© 1989 Heron Publishing—Victoria, Canada
Frost hardiness of Picea rubens growing in spruce decline regions of the Appalachians
L. J. Sheppard, R. I. Smith and M. G. R. Cannell
Institute of Terrestrial Ecology, Bush Estate, Penicuik, Midlothian EH26 0QB, Scotland / Received July 14, 1988
Summary
It has been proposed that pollutants predispose Picea rubens Sarg. growing in the high Appalachians to frost damage. The pattern of autumn hardening of P. rubens growing at Whiteface Mountain, NY, and Newfound Gap, NC, was monitored by detaching shoots at 1–3 weekly intervals, air freighting
them to Scotland, and freeze-testing them. The temperatures that produced freezing injury from August 1986 to January 1987
were compared with minimum air temperatures recorded in those months at nearby meteorological stations over 22 previous years.
There was only weak evidence that the onset or degree of frost hardening was inadequate to protect the trees from direct freezing
injury (as opposed to winter desiccation). Historically, minimum air temperatures occasionally fell below the lethal temperature
for a 10% kill (LT10), but they rarely fell below the LT50. The trees hardened rapidly in the autumn (max. 2.2 °C day–1) to between –30 °C and –40 °C by January (LT50), including trees showing visible decline on Clingman’s Dome, TN. Individual trees differed in hardiness by up to 10 °C.
It is concluded that any pollutant-induced susceptibility to freezing injury is insufficient, on its own, to account for forest
decline in the Appalachians.
