Navjot S. Sodhi, Straits Times 8 Dec 07;
Take heed: Man's unsustainable exploitation of nature is precipitating a global extinction crisis
WE HUMANS have badly mauled the planet, but all is not lost - yet.
The majority of native habitats and species are in decline. Our actions are precipitating a global extinction crisis - the 'sixth mass extinction', comparable to past extinction events, such as the one that wiped out the dinosaurs 65 million years ago.
Unlike those in previous eras, which were attributed to natural catastrophes, such as volcanic eruptions, meteorite impact and global cooling, the current mass extinction will primarily be caused by us.
It is estimated that, currently, at least a few thousand species are being extinguished annually.
Why should humans worry about vanishing nature?
Being the dominant species and earth's de facto custodians, humans have a moral obligation to ensure the long-term persistence of the mountains, rainforests, coral reefs, tigers, lions, rhinoceroses, elephants and numerous other creatures.
All these make this planet awesome. Our imagination will be bankrupt if wild nature is obliterated.
In addition to moral and aesthetic reasons, we have a selfish reason to preserve nature: It provides countless goods and services.
Stanford University's Professor Paul Ehrlich calls nature's goods and services 'ecosystem services'.
According to Dr Peter Kareiva of the conservation organisation, The Nature Conservancy, and Dr Michelle Marvier of Santa Clara University, these services can be broadly categorised into four areas: provisioning (for example, food and medicinal plants), regulating (flood protection), cultural (spiritual well-being) and supporting (soil formation and pollination).
Researchers at the University of Vermont estimate that the total economic value of these services was higher than the gross domestic product of all countries combined.
While this estimate is debatable, the fact remains that nature is priceless.
Realising the value of nature's ecosystem services, the United Nations in 2000 initiated a historic study, the Millennium Ecosystem Assessment, that involved over 1,300 international scientists.
The assessment concluded that over half of the planet's natural ecosystem services are in decline as a result of unsustainable use by humans.
Highlighted below are some of the consequences of eroding nature. Examples pertain mainly to deforestation because it has been unprecedented in South-east Asia.
Human-driven climate change is turning out be a clear and present danger.
Carbon dioxide is the main greenhouse gas responsible for human-mediated global warming. After fossil fuel consumption, removal of vegetation is the next major cause of global carbon emissions.
It is believed that deforestation in South-east Asia alone releases approximately 465 million tonnes of carbon dioxide into the atmosphere each year, accounting for about a quarter of the total global carbon released resulting from deforestation.
Scientists have also postulated that unabated deforestation may reduce rainfall, resulting in warmer and drier conditions.
Deforestation can also alter natural water cycles, leading to higher frequencies of catastrophic floods and droughts.
Australian and Singaporean researchers reported recently that deforestation is one of the major factors for the higher frequency and severity of floods in the developing world.
Forest canopies reduce the impact with which rainwater hits the soil, reducing erosion, and enabling tree roots to bind soil so that it is less likely to be washed away during flooding.
The loss of topsoil due to deforestation can reduce rice output by 1.5 million tonnes a year, an amount that feeds up to 15 million people annually.
Further, deforestation-driven siltation shortens the life of dams, clogs natural waterways, and damages offshore fisheries. Forests are responsible for the regulation of about half of the world's water drainage systems, and roughly fivebillion people rely on this water.
Destruction of rainforests may also help spread disease.
Deforestation seems to facilitate an increase in the distribution of mosquitoes and corresponding increases in mosquito-borne diseases.
It improves the habitat of mosquitoes by compromising drainage, increasing light and temperature to facilitate the growth of algae (the main food of mosquito larvae) and deacidification of standing water.
Several Anopheles mosquito species responsible for spreading malaria are expanding their ranges in South-east Asia, very likely because of changes in land use.
Ironically, at least a quarter of medicine patented by Western pharmaceutical companies are derived from medicinal plants. Medical advances may thus be hampered because of ongoing deforestation.
Tropical forests are also a major source of food, natural products and construction materials for many local communities.
Deforestation has ramifications beyond the direct effects of vegetation removal.
The majority of flowering plants in tropical rainforests are pollinated by animals, and an estimated one-third of the human diet in tropical countries is derived from insect-pollinated plants.
A decline of forest-dwelling pollinators may impede plant reproduction not only in forests, but also in the adjacent croplands.
For example, lowland coffee is an important cash crop, and it depends on bees for cross-pollination. A Stanford University study found that forest bees increased coffee yield by 20per cent in fields within 1km of the forests in Costa Rica.
Between 2000 and 2003, the pollination services provided by forest bees were estimated to be worth US$60,000 (S$87,000) to a farm there.
Additionally, many predators, such as forest birds, are the natural enemies of pests in agricultural areas and are important in their control. It is estimated that the natural enemies of agricultural pests save humanity US$54 billion annually.
We have recently tasted the consequences of environmental degradation.
In 1997 and 1998, South-east Asia experienced widespread episodes of forest fires when more than fivemillion hectares of rainforests were burnt in Sumatra and Kalimantan.
These fires, unprecedented in scale in modern times, were a result of the combination of the El Nino-mediated drought conditions and poor land-use practices.
The resulting haze from these fires blanketed much of Indonesia, Malaysia, Singapore and even northern Australia.
This haze not only jeopardised the health of approximately 20 million people, but also disrupted the economies of these nations because of a decline in tourist numbers.
These fires cost an estimated US$4.4 billion in terms of tourism revenues and increased health-care costs.
Similarly, it has been suggested that the catastrophic losses of lives and properties brought about by the Asian tsunami in 2004 would have been lessened, had the mangrove forests not been cleared on the affected areas.
The unsustainable exploitation of nature is detrimental both to biodiversity and humans.
Let's be wiser.
The writer is professor at the National University of Singapore's biological sciences department. He has co-authored books such as Tropical Conservation Biology (Blackwell, Oxford) and South-east Asian Biodiversity In Crisis (Cambridge University Press).
