THE DISTRIBUTION OF MYCELIA IN EUROPEAN LARCH BARK, IN RELATION TO THE DEVELOPMENT OF CANKER

The paper presents fully evidence to support the following conclusions.

1. The living bark of European larch (Larix decidua Mill.) maybe expected to be infected with a microflora which containsboth fungi and bacteria and which may sometimes include Dasyscyphawillkommii (Hart.) Rehm.
2. The necrotic areas which constitutecankers can be found tocontain a similar flora including Cytosporaabietis Sacc., C.curreyi Sacc., and Coniotbyrium fuckelii Sacc.This flora mayinclude D. wilkommii but it is not necessarilythe most abundantnor is its presence necessary for the developmentof larch canker.
3. Inoculation experiments at Mynydd Ddu, wherecanker and die-backof branches is severe, with the above speciesof fungus, showthat inoculations stimulate extensions of deadbark. Under differentsite conditions and in a canker-free plantationat Southmoor,similar inoculations only produced extensionsgreater than thoseobserved in control treatments, where thetrees inoculated hadbeen partially girdled.
4. A mass of myceliumof the usual species inhabiting living larchbark may, undersuitable conditions, have an influence whichfavours cankerextension but some special stimulus, of whichthe conditionof the tree may be an important factor, is neededto enablethem to influence the living bark of the host adversely.Muchmore careful study is needed before conditions which accompanycanker development are accurately known.

     

The Dean Nestbox Study, 1942-1964

Regular observations began in 1948 in the Forest of Dean, Gloucestershire,England, on an area of 60 acres carrying eventually c. 275 nestboxes.The area, planted to Quercus robur in 1814, has the appearanceof a Quercetum petraeae. Three-quarters, not grazed since 1947,has a varied shrub layer and a field layer distinguished bybrambles and bracken; the grazed area has a bracken/bluebellfield layer. Invertebrate life has been studied mainly in relationto the food of titmice Parus spp. The breeding bird communityincludes most of the species of British oak woodland. The mainoccupants of the nestboxes are two summer visitors, the PiedFlycatcher Ficedula hypoleuca and Redstart Phoenicurus phoenicurus,and two residents, the Great and Blue Tits, Parus major andP. caeruleus. There is some evidence of interspecific competitionfor nestboxes, but blocking of the entrances to exclude theresidents and favour the summer visitors gave inconclusive results.The populations of both seem to fluctuate independently (Fig.2). All the species were able to tolerate each other as neighbours.The effect of hard weather on the residents is demonstratedgraphically, but is only one factor in a complex situation.No evidence has emerged from the study that small insectivorousbirds can contain a major larval infestation.     

TWO-STORIED HIGH FOREST

The system has been adopted at Dartington with Japanese larch(Larix leptolepis), and it has been suggested that it worksthere because Japanese larch grows fast. It is argued in thispaper, however, that the system is best adapted to rather slowlygrowing trees, and the reason for its use with Japanese larchis that this species is characterized by a rapid height growthbut a small current annual increment, so that, unless the treesare isolated, they make extremely narrow annual rings. WithDouglas fir (Pseudotsuga taxifolia) and Sitka spruce (Piceasitcbensis) the annual rings might become too broad if thistreatment were applied, except at a rather advanced age. Nevertheless,the system has certain other advantages and, to attain these,it may be useful to adopt it more extensively, even if the annualrings become broader than we like.     

Monitoring of changes in tree and shrub layers in Wytham Woods (Oxfordshire), 1974-1991

In 1974–76 164 permanent 10x10 m plots were recorded atalternate intersections of a 100x100 m grid in Wytham Woods,Oxfordshire. Tree and shrub data were collected from all theplots in 1974–76, from 27 in 1984–85 and from allbut one in 1991–92. Changes in the structure and composition of the wood were assessedin terms of canopy cover, mean tree diameter, basal area andspecies occurrence. The wood has become more open (reduced canopycover) partly through management, partly through natural processessuch as windthrow and disease. The shrub cover has also declinedgreatly, probably because of increased deer browsing. Most standsare predominantly young growth and for the wood as a whole meantree diameter, basal area and tree height have increased. Theoverall composition of the wood has changed little, but therehas been a significant decline in mean woody species numberper plot from 5.8 to 4.1, mainly through declines in understoreyspecies and young oak (Quercus spp.). Elm (Ulmus spp.) coverhas been reduced by disease and birch (Betula spp.) sufferedpreferentially from windthrow. The results are used to indicate gains and losses in natureconservation terms for the wood as a whole. The strengths andweaknesses of this system may hold lessons for future woodlandmonitoring exercises.     

