Scientists are warning of yet another growing threat to biodiversity in Southeast Asia: rubber plantations. Over the past decade, more than 2 million hectares of forests and farms worldwide have been turned into rubber plantations. The biggest impact has been in Southeast Asia—including the Xishuangbanna region of southwest China—which hosts 84% of the world's 9.9 million hectares planted with rubber trees, according to a new review. The driver is growing demand for rubber products, particularly tires, which consume 70% of annual rubber production. But conservationists hope new efforts to grow rubber more sustainably could curb the ecological impact.
For the moment, however, the expansion of rubber plantations is taking a growing toll on flora and fauna. The researchers surveyed previous studies and found that conversion of forest to rubber monoculture significantly decreases the number of bird, bat, and insect species. The change in landscape is particularly hard on specialized and often threatened birds that feed on the fruit and insects found in forests. The team reports that no studies have documented the impact of forest conversion on ungulates, primates, large predators, or waterbirds, but they conclude that it is unlikely these larger animals are unaffected.
The impact goes beyond the boundaries of the plantations. Pesticide, herbicide, and sediment runoff leads to eutrophication of area streams, affecting aquatic life. The loss of smaller trees and shrubs leads to soil erosion and increased landslide risk. And rubber trees soak up deep soil moisture, making it harder for native vegetation to thrive.
Not all the rubber plantations have the same deleterious effects. Some growers embrace agroforestry practices, in which rubber trees are mixed in with native vegetation. Agroforests are more benign for biodiversity. But rubber yields are lower than in monoculture plantations where rubber trees completely supplant original trees and shrubs.
"Together, these findings show that rubber expansion could substantially exacerbate the extinction crisis in Southeast Asia," report Eleanor Warren-Thomas, a conservation scientist at the University of East Anglia in Norwich, U.K., and colleagues online today in Conservation Letters.
The situation is likely to get worse. The researchers cite separate studies suggesting that global rubber consumption will grow 3.5% annually in the near term. The team then projected what this would mean for rubber land use under various scenarios, including expansion of rubber plantations at current yields, more intense cultivation that increases yields, and the possibility of losing land now planted in rubber to oil palm. "We estimate that 4.3–8.5 million ha of additional rubber plantations are required to meet projected demand by 2024, threatening significant areas of Asian forest," the researchers write.
There may be hope. Warren-Thomas told ScienceInsider that sustainability certification schemes have been successful in reducing the negative impacts of oil palm and paper and pulp growing practices. A significant number of corporations have agreed to purchase only certified products, and 400 of the world’s largest corporations have pledged to make their supply chains free of deforestation by 2020. A similar effort for rubber has just gotten started. The Sustainable Natural Rubber Initiative launched its pilot phase in January seeking to get growers, processors, traders, and users to comply with voluntary guidelines to produce rubber more sustainably. Warren-Thomas says that with many local governments still eyeing expansion of rubber crops as a development strategy. "At the moment, certification schemes are really one of the only ways to lead to change in these big industries," she says.
She adds that more research is needed to determine the optimum mix of preserved areas, high-yielding monoculture plots, and low-yield agroforests that will meet both conservation and supply goals.
One worry is that the certification efforts have been slow to catch on in China, which is the world’s largest consumer of rubber. Warren-Thomas hopes that the world's major tire manufactures, all of whom do business in China, will embrace the effort.
In a sign that the sustainability movement might be gathering strength, yesterday the International Union for Conservation of Nature released a report titled No Net Loss and Net Positive Impact: Approaches for Biodiversity that details how some environmental groups and companies are going beyond the sustainability standards. The report contends that if done right, commercial agriculture and forestry can have a net positive impact on biodiversity.