APPROACH AND PERSPECTIVE IN FOREST PATHOLOGY

The author reviews briefly the lines along which forest pathologyhas developed from its emergence as a separate science up tothe point now reached, where the influence of environment onthe tree is too generally regarded as of greater importancethan the actual pathogen attacking it. He would correct a majorassumption, made by this school of thought, that the ‘natural’forest necessarily provides the ideal environment, and thattherefore any departure from nature, e.g. the use of pure standsor the planting of exotics is bound to encourage disease. Heconsiders that forest diseases are mostly complexes, in eachof which site and pathogen play very variable roles of differingimportance. Any attempts at this stage to draw broad conclusionscovering a large number of diseases are certain to lead to error.He suggests that, as producers of trees on a limited range ofsites, and not as preservers of nature, we must avoid behavingas though ‘unnatural’ was the same thing as ‘unhealthy’.     

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.     

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.     

'New Perspectives in Forestry': a Basis for a Future Forest Management Policy in Great Britain?

Common forestry practices are being increasingly questionedin many countries. In Great Britain, controversy has surroundeda number of issues, including upland afforestation, single-speciesplantations and water acidifcation. With increasing internationalattention being given to the issues of sustainability and biodiversity,there will be pressure for developed countries to evolve policiesthat will satisfy their own internal responsibilities beforethey attempt to impose ‘sound management principles’elsewhere. Many of the principles currently being discussedhave been brought together under the term ‘new perspectivesin forestry’, although some of these were actually developedand practised in Europe during the last century. Multipurposeforestry has been advocated as a means of achieving many goals,but a genuine application of this approach will require furtherchanges to existing priorities and practices. Under ‘newforestry’ principles, forests are seen as ecosystems andmanagement practices seek to ensure that the integrity of theecosystems is maintained. In addition, a greater involvementof all interested parties is sought, both in the forest planningprocess and in subsequent management.     

A STUDY OF GROWTH RINGS IN TREES

The frequency of ‘lines’ of denser wood within theannual ring in larch (Larix decidua Mill.) was compared withmonthly records of rainfall and tables of droughts and rain-spellsin the Bristol region. Moderate correlations were found withJune rainfall (inverse), days in summer droughts, and a ratiogiving a measure of the maximum dry-wet contrast between successivemonths from May to August. This ‘contrast ratio’showed a high degree of parallel variation with ‘line’frequency. A study of individual years suggested that the formationof a pronounced ‘line’ is associated with the occurrenceof a spell of dry weather followed by a wet spell during thelater part of the summer. ‘Mid-lines’ were foundto be associated with a June drought breaking in July; late‘lines’ with a dry-wet contrast in July or August,but in some trees these may be suppressed by the stoppage ofgrowth. Vaguer ‘lines’ of lower frequency were associatedin certain years with wet spells not preceded by noticeabledrought. Individual ‘lines’ can thus be identifiedand roughly dated by some weather feature, so that their positionsheds some light on the length of the growing season. It issuggested that ‘lines’ of denser wood may be occasionedby the killing or inactivating of mycorrhizal rootlets eitherby drought or by waterlogging, followed by partial recoverywhen the weather changes. This would accord with the theorythat summer wood formation is normally associated with a developingwater-deficit in the wood.     

The Effect of Drying Quercus robur Acorns to Different Moisture Contents, followed by Storage, either with or without Imbibition

Freshly harvested Quercus robur acorns were spread out, twodeep, in trays, and dried/stored (at +2°C over the courseof 28 weeks) to either 45, 40, 35, 30 or 25 per cent moisturecontent (fresh weight basis). Drying/storage significantly reducedthe germination percentage (P< 0.01). The acorns at eachmoisture content were then either ‘soaked’ or ‘notsoaked’, before immediate germination; or returned tothe same cold store at +2°C, this time in loosely tied polythenebags. Soaking raised the acorns moisture content (M.C.), andalso brought about a significant increase in germination capacity(P<0.01). Regardless of the moisture content immediatelybefore soaking, "soaked" acorns in loosely tied polythene bagsstored better than ‘unsoaked’ acorns. All ‘bagged’acorns (whether ‘soaked’ or ‘unsoaked’)stored better than acorns dried/stored in open trays.     

Volume Tariff Systems

A volume tariff system is a ‘harmonized’ set oftree volume tables, with one independent variable, for estimatingthe volume of trees and stands of even-aged forests. A number of systems have been compiled empirically on the ‘volumeline’ concept for different species and silviculturalconditions. They vary in structure. It is suggested that these variations in structure can be explainedas special cases of a general relationship between the regressionconstants and coefficients of the individual volume lines (tariffs)which form the system.     

