The paper which this Corrigendum refers to is available here: Environmental control of winter stress tolerance and growth potential in seedlings of Picea abies (L.) Karst

The findings of various N.Z. Forest Products Limited laboratory studies on the effects of tree age on kraft pulping of P. radiata are described. The most important effect of increasing tree age is to increase the basic density of the wood. Results showed that kraft pulping characteristics and pulping properties are closely related to and can be predicted from pulpwood basic density.

In this paper the emphasis is placed on comparing the kraft pulping of youngwood (12-, 13-year-old thinnings) with that of the normal pulpwood supply to the Kinleith mill (effective tree age of about 30 years). The youngwood chips showed a lower packing density, but pulped at a faster rate and produced a higher yield of pulp at a given Kappa.

Calculations which took these 3 factors into account showed that the production capacity of a pulping digester would be more than 10% lower when utilising the youngwood in place of normal Kinleith pulpwood. Youngwood pulps were easier to beat to a given handsheet bulk or bonding strength property (burst or breaking length), but had much lower tear strengths than pulps from older wood. The tear index at 6.0 burst index for pulp from youngwood thinnings was about 25% lower than that of pulp from normal Kinleith pulpwood.

The availability of the kraft pulping by-product, crude tall oil, was found to be significantly lower for youngwood and the tall oil contained a lower proportion of resin acids.

The effects of wood age (internodes from apex, growth ring number from the pith) on the papermaking properties of kraft pulp from radiata pine are discussed. In 40-year-old trees the tear strength of pulps from 30th internode material (that which contains 30 growth rings) was almost twice that of 10th internode material. Similarly in 18-year-old thinnings, the 15th internode pulps had higher tear index than the pulps from 10th or 5th internodes. Pulps from all types of material were readily beaten to good burst and tensile strength, the ease of beating decreasing with increase in wood age.

In studies of 5-ring-group material numbered from the pith it was found that the outer wood pulps from mature trees had tear strength 3 times that of pulp from growth rings 1-5; the inner wood pulps formed sheets of higher density than pulps from outer wood, since the fibres were more readily collapsed.

As expected, slabwood pulps gave pulps with highest tear strength. The data on slabwood and those for internodal and ring-group pulps indicate that the strength parameter most affected by wood age is tear index. As tree age increases tear strength of pulps also increases. It is concluded that the use of slabwood pulp to supplement whole-log pulps will be necessary for both export pulp and for certain packaging grades of paper. Empirical procedures for estimating the effects of forest age on the tear index of pulps based on ringgroup sampling are described.

The distribution of extractives, lignin, and carbohydrates in radiata pine and their variation with tree age are reviewed.

Extractives, their nature, and amount depend on the heartwood content of the tree, and thus upon wood age. Lignin decreases in the pith-to-bark sequence; pentosans content decreases over the first 10-15 growth rings from the pith, after which it is approximately constant.

Cellulose content of radiata pine increases over the first 10-15 growth rings from the pith, after which it is approximately constant. The carbohydrates in radiata pine are also briefly described.

The basic densities and tracheid lengths of the wood of nine 52-year-old radiata pine trees from the same site in Kaingaroa Forest were measured and related to kraft pulp and handsheet properties. From each tree core wood (wood billet containing 15 growth layers) and slabwood (outer 20 growth layers of a wood billet containing 40 growth layers) samples were chipped and pulped to kappa numbers of 27 ± 2. An additional 7 samples were taken at 5 internode intervals (5 growth layers) from the 10th to the 40th internodes of 3 trees with average basic densities. Each internode sample from each of the 3 trees was combined on equal oven-dry basis, and kraft pulps were prepared.

Wood basic densities, chip basic densities, and wood tracheid lengths for each of the 25 samples were compared with weighted average pulp fibre lengths, pulp fibre cross-sectional dimensions, fibre wall thickness : fibre diameter ratios, and pulp fibre coarseness. For all 25 pulps, chip basic density was found to be the wood property most closely related to pulp and handsheet qualities. About 80% of the variation in handsheet tear, burst, and density properties were accounted for by variations in chip basic density. Inclusion of pulp fibre length in the regression analyses increased this variation accountability by 5-10%. Of the pulp properties measured, the wall thickness : fibre diameter ratio was most closely correlated with chip basic density and therefore with the selected handsheet characteristics. Fibre coarseness was slightly less highly correlated but probably of more practical importance because of the relative ease of measuring this pulp parameter.