Effects of climate and management history on the distribution and growth of sycamore (Acer pseudoplatanus L.) in a southern British woodland in comparison to native competitors

Sycamore (Acer pseudoplatanus L.) is an invasive, non-nativespecies in Great Britain and its management in conservationareas is controversial. Climate change adds further uncertaintyto decision making. We investigated the role of management historyin determining present-day abundance and the effects of climaticvariability on growth, photosynthesis and phenology at WythamWoods, a UK Environmental Change Network (ECN) monitoring site.Relatively few sycamore trees were found in undisturbed ancient,semi-natural woodland and recent plantations, despite beingcommon in other areas of the site. Sycamore grew more slowlythan ash (Fraxinus excelsior L.), its principal competitor,but at a similar rate to pedunculate oak (Quercus robur L.)in the period 1993–2005. There were fewer sycamore thanash seedlings, regardless of which species dominated the canopy.Growth of sycamore was slower in dry periods than wet ones andlower photosynthetic rates were measured in canopy leaves underdry compared with wet soil conditions. This study thereforesuggests that sycamore does not present a serious threat toundisturbed ancient woodland on the site and that it may eventuallydecline in areas of the site where it competes with ash, inthe absence of disturbance. It may also decline under climatechange if summer droughts become more frequent.     

Managing birch woodlands for the production of quality timber

Interest in silver birch (Betula pendula Roth) and downy birch(Betula pubescens Ehrh.) has greatly increased in recent yearspartly as a result of pressures to restore and expand nativewoodlands but also due to renewed interest in birch as a treecapable of producing quality timber. Despite the many advantagesof birch as a commercial timber tree—ease of establishment,fast growth on good sites, high value timber and a short rotation,it has a poor reputation in Britain largely as a result of thepoor form of the existing, mainly unmanaged resource. The followingpoints need to be considered if stands of quality birch treesare to be produced in an economical timescale. (1) Sites: silverbirch needs good sites that are relatively well drained withlight mineral soils. Downy birch does well on moist to wet sites.(2) Regeneration: natural regeneration through a shelterwoodis the preferred system of regenerating birch as some overheadprotection is beneficial to germination success. About 20–40seed trees should be left per hectare. Good ground preparationand control of grazing are essential. The vast majority of seedlingsare recruited in the first year of the regeneration cycle thereforeplanting should be considered if the initial regeneration successis poor. Direct seeding is also a successful method of regeneration.Birch readily regenerates naturally into suitably prepared openareas next to existing birch woods but these should not be toobig, e.g. gaps or strips 20–60 m wide have been suggestedin the literature. (3) Maintenance: density of regenerationneeds to be reduced to about 2500–3000 stems ha^–1by the time the trees are about 3–6 m tall. Birch seedlingsmust always be taller than the competing vegetation. (4) Thinning:thinning should begin when the mean height of the stand is about8–10 m. At this point at least half the number of treesshould be removed with the emphasis on retaining dominants andco-dominants of good form. The aim is to maintain about halfthe height of the tree as living crown to sustain a high rateof growth. Additional thinnings will be required at intervalsof 5 to 7 years and final thinning should leave around 300–500stems ha^–1. (5) Rotation: a rotation of 40–50 yearsis possible on good sites and perhaps 50–55 years on lessfavourable sites.     

Establishment and Provenance of Walnut in Britain

This article reviews the silviculture of walnut in Britain andconsiders the case for planting common walnut (Juglans regia)or black walnut (Juglans nigra), neither of which is nativeto Britain. In addition the results of four provenance experimentsplanted in southern Britain in 1986–87 are described.The results of the experiments confirm that walnut is extremelysensitive to site conditions and should only be planted on themost suitable frost free, fertile, well drained and deeply rootablesites. Species comparisons show that J nigra is more tolerantof poor sites than J. regia, but at the only suitable site forplanting walnut there was little difference between the twospecies. Vermont, Ohio and Illinois provenances of J. nigraall performed well on the best site in the Chilterns and relativelywell on the other poorer sites.     

