The "Schlaufen" (cloth strips on the shoulders of the tunic) were authorized on January 3, 1917, so the photo would have been taken some time after that. He was a some point in a unit that was part of the "Alpenkorps" (roughly a division), an elite alpine unit, as evidenced by the Edelweiß flower insignia on the side of his cap. His shoulder straps have been removed for the photo, so it is not possible to determine his exact unit. Actually, the Bavarians did not wear the gray-green band on their Einheits-Mützen (universal caps). Their version of this cap had a field gray band in the same color as the rest of the cap. In this case, however, I think he is wearing a normal (most likely red) cap band.
Zwiesel is located near the Czech border in the Bayerischer Wald. It was located in the Bavarian III Army Corps, so I suspect he was in one of the units of that corps. You might be able to figure out which unit he was in by cross referencing the units that made up the Alpenkorps with this corps district roster. The Alpenkorps was not all Bavarian, so it might be possible.
Chip