Variation in wood density, tracheid length, resin content, and incidence of compression wood in radiata pine are documented and discussed with respect to their potential influence on pulp and paper manufacture.

In general terms, each of the properties mentioned tends to decrease southwards within New Zealand. Tree average wood density, for instance, drops 20% from Auckland to Canterbury Conservancies (455 to 380kg/m3). This decrease will result in increased handling costs and wood consumption per tonne of pulp produced, and reduced chemical pulp digester yields.

For paper quality, variations in tear index as a consequence of wood property changes are predicted to be substantial. Thus regional wood resource qualities need to be matched with those paper and paperboard products which can be most effectively manufactured from them. Packaging grades of kraft pulps which require high tear strength should, therefore, be produced from the higher density wood found in parts of the Auckland, Rotorua, and Nelson Conservancies.

The study examined 10 52-year-old trees in considerable detail and described variations in moisture content, wood density, and tracheid length. Where meaningful, comparisons were made between properties within trees, between trees, and between density classes (low, medium, and high). An attempt was also made to segregate the trees into major components (sawn timber, pulpwood, and slabwood) and assign values of important wood properties. Basic densities averaged 380 kg/m3 (range 339 to 419 kg/m3) for sawn timber, 412kg/m3 (364- 458kg/m3) for pulplogs, and 467 kg/m3 (403-551 kg/m3) for slabwood. Tracheid lengths averaged 3.5 mm (3.3-3.8 mm) for pulplogs and 4.0 mm (3.5-4.2 mm) for slabwood.

A study was made of aerial photographs that showed wind damage in Pinus radiata stands on the Canterbury Plains and in Kaingaroa State Forest. This study revealed a consistent and characteristic pattern of wind damage associated with exposed stand edges of closed canopy stands. These exposed edges resulted from forest margins, abrupt increases in stand height of at least 5 m, and breaks of at least 40 m confronting the oncoming damaging wind. The associated damage was usually concentrated in the first 100 m or 200 m of the stand downwind from these edges. This pattern of damage calls into question the safety of laying out stands in narrow strips with abrupt changes in height confronting a potentially hazardous wind, viz the "strip system" in Canterbury.

Additionally, it was observed that in widely spaced stands, before canopy closure, there was no apparent fall off in damage downwind from exposed edges; wind forces acting on trees evidently remain high over the whole stand. The adoption of wide spacings on sites prone to wind damage could result in stands being less wind stable for at least part of the rotation.

Where clearfelling in closed canopy stands has exposed a new face to a damaging wind, the consequent damage has often been severe, extending in long drives downwind. In some instances there appears to have been an upwind as well as a downwind exposure from clearfelling.

Thinning temporarily increases risk of damage. This, and increasing vulnerability with stand height, indicates that thinning should be done as early as practicable.

Butt log pruning can affect wind stability of young stands, but whether it has an advantageous or detrimental effect may depend on wind, stand, and site characteristics.

Replicated plots in a 15-year-old plantation of radiata pine (Pinus radiata D. Don) of basal area approximately 40 m2/ha were thinned from below to approximately 11, 18, 23, and 28 m'-/ha respectively. The plots were re-thinned periodically thereafter to these same basal areas; one replicate of plots was retained relatively unthinned. Regression equations relating needle dry weight to branch cross-sectional area were developed and used to examine the distribution of foliage of various ages within the crowns. In the upper crown (70-80% height decile and above), the percentage of 1-year foliage increased acropetally from 52 to 75% whereas that of 2-year and 3-year and older foliage decreased slightly (28 to 22%) and markedly (20 to 3%) respectively.

In the middle and lower crown, i.e., all deciles below the 70-80% decile, the distribution of foliage across age classes was approximately constant at 37% (1-year), 28% (2-year), and 36% (3-year and older). The combined biomass of 1- and 2-year leaves within the whole crown averaged 73% of total leaf biomass under all thinning regimes.

