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.     

THE INFLUENCE OF ARTIFICIAL SHADING OF THE GROUND VEGETATION ON THE NUTRITION AND GROWTH OF SITKA SPRUCE (PICEA SITCHENSIS CARR.) IN A HEATHLAND PLANTATION

A marked stimulus has been obtained by shading the heather vegetationsurrounding the trees by means of wooden laths. The increasedgrowth was accompanied by significant increases in the concentrationof nitrogen, ash, and manganese in the needles, indicating asubstantial increase in the availability of these nutrientsto the trees. A similar shading experiment on plots from whichthe heather (Calluna vulgaris Hull) had been previously removedby screefing produced only doubtful responses. Heather plantsgrowing beneath the laths were found to contain appreciablylower concentrations of nutrients in the foliage than unshadedplants. Whilst the response of the trees to shading of the groundvegetation is to be attributed largely to reduced competitionby the heather for available nutrients in the soil, especiallynitrogen, the mulching effect of the heather in maintainingsatisfactory moisture conditions during dry periods must alsobe taken into account. These findings offer an explanation forthe improvement in the growth of spruce in mixture with nursetrees when the latter form a closed canopy and suppress theground vegetation.     

Movement of Injected Dyes in Gymnosperm Stems in Relation to Tracheid Alignment

The path of upward movement of acid fuchsin dye was traced inpole-size stems of Japanese larch (Larix leptolepis Murr.),European larch (Larix decidua Mill.), Lawson cypress (Chamaecyparislawsoniana (A. Murr. Parl.)), Sitka spruce (Picea sitchensis(Bong. Carr.)), Norway spruce (Picea abies (L.) Karst.), andScots pine (Pinus sylvestris L.). In all of these species amarked, preponderantly clockwise spiral pattern of dye ascentwas observed. In general the upward movement of the dye followedtracheid alignment, except at the sapwood-heartwood boundary.The characteristic patterns of dye movement indicated that spiralgrain was much commoner than was straight grain among the pole-sizegymnosperms investigated. Large differences in spiral grainwere found among species, among trees within species, in differentannual rings within trees, and at different stem heights. Patternsof dye uptake were influenced somewhat by the method of injection.Dye injections through tubes driven into the stem were foundmore suitable for determining tracheid arrangement than wereinjections through individual roots immersed in dye. Factorsinfluencing spiral grain development and applications of thedye injection technique to spiral grain determination are discussed.     

AN EXPERIMENT ON THE SAMPLING OF EARLY THINNINGS

Several subjective and objective methods of sampling the averagevolume per tree in first and second thinnings were tested instands of Sitka spruce (Picea sitcbensis Carr.), Norway spruce(Picea abies Karst.), Scots pine (Pinus sylvestris L.), Corsicanpine (Pinus nigra var. calabrica Schneid.), Douglas fir (Pseudotsugataxifolia Brit.), and European larch (Larix decidua Mill.).Altogether 7,000 thinnings were measured at Fernworthy in Devon,Thetford Chase in Norfolk, Forest of Ae in Dumfriesshire, andKinellar in Aberdeenshire. The subjective methods, consistingof visual estimates and the measurement of groups of trees selectedas appearing representative, tended to give biased results nomore precise than those obtained by the objective methods whichare unbiased. The objective methods tested were random groups,systematic sampling by trees, and systematic sampling by rows.The systematic sampling by rows was the most satisfactory incombining a reasonable degree of precision with simplicity inexecution.     

Growth and mortality in underplanted tree seedlings in response to variations in canopy closure of Norway spruce stands

Six broadleaved tree species and Picea abies (L.) Karst. wereplanted under spruce plantations of varying densities, in Sweden.Treatments included control (994 stems ha^–1), dense (538stems ha^–1), sparse (294 stems ha^–1) and gap (0stems ha^–1) overstory treatments. There was an increasein height and diameter growth from control to sparse overstorytreatment of all underplanted tree species except for ash (Fraxinusexcelsior L.) and Norway maple (Acer platanoides L.). Site conditionsmay have hampered the growth of these species, as well as wildcherry (Prunus avium L.). Both oak (Quercus robur L.) and sprucehad greater growth in the gap treatment, relative to the othertreatments. Insecticide application did not influence seedlinggrowth or survival. The performance of beech (Fagus sylvaticaL.), lime (Tilia cordata Mill.), spruce and oak was consistentwith shade tolerance ranking. Beech and lime had a very highsurvival rate, even under the densest canopy. The growth andmortality of ash, maple and wild cherry differed significantlyfrom what was expected. This experiment demonstrated significantvariation in interspecific growth and mortality between sevenplanted tree species in relation to canopy density. Correctsite and species selection is crucial when underplanting inshelterwood systems.     

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.     

