Do beavers chew the bark off fruit trees and some magnolias to reach the sweet sap?
Traditionally the reference for the beavers chewing on the water pines were in the central and eastern parts of North America. However, since some early introductions were made in the Pacific Northwest and trees such as the giant sequoia were planted along the West Coast, it has spread a little bit out of place.
Beavers were originally used as an animal fur resource, and then later utilized as a control of erosion. The dams were used to control flooding, which was a huge issue. And you also have a brown or black circle where a beaver is digging out the mud to get at the pond. This circle is often called the beaver track. While some will use it to term a large beaver pond or meadow.
There have been reports in New England where beavers have started to invade trees, but this appears to be very few and far between. Most likely, trees are being damaged by woodpecker or squirrels.
I'm not sure how accurate a reference this website is.
No, beavers don't chew off parts of trees, although they may be the reason for your bark on trees to be slightly thicker. For that matter, I've only seen squirrels and chipmunks at one of my local parks, but I imagine squirrels and chipmunks at your park are just as likely to chew the bark off of a tree.
As far as how beavers do it, since beavers' front teeth are far too broad to actually "chew" (I think they just gnaw and use their teeth to grind things down and modify them), beavers' rear teeth are used to break down and eat bark and other plant matter.
These are just a couple of examples of a large beaver chompin' on trees in Canada.
In Toronto, this is what I found. It's actually pretty difficult to find a nice beaver photo. I've seen several in my travels.
The St. Clair River near Port Credit.
On the Delta side of the US, I remember seeing a beaver building a lodge. It was an entire lodge, with different levels and gophers on top of it to prevent easy entry. My father wanted to take a picture. He left his camera next to the tree and went back to the camper. Upon his return, the beaver had torn the tree down and carried the roots to a dam a few miles upriver. He had to hike it up there, so he did not have a chance to finish his photo op.
This one was a nice three-season lodge. I used to live by the river where this photo was taken. It was not near Toronto.
These can be found all over Canada. I'm no expert on it, but the life cycle of these things makes a lot of sense. They are very food-cognizant. I've also seen a pond where a beaver builds a lodge, but I don't think it was three seasons.