THE PLACE OF A SPECIES IN THE FOREST, WITH SPECIAL REFERENCE TO WESTERN NORTH AMERICAN SPECIES OF CONIFER USED IN BRITAIN

The nature of the differences between the climates of the QueenCharlotte Islands and of England and Wales are discussed briefly.The author then examines the site tolerance of the principalspecies within their own natural range, comparing particularlythe place of Sitka spruce (Picea sitcbensis Carr.) in the foreston Graham Island with its place around Terrace and describingthe Douglas fir forests of the drier eastern side of VancouverIsland and the place that Sitka spruce has in them. Factorsaffecting the growth of Douglas fir (Pseudotsuga taxifolia Brit.)are discussed. It is suggested that care is needed before itis assumed that a markedly dry summer period such as occursin much of the Douglas fir region entails a ‘dry’period as regards supply to the tree. Illustrations are givenfrom eastern North America of changes in type of site occupiedby a species with change in climatic or edaphic environment.Observation of the relative position of a species in the forestas climate changes makes it possible to suggest the place ofSitka spruce and Douglas fir in Great Britain.     

The Interaction of Green Spruce Aphid and Fertilizer Applications on the Growth of Sitka Spruce

In an 11-year-old stand of Sitka spruce (Picea sitchensis [Bong.]Carr.) application of nitrogen fertilizers, at a rate of 10kgN ha^–1 month^–1, increased mean diameter incrementby 12 per cent, while the further addition of phosphorus, at5 kg ha^–1 month^–1, resulted in a 23 per cent increase.An attack by the green spruce aphid (Elatobium albietinum Walker)occurred during the period of fertilizer addition. The mostseverely affected trees showed a reduction in diameter growthof 50 to 56 per cent but the severity of the attack betweentrees was unrelated to the treatments applied. However, fertilizerapplication did hasten the recovery of diameter growth afterdefoliation.     

Sitka Spruce and Douglas fir Seedlings in the Nursery and in Cold Storage: Root Growth Potential, Carbohydrate Content, Dormancy, Frost Hardiness and Mitotic Index

Seedlings (transplants) of 2+1 Sitka spruce (Picea sitchensis(Bong.) Carr.) and 1 + 1 Douglas fir (Pseudotsuga menziesii(Mirb.) Franco) were grown in a nursery at the Bush Estate,Scotland. Batches were lifted and cold stored at 0.5°C inNovember, December and January. Changes in growth, shoot apicalmitotic index, root growth potential (RGP), carbohydrate content,bud dormancy and shoot frost hardiness were monitored throughoutthe winter by taking samples at intervals from the nursery andfrom cold storage. Frost hardening occurred during the later stages of bud development(as mitotic indices decreased); autumn hardening was arrestedwhen seedlings were put in cold store, and some dehardeningoccurred in cold storage, especially in spring. Bud dormancystarted, and was greatest, just after bud growth (mitotic activity)virtually ceased; chilling in cold store was almost as effectivein releasing dormancy as natural chilling. The concentrationof total nonstructural carbohydrates stayed more or less constantat 100–150mg g^–1 from September to April in thenursery; in cold storage carbohydrates were depleted at 0.4–0.6mgg^–1 d^–1 (corresponding to respiration at 0.03–0.05mgCO₂ g^–1 h^–1) until there was only 40–50mgg^–1. Root growth potentials in the nursery increased in December,once the buds ceased growth, became dormant and had receivedsome chilling. Sitka spruce was ‘storable’ in November,before RGPs increased, but they then failed to achieve maximalfrost hardiness or ROP. Winter RGPs were high in Sitka spruceand were increased or maintained in cold storage, whereas RGPswere low in Douglas fir and decreased immediately after storage(except when stored in January). By the end of April, the RGPof cold stored Sitka spruce was much higher than that of directlifted plants. ROP changes in the nursery and in cold storagewere not consistently related to changes in seedling carbohydratecontents, shoot frost hardiness or bud dormancy. In practical terms, it was concluded that (1) the optimum dateto start lifting bare- rooted conifer transplants in the autumnis when their shoot apical mitotic indices have decreased tonear zero, and their RGPs have risen sharply; (2) high RGPsmay depend as much on the morphology of the roots (e.g. numberof undamaged root apices) as on the physiology of the shoots(e.g. carbohydrate status, dormancy and frost hardiness); and(3) in spring, transplants kept in cold storage since November,December or January are more frost hardy, slightly more dormant,and (in May) have higher RGPs than transplants lifted from thenursery.     

