Electrical impedance and its relationship to frost hardiness in Pinus radiata

The seasonal trend of stem electrical impedance in Pinus radiata D. Don seedlings over an 18-month period was found to be similar to that in published data for other conifers. Comparison with the seasonal pattern of frost hardiness averaged over three different years at the same site implied that impedance may be related to frost hardiness. However, there was a distinct hysteresis in the relationship between impedance and the hardening and dehardening phases of the seasonal hardiness pattern. In seedlings induced to harden in controlled environments, a close relation-ship between impedance and frost hardiness was demonstrated but only for the period when the seedlings were actively hardening. From this relationship, impedance values of outdoor-grown seedlings were shown to correspond to their frost hardiness during the hardening phase (April to June in the Southern Hemisphere)