And its chokecherries lips to kiss good-by,
Then lets it snap back upright in the sky.

This simply means that the bear ate some chokecherries. It uses an anology, "As if it were a lover". Therefore the bear reaches up and looks like its kissing or being affectionate to a tree. 

Her next step rocks a boulder on the wall
(She's making her cross-country in the fall).

She, "The bear", is making her trip to her den for the winter. This is supported by the fact that in the lines before this, she was hoarding food. This is also supported becayse it says, "cross-country" in the fall. Thsi is understandable because fall is when bears start to gather food for hibernation.

Her great weight creaks the barbed wire in its staples
As she flings over and off down through the maples,
Leaving on one wire tooth a lock of hair.

This means that as the bear was simply passing through, it gets stuck in a barbed wire. When she does this, she looses a lock of hair.

Such is the uncaged progress of the bear.

The bear goes through this type of thing all of the time. He uses the word uncaged because he knows that a cages, (zoo) bear is not a hard life.

The world has room to make a bear feel free;
The universe seems cramped to you and me.

This says to me that on the main, people give bears alot of respect and alot of free roaming area. However it contridicts itself and says that the universe is to cramped.

Man acts more like the poor bear in a cage,
That all day fights a nervous inward rage,
His mood rejecting all his mind suggests.

This is an important section beceause he is comparing the small cage of a bear to the very purpose and inner emotions of a human. He says that humans are fighting with themselves on the inside, within their own subconsience. He also suggests that humans are moody, and that if the mind makes a suggestions, if a human is in a bad mood it will reject it. This is a careful comparison because the bear does not know moods. It only knows how to survive, therefore it would not reject and suggestions.

He paces back and forth and never rests
The me-nail click and shuffle of his feet,
The telescope at one end of his beat,
And at the other end the microscope,
Two instruments of nearly equal hope,
And in conjunction giving quite a spread.

He says here that humans are always up moving and tryign to prove things. Humans are always obsessed with being in a rush and finding things out. While in comparison to the bear, the beat leaves a very simple life.

Or if he rests from scientific tread,
'Tis only to sit back and sway his head
Through ninety-odd degrees of arc, it seems,
Between two metaphysical extremes.

This says that the only time humans rest from scientific discoveries, is when they sleep. This is true because a 90 degree arc is putting your head down. and being between two metaphysical exetremes is the physical world, and the dream world.

He sits back on his fundamental butt
With lifted snout and eyes (if any) shut
(He almost looks religious but he's not),
And back and forth he sways from cheek to cheek,
At one extreme agreeing with one Greek
At the other agreeing with another Greek
Which may be thought, but only so to speak.

This means that people like to agree with fervertly with other people, then go right around and agree with different people. 

A baggy figure, equally pathetic
When sedentary and when peripatetic.

This is the final analysis where he says both the bear and the human are pathetic, sedentary and peripatetic.