Though stand density had little effect on proportionate distribution of foliage by position in the crown or leaf age, the total amounts of foliage varied greatly. Total foliage biomass ranged from 4.9 to 11.3 tonnes/ha and annual foliage production from 2.4 to 4.3 tonnes/ha in stands of mean stand density ranging from 15m2/ha (biomass) or 21 m2/ha (annual production) to 46 m2/ha.

Radial increment patterns were studied in 18 stand-grown Pinus radiata trees after thinning and fertilisation. Patterns in ring width increment along the bole were significantly correlated with bending stress, crown growth activity, and their interaction. Bending stress appeared to regulate growth in the upper 20% of the bole and crown growth factors dominated in the lower bole. No significant effect of fertilisation was found in patterns of stress or crown growth activity in any of the years analysed although a large shift in form factor associated with fertilisation was noted in one year.

Three distinct resin pocket type defects are recognised in Pinus radiata in New Zealand.

Type 1 is well documented in the literature as a radially narrow discontinuity in the wood, which is oval in the tangential-longitudinal plane and is filled with free resin, callus, and sometimes nodules of callus that contain differentiated woody tissue.

The Type 2 resin pocket originates as the Type 1 defect, i.e., a tangential separation in the cambial zone which expands radially as it fills with free resin under pressure. A rupture then occurs through the cambium and external resin bleeding results. Any remaining live cambium adjacent to the original separation may continue to function at a reduced rate. The whole defect, including any retarded cambium, is occluded by surrounding healthy cambium and an occlusion scar results. The occluded defect may contain any of: dry resin, callus, bark, and occluded wood; the latter is wood derived from damaged cambium or differentiated callus cells and is mostly separated from normal wood by other than woody tissue.

The Type 3 defect is a narrow longitudinally-oriented break in the continuity of wood, filled with dry resin and parenchymatous tissue. This defect originates as a lesion in the cambial zone. A rupture through the cambium results in external resin bleeding. Surrounding healthy cambium occludes and causes a similar occlusion scar to a Type 2 resin pocket.

Sixty-three straight pruned radiata pine butt logs 4.9 m long were sawn exclusively to 25 mm boards under a standard pattern in three timber grade studies. Produce was graded by the National Timber Grading Rules (NZS 3631 : 1978) and timber prices from the Waipa Wholesale Price List 1978 were applied. No price was available for clears so a range of three was used. Variation in the price for clears was found to have a very significant effect on log values. Because the random occurrence of resin pockets can confound results, basic data used in this paper are from grades produced when resin pockets were ignored.

Results showed the production of clearwood and values and grades realised from pruned butt logs are determined by three major factors: log size, defect core size, and log conversion percentage. A Grade Index has been derived in which the relationship of these factors is expressed as:

Grade Index = (dbh x log conversion)/defect core.

Data from the 3 studies were combined in a Grade Index Model which defines a pruned log value gradient, the expected outturn in clears, and gives an approximation of the proportions in other grades. Results from an independent fourth sample of 12 logs were used to validate the Grade Index Model.

Because the Grade Index is an expression of the quality of pruned butt logs which may be used either predictively or reflectively, applications to stand planning, evaluations of silvicultural regimes, and evaluations of existing pruned stands are proposed. Future application of Grade Index to real stands would be facilitated by more detailed forest records on the timing, implementation, and result of pruning operations. Further research into the classification and effect of deviations from straightness in pruned butt logs is also necessary because at present the index is confined to straight logs.

Because the principles are fundamental, it is likely that the Grade Index could be applied to some species other than P. radiata and adapted to accommodate other sets of grading criteria which differentiate between pith and knotty grades, clearcuttings grades, and clear grades.

The total plant dry matter in a mature beech/podocarp community was estimated at 703 t/ha. The principal species and their above-ground dry matter (d.m.) content (in t/ha) were: Nothofagus truncata (145), N. fusca (36), Podocarpus ferrugineus (25), and Weinmannia racemosa (63); d.m. was distributed among the major components as follows: stem wood (201), stem bark (23), branch wood (50), branch bark (19), dead branches (6.5), and foliage (5.7). Dead standing trees contributed a further 22 t/ha. Together, these aboveground components comprise 47% of the forest d.m. content. The forest floor detrital matter was estimated at 226 t/ha and, when roots were included, 373 t/ha or 53% of the forest d.m. content. Commercial logging extracted 27% of the dry matter as utilisable logs; and of the residual 73%, 36% comprised material already dead and in various stages of decomposition.

