It is a hard robotics problem. Saying that "it would need a wide scan" is a vast underestimation. Try looking up some papers on obstacle avoidance. Also, consider the costs of sticking the additional sensors on the robot, processing that data in realtime, and still powering the whole thing.
I am guessing the biggest problem is the noise. Yeah, it's easy to figure out if there is a giant wall standing in front of you, but what about snow that constantly blocks its lens? Some leaves may be attached to tree so it might be required to circumvent, but some might not even be worth circumventing if it's just a piece of leaf falling.
Seek A Avoid B
In your case, a ton of Bs in terms of leaves, branches and etc.
I guess it would need a wide scan to detect if there is a path either vertically or horizontally.