By Mark Kinver
Science and environment reporter, BBC News
Areca nut plantations provide a suitable habitat for rare forest bird species
Certain farming methods can help sustain the biodiversity of tropical forests, a study has shown.
Researchers found that an areca nut plantation in south-west India supported 90% of the bird species found in surrounding native forests.
The low-impact agriculture system has been used for more than 2,000 years and should be considered as a new option for conservation efforts, they added.
The findings appear in the Proceedings of the National Academy of Sciences.
The team of scientists from the US and India chose the site on the coastal fringes of the Western Ghat mountain range because it met a number of attributes the study required:
- a long history of continuous agricultural production
- intense human pressure
- extensive natural areas still remaining
The landscape consisted of a mixture of intact forest, "production forest" (where non-timber products, such as leaves, were allowed to be removed) and areas of cash crops, primarily areca nut palms (Areca catechu).
"We found a total of 51 forest (bird) species in this study system," the researchers wrote.
"These species were broadly distributed across the landscape, with 46 (90%) found outside of the intact forest.
"Within areca nut plantations, we recorded threatened forest species, such as the great hornbill (Buceros bicornis) and the Malabar grey hornbill (Ocyceros griseus)."
The team said the combination of the height of the areca nut palms (Areca catechu) and the plantations' close proximity to the intact forest created the necessary ecological conditions to support forest bird species.
Farmers use leaf litter from surrounding forests in their plantations
They added that data showed the distribution of species in the area had been relatively stable for more than 2,000 years, before the first farmers cultivated the area.
As well as having a high ecological value, the plantations were also economically productive.
The areca nut is consumed by about 10% of the world's population, predominantly Asian communities.
The shade provided by the palms' canopy also created the conditions that allowed farmers to grow other high-value crops, such as pepper, vanilla and bananas.
Rather than expanding the plantations, the farmers relied upon the leaf litter from the surrounding production forests to produce mulch for their crops, rather than using costly fertilisers.
The researchers also said alternative crops that could be grown in the wet lowlands, such as rice, yielded lower returns both economically and ecologically.
Lead author Jai Ranganathan, from the US National Center for Ecological Analysis and Synthesis (NCEAS), said the findings provided another option for conservationists to consider.
"It identifies another tool that can be used by conservationists," he told BBC News.
"If it is not possible to make places completely protected areas then they can look at whether a system like this will help support the rich biodiversity."
While the production system delivers economic and environmental benefits, health officials have voiced concerns about how the areca nut, which contain a stimulant called arecoline, is primarily consumed.
The native forests and farmers have lived side-by-side for 2,000 years
It is chewed either by itself or as a part of "betel quid", which generally consists of a betel leaf (from the Piper betle vine) wrapped around pieces of areca nut, slaked lime (calcium hydroxide) and generally tobacco.
In 2003, the International Agency for Research on Cancer (IARC) issued a warning that linked chewing areca nuts to an increased risk of cancer.
An IARC working group stated: "A previous evaluation in 1985 had found that chewing betel quid with tobacco is carcinogenic to humans.
"The new evaluation goes further to conclude that chewing betel quid without tobacco is also carcinogenic to humans.
"The working group also concluded that the areca nut, a common component of many different chewing habits, is carcinogenic to humans."
Dr Ranganathan said the researchers were aware of the health concerns associated with the crop, but the purpose of the study was to understand how tropical agriculture and biodiversity could co-exist in close proximity.
"Areca nut cultivation has an extremely long history in south and south-east Asia and is likely to continue for the foreseeable future," he said.
"Given this persistence, I feel that it would be a shame to overlook the potential benefits of this cultivation system for biodiversity."
Dr Ranganathan said that he intended to look for further examples of established agriculture and cultivation practises in the region that provided habitats that supported a high level of biodiversity.