Young Aspen Rebound Following Beaver Activity
Where There is a Willow There is a Way-Beavers are considered nature’s engineers. Unfortunately, because of their innate nature to build dams by removing tree vegetation along streams and “destroying” visual aesthetics, they are frequently viewed as nuisances. Preventative measures such as tree wrapping (wire mesh installed around tree species preferred by beavers) are used to deter excessive beaver foraging. Dam removal and the destruction of these “culprits” are also conducted when deemed necessary. There are however, numerous studies on the regrowth of aspen and willow trees following beaver foraging which provides a clearer understanding that beaver activity along streams is not as harmful as some may believe and does actually lead to regeneration of the area within a relatively short time-frame.
Aspens and willows are the preferred species for beaver foraging with aspen being more favoured. It has been recorded that beavers may travel > 200m to forage aspen however, typical use of trees occurs within 30 m of water. Beaver activity consists of targeting incompletely felled trees (with fibers still attached to the trunk) and stumps (trees that are completely removed). Both types of felling produce regrowth greater than undisturbed trees. Incompletely felled willows produce more growth from the trunk, and their stumps produce 1 m shoots after one growing season and up to 2.5 m after two years. Stems and biomass of willows are rapidly regained within two years following simulated complete removal by beavers. Similarly, aspen regrowth following beaver foraging was found to be more significant for both active sites and those abandoned from beaver foraging within three years than undisturbed trees or those abandoned greater than three years. Aspens reproduce through their root system, whereas willows regenerate from cut stumps, severed branches and drift of vegetative fragments. Beavers have a very keen sense of smell that cues their decision of tree selection. The palatability of the new shoots of both aspen and willow to beavers are low due to naturally occurring chemical compounds present within the shoots that deters beavers from further harvesting this new growth so they move to other areas where the trees are more edible.
Riparian shoreline area restoration is one of the projects frequently undertaken by TUC. Bioengineering techniques are used to strengthen the soils along areas of streams that have eroded or are susceptible to erosion. Since willows propagate from cut branches, live willow stakes (and poplar) are planted along the banks either individually or within wattle fencing where slopes are steeper. In essence, the wonderful adaptations of willows and poplars to withstand disturbance by beavers and floods plays a critical role in the work we do towards habitat recovery.
Beavers are part of the natural landscape. Their selection of aspens and willows for dam building and sustenance should be viewed as a wonder of nature, as these tree species regenerate without human intervention. Natural beaver disturbances such as tree foraging and dam building are means by which nature demonstrates its resiliency and protection of some of earth’s most important resources.
Kommentare