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Case Study - Desertification and Alien Species in Australia

個案研究 - 澳洲沙漠化與外來物種生態危機

我馬子蘋果  譯

Within 200 years after English settlers arrived in Australia in the eighteenth century, they had destroyed most of the country’s forest cover, eliminated or endangered 70% of its mammal species, caused widespread erosion and salting of the soil (leading to desertification throughout much of the country, Figures 12-25 and 12-26), and decimated the once-sizable aboriginal population. Topsoil is now eroding 50 times faster than it did prior to 1788.

近 200 年來，自英國移居至澳洲的墾荒者開發大片森林、宰殺當地 70% 哺乳動物，因而導致澳洲土地嚴重之侵蝕與鹽化，(此為該國日益嚴重之沙漠化主因。見圖12-25、26) 並屠殺當地曾一度興旺之原住民。相較於 1788 年，澳洲表土層現正以 50 倍之速度侵蝕中。

In 1859 Thomas Austin, longing for home pastimes, imported and released 24 English rabbits into the Australian countryside for hunting. Without any natural enemies the rabbits multiplied so rapidly that within 10 years they numbered in the millions, and like hordes of locusts they began munching their way across the continent. They ate crops, competed with livestock for grass, and destroyed wild vegetation, displacing and endangering many native animal species.

1859 年，英國僑民 Thomas Austin 氏因懷念家鄉狩獵休閒活動，將英國種野兔 24 隻引進澳洲。因無天敵之故，10 年間快速繁殖至數百萬之多。如蝗災一般，野兔大軍沿路啃食；舉凡穀物、野外綠地等，無所不吃，與家畜爭食。迫使數種哺乳類動物瀕臨絕種，殃及全澳。

Australians tried without success to contain this plague of rabbits until the 1950’s, when they introduced a virus that killed off 99% of the rabbits. Now, however, the rabbits are back. Through natural selection the remaining 1% became resistant, began multiplying, and now number more than 200 million, causing about $75 million of damages per year to grazing land. Farmers and ranchers attack the rabbits with guns, dogs, poison, and dynamite, but they keep multiplying. Australian scientists are using genetic engineering in a desperate attempt to develop stronger viruses before the country is again overrun.

澳洲當局遲未能有效控制此一發不可收拾之兔災。直至 1950 年間，引進一種病毒，方才殺死其中之 99%。剩下 1% 的兔子，通過了天擇考驗，產生了對該病毒的抵抗力，存活下來並繼續繁殖，目前為數已達 2 億，造成澳洲每年約 7 千 5 百萬美元之農損。不論農人牧人用槍、獵狗、毒藥、甚至炸藥都無法遏阻牠們繁衍之勢。無計可施之下，澳洲科學家只好利用基因工程技術開發出更強之病毒，試圖預防兔災再次爆發。

In the 1930s someone came up with the bright idea of importing the South American cane toad to help control beetles that were devastating the sugarcane crop. Unfortunately, these plump 0.5-kilogram (1 pound) toads stayed on the ground, while the sugarcane beetles flew above; so they never met. Then now occupy 40% of Queensland and are moving into New South Wales and the Northern Territory. The poisonous toads are almost impossible to kill. Toads that are shot recover and hop away. The ones that are run over by a car simply swallow their squashed guts and limp away.

另一例發生在 1930 年間，有個傢伙想突發奇想，想藉由引進南美一種藤蜍來捕食為害當地甘蔗栽種的一種小甲蟲。不幸地，這種蟾蜍只在地上爬，蟲子卻在甘蔗枝上飛，所以彼此永不相遇。不料現在這些重約 1 磅的大蛤蟆，侵占了昆士蘭 40% 的土地，進而蔓延至新南威爾斯及北部地區。更不幸地，這種有毒性的蟾蜍幾乎不可能被殺死；拿槍射，要是沒射死，等到再生痊癒後，即可重現往日雄風；用車輾，牠們會先吃掉自己被壓爆出的內臟，再一跛一跛地爬開。

Australians are now trying to reverse some of the consequences of their centuries of destruction and thoughtless introductions of alien species. The government has abolished tax advantages for clearing land and replaced them with incentives for planting trees, preferable the native species they destroyed. They have a daunting task.

面對過去數個世紀以來先祖無知地濫墾濫捕、隨意引進外來物種導致當地的生態危機，今日澳洲人試圖力挽頹勢；政府現已停止整地的賦稅優惠，鼓勵植樹；過去曾遭濫墾之本國品種，優先栽種。然而，這肯定會是件苦差事。

(Figure 12-26 Desertification in this arid outback region of Australia was caused by cattle overgrazing the vegetation. Livestock cropped plants so short that the vegetation died; trampling kept new seedlings form growing. Overgrazing is the biggest cause of desertification.)

(圖 12-26：無限制放牧所導致之澳洲乾燥內陸沙漠化。過度放牧致使青草生長不及而枯竭，並牲畜踐踏妨礙幼苗發育，此為沙漠化之主因。)