Provisional guidelines for fall lifting for frozen overwinter storage of nursery stock

Abstract

An experiment was started in the fall of 1972 to study the effects of the date of fall lifting on the post-planting performance of overwinter stored white spruce and jack pine. Storage at two temperatures was used, 0°F (−18 °C) and 26°F (−4 °C), with the former a failure, the latter successful. Spring planting indicated that "too early" outplanting is possible. Stored white spruce may be used to extend the planting season into late spring, but not jack pine.Degree-Hardening-Days, D-H-D, i.e. cumulative daily differences below 50°F from soil temperatures at 15 cm depth, is suggested as a possible criterion of stock readiness for storage. White spruce was about 200 D-H-D and jack pine about 375. By inferences from other experiments white pine is about 225 D-H-D and red pine about 300.

An operational method for estimating cold tolerance thresholds of white spruce seedlings in forest nurseries

“…The second phase of shoot hardening is temperature-dependent , so if bareroot and container seedlings produced in the same nursery are compared at a similar DHD value, the shoots of the containerized seedlings will be more hardened than those of the bare-root seedlings. All this leads us to believe that the threshold value recommended by Mullin and Parker (1976) is conservative when applied to containerized seedlings. Among the three variables used to estimate the thermal time in this study, the hardening degree days (HDD) were the most strongly correlated with shoot and root cold damage assessment variables (Tables 3 and 4).…”

“…This means that these two threshold values are definitively neither equivalent nor interchangeable. According to Mullin and Parker (1976), bare-root white spruce seedlings are ready for cold storage after a minimum accumulation of 200 degree hardening days (DHD). By October 28, our last sampling date, only 155 DHD had been accumulated.…”

“…Chilling sum (hours) was calculated by summing the numbers of hours when the temperature measured 2m above the seedling bed was under 5°C (Lambany 1994). DHD were calculated following the method described by Mullin and Parker (1976). DHD were based on the minimum daily rhizosphere temperature and calculated by summing the degrees below a threshold value equal to 10°C.…”

“…In Québec nurseries, white spruce (Picea glauca [Moench] Voss) bare-root seedlings are considered ready for cold storage if the chilling sum, calculated by cumulating the number of hours when temperatures are less than 5°C, has reached a sum of 200 hours (Lambany 1994, Lamhamedi et al 2005. According to Mullin and Parker (1976), white spruce bare-root seedlings are ready for cold storage if a minimum of 200 degree hardening days (DHD) have accumulated. In this last study, DHD were based on soil temperature and calculated by summing the degrees below a threshold value of 10°C.…”

“…Furthermore, estimation of chilling sum is based on a threshold air temperature value equal to 5°C (Lambany 1994). Mullin and Parker (1976) based their DHD on a threshold soil temperature value equal to 10°C. According to Greer et al (2001), the threshold temperature above which no cold hardiness development in white spruce occurs is 14.5°C.…”