About how many trees can a beaver cut down in a year?

Beavers live on the bark of trees, that of aspen being their favourite, but birch, cottonwood, willow, and alder also are used. When these are in short supply other plants are eaten, but conifers are rarely cut except for building materials. In one night a single adult beaver can fell a seven- to 10-centimetre (three- to four-inch) poplar, cut it into sections one to three metres long, and drag the logs to the water. Normally, beavers do not cut up logs over 15 centimetres (six inches) in diameter, although they will fell trees considerably larger. The largest tree on record cut by beavers was 115 centimetres (46 inches) in diameter. The cutting of trees is apparently done at random, with all gnawing likely to be on one side, unless the tree has a large diameter, in which case it may be gnawed all the way around. Because trees normally fall downhill, hence toward a pond, this is probably the origin of the legend that beavers can make trees fall as they wish.---From Encyclopaedia Britannica Online