Busy beavers are ecologically valuable despite nuisance factor
During this magical season of new growth, you may notice trees that have been felled with crooked-looking stumps. Besides hurricanes like Fiona, there are creatures that make a habit out of knocking down perfectly good trees. In fact, we think so much of the beaver, that we put it on our nickel. This toothy animal, in some ways, helped determine how some parts of our nation were settled due to the early routes of the fur traders who were then after the plentiful beaver population.
Beavers can be a real nuisance and create dangerous situations for some landowners and managers. The reason is simple - numbers. There are more beavers in Nova Scotia in recent years than at any time in recent history. Today, land-use practices favour beavers. Many trappers have found beavers unprofitable to trap because fur prices have been depressed for several years. This has resulted in increasing beaver populations.
Beavers build dams to create ponds, which provide a safe haven of deep water for them to live in. The water must be deep enough to allow underground entry to their den, or lodge, and to store a winter supply of food between the bottom of the pond and the thick ice of late winter. Most dams in Nova Scotia are less than 1.2 m high, but some have been over 2.1 m. Dams in other locations have been more than 5.4 m high. One dam was reported to have been one-half of a kilometre long.
The underwater stored food, or “cache,” consists of fresh green branches from red maple, aspen and willow trees. The cache is sometimes weighed down with alder branches. Throughout the winter, beavers swim under the ice to their cache, select a branch, and return to their lodge to dine on the inner layer of bark. Food caches are stocked in a surprisingly short time around the first fall frost.
The dam is constructed from sticks that are cut, dragged, and floated to the chosen site, which is usually a section of swift-running water. The sticks are laid parallel to the stream flow, with the butt end downstream. Additional sticks are poked, shoved, and woven into the structure. Beavers use their front feet to dig and carry bottom materials such as mud and moss into the upstream side to seal any bubbling and gurgling leaks. It seems they do not like the sound of running water and work until they can create a calm, quiet pond with their damming of the rushing water.
An area flooded by beavers goes through a series of changes over a period of many years. Each stage is valuable to a specific group of wildlife species. Following the initial flooding, live trees and shrubs in the newly flooded area die and fall over. More sunlight reaches the water’s surface, aquatic plants appear, and miniature openings in the forest are created around the pond edge as beavers cut trees of all sizes for food. Young shoots in these openings attract deer, moose, and hares. Later, when beavers have literally eaten themselves out of house and home, they move on to a new site, and the dam falls into disrepair and eventually falls apart. Grass and sedges invade exposed mud and silt, which become semi-permanent openings in the forest. The openings gradually fill with alder, larch, aspen and other invading species, which may eventually evolve into a forest.
A new dam and the flooded area stabilize stream flow and trap silt, protecting downstream sections. Deep water habitat is created in what, otherwise, may have been shallow stream conditions. Not only does the pond increase the total amount of aquatic habitat, but the quality of this habitat is often enhanced. Brook trout find resting and feeding areas in the many downed trees, root tangles, and over-water maze of alder bushes. Hungry mink, prowling otters, and even the frustrated angler trying to cast worm through the maze, may have difficulty finding their query here.
Fish passage around beaver dams is not usually a serious problem. Beaver, speckled trout, salmon, gaspereaux, smelt and other fish all evolved together in North America. Trout and salmon wait for a period of high water following heavy rains, passing over or around the obstruction. When a spawning run of smelt or gaspereaux must get up or downstream in a limited time frame, authorized experts or others with proper permits can cut a channel in the dam to allow passage.
As a pond matures over five years, its value to waterfowl decreases significantly, but it is still valuable to other species. At this stage, the flooded area likely contains large numbers of dead, standing trees. These are attractive to flickers, woodpeckers, and tree swallows. The swallows nest in cavities excavated by woodpeckers. Insects are abundant over the water and the open nature of the flooded area provides these insects with needed air space.
Beaver ponds are often used by muskrats, mink, and raccoons. Frogs, salamanders, and toads enjoy new breeding and wintering habitat. The wildlife throughout the area has changed and diversified. Once a pond has been abandoned by a beaver, landowners can speed up the rejuvenation process. They can completely remove the dam and plant hardwood species, such as willow and aspen, on the exposed bottom soils. In a few years, the area will again be attractive to beavers. They will move back on their own or they can be reintroduced.
Beavers play an important and valuable role in the ecology of our woodlands and streams. We should make every effort to recognize this role and live with them. In cases where beavers are genuinely causing a real problem for people, such as washing out roads, action can be taken to control the specific situation.