Beavers only have one litter per year and rarely overpopulate since two-year-olds leave each spring to seek new homes, and reproductive rates decline as the area is filled. Removing beavers rarely gives a lasting solution since survivors have larger litters, and others from surrounding areas will soon replace any that are removed.Beavers prefer fast-growing trees, such as poplar, willow, cottonwood and alder, which normally have little commercial value. Although the felling of these trees appears destructive, such pruning often results in more, bushier growth in the spring. For example, each cut willow stem can lead to three to four new stems. If the beavers then use the branches for a dam that creates a wetland, great benefits can result, such as erosion abatement, flood control, water cleansing and more biodiversity.When it is desirable to protect trees from beaver felling, consider that most cutting occurs within five yards of shore, and that the likelihood of damage decreases as the distance from shore increases. Also, while beavers prefer certain tree species, they do not necessarily take them in order of preference. When planting trees along shorelines, consider less palatable varieties, such as spruces in the eastern U.S. and cascara in the West.
Cylindrical cages are the best way to protect valuable trees. Use 19-gauge hardware cloth or sturdy 2 x 4 inch welded wire fencing (not chicken wire), about three feet high. Encircle the trunk, leaving a space of about six inches between the tree and the wire – this is very important to allow the tree room to grow. Bend every other horizontal wire into hooks to connect with the other side.
A newer method to prevent beaver gnawing involves coating mature tree trunks with a sand and paint mixture. The paint can be color-coded to match the trees. Use 32 ounces of mason sand to one gallon of outdoor latex paint. Stir often and paint trunks about four feet high. Make only small batches at a time on the day it will be applied. Using too much sand causes mixture to roll off the tree. Young trees should not be painted. They should be protected with wire mesh cylinders.
Low fences can be used to protect groups of trees, and normally need not surround the entire stand, since beavers dislike being separated from the water. Have the fence fit tightly to the ground and trail each end toward the water. Monitor often in the beginning for burrowing. If digging occurs, two concrete blocks tied together can be used to block the tunnel.
Reference source: 911 Wildlife