BANSALAN, Davao del Sur - When you cut trees, as in the case of logging, flood ensues. During heavy rains, the water from the uplands devoid of forest cover comes rushing to the lowland areas. As a result, houses are inundated, crops uprooted, and bridges destroyed. That's elementary.
But what happens to the topsoil that goes with the water? Topsoil makes the clear water turn into something chocolate brown if not muddy. So what are the consequences of soil erosion?
"Soil erosion is an enemy to any nation, far worse than any outside enemy coming into a country and conquering it because it is an enemy you cannot see vividly," decried American missionary Harold R. Watson.
"It's a slow creeping enemy that soon possesses the land. We must consider ourselves in a state of emergency; our topsoil is all going," he said.
Watson made the statement in 1985, the year when he received the prestigious Ramon Magsaysay Award, touted to be the Nobel Prize of Asia, for peace and international understanding. He was cited for promoting technologies that could sustain farming and considered environment-friendly.
"The topsoil is the primary resource of agriculture," said Roy C. Alimoane, the director of the Mindanao Baptist Rural Life Center (MBRLC) Foundation, Inc., a non-government organization based in Kinuskusan, Bansalan, Davao del Sur.
"Without it, there would be no farming. Should a land area devoid of topsoil, food crisis is likely to happen," he said.
"We are hardly aware of this enormous loss which is progressively eroding away our most fertile soil and thus our ability to produce food for an expanding population," the Catholic Bishops Conference of the Philippines (CBCP) noted in a pastoral letter almost two decades ago. "Any comprehensive land reform must address this most serious threat to our food supply."
And yet no one pays attention to it. Soil scientists claims 58 percent of the country's total land area of 30 million hectares is susceptible to erosion.
"For one, the magnitude of soil erosion in cultivated sloping areas has reached an alarming proportion," deplored Angel C. Alcala, former secretary of the Department of Environment and Natural Resources (DENR) and also a Ramon Magsaysay Awardee.
A compilation of more than a dozen American studies analyzing the effects of erosion on land productivity found that losing an inch of topsoil reduces corn and wheat yields by an average of six percent.
"The soil is the world's most precious natural resource," pointed out Edouard Saouma, former director-general of the UN Food and Agriculture Organization. "Yet it is not valued as it should be. Gold, oil, minerals and precious stones command prices which have led us to treat soil as mere dirt."
Soil, aptly described as "the bridge between the inanimate and the living," consists of weathered and decomposed bedrock, water, air, organic material formed from plant and animal decay, and thousands of different life forms, mainly microorganisms and insects. All play their part in maintaining the complex ecology of a healthy soil.
In the humid tropics, starting from a sandy base, a soil can be formed in as little as 200 years. But the process normally takes far longer.
"Under most conditions," Watson said, adding that "soil is formed at a rate of one centimeter every 100 to 400 years, and it takes 3,000 to 12,000 years to build enough soil to form productive land."
"This means that soil is, in effect, a non-renewable resource," says a FAO publication. "Once destroyed, it is gone forever."
Although soil erosion does occur naturally, the process is slow. However, man's intervention has increased the rate of natural erosion. According to David Pimentel, an agricultural ecologist at Cornell University, exposed soil is eroded at several thousand times the natural rate.
Under normal conditions, each hectare of land losses somewhere between 0.004 and 0.05 tons of topsoil to erosion each year, far less than what is replaced by natural soil building processes.
"No other soil phenomenon is more destructive worldwide than soil erosion," wrote Nyle C. Brady in his book, The Nature and Properties of Soils. "It involves losing water and plant nutrients at rates far higher than those occurring through leaching. More tragically, however, it can result in the loss of the entire soil."
Soil erosion makes farmlands infertile. Studies have shown that loss of a few centimeters of topsoil can reduce the productivity of good soils by 40% and poor soils by 60 percent.
Lester R. Brown and Edward C. Wolf, authors of Soil Erosion: Quiet Crisis in the World Economy, argued that erosion affects crop production in two ways. "The loss of topsoil reduces the inherent productivity of land, both through the loss of nutrients and degradation of the physical structure," they explained.
"It also increases the costs of food production," they added. "When farmers lose topsoil, they may increase land productivity by substituting energy in the form of fertilizer. Hence, farmers losing topsoil may experience either a loss in land productivity or a rise in costs of agricultural inputs. And if productivity drops too low or agricultural costs rise too high, farmers are forced to abandon their land."
According to Brown and Wolf, the immediate effects of soil erosion are economic but in the long run, its ultimate effects are social.
"When soils are depleted and crops are poorly nourished, people are often undernourished as well," the two authors said. "Failure to respond to the erosion threat will lead not only to the degradation of land, but to the degradation of life itself."