Iturria:
Science Daily
ScienceDaily (Aug. 6, 2012) —
Compared with open farmland, wooded "shade" plantations that produce
coffee and chocolate promote greater bird diversity, although a new
University of Utah study says forests remain the best habitat for
tropical birds.
The
orange-billed nightingale-thrush is an insect-eating bird that lives on
Costa Rican “shade” coffee plantations. A new University of Utah study
indicates that, compared with open farmland, wooded “agroforests” like
shade coffee and cacao plantations promote bird diversity and also the
“ecosystem services” birds provide to human society, including insect
control, spreading seeds and pollinating crops. (Credit: Çağan
Şekercioğlu, University of Utah)
The findings suggest that as open farmland replaces forests and
"agroforests" -- where crops are grown under trees -- reduced number of
bird species and shifts in the populations of various types of birds may
hurt "ecosystem services" that birds provide to people, such as eating
insect pests, spreading seeds and pollinating crops.
"We found that agroforests are better overall for bird biodiversity
in the tropics than open farms," says study author Çağan H. Şekercioğlu
(pronounced Cha-awn Shay-care-gee-oh-loo), an assistant professor of
biology at the University of Utah.
"This doesn't mean people should farm in intact forests," the
ornithologist adds. "But if you have the option of having agroforest
versus open farmland, that is better for biodiversity, with shade coffee
and shade cacao [the source of cocoa and chocolate] being the prime
examples."
Şekercioğlu's new study, funded by the University of Utah, is being published this month in the
Journal of Ornithology. He will present the findings on Aug. 9, at the Ecological Society of America's annual meeting in Portland, Ore.
If consumers wish to support bird diversity and agroforests, "a good
way is by choosing certified, bird-friendly, shade coffee or shade
chocolate," he says. While such coffee or chocolate often cost more
because they are more labor-intensive to produce, the certification "is
usually better for the farmers' income as well."
He adds: "There are trustworthy environmental organizations that
certify shade coffee," including the Smithsonian Institution, the
Rainforest Alliance and the Rainforest Action Network.
Other crops grown in shade include cardamom, which is a spice, and
yerba mate, which is steeped in hot water to make a beverage popular in
South America.
Study Focuses on Birds of Forests, Farms or Both
An agroforest "is a type of farm where the crops are grown under
trees at a reasonable density," Şekercioğlu says. "Often, it's not like
forest-forest -- it feels more like a open park," although in Ethiopia
"commercial coffee is grown under full-on forests in its original native
habitat."
Şekercioğlu conducted the study in two steps. First, "I used my world
bird database that has information on all the 10,000-plus bird species
of the world," he says. "I sorted birds based on habitat choices and
compared species that prefer forests to those that prefer agricultural
areas and others that prefer both forests and agricultural areas."
Next, he reviewed about 40 previously published studies that examined
bird communities in forests, agroforests and open agricultural areas.
"The global analysis of all the birds species mostly agrees with the findings of detailed local bird studies," Şekercioğlu says.
The study focused 6,093 tropical bird species, including migratory
birds, in which their top three habitat choices (out of 14 possible
habitats) included forests, farms or both, with the latter described as
agroforest birds. So the study found 4,574 bird species that include
forest but not farms in their top three habitats, 303 species that
include farms but not forests in their top three habitat choices, and
1,216 agroforest species tha include both forests and farms among their
top three habitats.
The findings suggest, but don't prove, that conversion of forest to
farmland may reduce ecosystem services, which are services birds provide
to people.
"As you go to more and more open agriculture, you lose some bird
groups that provide important ecosystem services like insect control
[insect eaters], seed dispersal [fruit eaters] and pollination [nectar
eaters], while you get higher numbers of granivores [seed and grain
eaters] that actually can be crop pests," Şekercioğlu says.
Specifically:
-- Insectivores or insect-eating birds do best in forests --
especially those that live near the ground in the understory, the layer
of plants below the tree canopy and above the ground cover. But small
and medium insect-eating birds, especially migrant and canopy species,
do well in agroforests. The number of insect-eating species declines on
open farms, where they help control pests.
-- Frugivores or fruit-eating birds, especially larger ones, "do best
in forest because they have more habitat and more food, and the large
ones often are hunted outside forests in agricultural settings. Overall,
frugivores -- especially smaller ones -- do OK in agroforests, but the
number of fruit-eating species decline significantly on open farms."
Frugivores help spread the seeds of the fruits they eat.
-- Nectarivores or nectar-eating birds help pollinate many plants.
They "tend to increase in agroforests compared with forests. A lot of
nectar-eating birds obviously like flowers, and many plants flower when
there's some light. When you have extensive forest its often pretty
shady so not many things are in flower at any given time." The nectar
eaters are less common on open farms.
-- Omnivores, which are birds that eat many things, "tend to do
better in agroforests and especially on open farms" than in forests,
because their diet is so generalized instead of specialized in certain
foods.
- Granivores, or grain- and seed-eating birds are "the only group
that significantly increases in open agricultural areas. A lot of the
seeds they eat are grass seeds, but also from crops. Some of these
seed-eating bird species are major agricultural pests, and that's
another reason for encouraging agroforests. In completely open
agricultural systems, you have more seed-eating birds that can cause
significant crop losses."
While the study found fewer species on farms than in agroforests, and
fewer on agroforests than in forests, Şekercioğlu says it doesn't
answer a key question: "Does the decline in the number species translate
into a decline in individuals providing a given ecosystem service?" If
so, farms and agroforests have lost birds that provide important
insect-control, pollination and seed-dispersal services.
"It is possible you may lose a lot of species, but some of the
remaining species increase in number and compensate and for the decline
in ecosystem services by the lost species," he adds. "It's one of the
biggest questions in ecology."
The Trend toward Sun Coffee
Noting that the study found forests have more tropical bird species
than agroforests, which in turn have more bird species that open farms,
Şekercioğlu says: "A lot of threatened species globally are found only
in forests, and most of them disappear from agroforests and open
agricultural areas."
He says many migratory birds that breed in the United States are in
decline -- even though the nation has a law to protect them -- and not
just because of U.S. environmental problems, "but due to problems in
their wintering grounds in Latin America, such as loss of habitat and
intensification of agriculture."
"Coffee was originally a mid- to high-elevation African forest
understory plant," he adds. "For centuries in Ethiopia and parts of
Central and South America, coffee has been grown as an understory plant
with shade traditionally provided by native trees."
But fungi can be a problem in humid shade coffee plantations, and
growers have come up with varieties that grow well in the sun with less
fungus and bigger yields, so in recent decades, there has been a trend
toward converting Central and South American shade-coffee forests to
open farms, Şekercioğlu says.
"As tropical forest is converted to increasingly open types of
agriculture, hundreds of endangered bird species are being lost," he
says. "Tropical forest is the only refuge for thousands of bird species
and hundreds of endangered bird species. Although agroforest is better
than open farmland, at the end of the day intact tropical forest is the
only suitable habitat for thousands of bird species."
