SYDNEY: A large-scale study has confirmed for the first time that biodiversity has a positive impact on the functioning of dryland ecosystems.
Scientists now understand that having a high number of various species of plants, not just a large number of plants, helps dryland ecosystems to perform many functions.
“It’s backing up what we would intuitively expect,” said David Eldridge from the University of New South Wales in Sydney, co-author of the study published in Science today. “Having a lot of the same plants is good but having a lot of different plants is, what we’re saying, much, much better.”
Biodiversity in the drylands
For years, biodiversity has been considered beneficial to the environment because having a high variety of species allows ecosystems to provide a large range of services such as food, carbon sequestration and nutrient cycling.
“Over the last 20 years the broader community has been told biodiversity is important,” said Eldridge. “There’s always been this underlying notion that a system that has more species functions much better. It provides essential services – oxygen, water and a better environment for everybody including humans. But this notion that diverse ecosystems are healthier and more functional have really been developed using experiments.”
These experiments, though useful in showing that biodiversity has a positive effect on artificial ecosystems in greenhouses, couldn’t be extrapolated to indicate the patterns of natural drylands. Small-scale studies of some drylands have also shown a benefit from high species variety but again, couldn’t be considered a basis for global inferences. To determine global dryland patterns, a global study was required.
A global endeavour
In the first large-scale study of drylands, Eldridge and his colleagues worked in over 220 drylands within 14 different countries that covered every continent except Antarctica.
Each dryland had large 30m x 30m plots set up to represent the main ecosystem. Within these plots the scientists measured numerous functions related to the cycling of carbon, nitrogen and phosphorous which are essential for life on Earth. The level of biodiversity in each plot was compared to other factors such as rainfall, temperature and soil composition.
The results indicated that biodiversity was an important attribute for the ecosystems studied, helping the soil maintain its multiple functions such as carbon storage, production and the build up of nutrient pools. Cooler temperatures and low sand content of soil were similarly important.
With Earth’s drylands covering 41% of the global land surface and supporting 38% of the world’s population, it is crucial that their ecosystems are understood. Warming temperatures from climate change could threaten the survival of many of these species and thus threaten biodiversity in these ecosystems, said Eldridge. The study highlights that this may have a flow-on affect to the soil’s ability to sequester carbon and protect from desertification, essentially escalating further warming.
Addressing an age-old problem
High biodiversity was not statistically more important than many of the attributes measured to determine the multiple functions of drylands, according to Rod Fensham from the University of Queensland in Brisbane, who did not take part in the research.
“In all those candidate models species richness [variety] was important. What is less clear when you conduct those analyses is how important,” he said. Fensham added that this research addressed an age-old problem, and future studies should look to find out why biodiversity is important for ecosystem functioning.