Comparative Performance of Containerised and Bare-root Sitka Spruce and Lodgepole Pine Seedlings in Upland Britain

Seedlings of Sitka spruce and Lodgepole pine were grown in fivedifferent container types; Ontario tubes, Kopparfors multipots,Finn peat pots, Japanese paperpots and Spencer-Lemaire root-trainers.They were planted in forest experiments in 1972/3 when 8-14weeks old and their subsequent performance compared with 2 years-oldbare-rooted transplants. After 2–3 years' growth, tubed seedlings proved consistentlypoorer than all other treatments for both height and survival.Finn peat pots were marginally the best of the other containerstested. Containerised plants generally showed poorer survivaland substantially less height growth than transplants, withdifferences being greater for Sitka spruce than for Lodgepolepine. For both species well-handled transplants appear the mostappropriate plant type for use in upland Britain. Implications for the future role of containerised seedlingsin upland forestry in Britain are considered. The benefits ofcontainer systems may be greatest in the production of seedlingsof ‘sensitive’ species or of high genetic quality.     

The effect of nitrogen supply on root growth and development in sycamore and Sitka spruce trees

Sycamore (Acer pseudoplatanus L.) and Sitka spruce (Picea sitchensis(Bong.) Carr.) were grown in sand culture in glasshouses withtwo levels of N supplied with irrigation 1.0 (deficient) and6.0 (sufficient) molNm^–3, all as NH₄NO₃. Providing trees with a sufficient N supply increased both theirabove ground growth and N content compared with the N deficientplants. Provision of the generous N supply also altered thedistribution of growth between leaves and roots, with the N-deficientplants having a higher root:leaf or root:needle ratio than thewell fertilized trees. Provision of a generous N supply stimulatedroot growth, especially at the later harvests, which was reflectedmainly in growth of the tap root in sycamore. There was an increasein both root mass and root diameter with N supply. When thegrowth of white roots was monitored using a borescope, it wasshown that there were significantly more new roots producedby the well-fertilized trees. The borescope data also showeddetail of the bimodal seasonal pattern of root growth underhigh N in Sitka spruce which related to trends in nitrogen uptake.     

CONIFEROUS LITTER AMENDMENTS AND THE GROWTH OF SITKA SPRUCE

The growth of semi-checked Sitka spruce (Picea sitcbensis Carr.)on heathland has been stimulated to different degrees by theannual application of litter of Scots pine (Pinus sylvestrisL.), Corsican pine (P. nigra var. calabrica Schneid), Lodgepolepine (P. contorta Dougl.), Japanese larch (Larix leptolepisGord.), and Sitka spruce, at rates corresponding to normal plantationconditions, following an initial heavier rate. Foliar analysissuggests that the response is at least partially attributableto the influence of the litters on the nitrogen nutrition ofthe spruce and differences between litters appear to be largelydetermined by their total nitrogen contents. In this respect,Japanese larch, with an annual needle fall generally greaterthan that of the pines and a higher nitrogen content, offersthe best promise as a nurse species for spruce.     

Developments in Yield Control and Inventory in British Forestry

Forecasting timber production many years in advance has becomea problem of considerable importance in this country becauseof the need to co-ordinate the rapid increase in productionwith the establishment of new timber-using industries. Thispaper describes a change in emphasis in state forest WorkingPlan Inventory methods employed in the predominantly young,coniferous forests of Great Britain and is a development ofthe methods described in a previous paper (‘Problems ofYield Control and Inventory in British Forestry’—D.R. Johnston, 1960, Forestry, 33, 19–36). Total enumerationof the growing stock is no longer the main objective of forestinventory and the new approach is directed towards (a) assessmentof the productive potential of each subcompartment and (b) theintensive enumeration of sample or ‘index’ subcompartmentsinitially and at each re-enumeration as a check on growth predictionsand yield control.     

