2852856262128128959548485757ASIAASIA
AFRICAAFRICAEUROPEEUROPEOCEANIAOCEANIAAMAMNORTHNORTHERICAERICAAMAMSOUTH SOUTH ERICAERICAinches^140160
inches120
100
80
60
40
2060304050708090°F691373660
778442100
50
25(^105)
Elevation(feet)
Over 9,000
7,000-9,000
5,000-7,000
3,000-5,000
1,000-3,000
0-1,000 48
5 studies
19
13
27
40
Location of 675 published tree
mortality sites
(1970-2018)
Boreal forest
Humid tropical forest
Nummortality sitesber of tree
WET
COLD & WET
HOT & WET
HOT & DRY
COLD & DRY
DRY
COL
D
HOT
Ann
ual^ a
vera
ge
TEM
PER
ATU
Annual RE
ave
rage
PRE
CIPIT
ATIO
N
Total sitesTotal sites
SHINTANI, NGMMONICA SERRANO AND CHRISTINA STAFF. SOURCE: WILLIAM ORSOLYA HAARBERG
AVERAGE OVER FIVE DECADES, FROMCLIMATE DATA SHOWN HERE REPRESENT THE 1970 TO 2018. HAMMOND ET AL., COMMUNICATIONSNATURE
How exactly do trees
die of thirst? As part
of a 20-year project to
answer such questions,
University of Basel
plant ecologist Ans-
gar Kahmen (at right)
and technician Lucio
Rizzelli regularly ride
into the canopy of a
research forest. Here
they’re measuring the
water vapor that a
Norway spruce sheds
through its needles.
SWITZERLAND
HÖLSTEIN, NEAR BASEL
WHICH TREES WILL
SURVIVE A HOTTER,
DRIER FUTURE?
ALL FORESTS
ARE AT RISK
Trees have a range of
climate conditions they
can withstand. But
when temperature and
precipitation change
in frequency, duration,
or severity, trees and
entire forests can fail.
Forests cannot grow in these
cold and wet
extremes.
unique sites of scientifically re-
ported die-offs
over the past
five decades
675
Die-offs in boreal forests and rainforests, both
critical absorbers and
storers of carbon dioxide,
are likely underreported.
WORLDWIDE LOSSES
Trees are facing unprecedented mortality events around the globe. These
die-offs are projected to accelerate as more frequent and severe droughts
and heat waves push trees—especially old-growth forests that matured
under bygone conditions—beyond their threshold of survivability.