The Concept of Actual and Potential Production as an Aid to Forest Management

The environmental and biological factors which influence treegrowth are analysed to provide a concept for estimating thepotential production of a tree crop on any site. Some of thefactors which influence growth cannot be controlled by management,and therefore set an upper limit to the growth which shouldbe possible. This is termed the Management Potential Production.The idea of considering the actual tree growth on a site asbeing some fraction of the potential, rather than as a basison which to improve, is discussed in relation to the managementand research implications.     

Recent pine woodland dynamics in east Glen Affric, northern Scotland, from highly resolved palaeoecological analyses

Glen Affric, a National Nature Reserve of international conservationimportance for plant and animal communities associated withScots pine (Pinus sylvestris) woodland is managed for natureconservation and woodland restoration at a landscape scale.Management plans have drawn on information on current standstructure and variation but have not used in any detailed waythe analyses of past tree population changes from sources, suchas pollen analyses. This paper reports the results of pollenanalyses from three small peat hollows at the head of Loch Beinna' Mheadhoin. The analyses demonstrate, first, that woods inthe east of the reserve several centuries ago were differentin species composition and were more varied than they are todayand, second, that the currently patchy Pinus wood in the westof the reserve, at the head of Loch Beinn a' Mheadhoin, is theresult of recent spread westward onto former heathland. Thistemporal and spatial variability in the recent past has implicationsfor the future management of the woods because future woodsmay not develop with the characteristics of the current stands,and may not be stable over time.     

A Study of Losses in Scots Pine caused by Fomes annosus

Data are presented from unreplicated Scots pine {Pinus sylvestrisL.) sample plots in Thetford Forest which have been differentiallyattacked by Fomes annosus (Fr.) Cooke. Volume production ofseverely infested crops differs markedly from that forecastby management tables. The volume of dead trees may not representthe total loss of volume in these plots as there appears alsoto be a reduction in the growth of the remaining live trees.These observations may have considerable significance in forecastingfuture volume production from stands attacked by F. annosusand also in deciding the optimum time for their replacement.     

A Note on the Dimensions of Shoots and Roots of Planting Stock

Published figures suggest that in Pinus and Picea spp. plantingstock raised in nurseries the top/root ratio increases fromthe first year onwards. Transplanting checks growth in heightthe more severely the longer the time that has elapsed sincethe last transplantation, but growth in weight and diameteris much less affected, so that the shoot of a transplant isstouter and heavier than that of a seedling of the same height.On the other hand, growth of the root, both in length and weight,is encouraged, so that the top/root ratio of a transplant ismuch less than that of a seedling of the same age. In seedlings of broadleaved trees top/root ratio is less thanin Pinus and Picea, and usually decreases for 2 or 3 years. The top/root ratio and dimensions of the plants are also subjectto some individual variation which might be either inherentor due to external circumstances, including espacement. Informationon such variation is too scanty and inconsistent to supportany generalizations, except that diameter of shoot increaseswith increasing espacement.     

STUDIES ON ULMUS: III. The Village Elms of Hertfordshire

A biometrical study of the elms of southern Cambridgeshire waspublished in Forestry, xxxi. 132. The present paper is a parallelstudy of the village elms of Hertfordshire. The number of samplescollected was 143. For each of these, 8 quantitative and 1 qualitativefoliar character were determined. The majority of the samplesfall into 9 biometrically defined groups, 7 pertaining to U.carpinifolia and 2 to U. procera. U. glabra was also encounteredand one putative hybrid between U. glabra and U. carpinifolia. The U. carpinifolia elms occur in the east of the county andappear to be of Roman introduction in at least one case. Ofthe two groups of U. procera, one with short petioles and lowbasal asymmetry is centred around St. Albans. The other group,with longer petioles and conspicuous basal asymmetry, appearsto have entered the county both from the Icknield zone in thenorth and from Middlesex in the south. Both groups of U. procerawere established by the end of the Middle Ages, but their introductioninto the county has not yet been closely dated.     

