Abstract To determine whether the physiological condition of Pinus ponderosa seedlings grown at 4 nurseries in California differs, the root-regenerating potentials (RRP) of seedlings were compared. At 15-day intervals from October through April, 1-0 seedlings grown from seed collected in two seed zones were lifted, root-pruned to 8 inches, and planted for 1 month in the greenhouse in sandy loam maintained at 20°C. The root systems were then examined and all newly elongated laterals 0.5 in. or longer counted to obtain a measure of the RRP. Seedling size was correlated with the Effective Night Temperature: Effective Day Temperature ratio which increases southward in the state, but seedling size was not reflected in the RRP. The RRP of seedlings at all 4 nurseries displayed the same overall seasonal trend, which involved an increase in the autumn, a peak in the spring, and a rapid decrease after the terminal bud broke. At the northernmost nursery, which is also at the highest elevation, the autumn increase in the RRP began earlier and the spring peak and subsequent decline developed later than at the others. At three of the nurseries the RRP was of the same order of magnitude; at one nursery it was significantly lower. Possible explanations are discussed. Data from this and earlier studies point to the inadequacy of any system of morphological grading when the physiological condition of the seedling is unknown. Since the RRP can readily be determined and is one measure related to survival, it is suggested that an assessment of the RRP be included in any future grading system developed for ponderosa pine in California.
Stone et al. (Sat,) studied this question.