Douglas Fir in Wessex: (With folder)

Douglas fir (Pseudotsuga taxifolia (Poiret) Britton) was chosenfor its first year's study by the newly formed Wessex SilviculturalGroup as a species of economic importance which might be grownmore widely. The paper is a record of the Group's observationsincluding site-types based on soils, volume production, thinning,crown density, natural regeneration, and troubles met with.     

Woodland Elms in Wessex

A study undertaken by the Wessex Silvicultural Group on thegrowth of elm in woodland disclosed the occurrence of potentiallyvaluable elm stands in many parts of south-west England. Thepaper discusses some aspects of cultivating elm in woodland,and provisional estimates of volume production are made. Muchof the information relates to English elm (Ulmus procera Salisbury),but other species and hybrids are briefly reviewed. Commentson some current elm problems are included.     

Variation of heartwood phenolics and oak lactones between the species and phenological types of Quercus petraea and Q. robur

Pressler cores were taken of Quercus petraea and Q. robur treesfrom young German provenance stands and mature mixed plantationsin England. The concentration of total phenolics extracted fromthe outer heartwood was measured and significant differencesfound between the two species. Concentrations of oak lactones,measured from provenance samples, also varied significantlybetween the species. However, the difference in total phenolicsbetween species was much lower among the trees from the mixedplantations than from the provenance trials. Q. petraea wascharacterized by lower levels of total phenolics but greaterconcentrations of oak lactones than Q. robur. A comparison betweenlate and early flushing Q. petraea trees found no significantdifference in total phenolics between these phenological types.     

The Dependence of Quercus robur and Q. petraea Seeding on Cotyledon Potassium, Magnesium, Calcium and Phosphorus during the First Year of Growth

Acorns collected from a range of Quercus robur L. and Q. petraea(Matt.) Liebl. populations were germinated and grown in an unheatedgreenhouse using a standard commercial compost. Total seedlingdry weight did not increase until the end of the growing season,with Q. robur and Q. petraea seedlings showing mean dry weightincreases of 211 per cent and 414 per cent respectively. Oakseedlings appear to depend upon cotyledon reserves of carbohydrate,P, K and Mg during most of the first year of growth, but relyon external sources of Ca. Seedlings become independent of thecotyledons at the end of the first growing season.     

A comparison of the autecology of Quercus robur L. and Q. pyrenaica Wild.: present habitat in Galicia, NW Spain

The biotopes occupied by pedunculate oak (Quercus robur L.)and rebollo oak (Quercus pyrenaica Willd.) in Galicia were characterizedusing different parameters, enabling a comparative analysisof its habitats. Thirty-nine plots of pedunculate oak and 40of rebollo oak were inventoried and 25 ecological parameters(physiographic, climatic and edaphic) were measured to describethe biotopes, along with 14 stand parameters to characterizethe structure and the silviculture of these forests; some ofthem were used in previous works about the autecology of bothspecies. Quercus robur was found to occupy a wider range ofecological habitats and their distribution is oceanic; Q. pyrenaicapresents a more Mediterranean phytoclimatic position. The resultsindicated that the distribution of oak forests in Galicia ismore closely related to physiographic and climatic featuresthan to edaphic, because the nature of the substrates that theyoccupy is similar. Analysis of fragility/aggressiveness betweenboth species and chestnut shows that the aggressiveness of bothoaks, mainly pedunculate, was much higher, except at high altitudes,and in areas with a high mean temperature, where rebollo ismore aggressiveness. Comparison of the two Quercus shows formost of the parameters that Q. robur is the more aggressivespecies.     

Species-specific drought effects on flower and fruit production in a Mediterranean holm oak forest

A holm oak forest was exposed to an experimental drought (reductionof 15 per cent soil moisture as predicted for this area forthe next decades by General Circulation Models and ecophysiologicalmodels) during 7 years to elucidate the reproductive responsesof the dominant species Quercus ilex L., Arbutus unedo L. andPhillyrea latifolia L. Soil moisture was partially reduced byplastic strips intercepting rainfall and by ditch exclusionof water runoff. During the period studied, meteorological conditionsand soil moisture were continuously monitored, together withflower and fruit production in the three dominant species. InQ. ilex and A. unedo, flower and specially fruit productionwere strongly correlated with annual rainfall, but not in P.latifolia. The experimental drought reduced flower and fruitproduction in Q. ilex by 30 per cent and 45 per cent, respectively.Reductions in flower and fruit production were not significantin A. unedo and were not observed in P. latifolia. A decreasein production of reproductive structures and the different responseof the species studied to a decrease in water availability couldinduce important changes in the competitive ability of the differentspecies and in the long term in the community species compositionand future distribution of these Mediterranean species.     

