About a year ago, beaver moved from an adjacent landowner's property to a pond on Natural Lands Trust's Burden Hill Preserve. They raised the water level a couple of feet by damming the pond's small waterfall and built themselves a nice lodge along the pond's edge. They have felled many trees (including this one that held an NLT sign!) for lodge and dam construction, and to more easily eat the tasty bark.
Some trees are girdled rather than felled completely. White oak trees seem to be especially tasty; they have completely girdled a number of oaks up to two feet in diameter or more. 
In this photo, Liz Eisenhauer (daughter of New Jersey Manager Steve Eisenhauer) poses by a large white oak that the beavers have been gnawing on. Girdled trees, even if they are not brought down by the beaver, may die within a year or two since their nutrient flow is cut off, preventing the tree from carrying nutrients to its limbs to support leaf growth in the spring.
Though it is interesting to see beaver on the preserve, it is always somewhat startling to see the amount of destruction they can cause to trees and shrubs. After humans, beavers are the animals that cause the most change in their habitats.