Control of the Pine Weevil, Hylobius abietis L., and of Hylastes species

Dipping the tops of plants, prior to planting, in a 5 per centoil-based emulsion formulation of DDT has given good controlof Hylobius but does not control Hylastes and may involve damagedue to phytotoxicity in some circumstances. Experimentationwith newly introduced water-based formulations of DDT and BHCconfirmed earlier findings that there are few significant differencesbetween possible materials. The need to dip whole plants inorder to control Hylastes, with minimum risk of phytotoxicity,has led to the use of 1.6 per cent water-based BHC on a fieldtrial scale with promising results.     

Comparison between empirical and theoretical biomass allometric models and statistical implications for stem volume predictions

Comparisons between empirical and theoretical allometric modelsfor estimating tree biomass and the statistical caveats attachedto empirical stem volume equations are presented in this paper.First, the elastic and stress similarity models, derived fromfirst biomechanical principles, as well as predictions obtainedfrom geometric similitude, were validated against allometricequations that relate dry above-ground tree biomass M to stemdiameter D. In addition, a recent geometric model which predictsthat M D^8/3 was also validated against a pooled dataset whichconsisted of 764 M-D pairs compiled from empirical studies conductedthroughout the globe and for several tree species. Moreover,59 empirical equations which relate M to D were selected froma European database to validate the aforementioned theoreticalmodels. The analysis indicated that the biomechanical and thegeometric models failed to describe the shape in M-D allometryfor the empirical datasets. Finally, the multicollinearity problem,which is directly related to the reliability of the predictions,was analysed for stem volume equations (V). In total, 23 empiricalmodels based on the six-parameter formula V = a + bD + cD² +dD³ + eH + fD²H were used in order to pinpoint the dependencybetween the parameters. It is illustrated that parameters a,b and c are highly related to each other, and parameter e isalso related to parameter f. It is concluded that the interrelationshipbetween D and stem height (H) could be one of the reasons forthis dependency and scepticism should be placed in the reliabilityof V estimates derived from these models.     

The threat of the ambrosia beetle Megaplatypus mutatus (Chapuis) (=Platypus mutatus Chapuis) to world poplar resources

We describe the life cycle of Megaplatypus mutatus (Chapuis)(=Platypus mutatus) and the damage it causes to poplar resourcesin Argentina. This insect, native to the subtropical and tropicalareas of South America, has extended its range into temperateregions, reaching as far south as Neuquén in ArgentineanPatagonia. The damage is caused by the adult insects, whichbore large gallery systems into living poplars (Populus spp.),willows (Salix spp.) and many other broadleaf species, includingimportant fruit trees species such as apples (Malus spp.), walnuts(Juglans spp.) and avocados (Persea spp.). The galleries degradethe lumber and weaken the tree stems, which often then breakduring windstorms. A recent introduction of M. mutatus to Italydemonstrates that this insect can be transported long distancesbetween countries, and therefore presents a threat worldwide—particularlyto poplar cultivation. We review the taxonomic nomenclaturefor this pest, provide a summary of the life cycle, hosts anddamage and summarize actions taken to reduce the risk of introductionof M. mutatus to Canada.     

