This is
the first time scientists have assigned a monetary value to the pest-control
benefits rainforest birds can provide to agriculture. Their study could provide
the framework for pest management that helps both farmers and biodiversity.
By Bjorn Carey
September 3, 2013
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The yellow warbler (Setophaga petechia) is a pest-eating bird
that
frequents coffee plantations. PHOTO: Courtesy of Stanford Report
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In recent years,
Stanford biologists have found that coffee growers in Costa Rica bolster bird
biodiversity by leaving patches of their plantations as untouched rainforest.
The latest finding
from these researchers suggests that the birds are returning the favor to
farmers by eating an aggressive coffee bean pest, the borer beetle, thereby
improving coffee bean yields by hundreds of dollars per hectare.
The study is the
first to put a monetary value on the pest-control benefits rainforest can
provide to agriculture, which the researchers hope can inform both farmers and
conservationists.
"The benefits
that we might get are huge," said Daniel
Karp, a graduate student in biology and lead author of the study.
"There's lots of unrealized value in these small patches of rainforest.
This looks like a sustainable, win-win opportunity for pest management."
The researchers hope
that the work will improve conservation efforts in heavily farmed areas by
illustrating to farmers the financial benefits of leaving some land in its
natural state, while also guiding governments toward the best conservation
methods.
Worldwide scourge
By some accounts,
coffee is the world's most economically profitable crop, and its harvest
supports the livelihoods of some 100 million people globally. Coffee beans
around the world, however, are threatened by the pervasive beetle.
The insect burrows
into the beans and eats its way out, ruining the beans. It originated in Africa
and has made its way into nearly every major coffee-producing country. It
arrived in Hawaii two years ago, and coffee plantations there are already
experiencing 50 to 75 percent less yield.
"It's the only
insect that competes with us for coffee beans," Karp said. "It's the
most damaging insect pest by far, causing some $500 million in damage per
year."
Stanford biologists
have been studying the intersection of nature and agriculture in Costa Rica
since the 1990s, in part because of the vast amounts of land in that country
dedicated to coffee production. The borer beetle arrived in the past few years,
and Karp's group began to investigate whether farms with protected forests, and
thus a greater biodiversity of insect-eating birds, fared better under attack
from the insects.
A 'not-so-glamorous' experiment
To quantify the
benefit birds provide to plantations, the researchers first calculated coffee
bean yield – the amount
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The coffee berry borer beetle (Hypothenemus hampeii) is coffee's
primary
insect pest and is consumed by native birds.
PHOTO: Courtesy of Stanford Report
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of healthy, beetle-free beans that could be harvested –
of infected plants that were housed in bird-proof cages versus yield from
infected plants in the open, where birds were eating the beetles.
Next, they needed to
confirm which species of birds were eating the beetles, and whether the birds
required forest to survive. This required a more unorthodox approach.
"We had the
not-so-glamorous task of collecting the birds' poop, and then taking it back to
Stanford and looking through the DNA within it to learn which birds were the
pest preventers," Karp said.
Five species of birds
contributed to cutting infestation rates in half, and these birds were more
abundant on farms featuring more forests.
"Depending on
the season, the birds provide $75 to $310 increases in yield per hectare of
farmland," Karp said. The birds' activity could become even more valuable
if the beetle infestation worsens.
The scientists found
that the closer the forests were to the farms, the greater benefit the birds
provided. Specifically, smaller stands of trees – roughly the size of a few
football fields – situated throughout crop fields provided better levels of
beetle protection than the much larger forest preserves set on the outskirts of
farms.
By differentiating
the financial gains of different conservation strategies – large but distant
preserves versus small, local stands of trees – Karp thinks the study could
provide a framework for introducing similar efforts in agricultural zones
around the world.
"This work
suggests that it might be economically advantageous to not farm in certain
areas of a plantation," Karp said. "We're going to start trying to
generalize these results so that farmers, conservationists, land managers and
governments can use them anywhere to make simple estimates of what they might
gain in pest protection by protecting certain patches of the landscape."
The study
was published in the online edition of the peer-reviewed journal Ecology
Letters. The work was co-authored by Stanford biology Professors Gretchen
Daily, Paul Ehrlich and Elizabeth Hadly; biology graduate student Chase
Mendenhall; Nicolas Chaumont, a software engineer at the Natural Capital
Project; and Randi Figueroa Sandi, a field assistant in Copal de Agua Buena in
Costa Rica.
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