Influence of Site Factors on the Response of Sitka Spruce to Fertilizer at Planting in Upland Britain

Data from Forestry Commission fertilizer experiments were analysedto determine the influence of site factors on the growth responseof Sitka spruce (Picea sitchensis (Bong.) Carr.) following applicationsof phosphate and potassium at time of planting. Multiple regressionanalysis revealed that growth response was influenced by soiltype and was related to the foliar nutrient levels of untreatedcontrols. Growth response to application of phosphate was alsoinfluenced by lithology. No relationships were found betweengrowth response and elevation or annual rainfall. Received 29 January 1990.     

Treatment of Severely Checked Sitka Spruce Trees with Injected Nutrients

Matched pairs of nutrient deficient Sitka spruce (Picea sitchensis(Bong.) Carr.) of mean height 3.0 m on a drained acid infertiledeep peat were injected in early summer by infusion with anaqueous solution of 40, 20, 66 and 0.2 g l^–1 N, P, K,Mg respectively, pH 7.2 and high conductivity. Three growingseasons later there were no responses in injected trees in treeheight increment, foliage nutrient levels of N, P, K, Ca, needlecolour, needle weight or crown density. Foliage Mg levels wereraised significantly. The injection procedure caused severetissue damage around the Infusion point and 84 per cent of thetrees had stain in stem cross sections 50 cm above the treatmentlocation.     

Some Ring-width Patterns in Sitka Spruce Timber from North America

Variations in ring-width pattern of Sitka spruce (Picea sitchensisCarr.) through most of its life in its natural habitat are demonstratedfrom photographs of ten crosssections. It is suggested thatin addition to the annual fluctuations in ring-width due toclimatic variation, the tree in the natural forest is subjectto periodic suppression and release and that it has considerablepowers of recovery; in plantations, therefore, Sitka spruceshould respond to thinnings made even late in the rotation.     

Timber Improvement: II. The Effect of Vigour on Young-Growth Sitka Spruce

A study of the effect of vigour on the within-ring componentsof young, plantation-grown Sitka spruce (Picea sitchensis (Bong.)Carr.) has been made as a contribution to a more effective selectionof timber having superior timber yields and to appraise thelikely effect of forest management practices which, by influencingvigour of growth, affect wood quality. It was found that as ring width in Sitka spruce increases:

1. Thereis an increase in early wood width without a correspondingincreasein late wood and so a greater proportion of early wood.
2. Thereis a reduction in the average density of the early woodcomponentof the rings.
3. Because of the combined effects of 1 and 2,there is a reductionin wood density as vigour of growth increases.
4. There is a lower minimum early wood density.

The significance of these observations on the growth and technicalperformance of Sitka spruce timber is considered. The possibility of appraising adult wood characteristics onthe basis of juvenile wood performance is examined and the scopefor assessing fibre length and density of adult wood from anexamination of wood laid down at about six years from the pithis demonstrated.     

Hybrid poplars: present status and potential in Britain

Past and potential future use of hybrid poplars for wood productionin Britain is considered, and preliminary results of trialswith new clones imported from Belgium in 1985 are given. A seriesof nine field experiments established in 1991, to a common protocol,was analysed using stepwise multiple regression. The superiorvigour of ‘Beaupré’ compared with ‘Ghoy’,‘Robusta’ and ‘Trichobel’ was clearin almost every case. For ‘Beaupré’ (Populustrichocarpa x P. deltoides) altitude emerged as the variableexplaining most variation in tree height after six growing seasons,height declining with increasing altitude. The four best siteswere characterized by low elevation and low rainfall. At the two older sites planted in 1987, at Ampthill and Bedgebury,the ‘interamerican’ hybrids (P. trichocarpa x P.deltoides) were the most vigorous, and the clones ‘Unal’and ‘Raspalje’, which were thought to be too rustsusceptible to release for commercial use in 1990, achievedsimilar stem sizes to those of ‘Beaupré’and ‘Bolelare’. The General Yield Class (based ona reference spacing of 8 x 8 m) calculated for ‘Beaupré’was 8 at Ampthill and 24 at Bedgebury. Future prospects for poplar planting are considered in relationto possible reform of the Common Agricultural Policy.     