Regression analysis was used for the trees and shrubs, and unit area harvesting methods for the remaining forest components.

In 1961 a large lysimeter was built in Kaingaroa Forest; together with the surrounding area it was planted with radiata pine (Pinus radiata). In the spring of 1974 the 13-year-old stand of trees was thinned, and 3 months later ¹⁵N enriched urea was applied to the Taupo silty sand in the lysimeter and in its immediate surround at a rate equivalent to 200 kg N/ha. In the following 3 years no apparent loss of N by leaching and no change in the rate of leaching of other nutrients was recorded.

The concentrations of KCl-extractable NH₄-N in the surface soil layers showed marked increases 1 week after the fertiliser application, and there were further increases between weeks 2 and 4. After 38 weeks, concentrations had returned to pretreatment levels. Increased NO₃-N concentrations were detected after 2 weeks; these were maintained for the duration of the experiment.

All of the applied N was still present in the litter and top 30 cm of soil 2 weeks after application. The proportion of applied N in the litter and top 30 cm of soil dropped to 60% after 4 weeks and later stabilised at about 50%. It is suggested that tree uptake accounted for a large part of this loss.

Detailed anatomical study of P. radiata grafts revealed that phloem tissues of incompatible grafts are abnormally thick. Grafts with thick phloem often displayed "pitted" stems. Thickened bark resulted jointly from overproduction of sieve cells and underproduction of tracheids. Normal pattern of phloem differentiation was altered and phloem areas formed which lacked axial parenchyma. Other internal symptoms in union zones of some incompatible grafts were suberisation and necrosis of cortex cells, excessive tannin accumulation indicated by abnormally darkly-stained bark tissues, formation of abnormal parenchyma in the xylem, and atypical dilation of horizontal ray cells and axial parenchyma. Increasingly more grafts developed symptoms of incompatibility as graft age increased: 10%, 24%, 35%, 54%, and 72% of 1-, 3-, 5-, 8-, and 13- to 18-year-old grafts, respectively. Possible interactions between occult viruses and true stockscion incompatibility may be responsible for the graft survival and vigour problems.

Second year cones were picked off 15 Pinus radiata D. Don trees in January 1979 (ripe cones) and from the same trees, but from the next year's crop, in July 1979 (green cones). Before seed extraction, the green cones were artificially cured and ripened in paper bags in a warm room (20-24°C) for 10 weeks.

Seed from naturally and artificially ripened cones was sown separately in replicated nursery plots in October 1979. In March 1980 seed germination, measured by the yield of plantable seedlings per 100 (presumed sound) seeds sown, averaged 77% for the naturally ripened cones and 80% for the artificially ripened cones. Seedling height averaged 23 cm in both groups. Artificially ripened cones thus produced apparently normal, fully-mature seed.

Winter harvesting of P. radiata green cones, followed by artificial curing, allows mature seed to be extracted in time for normal spring sowing in October, avoiding the usual one year delay in establishing progeny tests from naturally ripened seed.

Tree breeding, integrated with an active programme of species and provenance testing, is being conducted in Eucalyptus botryoides, E. saligna, E. regnans, E. delegatensis, E. fastigata, E. obliqua, and E. nitens. The programmes involve provenance trials and family tests to give a broad base of genetic variability of the different species, and to form genetically improved local seed sources. Several other species are being tested on a small scale.

Selection criteria vary somewhat among the 7 main species, but fast growth, good stem form and branching characteristics, and useful wood are needed in all species. Genetic variation of practical significance has been found in the tolerance of E. regnans and E. fastigata to frost. Considerable emphasis is being placed on searching for strains of E. nitens which are less palatable to the Eucalyptus tortoise beetle, Paropsis charybdis.

The breeding method used entails selecting the best trees in the most promising provenances, followed by intermating among these to produce the improved seed via seed stands, seedling seed orchards, clonal seed orchards, and progeny-tested seed trees.

