I have to agree, based on what I have seen in my patch right her close to home (that I can water) that even a slight difference in evening sun exposure can mean early death or survival.
I have a little spot where I transplanted 10 lil 2 prong rootlets in the fall of 2009. 9 of those came up that next spring and they all did nicely that year. They all lasted until fall and did the normal yellowing process late september, early october.
Then last year, we had a similar extreme heat (95+ for weeks) and no rain for weeks... and some of those plants died off early, where others made it a little longer.
I had the bad luck of two trees (just west of that little patch) that died, which is giving them a lot more evening sun than they were getting originally.
From April thru June, as long as we have had cooler temps and rain, they all did really well. But when this bad hot dry spell kicked in, those that were getting just a little more evening sun than the others, they kicked the bucket quick.
In my seed producing bed, just about 30' from that location, the light conditions are about right. But the plants up at the top of the bed do get a little more evening sun than the ones down the hill on the lower end of the bed. The plants up at the top are much more stressed looking now than the ones at the bottom.
When it comes to sunlight and seng - one thing I am sure of is if your patch is going to get a lot of sunlight for part of the day, it needs to be early morning sun, not late evening sun.
Of course that may vary by location some, for example that is absolutly true down in the southern states, but may not be so up in Main.
Of my 9 little transplant roots, 2 of them are planted at the base of a rise, and that rise has a log/stump on top of it and it completely blocks the evening sun from those 3 little 3 prongs, and they are doing nicely. Where others just 4-5' away are dead/brown.
The difference there is simply evening sun.
One thing I have noticed, is that even though those plants come up in April, and may expire by July, they are still getting a bit larger each year.
So they are making some progress. The real bummer is if they expire in July, no berries.
So I am fixing to move them on down the hillside a bit, and plant them at the base of a rise where they will be protected well from the old evening sun.
Good Luck to you guys !
TNhunter