[SCMP Column] Invasive Species

May 28, 2016


As red fire ants begin their reign of terror over large tracts of Hong Kong village land, and as the sprawling Mikania micrantha smothers so many bushes and trees across rural Hong Kong, my thoughts turn to pesky invasive species – and how comparatively lucky Hong Kong is, in spite of our role as one of the world’s most powerful vectors for the movement of such all-conquering aliens.

In truth, I began thinking about them over a month ago, when I learned of the threat from the fungus fusarium to our precious Cavendish bananas. Since first being detected in 1990, when the fungus destroyed banana plantations in Taiwan, fusarium has spread through Indonesia, Malaysia, the Philippines, and now into Australia, where a 400 acre farm in Tully, Queensland has been quarantined in a desperate fight against a banana plague that is threatening the world’s US$36 billion banana industry.

The plague is called Tropical Race 4 strain of Panama disease – TR4 for short – and the problem is potentially catastrophic because around 95% of the world’s bananas today are the single Cavendish species.  Apparently, up to 1950, the world’s banana trade was dominated by the Gros Michel banana, but this was totally destroyed by the first strain of Panama Disease – TR1. The TR4 plague is critical not just because it is destroying one of the world’s most important food crops, but because we have allowed ourselves to become so wholly reliant on a single banana variety.

Combine reliance of a small number of food sources, with the challenge from invasive species, and you have problems that make fire ants or mikania a minor matter. According to the UN’s Food and Agriculture Organisation (FAO), since the 1900s, around 75% of plant genetic diversity has been lost as local varieties have been lost, and as big farm businesses have developed genetically uniform, high-yielding food varieties. Today, according to the FAO, 75% of the world’s food comes from just 12 plants (sugar cane, maize, rice, wheat, potatoes, soybeans, cassava, tomatoes, bananas, onions, apples and grapes) and five animal species (pigs, chickens, cattle, sheep and goats), and 90% of crop varieties have disappeared from farmers’ fields.

A study by the Royal Botanic Gardens at Kew near London found that thousands of plant species are today at risk of extinction from threats ranging from climate change, habitat loss, disease and invasive species. Conservationists have now logged around 5,000 invasive species around the world, and the global cost of tackling invasive species alone is estimated at nearly 5% of global GDP. The annual cost just to the United States economy is estimated at $120 billion a year, with over 100 million acres (an area roughly the size of California) suffering from invasive plant infestations, according to The Nature Conservancy.

To explore these invasions is simply fascinating. Who could imagine that something as benign-sounding as South African lovegrass could destroy 10 percent of southern Brazil’s grazing lands, severely damaging the area’s cattle industry? Or that the emerald ash borer from Asia has destroyed US$10 billion-worth of US ash trees? Or that Harlequin ladybirds, introduced into Europe to control aphids, would destroy almost half of the UK’s two-spot ladybirds in the past decade?

Not all invasions have been malign. Honey bees and earthworms were both introduced to the US in the 17th century, with only beneficial results. But benign or malign, this invasive upheaval is occurring on an unprecedented scale. As a Financial Times feature noted in its Chelsea Flower Show edition a week ago: “As global trade and mass transit have bloomed, the great global reshuffling of flora and fauna has accelerated. We are talking about the widespread redistribution of life on earth, and there is no precedent in the fossil record.” This is “mass species dislocation”.

Some invasions – like that of TR4 – come in the mud on farmers’ boots. Others arrive in bird droppings. But others are more subtle. Some travel in the wooden crates that global cargos are carried in. It is estimated that in any 24 hours, around 10,000 different species, such as molluscs, crustaceans, seaweed and plankton, are moved around the world in ballast water in ocean-going ships.

In the middle of all this “mass species dislocation”, Hong Kong clearly plays a massive vector role – not just for plants and insects, but for humans too. Our role as a massive air and maritime hub, and Asian locus for trade in all forms, makes us the perfect medium by which this “dislocation” can occur. Hong Kong currently has over 3 000 plant species, but around one-third of them are alien species, including some common fruit trees and ornamental plants. A large number of introduced species have long been naturalised in Hong Kong, and have no significant impact on the local ecology. While some of these alien species have been beneficial to local agriculture, horticulture, forestry and aquaculture, a few have been troublesome, including apple snails, red fire ants, Sonneratia and the infamous Mikania micrantha. You could include House Crows and Sulphur-crested cockatoos as well, if sound pollution is a concern to you.

Of course the most significant invasive species of all for Hong Kong are of the humanoid variety. As travellers and entrepreneurs have landed on Hong Kong’s shores over the past two centuries, settling here and mixing with the local population, so we are without doubt watching “widespread redistribution of life on earth”, as the Financial Times so elegantly put it. I suppose it is still an open question whether this human species dislocation has on balance been malign or benign. Many of the “localist” political groups to have sprouted in the past year would without doubt say these are malign. I prefer to think of them as benign, but of course I am likely to be biased.
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