As Much as Half the World's Productive Soil Has Been Degraded in the
Last Half Century
by Robert Sanders
In a sobering report appearing in the July 21 issue of Science magazine, a Berkeley scientist estimates that nearly half the world's vegetated land has suffered a drop in agricultural productivity in the past 50 years as a result of human activity.
Gretchen Daily of the Energy and Resources Group estimates conservatively that 43 percent of the Earth's vegetated land has been degraded over the past half-century, primarily as a result of destructive agricultural practices and deforestation.
All told the planet has lost 10 percent of its total productive value, that is, its capacity to provide crops and pasture, or to serve as a source of forestry, medicinal or industrial products, she concludes.
"Today 10 percent of the Earth's capacity to supply us with food and other benefits has been lost and seems unlikely to be rehabilitated because of short-sighted socio-economic policies, and 1 percent of the planet's productive value has already been irretrievably lost," Daily said. "If we continue on our present course, how can the estimated doubling of the world's population in the next 25 years be supported?"
On an optimistic note, however, Daily points out that "the Earth has an enormous potential for recovery, if humanity will foster it."
If strong efforts are made to stop land degradation and to actively encourage the land's natural recovery, she says in her report, in the next 25 years the lost 10 percent could be reduced by half to 5 percent of the Earth's vegetated land surface.
Alternatively, if the world chooses to ignore this problem and continues business as usual, Earth's lost productive value could increase to as much as 20 percent, with some degree of degradation affecting more than 90 percent of the planet's useful land.
"Historically, land degradation has been implicated in the fall of great civilizations and merits serious attention by this one," she states in her report.
The study appears in the July 21 issue of Science along with eight other research articles on the topic "Frontiers in Ecology." Daily, Winslow-Heinz Foundation Research Fellow in the Energy and Resources Group, is now at Standord.
She restricted her analysis to an estimate of the measurable benefits of the Earth's vegetated land, such as food and fuel, and excluded the hidden benefits, which she refers to as "ecosystem services." These include the many essential roles soil plays in supporting day-to-day human well-being, such as recycling and detoxifying waste and absorbing and parceling out precipitation.
She also considered only direct and readily measured impacts on the land since 1945, excluding the effects of pollution, ozone depletion and climate change.
One of the primary causes of land degradation, Daily found, is loss of topsoil because of overgrazing, deforestation, destructive agricultural activities and over exploitation of wood for fuel. Once the topsoil has washed down river it can take thousands of years to regenerate.
"Agriculture is arguably the most critical element of the human enterprise, but it's the thing no one wants to think about," she says. "If we want to maintain the carrying capacity of the land the first step is to protect the natural underpinnings of agricultural productivity, especially soil."
This problem is not restricted to developing countries, she warns. The percentage of land degraded by topsoil loss is around 20 percent for Europe, the U.S., Asia and Africa.
Even though the U.S. invests heavily in agriculture, much of this investment goes toward only temporary improvements with hidden long-term costs, she says. There is increasing evidence that heavy U.S. dependence upon agricultural chemicals poses a serious threat to human and ecosystem health, for example.
Meanwhile other critical problems remain unaddressed--the encroachment of urban areas on the most productive farmland, increased soil salinity in important areas such as California and depleted aquifers.
"In the United States alone we could move to more sustainable agriculture, to better maintain our life support systems," she says. "We need a better vision of what a sustainable U.S. would look like overall."