important landscapes. In 2019, nearly half of
the nations in the Bonn Challenge planned to
sow tree plantations and log them regularly for
timber or pulp rather than grow wild forests.
That, despite the fact that natural forests on
average sequester far more CO 2.
So, what should we do?T
O BRANCALION, THE ANSWER is
obvious: Restore native forests,
mostly in the tropics, where trees
grow fast and land is cheap. That
may require planting. But it also
may call for clearing invasive grasses, rejuve-
nating soils, or improving crop yields for farmers
so that less land is needed for agriculture andimpor tant: How long will it last? Using num-
bers of trees as a magic “proxy for everything,”
Brancalion says, you “spend more money and
get lower levels of benefits.”
You can literally miss the forest for the trees.
T
REE PLANTING SEEMS like a simple,
natural way to counter the over-
whelming crises of climate change
and biodiversity loss. Trees provide
wildlife habitat and slurp carbon
dioxide from the atmosphere.
No wonder trees are hailed as the ideal
weapon. Why not plant more and solve more
problems? Yet for every high-profile planting
operation, devastating failures have occurred.
In Turkey, Sri Lanka, and Mexico, mass plant-
ings have resulted in millions of dead seedlings
or have driven farmers to clear more intact for-
est elsewhere. Trees planted in the wrong places
have reduced water yield for farmers, destroyed
highly diverse carbon-sucking grassland soils, or
let invasive vegetation spread.
“I don’t think tree planting is a simple solu-
tion,” says Karen Holl, a restoration ecologist
at the University of California, Santa Cruz, who
collaborates with Brancalion. Reforesting the
planet can’t substitute for cutting coal, oil, and
natural gas emissions. Tree planting also can’t
replace old-growth forests. It took hundreds
or thousands of years to hone those intricate
biological (and carbon-sequestration) systems.
Saving them is even more important than grow-
ing new forests.
A tree’s true value is that it’s long-lived, which
means someone must make sure it doesn’t die.
Ethiopia, to great fanfare in 2019, claimed to
have planted 350 million trees in one day, but
Holl and her students have found little data to
show how well those trees have fared. When Holl
reviewed tree- planting proposals for the World
Economic Forum, she found that even the best
efforts monitored results for only 24 months. If
the goal is carbon storage and biodiversity, “we
can’t judge that in two years,” she said. Rather
than simply planting a trillion trees, it’d be
better to grow half as many but then make sure
they’re “alive in 20 years.”
Where—and how—they get planted matters
too. Adding trees in the snowy far north darkens
the landscape, letting it absorb more sunlight,
potentially increasing climate warming. Planting
them in native grasslands can damage equally
Workers on a former
eucalyptus plantation
are transforming it into
a native forest on an
experimental farm run
by the University of
São Paulo. Anderson
da Silva Lima and Eder
Araujo plant seedlings
of Rapanea trees, a
species prevalent in
Brazil’s Atlantic Forest.
VICTOR MORIYAMA130 NATIONAL GEOGRAPHIC