Widespread losses of plant species and varieties are not only eroding the foundations of agricultural productivity but also threatening the supply of other plant-based products, particularly medicinal compounds, according to a Worldwatch Institute study.
Plants provide people throughout the world with irreplaceable resources but biotechnology could not be expected to make up for the destruction being caused by human activity and over-harvesting, concludes the study by the institute's research fellow, Mr John Tuxill, an authority on biodiversity and conservation. It was published in the US at the weekend.
"The genetic diversity of cultivated plants is essential to breeding more productive and disease-resistant crop varieties. But with changes in agriculture, that diversity is slipping away," warns the institute, an independent agency which evaluates threats to the global environment.
In China, farmers were growing an estimated 10,000 wheat varieties in 1949, but were down to fewer than 1,000 by the 1990s, while Mexican farmers were raising only 20 per cent of the corn varieties they cultivated in the 1930s, it notes.
Biotechnology was no solution to this loss of genetic diversity. "We are increasingly skilful at moving genes around, but only nature can create them. If a plant bearing a unique genetic trait disappears, there is no way to get it back," Mr Tuxill said, after publication of Nature's Cornucopia: Our Stake in Plant Diversity.
The effects of plant loss extend far beyond agriculture, it warns. One in every four medicines prescribed in the US is based on a chemical compound originally found in a plant. Some 3.5 billion people in developing countries rely on plant-based medicine for their primary health care. Plants also furnish oils, latexes, gums, fibres, timbers, dyes, essences. People living in the rural areas of developing countries depend on plant resources for up to 90 per cent of their total material needs.
Loss of habitat, pressure from non-native species and over-harvesting have put one out of every eight plant species at risk of extinction, according to the World Conservation Union.
"Those that we rely upon most heavily are declining, too. Some two-thirds of all rare and endangered plants in the US are close relatives of cultivated species. Crop breeders often turn to wild relatives of crops for key traits, like disease resistance, when they cannot find those traits in cultivated varieties."
Many medicinal plants were also threatened by over-harvesting and destruction of habitat. The bark of the African cherry tree is used widely in Europe for treating prostate disorders, but the medicinal trade has led to severe depletion of the tree in central Africa. Since fewer than 1 per cent of all plant species have been screened for bioactive compounds, every loss of a unique habitat and its species is potentially a loss of future drugs and medicines.
