also listed as one of the world’s 100 worst invading species, prompting further studies and watchgroups to monitor its spread and containment.
Mikania is propagated by windborne seeds. Each plant produces hundreds of seeds and can regenerate from very small stem fragments. Its natural resistance to herbicides has forced many countries to research alternative methods of controlling the plant, or resorting to more potent and harmful herbicides.
Experimental containment campaigns in India have had respectable success using the fungus Puccinia spegazzinii. Other natural-based control programs have included the use of a bug, Teleonemia, several beetles and Acalitus, an eriophyid mite. Hong Kong, China, and Australia have forgone using alternative methods and opted for the use of herbicides including the dangerous sulfometuron-methyl, glyphosate and 2,4-D, and paraquat.
Mikania is difficult to permanently remove from an area. On a small scale, for the gardener, regular maintainence and removal is neccesary to effectively control the spread of mikania.
Compiled by Owen Kozlowski