Eleven characters of the stem and branches, studied in 28 open-pollinated families, showed highly significant additive-genetic variance (P < 0.01 or P<0.001). Estimates of heritability ranged from 0.12 to 0.50.

For malformation, heritability was estimated as 0.17, but the assessment of this character was crude and, since the malformation may have had two or more independent origins, it may be best to regard this result merely as evidence that some genetic variation was involved.

Estimates of heritability for crookedness, butt sweep, number of branch clusters on the stem at age 7, and mean branch angle were from 0.4 to 0.5; those for the number, size, and distribution of the branches were from 0.1 to 0.2. These lower values reflect, in some degree, errors arising from the difficulties of sampling within the tree, but they also suggest that most of these characters were extremely sensitive to variations in the environment. Genetic correlation coefficients were estimated for all possible pairs of characters. Although these correlations were not tested for significance, a comparison of 21 of them with their counterparts from an independent study by other New Zealand workers showed good agreement. Among the characters related to branching, several estimates of genetic correlation were close to +1 or -1. It is postulated that these represent associations resulting from pleiotropism rather than from linkage.

If these intimations of genetic correlation are at all accurate, they have important practical implications. Strong or even perfect genetic correlations, such as those indicated, could impose severe constraints on artificial selection, because one would expect directional selection applied to one character in a nexus of correlated characters to evoke correlated responses, some of which would be favourable and some detrimental to log quality.

In 1971, 220 of 588 wind pollinated Kaingaroa plus-tree progenies of the "268"

Root configuration of radiata pine (Pinus radiata D.Don) seedlings in the nursery was examined in relation to nutrient supply, and the configuration of the regenerated root system after transplanting was examined in relation to seedling treatment and soil temperature.

In the nursery an increase in shoot growth owing to high soil fertility was not accompanied by a similar response in root growth, resulting in a high shoot-root ratio. High soil fertility decreased mycorrhizas. Nitrogen and phosphorus deficiencies reduced the weights of the shoot and root but had little effect on root configuration. Changes in root weight can lead to faulty conclusions about root development. Even when nitrogen deficiency was extreme the root system possessed a remarkable ability to adjust the number and length of first and second order laterals, and so lessen the effect of stress on configuration. Similar, but lesser, effects were found under phosphorus deficiency. This ability may be important for the survival of seedlings in naturally regenerating forests. A decrease in the mean extension rate of root members seems to be the major reason for the reduction in root length in nutrient starved plants.

The configuration of roots regenerated after transplanting is closely related to the initial configuration of the planting stock, the number and length of the first order laterals capable of regeneration being the most critical basic framework for the new root network. However, the number of first order laterals appears to be not amenable to manipulation by nursery management practices.

Radiata pine seedlings developed strategies to cope partly with the effects of nutrient deficiency or low temperature on root configuration.

This review presents a synthesis of current knowledge on Root Growth Potential (RGP) of nursery-grown forest seedlings. RGP, the measure of a transplanted seedling's ability to rapidly produce new roots, is a key indicator of seedling vigour and survival after planting. Physiologically, RGP appears to be closely linked to bud dormancy. It peaks when the chilling requirement for dormancy release is fulfilled, then declines, presumably reflecting the internal allocation of current photo-assimilate to shoot growth. RGP can be manipulated in the nursery through practices that induce dormancy, increase root fibrosity, and enhance carbohydrate reserves. Autumn and winter nursery temperatures influence RGP through their effect on dormancy release. Date of lifting establishes the dormancy status of seedlings when they enter storage, and temperature and duration of storage further influence the dormancy status at the time of planting. Improper handling and misplanting can reduce RGP expression, as can low soil temperature, low soil water potential and soil compaction on the planting site.

The use and manipulation of the mycorrhizal symbiosis has enormous potential benefits in tree nurseries and in artificial regeneration programmes. This paper discusses the role of a mycorrhizal inoculation programme in reforestation. Included in this discussion are type of inoculation and response of the host to inoculation. The direct impact of a mycorrhizal inoculation programme will depend upon the symbionts selected and, of course, site characteristics. Inoculation generally improves survival and growth following outplanting. However, this advantage may be a function of the larger seedling size resulting from inoculation rather than from transplanting fungal inoculum to the forested site. This paper also points out current problems and future directions of any inoculation programme.