The chemical composition of needle and leaf litter from Scots pine, Norway spruce and white birch in Scandinavian forests

Needle litter from 14 stands of Scots pine (Pinus silvestris,L.), 13 stands of Norway spruce (Picea abies (L.) Karst.) andleaf litter from three stands of white birch (Betula pubescensEhrh.) were analysed for chemical composition. The concentrationsof the elements N, P, K, Ca, Mg and Mn as well as solid organiccomponents (lignin, cellulose and hemicelluloses) and solubleswere determined. When the average chemical compositions werecompared the Scots pine needle litter was clearly the most nutrient-poorlitter type. Of the solid organic-chemical components the ligninfraction dominated in the spruce and birch litter whereas thecellulose dominated in the pine needle litter. When Norway spruce and Scots pine were growing in adjacent standson soils with the same bedrock origin the spruce litter hadsignificantly higher concentrations of nutrients (N, P, K, Ca,Mg, Mn) than the pine needle litter. At sites where Norway spruceand white birch were growing in adjacent stands, the birch leaflitter had generally higher concentrations of nutrients. However, significant or nearly significant differences were onlyobtained for Mg (P = 0.002), K (P = 0.056) and N (P = 0.087),probably due to the few replicates of stands compared. Concerningorganic chemical components, the spruce needle litter had significantlyhigher concentrations of lignin and mannan than all the otherlitters and lower levels of ethanol-soluble substances, celluloseand galactan than the pine needle litter. Further, it had lowerconcentrations of water solubles, rhamnan and xylan than thebirch litter. No relationships were established between the nutrient statusof the conifer litters and the site index H100 (the dominantheight of the trees at a reference age of 100 years) of thestands. Concentrations of solid carbohydrates in the litterswere, however, positively correlated with site index (P <0.001). Further, the concentration of nitrogen in the pine needlelitter was negatively correlated with the latitude of the sites(P < 0.01). The influence of litter chemistry on the decompositionof litter and nutrient cycling of forests is discussed.     

Effects of water and nutrient availability on physiological responses of woody species to elevated CO2

The growth responses to elevated CO₂ found in experiments arehighly variable and depend on other experimental parameterssuch as irrigation, fertilization, light regime, etc. As yet,the strength or even the sign of most interactions is all butimpossible to predict from first principles. Experiments inambient and CO₂-enriched ambient air (+250 p.p.m.) have beenconducted in specially adapted greenhouses (Solardomes) at LancasterUniversity for the past four seasons on Sitka spruce (Piceasitchensis (Bong.) Carr.), wild cherry (Prunus avium L.), beech(Fagus sylvatica L.) and pedunculate oak (Quercus robur L.).These experiments are reviewed together with other publishedstudies on interactive effects of elevated CO₂ and water andnutrient supply on physiological processes, in particular gasexchange, in tree species. It is often assumed that drought tolerance will increase inelevated CO₂ because of a suppression of stomatal conductanceand an increase in instantaneous water use efficiency. Thereis, however, some evidence that such effects could be more thanoffset in beech by CO₂-induced increases in leaf area. It istentatively suggested that in beech, drought tolerance couldalready have been reduced by the increase in atmospheric CO₂over the last century.     

The Dependence of Volume Increment of Individual Trees on Dominance, Crown Dimensions, and Competition

A study of the volume increment of individual trees over onegrowing season in a 23-year-old stand of Sitka spruce (Piceasitchensis Carr.), indicated that narrow crowned trees weremore efficient producers of increment. Other factors being constant,trees of greater girth at breast height were found to be inherentlybetter producers. Trees of the upper canopy were generally moreefficient than those of the lower canopy under varying conditionsof competition. Shorter periods of growth were recorded in lowercanopy trees and with trees under conditions of greater competition.     

Decay in Norway Spruce Caused by Stereum sanguinolentum Alb. & Schw. ex Fr. Developing from Extraction Wounds

In two stands of Norway spruce (Picea abies (L.) Karst.), plantedin 1952 and 1929 in Yair Hill Forest and Glentress Forest, BordersRegion, two per cent of the trees examined in 1983 had extractiondamage on stems and superficial roots. Extraction wounds were4 and 8 years old respectively and ranged in size from 52 to1099 cm². Infection frequency of the damaged trees was 47 percent and 54 per cent respectively. Stereum sanguinolentum wasthe most common fungus isolated, accompanied by Trichodermaviride Fr; Chaetomium cochlioides Palliser and Heterobasidionannosum (Fr.) Bref. The frequency of isolation of S. sanguinolentumincreased progressively in samples taken from the outside ofstems inwards, whereas the other microorganisms present showedthe opposite pattern. In four trees, T. viride overgrew S. sanguinolentumin the the decay columns. Positive correlations were demonstratedbetween surface area of wounds and vertical extension of decay,tree volume and decay volume, and diameter of stem at breastheight (DBH) and decay volume; whereas a negative correlationoccurred between number of growth rings per 5 cm (measured inwardsfrom the outside of the bole) and radial penetration of decay.The results confirm the importance of S. sanguinolentum as awound pathogen.     

