The friction force between the tree and the bear is 3000 N. The acceleration is 0 since the bear slides down at a constant velocity. The sum of the forces is 0. Thus;
Upward friction + downward weight = 0
F-mg = 0
F = mg
F = (300 kg) (10 m/s² the acceleration due to gravity)
F = 3000 N frictional force