The use of electrical impedance techniques with plant tissues is briefly reviewed, after which several annual electrical impedance trends in the stems of several Ontario coniferous species at three different locations are examined. The trends in spruce are always more pronounced than those in pine. The impedance trends of cold stored stock are significantly higher than those trends of the outdoor stock. It is inferred from the multiple regression analyses that to some degree impedance measures dormancy and frost hardiness.

Despite a relatively large literature discussing the roles of auxins, gibberellins, cytokinins, and inhibitors (abscisic acid) in the physiology of woody perennial plants, relatively few data relate these compounds to seedling vigour. Possible reasons for this deficiency include an inability to detect accurately the low concentrations of these compounds, especially the gibberellins and cytokinins, and an inability to distinguish between physiologically active hormones and similar but bound compounds. However, the past decade has seen the development of analytical techniques with potential for detecting picogram quantities of growth substances. Such precision may reveal definite relationships between seedling growth vigour and levels of plant hormones.

The role of food reserves in tree growth are discussed in relation to a recently completed study with Pinus banksiaria Lamb, seedlings. Besides carbohydrates, lipids are also important as food reserves. All tissues are important for storage of food reserves but not of equal importance simultaneously. Their importance depends on their relative volume and physiological state. Root and needle volume is greater than that of xylem and bark in young seedlings whereas in mature trees these relations will be different. In seedlings, roots will be more important for storage in early autumn than needles, but needles will be more important during the later part of autumn. Large amounts of photosynthates are used in respiration and wood formation is directly dependent on current photosynthate.

ome problems involved in using the colour of leaves as an indicator of plant condition are discussed in the paper.

Results are presented demonstrating that the chlorophyll content of conifer seedlings differs due to species, needle age, nursery treatment and time of the year. Similar results are shown for a 20-year-old stand of Scots pine. The nonspecific feature of chlorophyll variation in leaves makes leaf colour unsuitable as a general indicator of plant condition.

On each sampling occasion there was a strong relationship between the concentration of chlorophyll and that of nitrogen in the needles. The ratio chlorophyll/nitrogen changed between the different sampling occasions, primarily as an effect of the seasonal variation in chlorophyll concentration. To be able to use chlorophyll content in leaves as an indirect measure of the nitrogen content, keys must be worked out for relevant time-spans. Each species and provenance within the stock will need its own key.

Caution should be exercised when using the colour of the leaves as an indicator of plant condition, unless good keys are available for the "normal" variation of chlorophyll in the stock.

The use of a porometer to measure stomatal conductance is described and the technique briefly reviewed. The relationship between stomatal conductance, gs and water potential, ψ on cut branches of Scots pine (Pinus sylvestris L.) is presented from measurements on two occasions. The changes in ^ ψ on branches with their cut ends in water were small compared with the rapid decreases in ip on the branches allowed to dry out. Stomatal conductance remained constant as ψ fell from -0.4 to -1.6 MPa but at lower ψ values gs fell rapidly. The likelihood that decreases in gs reduce growth rates and the use of the techniques to assess this at different stages of tree growth are discussed.

Root-pruning of Pinus radiata D.Don seedlings resulted in a sharp increase in stomatal resistance and a concurrent drop in net photosynthesis. Eight days after root-pruning leaf water potential was restored to pre-pruning levels and within 12 days photosynthesis showed signs of recovery, accompanied by a decrease in stomatal resistance. Proliferation of new roots took place and thereafter the recovery process intensified. By day 32 photosynthesis was restored to about 60% of the initial rate prior to root-pruning. Translocation of ¹⁴C assimilate was restricted by root-pruning. An hypothesis concerning the physiological processes involved in root-pruning and hardening of nursery stock is discussed.

Water potential differences were measured between the soil, roots and shoots of Pinus radiata D.Don and P. brutia Ten. seedlings grown under controlled climatic conditions. Root growth under stress was strongly affected by climatic treatment, particularly temperature. In both species, water potentials in the cool climates were always less negative than in the warm climates. The relations between shoot (ψ_x) and root (ψ_r) water potentials were analysed; regression of ψ_x over ψ_r with increasing water stress was linear in Pinus radiata and curvilinear in P. brutia. The implications of the findings are discussed.

