Biologists traditionally measure biodiversity by calculating the number of a species in a given area, but the new method uses statistical analysis to see how one species affects others in an area.
The researchers reported the new method — 'individual species-area relationship' (ISAR) — in the Proceedings of the National Academy of Sciences.
ISAR ( 'individual species-area relationship' )
Botanists from the University of Peradeniya in Sri Lanka and the Helmholtz Centre for Environmental Research in Germany looked at how individual tree species suppress or encourage the growth of other species nearby.
They used the method in tropical forests of Barro Colorado Island in Panama and Sinharaja in Sri Lanka to see whether individual species increased or decreased local biodiversity, or had no impact.
They found that more than two-thirds of species did not have much impact on  large forest areas. The remaining third impacted only on a small scale, up to a radius of 20 metres.
The scientists say this supports the theory that the diversity of forests and similar complex natural biological systems does not depend on the characteristics of a few dominant species but on the overall interactions among all species.
"It is a step towards understanding why and how the tropical moist forests maintain such a high species richness," Nimal Gunatilleke, professor of botany at the University of Peradeniya and an author of the paper, told SciDev.Net.
Gunatilleke says the ISAR method should be tried in other tropical forests and temperate forests, to verify and improve it if necessary. The method has potential for use in scientific conservation management of forests and predicting forest health, he says.
Thorsten Wiegand, one of the researchers from the Helmholtz Centre for Environmental Research, told SciDev.Net the new tool should be used along with other standard biodiversity tools to provide a more complete picture.
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A drawback of the new method, says Wiegand, is that it requires an enormous amount of data. For example, tropical forests require mapping individual trees in plots of more than 25 hectares. There are few plots of this size available worldwide.
"However, the insight gained will improve the understanding of factors and processes that govern species-rich communities and therefore may have an indirect impact on conservation of species rich communities," he added.