Distribution and Spread of the Great European Spruce Bark Beetle, Dendroctonus micans, in Britain--1982 to 1989

The great European spruce bark beetle (Dendroctonus micans),which had for many years been seen as a potential threat toBritain's spruce plantations, was first discovered in Britainduring August 1982, breeding in Sitka spruce. Surveys in spruceplantations were initiated to determine the distribution ofthe beetle, a necessary background for development of controlstrategies. This paper reports the development and evolutionof survey techniques from 1982 to 1989, as well as the spreadof the D.micans populations during this time. Details of controlstrategies and legislation to contain the outbreak are alsogiven, along with conclusions concerning the natural dispersalof D.micans. Received 23 July 1990.     

Timber Improvement: I. A Study of the Variation in Wood Characteristics in Young Sitka spruce

As part of a programme aimed at improving Sitka spruce timber(Picea sitchensis (Bong.) Carr.), a study has been made of thevariation in some wood characteristics of significance in affectingtechnological behaviour, and the effect on these characteristicswhen trees of outstanding form and vigour are selected. It wasfound that:

1. There is a similar pattern of within-tree variationin density,tracheid length, and grain inclination for bothselected andaverage, final crop trees.
2. There is a very appreciablevariation in these timber characteristicsbetween trees at comparableages, indicating the potential forimprovement by selection.
3. There is a reduction in density and some increase in graininclinationbut no difference in tracheid length in vigorouscompared withaverage-growth trees at comparable ages.
4. Thereis no evidence that selection for above average densityhasan adverse effect on tracheid length; it tends to favourtreeshaving a high minimum early wood density and, to a limitedextent,wood with narrow cells.

     

NATURAL REGENERATION OF PINE AND BIRCH ON THE HEATHER MOORS OF NORTH-EAST YORKSHIRE

Both pine (Pinus sylvestris L.).and birch (Betula pubescensEhrh.) usually invade after a fire, the invasion reaching greatestforce after 3 to 5 years, then falling off rapidly probablywith the return of the heather (Calluna). Pine seedlings onlygrow vigorously if their tap-roots reach the pan, when secondaryroots are developed extensively. In birch the tap-root is notwell developed, but secondary roots spread vigorously sendingdown sinkers to penetrate the pan. Regeneration of birch ishelped by rotten stumps and roots which its mycorrhizal rootsexplore. The root forms are compared and contrasted and thefindings compared with the work of Laitakari and Erteld.     

Silviculture of the Spruces in West Scotland

An account of the silviculture of Norway and Sitka spruce (Piceaabies and P. sitchensis) practiced in the West (Scotland) Conservancyof the Forestry Commission in the past 50 years. Present methodsare summarized and future developments forecast. A more intensiveform of silviculture is advocated for Sitka spruce.     

Establishment of the Second Rotation in the Jutland Heath Plantations

The paper describes briefly the silvicultural methods used toregenerate stands of pure Norway spruce (Picea abies Karst.)or Norway spruce mixed with a small proportion of Silver fir(Abies alba Mill.) on the poor heath soils of Jutland. Regenerationafter clear felling, uniform shelterwood, and shelterwood stripfelling is described. The last method has advantages over theother two.     

THE INFLUENCE OF HEATHER MULCHING ON THE GROWTH AND NUTRIENT STATUS OF LAWSON CYPRESS

The application of a heather mulch in a heathland plantationof Lawson cypress (Cbam?cyparis lawsoniana Parl.) has over aperiod of 8 years more than doubled the height of the treescompared with untreated controls. Analysis of the current foliageof trees from mulched and control plots reveals considerablyhigher concentrations of nitrogen and phosphorus in the former,indicating an increase in the availability of these nutrientsto the trees presumably from decomposition of the mulching materialand the suppression of the competing heather vegetation. Muchof the beneficial influence of the mulch must however be attributedprimarily to better moisture conditions, particularly duringdry periods when the superficial roots of the trees are otherwiseliable to desiccation.     

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.     

The Geographical Distribution of Gilpinia hercyniae Hymenoptera: Diprionidae in the United Kingdom

Since 1906 when the European spruce sawfly, Gilpinia hercyniae(Hartig), was first recorded in Britain, in the New Forest,Hampshire the species has spread into 18 counties in Englandand Wales. In 1970–74 it achieved pest status in mid-Wales,but has remained at an endemic level elsewhere. G. hercyniaehas not become well established in northern England and hasnot yet been found in the extensive spruce plantations in Scotland.     

Fomes annosus Butt-Rot of Sitka Spruce IV. Observations on the Distribution of Cryptosporiopsis abietina (Petrak) in the Stems of Rotted Trees

Cryptosporiopsis abietina was isolated from the heartwood of12 out of 18 Sitka spruce suffering from butt rot caused byFomes annosus, but from none of eight healthy trees from thesame plantations. C. abietina was present in a distinct zoneabove the tissue colonised by F. annosus. It was present inboth sound wood, and in wood with stain or incipient decay. C. abietina inhibited the growth of F. annosus on malt agar,and to a lesser extent in autoclaved Sitka spruce heartwood.The possible influence of this potentially antagonistic funguson infection by F. annosus is briefly discussed.