Bark is Beautiful

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Meanwhile, a trees inner bark develops a complex structure of tubelike conductive cells that serve as the trees nutrient delivery system. Starting each spring, the tree absorbs water through its roots and conducts the mineral-rich liquid through thousands of tiny hollow vessels in the wood to the leaves above. But its the inner barks conductive cells that carry the concentrated sugars and other carbohydrates produced by photosynthesis back down through the stem and into every living cell of the tree. In hardwoods, the cells are long and strawlike, stacked end to end and connected to horizontal ray cells that distribute the liquid food to the trees innermost tissues. In the inner bark of conifers, densely packed sieve cells with minute pores in their walls pass the nutrients slowly from cell to cell.

Habitat and Highway

From an animals point of view, tree bark is anything but dead space. For some, its a roof over their heads. North American gray tree frogs and adult mourning cloak butterflies spend the entire winter beneath loose bark, semifrozen but sufficiently protected to emerge in spring full of hop and flutter. In nesting season, a mother-to-be brown creeper seeks out a dead tree with a long, peeling bark scale and builds her nest around and beneath it, raising as many as six fledglings inside the bark-covered shelter.

For countless insects beetles, moths, flies, termites, mealybugs and more bark is either home, hiding place, snack bar or all three. So closely associated are some moths and other insects with certain kinds of tree bark that theyve evolved to look like it, their bodies and wings mimicking the colors and patterns of the bark they occupy to camouflage their presence from predators. Of course, many insects beetles especially can be harmful to trees, boring into the bark and laying eggs that produce tunneling, tissue-gobbling larvae. The good news is that these same bark-invading insects turn the tree into a vertical platter for birds such as nuthatches and woodpeckers.

Other creatures use tree bark to their advantage, too. Chickadees pluck the heads off insect prey, then stuff the bug bodies beneath bark scales as snacks to be retrieved in winter. Northern flying squirrels make their nests primarily of finely shredded bark. Mice, rabbits, porcupines and deer strip away the outer bark of young trees to nibble at the nutritious inner bark.

Tree bark also serves as a conduit for all sorts of creatures seeking higher places. For squirrels, raccoons and other tree dwellers, bark is the pavement to their front doors. The rough surface of tree-bark terrain furrows, cracks, crevices gives protein-seeking snakes a foothold, making smooth-barked trees safer sites for nesting birds and animals.

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