National Geographic : 1990 Sep
Deadwood metropolis FTER FIVE CENTURIES of life, a Douglas fir lives on by proxy for another half millennium as a downed log (shown in cutaway in the paint ing at left). It may once have housed in its branches a secre tive marbled i murrelet (right), a bird whose nest is so rarely seen in the trees of North America That this one is only the fourth ever recorded. *0 Researchers Nancy Naslund and Robert Burton made the discovery in California's Big Basin Redwoods State Park. Now, however, the dead log supports an immense colony of small life - from a crack in the bark, used by a folding-door spider I for its nest, to the log's center, where black heartrot fungi 2 consume the heartwood. Boreholes of Douglas fir bark beetle larvae 3 remain long after the insects have damaged the tree. Large larvae of the ponderous borer 4 and golden buprestid 5 tunnel their way through bark and sap wood to the heartwood. Fungi such as white pocket rot 6 spread through the wood, cracking apart the annual growth rings and opening the tree to invasion by the elements. Eventually termites follow, with thousands of soldiers and workers building citylike chambers 7. Below ground, living Douglas fir roots 8 benefit from yellow and black mycorrhizal fungi 9, which pass along nutrients. Some of the fungi fruit as truf fles 10 to be dug and eaten by the red-backed vole II. Hunters, such as the pseudo scorpion 12 and the centipede 13, and scavengers, like the orib atid 14 and the earwig 15, prowl loose bark for a meal. When a flying squirrel 16 alights to dig for truffles, it can come to a quick end in the jaws of a marten 17; the limbs of a tree provide relative security but no guarantee against the talons of a spotted owl 18. Logs that rot in streams create pools, retard erosion, and enrich fisheries. When a log falls partly into a stream, it creates a mini-rapid, where the water is aerated and cooled by turbulence. Aquatic insect lar vae 19 thrive in the clean water and use bits of wood for food and habitat building. This cool, oxygen-rich water is vital for coho salmon 20 and steelhead 21, and they in turn feed on the aquatic insects. Saps and resins help living trees keep insects in check, but the dead log provides shelter and food to insect armies, which turn it into a sponge that stores moisture and renews forest soil. Biologists find at least 116 vertebrates at home in an old growth stand, and more than 40 species may need such a habitat to survive. Though not as diverse as a tropical rain forest, this temperate rain forest surpasses it in sheer mass of life by seven to one. PAINTINGBYJACK UNRUH CONSULTANTS:JERRY F. FRANKLIN,UNIVERSITY OF WASHINGTON;LOGANNORRIS, OREGONSTATE UNIVERSITY;CHRIS MASER Old-Growth Forests: Will We Save Our Own?