Both the morphological and physiological characteristics of forest planting stock vary widely with nursery culture and environment. Through the control of environmentally determined variation in phenotype, stock can be adapted to both the stress of transplanting from nursery to forest site and the particular environmental conditions of the forest site. Evidence is discussed that indicates that the stress of transplanting is primarily water stress, resulting from (i) the confinement of roots to the planting hole, (ii) poor root–soil contact, and (iii) low root permeability. These deficiencies are overcome by root growth, which is thus a central process in plantation establishment. Root growth depends largely on current photosynthesis. Photosynthesis depends on the assimilation of carbon dioxide at the expense of lost water in transpiration. Transpiration is limited by water uptake and hence depends on root growth. Root growth and photosynthesis in newly planted trees are thus mutually dependent. Because of this relationship, plant water status immediately after planting, or as soon as conditions favorable to root growth occur, is a crucial factor in determining plantation establishment success. High plant tissue water status immediately after planting, or as soon as environmental conditions permit root growth, allows the onset of a positive cycle of root growth supported by photosynthesis and photosynthesis supported by root growth; whereas low tissue water potential immediately after planting can lead to the inhibition or root growth by a lack of photosynthesis and the inhibition of photosynthesis by a lack of root growth. Stock characteristics that enhance plant water status immediately after planting are reviewed and the scope for their control considered. Stock characteristics affecting adaptation to particular planting site conditions, or capable of affecting postestablishment plantation performance, are also discussed.

Observations were made on the growth of white spruce (Piceaglauca (Moench) Voss) and Engelmann spruce (P. engelmanni Parry), each planted at a single location in the interior of British Columbia. In both species bareroot stock (either 2 + 0 seedlings or 2 + 1 transplants) with a low root growth capacity made only limited height growth during the first two seasons after planting. In the first season, many short stem units were formed, whereas in the second season, stem units were much longer but many fewer. The length of needles formed after planting by the bareroot trees was, in the first season, only about half that of needles formed the previous year in the nursery. Needle length increased slightly in the 2nd year. Container-grown trees (1 + 0 seedlings from 336-mL containers), which had a high root growth capacity, made relatively good height growth in the first season when they formed long needles and stem units. Height growth by these seedlings was much less in the second season, however, as were needle length and stem unit number, but not stem unit length. Application of slow release N,P, and K fertilizer at planting improved shoot growth by bareroot trees more in the second season than the first. In contrast, the container-grown stock made a large shoot growth response to fertilization in both the first and the second seasons. The results are consistent with the hypothesis that, as root establishment proceeds, shoot growth tends to be limited by the supply, first of water, then of mineral nutrients. This implies that the early growth of planted spruce can be maximized by using stock with a high root growth capacity, or other adaptations to drought, and applying slow release fertilizer at planting. Observations on the white spruce revealed an acceleration in shoot growth by both stock types during the third season. This followed the establishment, by the end of the second season, of root systems several metres in diameter. A large difference in height: diameter ratio, observed at the time of planting, between the container-grown and bareroot white spruce disappeared entirely in the course of the first three growing seasons.

The survival of lodgepole pine (Pinusconforta Dougl.) planted in the spring under a variety of conditions was found to be closely related to its root growth capacity as measured by two newly developed methods. One method employed a displacement technique to measure the root volume of test seedlings, nondestructively, both at the beginning and end of a period of growth under standard conditions. The change in root volume that occurred during the test was taken as a measure of root growth capacity. The other method for measuring root growth capacity was to record, by means of a semiquantitative scale, the number of newly elongated roots possessed by test seedlings after a 1-week period of growth under standard conditions. For comparative purposes, it was found that very similar results were obtained in root growth capacity tests of this type run at two widely differing temperatures (30 °C day – 25 °C night temperature, and a constant temperature of 15 °C).

The volume of intact plant parts can be measured rapidly by means of a simple displacement technique. The procedure is to dip the root, shoot, or other plant part to be measured into a vessel of water standing on a top-loading balance and take the resulting change in the reading of the balance as an estimate of tissue volume. The method has been found capable of yielding highly reproducible measurements of conifer seedling shoot and root volumes. One use that has been made of the technique is in the non-destructive determination of the shoot:root ratio of seedlings which are subsequently to be used in growth studies. Another has been in the estimation of root growth capacity from measurements of the root volume of test seedlings made both at the beginning and end of a period of growth under standard conditions.

Laboratory assays for measuring the root growth capacity (RGC) of forest tree seedlings were first developed in the belief that root extension immediately after planting is a major determinant of establishment success. An assumption underlying the development of these tests was that root growth under standardized conditions in the laboratory is indicative of root growth under the generally quite different and often highly variable conditions in the field. Evidence in support of this assumption is slight. Recently, it has been proposed that RGC affects seedling performance, not directly, but by virtue of a correlation with cold hardiness or other types of stress resistance that directly affect performance. For this hypothesis, also, the evidence is slight. There is a need for a clearer understanding of the relationship between RGC and seedling establishment to decide how best to measure and interpret RGC as a gauge of stock quality. This is illustrated by a discussion of the optimum conditions for measuring RGC and of the quantitative relationship between RGC and early performance of planted stock.