Colonization of Two Nothofagus species by Lepidoptera in Southern Britain

Between 1975 and 1982 a study was made of the invertebrate faunacolonizing two deciduous species of southern beech, Nothofagusobliqua and N. procera, introduced into Britain from South America.Special attention was paid to the folivorous larvae of Lepidopterawhich were sampled at 15 localities in southern England, mostlyin Forestry Commission trial plots and arboreta in Gloucestershire. The literature describing the native insect fauna of Nothofagusin Chile and Argentina is briefly reviewed. Mention is alsomade of the few previous records of lepidopterous larvae observedfeeding on Nothofagus in Britain. The larvae of 81 species Lepidoptera are recorded from Nothofagus.Seventy-eight of these were feeding on the foliage, of which73 were found on N. procera and 62 on N. obliqua, although approximately62 per cent of all the larvae collected were from N. obliqua.Faunal differences between the sites studied are briefly described.Two additional species of cutworm larvae are also reported attackingthe roots of Nothofagus seedlings. The changing lepidopterous fauna on Nothofagus from May untilSeptember is described and discussed. Spring-feeding larvaeof Operophtera brumata (L.), Agriopis aurantiaria (Hübn.)and Erannis defoliaria (Clerck) comprised 55 per cent of alllarvae collected on the two hosts, and represented between 68per cent and 87 per cent of those larvae in beating samplescollected in late May and early June. Most of the larvae collected were reared to adult in the laboratoryon a diet of Nothofagus leaves. The majority of these are regardedas polyphagus species although 64 are known to have one of thetwo native Quercus as a host-plant, while 24 have been recordedas feeding on Fagus sylvatica. The relevance of these two generaas sources for the Lepidoptera fauna colonizing Nothofagus isdiscussed. Nothofagus obliqua and N. procera are shown to have acquireda substantial lepidopterous fauna since their introduction intoBritain near the beginning of this century, although most ofthe trees sampled were less than 25 years old. These two speciesof Nothofagus may be vulnerable to defoliation by several speciesof caterpillar, especially if planted as monocultures in areaswhere oak and beech are plentiful. However, their surprisinglylarge insect fauna may be seen to have some value for natureconservation purposes.     

The Ecology of Armillaria mellea Vahl (ex Fries) in the Indigenous and Exotic Woodlands of Rhodesia

A. mellea is the cause of severe killing in young plantationsof Pinus elliottii in Rhodesia. P. patula is more resistantthough it may act as a carrier of the fungus; its resistancemay be overcome when planted in conditions of high inoculumconcentration such as clear-felled areas of P. elliottii whichhave a previous disease history. The source of infection isthe stumps of felled indigenous trees. Subsequent spread inthe pine is from tree to tree by root contact. The rate of increasein the incidence of the disease up to thirteen years from plantinghas been plotted. An initially logarithmic increase of killingshows a significant decline when the plantation is eight toten years of age. Viable basidiospores of A. mellea are presentin the air spora but little evidence of their importance inthe spread of A. mellea could be found.     

The Summerwood: Springwood Ratio in Conifers: How it arises, varies, and affects end use for timber, board, and paper

A theoretical discussion of variation in summerwood and springwoodcontents among conifers. Three methods of measuring these, bycross-sectional area of logs, by dryweight fibre percentage,and by nominal specific gravity, are compared. High-summerwood tissues have a nominal specific gravity of 0?45or over; low-summerwood tissues have a specific gravity below0?45. All conifers have a low summerwood content in their juvenilewood or core wood formed towards their stem-tips. In Pinus,Larix, and Pseudotsuga the summerwood percentage increases markedlywith age, but only in the outer layers towards the butt; inPicea, Abies, and Tsuga similar increases occur, but high-summerwoodtissues are seldom found. Within any species, and for any particulargrowth rate, low-summerwood tissues are characteristic of regionsof high relative humidity where summer water deficits rarelyoccur, such as high altitudes, far northern latitudes, and themaritime climate of western Britain. High-summerwood tissuesdevelop where summer temperatures are high, with associatedstrong sunshine, low relative humidity, and frequent summerwater deficits. High-summerwood tissues have greater strength in compressionand bending, relative to volume; but low-summerwood tissueshave greater strength relative to their weight. Low-summerwoodmaterial has proved satisfactory for most structural purposes,and for the manufacture of several kinds of artificial board.Its technical properties for the making of many types of paperare excellent, provided high resistance to tearing is not required.Likely summerwood content should guide planting programmes andmarketing policies.     

A LITTLE-KNOWN BORER IN IMPORTED SOFTWOOD; SERROPALPUS BARBATUS SCHALL. (COLEOPTERA, MELANDRYIDAE). REVIEW OF LITERATURE AND RECENT OCCURRENCES IN GREAT BRITAIN

A brief account is given of the biology and world distributionof this comparatively unimportant timber insect, which is responsiblefor a type of damage indistinguishable from that caused by wood-waspsof the family Siricidae, and with which it may have been confusedin the past. The presence of such damage is of interest in connexionwith the recently intensified quarantine measures in Australiato prevent the introduction of Sirex spp. in imported timber.Recent records have been associated in most cases with whitewood(Abies spp.) imported from Yugoslavia, but there is no evidencethat this beetle has become established or is an important timberpest in this country.