Determining productivity gains from herbaceous vegetation management with 'age-shift' calculations

Gains in stand volume that result from competition control andfertilization are sometimes reported as ‘percentage gains’.Because percentage gains arithmetically decline over time asstand volume increases, plantation managers have difficultyin using percentage gains to project growth and revenues. The‘age-shift’ method quantifies the year advancementsin stand growth due to silvicultural treatments and, for herbaceousvegetation management, it has been proposed that this metricis less likely to change after the juvenile growth phase. Totest the sensitivity of the ‘age-shift’ method totime and hardwood competition, we used 20-year volume data from11 loblolly pine (Pinus taeda L.) studies that had early completeherbaceous and woody competition control. Volume growth gainswere expressed in terms of percentages and ‘age-shifts’.On all sites with no woody competition, percentage gains declinedfrom age 8 years to age 20 years. In contrast, age-shift estimateson these plots either remained constant or increased over time.However, in four cases where woody basal areas were greaterthan 4 m² ha^–1 at age 15 years, age-shift gains due toherbaceous control decreased and eventually resulted in volumelosses. When evaluating the response to early herbaceous competitioncontrol, age-shift calculations have promise as a useful predictivetool on sites with low levels of hardwood competition. Fivemethods for calculating age-shift are presented.     

The potential for developing a normal age-structure in managed ancient woodland at a local scale in three English counties

This paper describes a model for assessing the potential forsustained management of ancient woodland at the local landscapescale, based on the premise that a ‘normal’ foreststructure is the best option for integrating nature conservationwith provision of a regular supply of timber. The concept of‘normality’ is applied to clusters of small ancientwoods which are considered together and treated as a whole. Data on ancient woodland distribution are used from West Sussex,Essex and North Yorkshire. At ten sample points within eachcounty the woodland area within a 25-km² block centred on thepoint was considered to see whether a normal forest structurecould be created and maintained by sustained management usinglikely minimum felling rates and average rotation lengths forthe main species for both high forest and coppice systems. Themodel was also tested for situations where small woods or woodswith conservation status were excluded from the system, as wellas for different minimum felling rates. The areas proposed forfelling within ancient semi-natural woods currently listed withinthe Woodland Grant Scheme (WGS) (II) are higher than can bemaintained in the longer term in West Sussex and Essex. The model provides a preliminary method for setting the contextof individual forestry schemes withn the wooded landscape asa whole.     

A Windthrow-risk Estimation for Coniferous Trees

A method of windthrow-risk estimation for young coniferous treesis proposed in this paper. This estimation is deduced from stembending theory. Fourteen pairs, each containing one dominant and one suppressedtree, were measured m a 15-year-old Scots pine thicket. Totallength of needled branches and stem diameter in the middle ofinter-whorl sections were measured for each whorl of each tree. The data were used to evaluate and compare growth strategy riskfor dominant and overtopped trees in the thicket. The strategieswere found to be qualitatively different. The suppressed treegrowth strategy was dependent on that of the dominant tree.Certain indices of ‘shelter effect’ for suppressedtree were also found.     

Floristic Diversity in Some Central Swedish Forests

The species of vascular plants present in 0·5 ha sampleplots were recorded in 19 areas of forest planted on formeragricultural land, 21 areas of old or ‘virgin’ forestand 102 areas of ‘ordinary forest’ in east centralSweden. In the case of the planted forest areas, the main correlationwith floristic diversity was with the amount of daylight reachingthe forest floor. In the ‘old forest’ and ‘ordinaryforest’ sites, however, the main correlations were withthe pH value of the surface soil, the amount which this variedwithin the sample plot, and the proportion of broadleaved treesin the tree canopy; these factors were inter-correlated witheach other to some extent. The ‘old forest’ sites,which had the most acidic surface soil and least diverse flora,did not appear to be serving any particularly useful functionin terms of conservation of the flora, at the present time.It is concluded that, if a diverse forest flora is requiredfor any particular reason, the complete closure of the canopyshould be avoided. A mixture containing some broadleaved treesis likely to be preferable to a pure crop of pine or spruce.There appears to be, however, considerable scope for the developmentof a diverse flora within timber-producing forests consistingmainly of spruce and pine.     

CORRIGENDA

Literature References. Wright and Will. Against Scott, R. O.,and Ure, A. M. (1957): Delete ‘Spectrophotometry’and substitute ‘Photometry’. Delete, N.Z.J. Sci.Tech. B. XXXVIII. 699–706 and substitute ‘To appearin The Analyst’.     

Some Aspects of the Growth and Spread of Fire in the Open

This paper describes some recent experimental and theoreticalwork on the growth and spread of fire in the open and discussessome examples of field data in terms of the theoretical calculationspresented. The lengths of flames from laboratory fires have been relatedto the size and rate of burning of the fuel by formulae derivedfrom a simplified dimensional analysis. The effects of a windblowing across a long fuel bed on the length and orientationof flames are also described. The scaling laws for flame heightsuggest that in the horizontal spread of fire, heat transferfrom the flames above the fuel bed is important primarily withshallow fuel beds. It is suggested that the main effect of a wind on crib firesis aerodynamic. The wind deflects the advancing fire front fromthe vertical, but perpendicular to this deflected front therate of spread of fire, at least for cribs, is roughly the sameas in still air. However, a theory of spread allowing for heattransfer through the fuel bed and radiation from the flamespredicts that there can be a stable ‘fast‘ spreadas well as a ‘slow’ spread. In ‘fast’spread the flames are thick and control the spread. In ‘slow’ spread radiant heat transfer from theburning zone is usually responsible for the spread. The flamesare thin and of low emissivity. The most important factors determiningthe rate of ‘slow’ spread R are ^pb the bulk densityof the fuel bed and ø the deflection from the verticalof the front of burning fuel which varies with wind speed. Rpb cos ø is approximately constant over a wide rangeof conditions with an order of magnitude of 5–10 mg cm^–2s^–1.     

