Bear cans are required through out most of the JMT but not all. The JMT traverses two National Parks (Sequoia-Kings and Yosemite) and two National Forests (Inyo and Sierra). Each of these are separate jursidictional areas and most of the bear can requirements follow the boundaries of these Parks or Forests.
It is all Federal lands and bound by Federal laws. Proper food storage is a Federal law under 36 CFR 2.10 (d). This applies whether it is a developed campground or the back country wilderness.
As Shelly states, in bear can required areas, it may be a hefty fine if caught without a canister. In areas where a canister is not required, then it is the law enforcement officer’s interpretation of Federal law on how well you stored your food.
Remember, food storage is a 24 hour requirement. It is not just a night time thing. If you take a break, lay your pack down and a bear gets your food, you probably just broke federal laws.
The JMT is very remote. Loosing your food to a bear would not only ruin your trip, it could mean a couple of days without food while you hike out the nearest exit.
It just doesn’t seem to me to be worth it to not carry a bear can on this trail even if you are in specific areas that don’t require it. Remember, you’re not only protecting your food, you’re protecting the bears too.
Jim