Performance and Frost Hardiness of Picea sitchensis x Picea glauca Hybrids in Scotland

The growth of seven Picea sitchensis x Picea glauca hybridswas compared with the growth of two P. sitchensis provenancesand Picea glauca var.albertiana at two sites in northern Scotland.The sites were at Aultmore (an exposed, dry site with a mineralsoil) and Shin (a frosty, wet site with deep peat). They wereof the type considered more suited to Pinus contorta than P.sitchensis. At age 10, in 1984, most of the hybrids, at both sites, wereabout 10 and 20 per cent taller than P. sitchensis of Masset(Q.C.I.) and Ketchikan (Alaska) provenance, respectively. P.glauca var. albertiana grew very poorly, especially at Aultmore. At Aultmore, the frost hardiness of three of the tallest hybrids,the two P. sitchensis provenances, and P. glauca var.albertiana,was tested at about 3-weekly intervals throughout 1982 and 1983.Detached shoots were subjected to artificial frosts in a programmablechamber. P. glauca var. albertiana was frost susceptible atbudburst, but at all other times it was relatively very frosthardy (eg. to^–10°C in mid-August). Also, the hybridswere consistently more hardy than P. sitchensis of even Ketchikan(Alaska) provenance from July onwards. However, the hybridswere less frost hardy than P. sitchensis of Masset (Q.C.I.)provenance in early spring (they dehardened a week earlier inMarch-April) and their buds were equally as frost susceptibleat the time of budburst. In 1983, trees of P. glauca var. albertianaburst their buds about a week sooner than P. sitchensis. It was concluded that P. sitchensis x P. glauca hybrids canperform better than P. sitchensis at sites considered ‘marginal’for P. sitchensis, and that their good performance may be partlyattributed to, or associated with, their greater summer andautumn frost hardiness. A programme of inter-specific hybridizationis being pursued.     

OAK

Four basic stages in the life of the oak wood (Quercus roburand Q. petraea) are defined and the factors which should influencethe manager's mind when he weighs density of stocking and lengthof bole against rotation to meet his particular requirementsare considered briefly in non-technical language.     

PRELIMINARY LIGHT-INTENSITY STUDY UNDER SESSILE AND PEDUNCULATE OAK

While study by continental and American workers has continuedover a considerable period, little has been published in connexionwith forestry. A method is described using photoelectric cellphotometers and the results given of measurements made undercomparable stands of sessile and pedunculate oak (Quercus petraeaLiebe and Q. robur L.). These results confirm that sessile oakcasts more shade than pedunculate oak.     

The tolerance of newly emerged broadleaved tree seedlings to the herbicides clopyralid, cycloxydim and metazachlor

In direct-seeded woodlands and nursery seed-beds, weeds canrapidly invade newly sown areas, leading to death or suppressionof tree seedlings. Hand weeding is usually expensive, and thesafe use of broad-spectrum contact herbicides is seldom possible.Hence in the work reported here, the tolerance of young treeseedlings to the potentially more selective, post-emergenceherbicides clopyralid, cycloxydim and metazachlor, was tested.Seedlings of Fraxinus excelsior L. (ash) with two to four expandedtrue leaves (2–4 ETL), Fagus sylvatica L. (beech) (2–4ETL), Acer pseudoplatanus L. (sycamore) (4–6 ETL), Prunusavium L. (cherry) (6–8 ETL) and Quercus robur L. (oak)(6–8 ETL) appeared to tolerate applications of cycloxydimat a rate of 0.45 kg a.i. ha^–1. Applications of 0.2 kga.i. ha^–1 clopyralid or 1.25 kg a.i. ha^–1 metazachloralso appeared to be generally tolerated, but did cause somesuppression of annual growth increment in Q. robur, P. avium,F. sylvatica and A. pseudoplatanus, particularly where repeatapplications were made to the earliest growth stages. Seedlingsurvival was unaffected by any herbicide treatment. Mixturesof all three herbicides were no more damaging than the sameherbicides applied separately. Therefore, depending on treespecies and growth stage, it appears that clopyralid could potentiallybe safely used to control a range of herbaceous weed species,metazachlor a variety of seedling or germinating weeds and cycloxydima range of established grass weed species, in direct sown woodlandsor nursery seed-beds, although further research is advisableto confirm crop safety.     