GROWTH STIMULATION OF FOREST TREE SEEDLINGS BY THE ACTIVITY OF FREE-LIVING MYCORRHIZAL MYCELIA

Observations by the late Dr. M. C. Rayner on a field experimentand the results of subsequent pot-culture experiments demonstratethat the soil activity of mycorrhizal fungi can improve thedevelopment of forest tree seedlings (Picea, Pinus, Betula)before actual mycorrhizal infection takes place. Further experimentsshow that ectotrophic mycelia are capable of stimulating endotrophictree species (Fraxinus excelsior, Cbam?cyparis lawsoniana, Robiniapseudacacia), i.e. that these ectotrophic mycorrhiza-formersbring about growth stimulation of the plant although no infectionis formed at a later stage. It is suggested provisionally thatat least some ectotrophic mycelia, Boletus scaber and Rbizopogonluteolus, may influence seedling growth by attacking soil organicmatter and liberating ‘nutrients’ from which thehigher plant benefits.     

The Influence of Shelter and Weeds on Early Growth of Sitka Spruce and Lodgepole Pine

An experiment in Helmsdale Forest (Highland Region, Scotland)examined the effects of shelter and weed competition on Sitkaspruce (Picea sitchensis (Bong.) Can.) and lodgepole pine (Pinuscontorta Douglas ex Loudon). Different levels of shelter fromwind were achieved by using netting and were measured usingtatter flags. Three treatments compared weed competition byremoving no vegetation, heather (Calluna vulgaris L.) only orall ground vegetation respectively. Results indicate a definiterelationship between material lost from tatter flags and treedry weight at five years. Even the smallest increase in shelterresulted in increased growth of Sitka spruce and the beneficialeffect of shelter became most apparent 4 to 5 years after planting.Tree dry weight was found to be correlated with root collardiameter and height but not fifth year height increment. Resultsfrom weeding treatments were unclear and differed between species.This was because bird damage interacted with weeding, the completelyweeded plots being most heavily damaged; and because the methodof hand weeding (pulling out the whole plant including roots)damaged fine tree roots. Bird damage was prevented by nettingbut in unnetted plots it was found impossible to separate birddamage from other factors although it was clearly more seriouson lodgepole pine.     

Some Methods of Cold Storage can Seriously Affect Root Growth Potential and Root Moisture Content and Subsequent Forest Performance of Sitka Spruce and Douglas Fir Transplants

Sitka spruce and Douglas fir transplants were kept under threecold storage regimes: (1) bare-root in a humidified cold store(H); (2) sealed in polythene bags in a humidified cold store(HP); (3) sealed in polythene bags in a direct cold store (D).Regimes H and D are routinely used in current practice. Plants of both species had significantly (P < 0.001) lowerroot moisture content (RMC) in treatment H within 4 weeks ofstorage; this difference was maintained throughout the periodof storage and potentially damaging levels of RMC were reachedwithin 8 weeks. Sitka spruce had significantly (P < 0.001)higher root growth potential (RGP) than Douglas fir throughoutthe storage period. Differences in RGP between storage treatmentswere not significant until 12 weeks after storage when treatmentH was poorer (P < 0.05) than treatments HP and D. The survival of plants from treatment H after 1 year in thefield was significantly poorer (P < 0.001) than the othertreatments in both species. Height increment was also less intreatment H than the other treatments (P < 0.001) after 1year. However, this difference disappeared in the second season.After 1 year there were no differences in root collar diameter(RCD) increment between storage treatments but Douglas fir showedgreater increment (P < 0.001) than Sitka spruce. Rapid assessment of RMC in slightly over 48 h makes this a potentiallyuseful test of planting stock quality during and after coldstorage.     

