"Tom: what's the definition of treeline? No trees at all, or krumholtz and stunted trees that are no good at all for hanging food? For example, Donahue Pass proper versus 500 feet lower, or thousand island lake. I've certainly run into people who've lost food to bears camping at more or less 9200 feet. I'm not disagreeing, just curious. (Of course, these people were at established campsites in popular areas.)"
My personal definition of tree line in the Sierra corresponds with your parameters, Krumholz and Whitebark pine. But there is another, even more important, variable, IMO: Human traffic. Based on those two variables, I decide how I am going to deal with potential bear problems. Absent significant human traffic, which covers the majority of areas where I hike, if I am at or above tree line, I will forego a canister of any kind and rely on camp sanitation, where/when I have dinner, and double bagging of my food in Nylofume bags to avert any potential bear problems. If I happen to be spending significant time in an area of high human traffic, which is not very often by design, I will use an Ursack where there is no formal "approved canister" requirement. Below tree line, it is a trivial matter to find a solid anchor for the Ursack. At tree line, either Krumholz or Whitebark pine will suffice. Above tree line, Wanda Lake for example, there are ample opportunities to anchor an Ursack to rocks, using various techniques. In areas where "approved canisters" are required, I will use an "approved canister". To that end, I have recently and reluctantly purchased a Bearikade Scout, which should suffice for any trip up to 9 days, the maximum I do these days. I hope this helps, and welcome additional comments by any and all. It is a subject that could use a lot of discussion.
