IN THIS SECTION LOST CONNECTIONS (A) Network map (B) Hub trees removed Gobi Desert By sharing resources, networked forests 47% connections lost Hub tree with healthy hub trees become more Fungal Pangaea network resilient. Researchers examined fungal EXPLORE Looming Crocodile DNA to map connections in a Canadian Younger Basic Instincts forest (A) and found that the selective tree removal of hub trees (B)—by loggers, Pop Omnivore for example, or from an insect invasion— could cause more connections to be lost 30 ft ILLUMINATING THE MYSTERIES—AND WONDERS—ALL AROUND US EVERY DAY than if trees were removed randomly. NATIONAL GEOGRAPHIC VOL. 233 NO. 6 Clear-cutting would destroy all links. All distances are to scale; tree diameters shown at larger scale.

BENEATH A SINGLE PATCH of forest soil lies a vast interconnected web of life. TALKING Forest ecologist Suzanne Simard likens it to a kind of hidden intelligence. By tracking specific chemicals, she and other scientists observed how trees in TREES the Douglas fir forests of Canada “talk,” forming underground symbiotic rela- tionships—called mycorrhizae—with DAISY CHUNG AND fungi to relay stress signals and share RYAN T. WILLIAMS resources with one another. Western spruce budworm

Douglas fir Douglas fir Paper Douglas fir (hub tree) (younger tree) birch (hub tree)

C E

h x

c e e Seasonal partners m s Understory nursery Pine preparation s i c Deciduous paper birch a s Douglas fir trees use the Fir trees infected with bud- u l

g and evergreen Douglas fir s a Douglas fir network to identify and t worms send stress signals to Ponderosa r

r e f trade resources seasonally. r (seedling) nurture related seedlings. s nearby pines. pine o s m s

i p g

h n o t In spring and fall, firs share a o l sy sugar with leafless birches. s nt he sis In summer, birches return Symbiotic the favor to shaded firs. fungal network

Resource pathways Sugar from trees Symbiotic fungal network Nutrients from soil Nitrogen, potassium, Enlarged section Mixed resources from network: phosphorus, and of tree root tip nutrients and carbon (from sugar) other nutrients Resource- Chemical stress signals exchange FOREST IN pathway DISTRESS Fungal thread

WARNING SIGNS Through the network, trees under 1 2 3 stress can transfer resources, such as Excess production Exchange of goods Deep connections water, and can send chemical signals Taller, older trees, called hub trees, A mass of fungal threads, or mycelium, Weaker firs in the shaded understory that trigger defensive mechanisms in often have more access to sunlight envelops the root tips of a hub tree, feed­ tap into the network as it swells with other trees. Threats like insect infes- and produce more sugar through ing it nutrients from the soil in exchange resources. Firs can also share with other tation and drought are expected to photosynthesis than they need. for sugar, which the fungus lacks. species, such as birch. increase as the climate changes. Tree root cell

26 NATIONAL GEOGRAPHIC ART: BEAU DANIELS. SOURCES: SUZANNE SIMARD AND CAMILLE DEFRENNE, UNIVERSITY OF BRITISH COLUMBIA; KEVIN BEILER, BEUTH UNIVERSITY OF APPLIED SCIENCES BERLIN DECODER