April 14, 2014 Furry wood-workers excel at forestry: Beavers
Beavers are formidable harvesters. They can drop a 10-inch diameter tree within minutes. Yet, they also know how to regrow forests and promote water conservation.
Beavers are the largest of all North American rodents, weighing a whopping 44 pounds. They move slowly and awkwardly over land and so they’ve mastered the path of least resistance – floating through the forest. In fact, they are experts in the world of fresh water.
Among their remarkable traits is the flat, hairless paddle-like tail that allows beavers to prop themselves up while standing and whack the water in a highly effective, loud warning mechanism. Their dense undercoat of fur provides excellent insulation in water. Their lips close behind the huge, ever-growing front teeth for underwater chewing. They have self stopping ears and nostrils for diving and large back feet with webbed toes make them powerful swimmers. Two serrated claws on each hind foot are used for combing water repellant oil through their coat. Small, agile front fingers allow delicate handling of tiny objects.
Huge, slightly yellowish teeth are perfectly designed for felling trees. Mostly nocturnal, beavers appear just after sunset and are active up till sunrise. They are expert dam builders. Placing layers of sticks, logs, roots and stones, plastered together with mud and sod – they regulate the flow of water through the forest which enables them to move to and from their feeding grounds.
Their main source of food is sugars, starches and vitamins inside tree bark and twigs. They prefer willows, birch, balsam poplars, cottonwoods and aspens. They also eat leaves, twigs and seeds of water plants. Conifers are the last resort for food. An acre of medium sized aspens is needed to support one beaver for one year.
Beavers are very thrifty and have special stomachs designed to break down wood. They cannot digest all the cellulose (the fibers which make up most of wood) and so they excrete the partially digested vegetation. They re-ingest it and the second time through their digestive system all the left-over nutrients are fully absorbed.
Beaver ponds are large, often reaching depths greater than 10 feet and interconnected with other ponds via elaborate canal systems.
When a pond reaches its critical size (deep enough so the water won’t freeze solid) a lodge is built. Constructed of sticks and mud, it can be 10 feet tall and 20 feet – an interior living space of 5 X 2.5 feet high and dry quarters, with ventilation at the top and at least two tunnels at the bottom.
During summer, fresh twigs are stored on rafts, tied to the bottom of the pond in water that will remain ice-free when winter arrives. These twigs sustain beavers over the winter.
Beavers are exceptional foresters. After all the trees in an area are felled, dams are breached, ponds are drained, and they move on. The flood waters cause the recently harvested poplars, aspens and willows to re-sprout new stems, thus regenerating the cut-over lands. Beavers return in a few years to once again harvest the new crop of trees.
Our furry wood-workers are truly “busy as beavers,” constantly working the land. Their female-dominated society’s have had a huge hand in shaping the exquisite forests’ of North America.
Earth Dr Reese Halter is a broadcaster, biologist, educator and author of The Incomparable Honeybee and The Economics of Pollination.
Text © by Dr Reese Halter 2014. All rights reserved.