A Possible Indicator of Shake in Oak: Relationship between Flushing Dates and Vessel Sizes

Previous work by Savill (1986) has shown that oak trees (Quercusrobur and Q. petraea) with large earlywood vessels appear tohave a much greater predisposition to shake than trees withsmaller vessels. The aim of the investigation described herewas to determine whether there are any externally visible characteristicscorrelated with vessel size, so that shake-prone trees can berecognized in the field. It was found that trees that flushlatest within a population tend to have the biggest vessels.Possible reasons for this correlation are discussed briefly.The finding has the practical value that oaks which are predisposedto shake can be marked at flushing time and removed in thinningoperations.     

AN ENUMERATION OF THE MATURE OAK IN THE FOREST OF BERE

The paper describes the methods used in the field and in theoffice to determine the standing volumes and increments of 100-and 130-year old oak in the Forest of Bere, Hampshire, duringworking-plan revision. The figures obtained show that the standingvolumes and increments of sessile oak (Quercus petraea Liebe)are considerably higher than those of pedunculate oak {Q. roburL.) on the three sites investigated, namely, clays, sands, andgravels, while for both species sands appear to be the mostfavourable and gravels the least favourable soil types. Therewas little difference in the mean values for increment and standingvolume between the 100- and the 130-year old pedunculate oak.     

Growing Oaks at Closer Spacing

The reasons for the scarcity of tall straight oaks (Quercusrobur L. and Q. petraea (Mattuschka) Liebl.) in Great Britainare discussed in this paper. It is argued that the historicalpractice of growing timber at very wide spacings in coppice-with-standardssystems rather than high forest, coupled with generations ofselection for crookedness rather than straightness, has resultedin a dearth of tall, well-formed trees. Evidence is presentedthat oak produced in conditions of quite severe competitionwill grow much taller than widely spaced trees. It is concludedthat the current practice of planting at densities of 1100 treesper hectare is unlikely to lead to the government's stated objectiveof encouraging an 'increase [in] the quality and value of timberproduced by broadleaved woodlands as a whole' (Forestry Commission,1985). The economic and other implications of considerably closerspacing are discussed. Received 15 October 1990.     

Genetic control of wood colour, density and heartwood ellagitannin concentration in European oak (Quercus petraea and Q. robur)

Pressler cores of young clones of Quercus petraea and Q. roburwere analysed from two sites in Germany. Variation of wood colour(defined by the CIELAB system), density and heartwood ellagitanninswas examined between clones, species and sites. Similar studieswere made of cores from another trial of 20 half-sib familiesof parent trees deriving from five German forests. The resultsfrom both the clonal and progeny trials indicate that heartwoodellagitannin content and wood density are under strong geneticcontrol, while sapwood and heartwood colour are less so. A largeproportion of between-clone variation in wood density and ellagitanninlevels occurred between the two species, while these propertiesvaried little among ramets of the same clone grown on two contrastingsites, despite a difference in growth rates. A large proportionof the total variation among progeny was attributed to forestorigins and could not be attributed clearly to either geneticor environmental causes because of limitations of the samplingdesign     

Autumn Frost Damage on Young Picea sitchensis 2. Shoot Frost Hardening, and the Probability of Frost Damage in Scotland

The natural increase in frost hardiness of detached shoots ofPicea sltchensis during August to November was measured usinga programmable freezing chamber. Oregon, Queen Charlotte Islandsand Alaskan provenances were compared, and the effects on hardeningof long days, warm temperatures and frosts were determined.A computer model was constructed to mimic the observed patternsof autumn frost hardening, as functions of air minimum temperatures,daylengths and the occurrence of frosts. The model was used(a) to describe the pattern of autumn frost hardening at differentsites in northern Britain, using past meteorological records,and hence (b) to determine when frosts occurred that might havedamaged young trees. The model accurately predicted known instancesof autumn frost damage at Kirroughtree and Carnwath. The predicted probability of autumn frost damage on young treesof P. sitchensis in upland areas of Scotland was much lowerthan that previously predicted for spring frost damage. Theestimated return time for autumn frost damage to an Oregon provenanceat Eskdalemuir was 8.3 years, and the return time for a Q.C.I.provenance was longer than 10 years. Most damaging frosts occurredin October, but frosts like those on 13–15 October 1971,which followed warm weather and caused wide spread damage inScotland, have been quite rare. Alaskan provenances would rarelybe damaged by autumn frosts, nor would trees of Q.C.I. provenancegrowing in lowland areas of Scotland, or at Masset on the QueenCharlotte Islands.     

