Losing bio-diversity can destroy a farmland's ability to bounce back from disasters such as fires and droughts, a Canadian study, one of the first to test the thesis in the field, suggests.

The study focused on long-term attempts to protect valuable pastureland from fire damage — a process that can lead to a loss of bio-diversity and, in turn, the inability to recover and regenerate should a fire occur.

But efforts to protect valuable tree species in timber forests and farmland likely also give rise to the risk of similar potential catastrophes, says lead author Andrew MacDougall, a biologist at the University of Guelph in Ontario.

Before European settlement, the oak savanna ecosystem was densely populated by native plants such as the purple camas lily and yellow western buttercup. (Andrew MacDougall/University of Guelph)

The findings, published Wednesday online in Nature, suggest that the extinction of local plant and animal species — and the accompanying loss of biodiversity — aren't just sad and unfortunate, but can also cause real economic harm to humans.

Managing farmland to favour certain crops, or forests to promote the growth of valuable timber is "like investing in one stock that's doing really, really well," Canadian biologist Andrew MacDougall says. "That's a winning strategy only as long as your stock continues to thrive."

Like a stock crash

The problem, he said, is sometimes a "market perturbation," such as a new competitor or, in the case of nature, challenges such as an invasive species, fire, or drought, can arise.

"The thing is, you don't know you're at risk until it's too late. You don't know your stock is going to crash until it crashes. That analogy pretty much describes what we found in our system."

In areas where fire has been supressed for decades, the savanna is dominated by exotic grasses. (Andrew MacDougall/University of Guelph)

The ecosystem that MacDougall studied for more than a decade was an oak savanna on Vancouver Island, grassland mixed with trees and surrounded by a Douglas fir forest. The grassland was dominated by "exotic" grasses planted by European settlers to feed their sheep and cattle when they settled the area in the 1840s.

To protect their families, homes and pasturelands, they took measures to stop fires — which used to be started frequently by First Nations people in the area — from breaking out and spreading.

"For the good of humanity, if you will, fire suppression was seen as critically important," MacDougall said.

While many native species were adapted to survive fires, many of them had been completely replaced by the exotic pasture grasses during the century and a half of fire suppression.

MacDougall set out to find out if burning plots at different intervals would cause the native plants to grow back, as some people thought they would.

What he discovered was that in most cases, there weren't enough native plants left for that to happen.

No comeback for native plants

The fire completely wiped out the exotic grasses, which weren't very fire resistant, leaving behind bare soil that was taken over by forest within one growing season, eliminating the pastureland once and for all.

"The rapid switch that we saw to woodland within one growing season is dramatic … it almost never happens," MacDougall said. "Once that happens, you're never going back.

"Basically the restoration assumption about fire creating this native 'Eden' again totally didn't work."

The only places where the savanna survived was where there had been an unusually high diversity of native plants.

While controlled laboratory experiments had previous suggested that a lack of biodiversity makes ecosystems more vulnerable to stresses such as fire, invasive species and droughts, MacDougall believes his study is the first to show that is what occurs in a natural ecosystem.

He warned that the findings illustrate the risk posed by the human tendency to grow a very small number of plant species with a consistent set of traits — such as high yields, but poor drought tolerance — at a time when climate change is increasing the frequency of events such as droughts and fires.

"We have to think about managing our portfolio more diversely to handle these environmental perturbations that seem to be increasing in frequency."