Pros and cons of using the pressure chamber technique for evaluating seedling water status are presented. Safe use of the instrument, sample preparation, and proper operation to obtain the best possible data are emphasised. Guidelines for determining and interpreting water potential (ψ_w) levels are given for bare-root and planted seedlings. Results from two Oregon studies concerning the effect of water potential on seedlings show the pressure chamber to be extremely useful in monitoring ψ_w at different stages of reforestation.

This paper reviews the equipment available for evaluating frost hardiness of forest tree planting stock. The procedures and precautions necessary in undertaking such work are also outlined. The most common and accessible method of evaluating frost hardiness is to raise plants at one or more field sites where plants grow, harden and freeze naturally. However, the frequency and severity of frosts in the field are unpredictable and uncontrollable. To overcome these problems various commercial cold rooms and cabinets, often modified to provide controlled rates of freezing and thawing, have been used. In some cases these cabinets are portable to allow field plants to be frosted in situ. Freezing bars have also been developed which allow samples of plants to be frosted over a range of temperatures at the same time. Recently, specialised radiation and advective frost rooms have been designed which, although costly to construct and operate, provide very precise, controlled and reproducible ''natural" frosts.

Most techniques can distinguish differences in frost tolerance between plants, but only those providing control of all phases of the frost treatment will allow the results to be extrapolated confidently from laboratory to the field. Access to more than one frost temperature is essential if differences in frost tolerance are to be quantified. The final test of the frost tolerance of forest planting stock, however, must remain its performance in the field.

The use of controlled environments in forestry research makes it possible to analyse the effects on tree growth of one factor while holding others constant. This paper reviews a number of research projects carried out in phytotrons as a means of demonstrating the advantages and limitations of the use of controlled environments in research with nursery planting stock. The phytotron has been a valuable tool in determining the role of temperature particularly in controlling shoot and root growth, especially with regard to frost effects at low temperatures. It is suggested the phytotron could be used more extensively to select genotypes adapted to particular temperature regimes, especially for frost resistance, and for research with herbicides. Use of controlled environments has problems and some of these discussed with particular reference to the CERES phytotron in Canberra, Australia.

Experimental results of artificial regulation of growth cessation, hardening off and growth potential in seedlings of Norway spruce are presented. A temporary drastic shortening of the day (12 hr) toward the end of the growth period when under field conditions daylength was approximately 18 hr, hastened the termination of growth, frost tolerance and storability in early autumn and increased nutrient accumulation within the needles. Irradiance showed a pronounced effect on the rate of hardening-off during short day conditions, and interactions with provenance, night temperature and mineral nutrition were also highly significant on the development of a capacity to withstand prolonged storage. The interaction between irradiance x nutrient concentration was the dominant factor affecting nitrogen accumulation and growth potential.

A Corrigendum to this paper is available here: Corrigendum for Sandvik, M. 1980: Environmental control of winter stress tolerance and growth potential in seedlings of Picea abies (L.) Karst

Results of two experiments conducted between 1977 and 1979 on overwinter storage of seven temperate zone hardwood species commonly planted in southern Ontario indicate that temperature of storage and method of packaging can markedly affect physiological quality of planting stock. Root growth capacity and overall growth potential of cold-stored stock at 0.5 and 5°C were comparable with those of normal spring-lifted controls. Storage at temperatures of -5 and -10 °C resulted in low root growth capacity and was generally detrimental to seedling performance in comparison with spring-lifted nursery control stock that had been exposed to winter chilling out of doors. At 10°C there was considerable root and bud growth during the storage period from November to April. Of the five packaging methods examined, seedlings totally enclosed, or seedlings with only their roots enclosed within Kraft bags with a plastic liner, with moist peat surrounding the roots, showed the least shoot water stress and generally had the highest root growth capacity. Root growth capacity of stored seedlings of Acer saccharum Marsh., Acer saccharinum L., Fraxinus americana L., Quercus rubra L., Juglans nigra L., and Betula papyrifera Marsh, was significantly correlated with shoot xylem water potential at time of removal from storage. Shoot xylem water potential appears promising as a rapid measure of physiological quality.