ERRATUM

THE author has called our attention to a mistake in her paper‘Squirrel Populations and their Control’ publishedin the recent Supplement to Forestry ‘Wildlife in theForest’. The mistake occurs in the second paragraph ofpage 19 where the fall in the estimated population of grey squirrelsfollowing a mast failure should be 468 to 66 and not 468 to466.     

Development of the Structural Root System of Sitka Spruce

Growth ring analysis was carried out on root systems of Sitkaspruce trees which had been planted 8 and 34 years previously.Retrospective measurements were made on root extension, andon cross-sectional area increment near the root base. The extensionof main lateral roots started slowly, then increased, and theyachieved a mean length of 4.4 m in 8 years. Differentiationinto roots of widely different radial growth rates took placeduring the first 6 years, resulting in 3 to 11 ‘major’woody roots and a large number of small ‘minor’ones, with some of intermediate vigour, radiating from the stump.The major roots established during the first few years constitutedthe main structural root system at 34 years. Many of the minorroots stopped growing in diameter after a few years, but werestill alive and extending at 34 years. The differentiation intomajor and minor roots is discussed with reference to their originon the root system, primary xylem diameter and the local environment.     

Beechnut Storage: A Review and Practical Interpretation of the Scientific Literature

Beechnuts are not easy to store or long-lived in storage. Theyexhibit storage characteristics between those of ‘orthodox’and ‘recalcitrant’ seeds. Superimposed upon thisis a pronounced dormancy which is overcome by between 4 and20 weeks of moist chilling. Pretreatment periods of 15–20weeks occupy most of the time between collection in Octoberand sowing the following April; hence short-term storage isa combination of moist storage and pretreatment. Most evidencepoints to the best short-term storage/pretreatment conditionsbeing 0–5°C at 28–32 per cent moisture content(m.c.) (fresh weight basis). Long-term storage requires a periodat low moisture content and the best conditions appear to be10 per cent m.c. and –10°C or below. The relative merits of overcoming seed dormancy before or afterdry storage are reviewed. There is no consensus about whichsequence is best but the former procedure is likely to be preferredby nursery managers because it allows storage of non-dormantnuts which can be withdrawn from store and sown immediately. Received 13 February 1990.     

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.     

Genetic diversity of Quercus glandulifera var. brevipetiolata populations in three forest communities with different succession stages

In order to understand the relationship between population succession and its genetic behavior, random amplified polymorphic DNA (RAPD) technique was used to analyze the genetic diversity of Quercu glandulifera var. brevipetiolata populations in three forest communities with different succession stages (coniferous forest, coniferous and broad-leaved mixed forest, evergreen broad-leaved forest). The results showed that 145 repetitive loci were produced in 60 individuals of Q. glandulifera using 11 primers, among which 120 loci were polymorphic, and the total percentage of polymorphic loci was 82.76% with an average of 64.14%. Estimated by the Shannon information index, the total genetic diversity of the three populations was 0.4747, with an average of 0.3642, while it was 0.3234, with an average of 0.2484, judged from the Nei index. Judged from percentage of polymorphic loci, Shannon inform at ion index and Nei index, the genetic diversity followed a decreasing order: coniferous forest > broad-leaved mixed forest > evergreen broad-leaved forest. Analysis of molecular variance (AMOVA) showed that 69.73% of the genetic variance existed within populations and 30.27% of the genetic variance existed among populations. The coefficient of gene differentiation (GST) was 0.2319 and the gene flow (N _m) was 1.6539. The mean of genetic identity among populations of Q. glandulifera was 0.8501 and the mean of genetic distance was 0.1626. The genetic identity between the Q. glandulifera population in the coniferous forest and that in the coniferous and broadleaved mixed forest was the highest. UPGMA cluster analysis based on Nei’s genetic distance showed that the population in the coniferous forest gathered with that in the coniferous and broad-leaved mixed forest firstly, then with that in the evergreen broad-leaved forest. The genetic structure of Q. glandulifera was not only characteristic of the biological characteristics of this species, but was also influenced by the microenvironment in different communities. __________ Translated from Journal of Northwest Forestry University, 2008, 23(1): 18–22 [译自: 西北林学院学报]     

The Commercial Impact of Oak Shake in Great Britain

The paper describes the results of a postal questionnaire surveyinto the extent of oak ‘shake’ in Great Britain.On average, 21 per cent of all oak was degraded by some formof shake. On a national scale, this represents a reduction inpotential harvesting revenues to growers of between £3million and £8 million annually, and larger sums if thecost of replacement imported hardwoods is considered.