The effect of heavy or 'free growth' thinning on oak (Quercus petraea and Q. robur)

Free growth is a type of heavy thinning which aims to maximizediameter increment and produce valuable timber on a relativelyshort rotation. An experiment is described which investigatedthe application of free growth to a stand of oak {Quercus petraeaand Q. robur) planted in 1930. At age 58 free growth thinninghad resulted in a mean diameter at breast height of 39.0 cmwith an estimated mean tree volume of 0.98 m³, compared with29.3 cm and 0.52 m³ for equivalent crown thinned trees. Discountedcash flow calculations showed that free growth thinning of oakcould be justified using a 3 per cent discount rate assumingthat the increased intensity of pruning results in a large proportionof veneer quality timber; an independent assessment indicatedthis may be possible. Free growth thinning of oak is not a commonpractice in British broadleaved silviculture probably becauseof the cost of controlling epicormic shoots. It is suggestedthat it may be more appropriate to other species such as ash,sycamore and wild cherry.     

杨树溃疡病引致幼树的生长量损失估测*

杨树溃疡病经常在幼树干部形成大溃疡斑，造成枝枯和死树。以胸径下病斑面积与树周面积的比值计算的发病程度（X5）与胸径年生长量（Y2）之间呈显著相关。通过回归建立了三个品种不同病情下的生长量模型：美×559：Y2＝0．15406＋118．52194／（102．9113＋X^25)加杨：Y2＝－0．4136＋278．32113／（133．0115＋X^25)小×黑：Y2＝－0．08487＋110．16972／（131．4548＋X^25)三个估算模型经数学检验合理；坐标曲线符合植物病理学原理，可作为该病病情分级和生长量损失估算的参考。     

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.     

Root anchorage and stem strength of black spruce (Picea mariana) trees in regular and irregular stands

A tree winching experiment was conducted, simulating wind actionand resulting damage, in order to assess mechanical resistanceof black spruce (Picea mariana (Mill.) B.S.P.) trees in standsof regular and irregular structures. The critical bending moment(M_c) of winched trees was determined and the relationship betweenM_c and tree and stand characteristics was investigated throughstatistical analyses. Stem mass (SW), average spacing betweentrees (S) and height:diameter ratio (H/d.b.h.) were initiallyselected by a screening procedure to predict M_c. Potential differencesbetween stand structures were tested in mixed models using differentsubsets of the data. Included fixed effects varied between thedifferent models. SW was the most useful and significant variablein all models and H/d.b.h. was significant only when snappedtrees were included in the analysis. When decayed samples wereexcluded, resistance to uprooting was higher in irregular stands.Decay seemed to play an important role in irregular stands andshould be investigated further. Since no difference was observedin the relationship between stem mass and critical turning momentbetween distant sites, relationships should be applicable acrosswide regions. This study provides some of the basic relationshipsrequired to model windthrow risk in irregular stands. However,the effects of stand structure on wind load for individual treeswill also need to be considered.     

Forest characteristics affecting the rate of shoot pruning by the pine shoot beetle (Tomicuspiniperda L.) in Pinus radiata D. Don and P. sylvestris L. plantations

Different variables, such as altitude and presence of defoliators,were studied in Bizkaia (northern Spain) in order to assessthe susceptibility of Pinus radiata (D. Don) and P. sylvestris(L.) stands to Tomicus piniperda (L.) (Coleoptera: Scolytidae).Altitudes higher than 400 m, presence of logs, degree of thinningand incidence of fires, all increased the susceptibility ofP. radiata monocultures to shoot attack by T. piniperda. P.sylvestris plantations were more affected at alti tudes lowerthan 400 m and by poor forest hygiene. The presence of the processionarymoth (Thaumetopoea pityocampa Den and Schiff.) had a significanteffect on the rate of shoot pruning on the trees; vigorous treesand those with bare leader were more affected by the bark beetleattack if T. pityocampa larvae were feeding on their needles,while trees with dominance taken by the side shoots were lessattacked when moth larvae were present.