It is recommended that autumn-lifted nursery stock of Fraxinus americana, Acer saccharinum, Quercus rubra, Tilia americana L., Betula papyrifera, and Acar saccharum be stored at a temperature of 0.5°C and Juglans nigra at 5°C with a relative humidity of 70-85%. Roots should be surrounded by moist peat and the total seedling tightly enclosed within a Kraft bag with a polyethylene liner.

Cool storage of bareroot southern pine seedlings has proven a successful Method to increase the successful establishment of plantations. This paper Attempts to relate the time of lifting, duration of storage, and planting date to The field survival and performance of southern pines. Limitations to successful Implementation of cold storage programmes are discussed. The Weyerhaeuser System is presented as an example of an operational system. Its limitations and Technology requirements are discussed.

The influence of provenance and length of storage on root growth capacity (RGC) was determined in 2 + 0 jack pine (Pinus banksiana (Lamb.), 3 + 0 black spruce (Picea mariana (Mill.) B.S.P.), and 3 + 0 white spruce (P. glauca (Moench) Voss.). All plants were random samples of spring-lifted production-run planting stock raised by the Ontario Ministry of Natural Resources and used in Canadian Forestry Service stand establishment trials in 1972 and 1973. Except for some fresh- and field-stored stock used in the first two RGC tests in 1972, all stock was cold stored, then withdrawn as required after specified storage periods of up to 5 months. The number of roots that elongated in solution culture during the 21-day tests were counted on a total of 3594 trees.

RGC differed greatly between the two test environments, but common to both were: a rapid decline with increasing length of storage; marked differences between species in the order jack pine > black spruce > white spruce; and substantial differences between provenances, the more northerly provenances showing higher RGC. The field significance of these results is examined in terms of survival and growth up to the fourth growing season after outplanting. Several correlations were significant, but relationships were generally obscured by great within-treatment variability.

Stress resistance and seedling quality are considered to be fully defined by the curve of future shoot growth. The factors controlling this curve's starting level, slope, and upper asymptote are analysed in terms of four major subsystems: substrate utilisation, photosynthesis, water, and information.

Published equations describing the first three of these subsystems are used to define a necessary and sufficient set of quality criteria. These include functional capabilities such as specific maintenance rate and photochemical efficiency, material properties such as elasticity and hydraulic conductances, environmental coefficients such as the temperature range for root growth, and lethal doses such as frost hardiness. In addition, they include variables describing the current state of the plant, such as leaf area, and water content.

The informational subsystem is considered to control the seasonal change, or "acclimation", in parameters of the other three subsystems, but is still too poorly understood for mechanistic description. Quality criteria arising from it include the extent to which chilling requirement has been fulfilled.

Applying such analyses to the business of reforestation consists of choosing a subset of the quality criteria according to past and future conditions in the crop and measuring them by methods such as those outlined here. Important methods include carbohydrate and infra-red gas analysis, porometry, the pressure-volume technique, and short-cut procedures derivable from these. Measurements of field-proven quality criteria can be compared with seasonal norms, or with values calculated from mechanistic models to be suitable for given site conditions. Practical decisions can then be made about nursery treatments, site preparation, planting, and genetic selections.

A model framework is presented in attempting to describe the production of forest tree seedlings as a continuous uninterrupted process according to general principles of systems theory. The growth and development of a seedling lot is considered to be the product of two hierarchical processes: the development and growth of the individual seedlings and the management techniques used in their production. The functional structure as the processes develop is described. For the detailed analysis, the growing process is divided into different phases each relating to the factors affecting the development of the seedling lot. The height distribution development of planted seedlings is given as an example. The use of culling and grading in the control of the growing process is examined.

Experimental trials with Pinus radiata D. Don and Eucalyptus regnans F. Mueller are presented. The trials relate to the effects of seedling size, chemical treatment, handling and storage period on subsequent survival and growth. The trials have led to operational changes in nursery practice, e.g. wider spacing in nursery beds, different fertiliser regimes and the more careful handling of plants between the nursery bed and the field planting site.