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Life Underfoot

Trod lightly when you walk through the north woods; there is life everywhere you step!

Each year the leaves and wood that fall combine with roots and humus matter to make food for an abundant and varied group of animals who live in the forest floor. These are tiny invertebrates, animals without backbones, that make up for their lack of size by sheer numbers.

Locked in frozen soil and dormant throughout the long northern winter, an abundance of life becomes evident in the spring. Studies by University of Alaska biologists show that the life in the floor of black spruce forest becomes more abundant as summer progresses. Soil mites, eight-legged relatives of the spiders, increase in abundance from 150,000 per square meter shortly after snow melt to 500,000 in each square meter by August. To convert that to more meaningful units, I drew a line around my size 11 boot and found that each step on the forest floor covers about 44 square inches. Thus, by August, each footstep pads down on more than 10,000 individual mites, the largest of them about the size of a pin head.

Second in abundance, at least in the (barely) visible range, are the springtails; these are small, primitive relatives of the insects. Like the insects, they have six legs, but throughout their evolutionary history they have lacked wings. Many of them react to danger by catapulting through the air using a springing organ otherwise kept tucked beneath the body, hence the name springtail. These animals reach a mere 2,000 or so per footstep.

Together, the soil mites and the springtails form a mass of about 34,000 pounds per square mile. That is equal to 320,000 field mice or 43 moose. With this much meat on the hoof, predators are sure to be found. The main predators of invertebrates are spiders and centipedes, multi-legged marauders of the northern forest floor. A view of the ferocious jaws of these animals quickly reveals their purpose in life. In tropical forests centipedes may grow to be 6 inches (15 cm) in length and inflict a dangerous poisoned bite, but evolution has spared us this risk in the north.

So a special posture is recommended for nature lovers in the northern forest: hands and knees on the forest floor, nose near the ground, eyes directed downward. As you search through the litter layer with magnifying glass in hand, you'll find a whole new world of life in miniature.