National Geographic - UK (2022-05)

Water

Cork

Phloem

Bark

Xylem

HEALTHY STRESSED

Healthy / Stre

RESERVES

Food

Water

Dry soil

retains water.

Root

Water

Airbubbles

Gatmreater ospheric

pull of water

OTHE

Rte

1/8 inch

Cedabeetr balerk

Life cycle

2 years

Life cycle

1 year

E

D

Pipiñonen Giant

sequoia

Fire

scarring

1

2

3

2

3

Inleasifde Needle

Ostpomen ata

Water

Clstoosematad

Food Food

Water

Root

Lwateress

CO 2 CO 2

Resin

Tunnels

Carbon dioxide

converted

to food

Water

1

ROOTS OF A CRISIS

As temperatures rise because of climate change,

trees are being hit with heat waves and drought,

killing them or weakening their resistance to a

cascade of pressures, from pests to rising sea levels.

OPEN ACCESS

To make food (car-

bohydrates) and stay

cool, the tree absorbscarbon dioxide and

releases water through

pores called stomata.

LOCKDOWN

Stomata close to avoid

water loss, but this stops

tdhe uptake oioxide. The tree canf carbon

die if it depletes its

food reserves.

Bark beetles b

taheir assault ttacking brab

where bark is

A healthy tree

chemical defe

abundant res

oweaut invaders; kens thos

Once inside, b

bore tunnels a

on the bark’s

ldayer that shistributing of

Rising temper

mcycles of somay speed upe

leading to mo

of attacks.

aHnd trees durinotter air pulls mg a drouore water ght, even from soil

as heat stress requires trees to pump

more water to leaves. To survive

mrarilounty shut down soming stressors, trees me processes.ay tempo-

Umnder repeated stress, even theost pest-resistant trees are at

risk. Bark beetles, previously not

known to kill giant sequoias, have

recently cient trees afelled dozens ofter droughts and f the an- fires.

WORKING FLOW

The atmosphere pulls

water from roots to can-

opy through the pipelike

xyuted via the phloemlem. Food is distrib. -

BROKEN FLOW

Lack of water can create

air bubbles in the xylem,

impairing water trans-

pofort and raisin tree death.g the risk

WET SOIL

Roots can expand or

contract their sur-face area and depth

in response to water

availability in the soil.

DRY SOIL

In a drought, a tree must

comsoil for water. The tree has pete with dried-out

greater demand for water

even as less is available.

HEAT AND DROUGHT PESTS

MNATHAN L. STEPHENSON, USGS; ANNA WONICA SERRANO, NGM STAFF; MESA SCHUM. SCHOETTLE, U.ACHER. SOU

HEALTHY STRESSED