A prime flaw in a lot of those types of trials in my observation is conflating mortality of small tender trees with lack of hardiness. Obviously there are reasonable limits to hardiness, but as you push against that boundary, youre apt to find individuals that can survive after establishment but that are still too tender when young. Nursery environments are tough to begin with too, while those type of selection efforts tend by their nature to be pretty brutal. Field growing is even harsher until the tree hits maturity and can hold its own.
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