FROM TOP: JAMES TRACY/TEXAS A&M UNIVERSITY/USGS; KATHERINE MAST; RICK AND NORA BOWERS/KAC PRODUCTIONS20 DISCOVERMAGAZINE.COM→
It’s a hazy Sunday morning in
early July as Levi Jamison pulls
to the side of the road in central New
Mexico. He grabs a camera, clipboard
and thick canvas insect net from the
blue Volkswagen van that is his travel-
ing home and office, and begins to hike
along an irrigation ditch just east of
the Rio Grande. A seemingly unending
thicket of tall, shrubby tamarisk trees
parallels the ditch. He stops just a few
feet in, picks a tree at random, and
sweeps the net over the dusty-green
leaves exactly five times. Then, he peers
into the canvas, quickly counting a
mass of tiny Diorhabda beetles already
crawling up the fabric to escape.
He scribbles the number — “160,”
he says — and the GPS coordinates in
his notes. That’s a drop from the 200
or 300 per net he’s seen here before.
Jamison, a biologist now with the
Colorado Plateau Research Station
at Northern Arizona University, has
long tracked the tamarisk leaf beetle
through the Southwest. One trip, hesays, these trees dripped with beetles.
Whether that’s a good thing depends
on whom you ask. These Old World
beetles were imported and released in
the early 2000s as a biological control
for tamarisk, a once-beloved Eurasian
tree that now monopolizes vast
stretches of western waterways.
And the beetles are doing their
jobs, munching away at tamarisk
leaves — their only food — and leaving
swaths of brown, defoliated trees
in their wake. A single feast doesn’t
usually kill the trees; it just weakens
them and temporarily halts their
summerlong seed production. But
repeated attacks year after year have
reduced tamarisk cover by up to 50 to
90 percent in some places. Everyone
was surprised how quickly the beetles
adapted to their new home, and how
quickly they spread.A WATER HOG?
The pretty, wispy tamarisk with its
scalelike leaves and delicate white or
pink flowers is thought
to have arrived in North
America as a decorative
plant sometime in the
early 1800s. Toward
the end of that century,
federal agencies were
celebrating the success of
the tree — also called salt
cedar — as a riverbank
stabilizer that could
tolerate drought.
In 1930, it was a cure-all
for erosion concerns in the
West. Before long, it was
vilified as a water-hoggingmonster. And by the 1950s, federal and
state agencies had galvanized to bring
the monster down.
But tamarisk isn’t quite the monster
it’s been made out to be. Sure, it’s highly
flammable, and it may salinate the soil
when it drops its salty leaves. But water
hog? Turns out, it uses roughly the
same amount of water as native ripar-
ian trees like willows and cottonwoods.
Since the middle of the 20th century,
humans have dramatically altered west-
ern rivers and made it harder for native
trees to compete. We’ve built dams and
diverted water, and we’ve tamed the
periodic floods that once spilled over
riverbanks to sprout new generations
of willows and cottonwoods. As we
engineered the rivers, tamarisk increas-
ingly had the upper hand.
In response, some native birds — like
the Southwestern willow flycatcher,
which loves dense shrubs along desert
waterways — turned to tamarisk trees
to make their nests.
And for vast swaths of western rivers,
tamarisks are now the only tree. They
are the third most prevalent riparian
tree in the West and can grow as a
monoculture. And that decreases
biodiversity of other plants, wildlife
and even fungi. “What’s problematic
is that when it grows aggressively, it
dramatically changes the landscape in
ways that negatively affect native fauna
and flora,” says University of Denver
ecologist Anna Sher, who studies
tamarisk and riparian restoration.CREEPING IN ON FLYCATCHERS
Controlling tamarisk is a herculean
task. Bulldozing just creates a Hydra,The Beetle, the Bird
and the Tamarisk Tree
Ecologists seek balance as one non-native species eradicates another.
BY KATHERINE MASTLevi Jamison nets and
counts tamarisk beetles in
New Mexico. The biologist
is tracking the insects as
they move through the
Southwest and threaten
habitats of native species,
like the Southwestern
willow flycatcher (below).Tamarisk
beetleNotes
From
Earth