Ecosystems need diversity to survive

By Joanna Egan 12 February 2013
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When native plants are removed from farmland, entire ecosystems are placed at risk, new research suggests.

BIODIVERSITY LOSS PUTS ECOSYSTEMS at risk of collapse after a bushfire, new research reveals.

About 40 per cent of the Earth’s surface is made up of farmland heavily regulated by people. Although land management practices – such as cultivating non-native plants, intensive grazing and stopping bushfires – lead to productive farmland, they also cause many native plants to disappear.

A study published in science journal Nature last week reveals how reduced biodiversity in these ecosystems causes them to become vulnerable to collapse following a major disturbance, such as a bushfire or drought.

“We demonstrated the hidden risks of biodiversity loss in managed systems,” lead researcher Dr Andrew MacDougall, from the University of Guelph in Canada, told Australian Geographic.

“Intensive land management is a bit like investing in only one stock that happens to be phenomenally successful,” he explains. “As long as the market is favourable, the strategy has a huge payoff. But with market perturbation, only a diversified strategy will be able to buffer against this change and maintain profit.”

The dangers of land management

During the 10-year study, Andrew and his team examined the effects of introducing bushfire to a series of grasslands. The area was dominated by invasive grasses introduced during the 1800s, and land managers have actively prevented fires there for about 150 years.

“As is the cases with many grassland systems globally, the entire range is characterised by fire suppression, habitat loss and extreme plant invasion,” says Andrew.

The study found that as long as the grasslands were managed by humans, and remained unaffected by outside disturbances (in this case a fire), they could be maintained. However, once the researchers set the grasslands alight, the ecosystems failed.

“When perturbation did finally occur, the effects of biodiversity loss were revealed: the system collapsed, except where collections of native species still happened to be persisting,” Andrew says.

“We were surprised [at] how quickly the collapse occurred,” he says. Without the buffering effect of biodiversity, areas that were covered in exotic grasses were rapidly taken over by invasive woody plants within the space of one year.

The findings highlight the importance of biodiversity in ecosystem stability. “The frequency of sudden disturbances appears to be increasing, via fires and climate change in particular,” Andrew says. “Our work suggests this combination of factors, management and perturbation, could lead to state-shifts – lost production, rapid invasion by commercially undesirable species – not seen in areas where levels of resident diversity are higher.”

The importance of native species for environmental stability

Andrew suggests land managers should embrace biodiversity by reintroducing native species in order to safeguard the landscape against the devastating effects of fire and climate change.

“You only become aware of the risk of not diversifying after the system has collapsed,” he says. “That’s what we mean by ‘hidden risk’.”

Professor David Bowman from the University of Tasmania in Hobart agrees that diversity is crucial to maintaining an ecosystem.

“This is a nice study of how biodiversity has effects that may be dormant, and hence the loss of biodiversity may make apparently productive ecosystems vulnerable to change,” he says.

“Any management regime that rips out diversity is vulnerable,” David adds. “Diversity matters as a stabilisation insurance.”