In North America, black bears are known to be good at climbing trees. In fact they are equipped with shorter, curved claws that are useful for climbing trees. They are also smaller in size than other bears and extremely fast and agile which helps make climbing a breeze. Whereas other types of bears such as polar bears and grizzly bears are not generally great at climbing trees. However, it should still be noted that all grizzly cubs and adult grizzly bears are still able to climb trees if the spacing of the branches is right and permits them to do so.
Bears usually climb trees for three reasons. They might climb a tree to try and escape danger, to eat nuts or fruit that is located in the tree, or to rest or sleep. When a mother bear brings her cubs out of their den one of the first things she often teaches them is how to climb a tree quickly when she gives them a signal.
Bottom line is, if you are trying to escape from a bear, climbing a tree in most cases is not going to help protect you. All black bears, grizzly cubs and adult grizzlies (though they do not always climb trees very well), are still able to climb trees if they decide it is something that they wish to pursue.
So the next time you encounter a bear, do not try climbing up a tree for safety. Instead it is suggested that you drop to the ground and lie flat and face down with your hands clasped behind your neck. Try your best to lie completely silent and still as resistance or running away will only provoke the bear. Before moving, make sure that the bear is in fact gone.