Growth and Wood Properties of Sitka Spruce (Picea sitchensis (Bong.) Carr.) in Nursing Mixtures Established on Nitrogen-deficient Mineral Soils

Rate of growth and wood properties of Sitka spruce (Picea sitchensis (Bong.) Carr.) were investigated in triplet mixtures with lodgepole pine (Pinus contorta Loud.) (Alaskan provenance) and Japanese larch (Larix kaempferi (Lamb.) Carr.), established on nitrogen-deficient, iron pan soils. These ?nursing? mixtures were compared with pure stands of Sitka spruce that had been either regularly or periodically fertilized with nitrogen. Japanese larch promoted a growth rate in Sitka spruce greater than that achieved in the lodgepole pine-nursed spruce and equivalent to the two pure spruce treatments over the duration of the experiment (current age 28 yrs). Growth of regularly fertilized pure Sitka spruce was not significantly greater than that of periodically fertilized pure spruce. Alaskan lodgepole pine controlled branch size on the lower part of the spruce stems more effectively than the other treatments, although this may have been a function of tree size. Branch characteristics of Japanese larch-nursed spruce, however, were similar to those of the pure spruce treatments. Japanese larch caused an imbalance in crown development in the spruce, although it is unclear from the present study whether this will have an influence on stem and wood quality by the end of the rotation. Overall, the evidence from this study suggests that Japanese larch is an effective nurse of Sitka spruce on nitrogen-deficient iron pans, maintaining a rate of growth similar to that of pure Sitka spruce periodically fertilized with nitrogen and higher than that observed in spruce nursed by Alaskan lodgepole pine.     

The Effects of Clear Polythene Cloches on Conifer Seedling Growth and Shoot Morphology

Nursery seedbeds sown with lodgepole pine, Scots pine, Douglasfir, Japanese larch and Sitka spruce were covered with clearpolythene cloches for 0, 8, 13 or 18 weeks from sowing. Sitkaspruce germinated poorly and was not studied further. In bothpine species longer durations of cloche cover increased thenumber and length of stem units resulting in taller 1 + 0 seedlings.The number of internodes held at the apex for elongation inthe second season was also increased but transplant shock preventedfull expression of this potential such that differences betweenthe treatments were reduced. Only when covered for 18 weeksdid Douglas fir and Japanese larch produce 1 + 0 seedlings whichwere taller than the uncovered treatments. Through the productionof ‘summer shoots’ in their second season Douglasfir and Japanese larch were able to compensate partially forthe reduction in ‘spring shoot’ length caused bytransplanting.     

Norway or Sitka Spruce?

The deep and wide continental range and climate occupied bythe European species Picea abies is contrasted with the long,narrow, and humid coastal strip which the American species Piceasitchensis inhabits. Norway is the more plastic spruce and cansuffer thinner soils and much more drought, but neither spruceis a shallow rooter where soils are good and deep. Of the two,the litter of Sitka is less harmful to the soil. To date thereis no evidence that height for height Norway is more stableunder high wind pressures, but the belief that it is less sensitiveto frost than Sitka is well established. Sitka is far superiorto Norway for planting at high altitudes and in exposed placesand on Molinia peatlands in Britain, which accounts for thevast preponderance of the American species used in the westand north of the British Isles. The present popularity of Norwayspruce with foresters and timber merchants is admitted, butthe point is made that in planting it where Sitka could growwell, only some 75 per cent, of the volume will be secured.Finally, the types of site which each spruce requires and alsowhich each cannot take are considered in detail. A plea is madefor mixtures in certain circumstances, and the belief expoundedthat only deeper and better cultivation of the hardpacked materialunder-lying thin soils will make it possible to extend considerablyour acreage of really stable crops of these high-volume producers.