North American Fruit Explorers mailing list at ibiblio

[Alan Haigh <alandhaigh@gmail.com>]

Tree survival in cold temps is strongly related to its level of hardening
off when extreme events occur.  The tree shuttles water from cells in
response to gradually colder days in the fall, but fluctuating temps can
reverse this process.  Too  much water in the cells and they burst.  I've
seen even spring events where temps were in the double digits F. kill trees
that in a fully hardened state can take -25 F.

The high desert is not a moderate climate, although I've seen 100 year old
apricots between Taos and Santa Fe near the Rio Grande.  River valleys seem
to create micro-climates conducive to tree survival.

There are also soil issues involved- when there is little snow cover roots
seem more vulnerable to cold in shallow or poorly drained soils.