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.     

Studies on Ulmus: VI. Fenland Elms

A biometrical study of the leaves of the elms of the Isle ofEly and of the Parts of Holland, Lincolnshire, is presented.The number of samples totalled seventy. Elms are sparsely distributedin the Fenland except in the Island of Ely. Most of the samplespertain to one of four groups of U. carpinifolia, to U. procera,to U. glabra or to the Dutch Elm. No type of elm is believedto be indigenous in the area. The only elms likely to be ofancient standing are two of the groups of U. carpinifolia inthe Island of Ely, one of which was probably introduced fromthe Cam valley and the other from Huntingdonshire about theRoman era. The mosaic of elm types in the northern Fens arebelieved to be much more recent, in many cases post-medieval;some of these, as at Thorney, were probably introduced as seedfrom the continent.     

The elms of Wales

Two methods of biometrical analysis were used to characterizea collection of 178 leaf samples assembled in the course ofan all-Wales survey of elms made in 1977–78. All sampleswere referable to either U. glabra, U. minor var. minor, U.minor var. vulgaris (= U. procera)orU. x hollandica. The variationwithin each taxon is described. Elm regions are demarcated tosupplement those already described for England. U. glabra isthe only elm believed to-be native. It is thought most likelythat the main Welsh population of U. minor var. vulgaris, inGlamorgan, was introduced from Somerset some time before theNorman Conquest. U. minor var. minor is rare throughout Walesand could be of 18th century origin; its possible spread alongdrovers' routes is considered. Some notomorphs of U. x hollandicamust have been introduced as such. Others probably arose inWales from hybridization involving U. glabra, U. minor var.vulgaris and U.x hollandica var. hollandica.     

Variation among Italian and French elm clones in their response to Ophiostoma novo‐ulmi inoculation

In 1995 a clone bank of elms from across Italy was created at Antella (Florence, I) under a European Union project. In 1998 an experimental planting of some clones from this source was established in Antella together with material from a similar clone bank in France and two reference clones: Commelin (relatively susceptible) and Lobel (relatively resistant). In May 2001, the elms were inoculated with Ophiostoma novo‐ulmi and disease development was assessed throughout that summer and the next. Significant differences in susceptibility were found between taxonomic groups, with putative natural hybrids between Ulmus minor and Ulmus pumila being the most resistant and Ulmus glabra the most susceptible. Significant differences were also found within U. minor, some clones being as resistant as Lobel. For U. minor, a statistically significant relation was found with latitude, southerly clones showing less disease than more northerly ones. Relationships were also found between disease severity and times to bud burst, these relationships applying both to the different taxonomic groups and within U. minor. Relationships between growth increment and disease severity were inconsistent. These results are discussed in relation to the intrinsic genetically‐controlled differences that exist between elms and to differences in susceptibility that occur as the growing season proceeds and as a consequence of environmental influences.     

Effects of Ophiostoma ulmi and Ophiostoma novo-ulmi culture filtrates on elm cultures from genotypes with different susceptibility to Dutch elm disease

Cell cultures of callus tissue cultures obtained from four elm genotypes (Ulmus minor; Ulmus minor×Ulmus pumila; [Ulmus carpinifolia×Ulmus glabra] × [Ulmus wallichiana×Ulmus glabra]; and Ulmus pumila), either susceptible or resistant to Dutch elm disease (DED) were exposed to culture filtrates of Ophiostoma ulmi and Ophiostoma novo-ulmi. Elm cells were largely affected by crude culture filtrate incorporated into the media. However, the correlation between ‘in vivo’ cell resistance and growth in the presence of culture filtrate was poor: the effects of fungal media components were greater than that exerted by fungal exotoxins. Therefore, it is concluded that these ‘in vitro’ assays cannot be used to evaluate resistance sources to DED in elms, or to assess specific pathogenicity of fungal isolates.     

Frost hardening and dehardening in Abies procera and other conifers under differing temperature regimes and warm-spell treatments

Frequent bud frost damage in cultivation of Abies procera Rehderand pending climate changes are the background for this studyof cold hardiness under varying acclimation regime (in closed-topchambers) and experimental warm spells during the cold season.LT₅₀ values were established by freezing tests at differenttimes of year. Damage and deaths were assessed on leader buds,subapical lateral buds, needles and cambium. Minor parallelexperiments involved Abies nordmanniana, Picea abies and Piceasitchensis. Lower acclimation temperatures resulted in deeperfrost hardiness during late autumn but less during spring, comparedwith ambient temperature controls. Elevated temperatures resultedin less deep frost resistance. Apical buds generally developeddeeper frost hardiness than lateral buds but less deep thanthe cambium, varying with species, however. Frost damage inbuds ranged from death over partially destroyed bud contentsresulting in distorted shoots to buds seemingly remaining dormant.Responses to warm spells differed with duration, timing andspecies, ranging from dramatic decrease in frost hardiness withor without subsequent recovery to no reaction. Furthermore,the reactions did not show any clear relation to dormancy level.For A. procera, exposure to fluctuating temperatures appearedto be particularly problematic. This explains why this speciesdevelops best in coastal climates, and in sites sheltered fromtemperature extremes either by hedging, a winter snow cover,or topography. The Christmas tree production will suffer severelyon sites with harsh temperatures due to losses of lateral andterminal buds, which destroy the crown symmetry. Clipping ofgreenery is less influenced by frost damages, although the developmentof normal branch whorls is often disturbed.     

Some Consequences of the 1975-1976 Drought for Dutch Elm Disease in Southern England

During the exceptionally hot, dry summer of 1976 the large elmbark beetle, Scolytus scolytus, was able to invade and successfullybreed in apparently healthy, undiseased elms. A conspicuousfeature was the clustering of wasps, bees and ladybirds on thestems, attracted by sap exudation. The trees were probably sufferingfrom drought, although many showed no symptoms. The phenomenonoccurred mainly on shallow soils over limestone; trees on chalkwere not generally affected. In 1976, and to some extent in 1975, the downward developmentof Ceratocystis ulmi through the tree was less than in previousyears, and only a low proportion of the numerous maturationfeeding wounds became infected. However the drought does notappear to have significantly influenced the course of the epidemic. The attacks by S. scolytus on undiseased trees are discussedin respect of 19th Century reports of attacks on elms, and itis concluded that the ability of S. scolytus to assume a moreprimary role may have been underestimated.     

Die mogliche Verbreitung des »UImensterbens« durch Wurzel-verwachsungen bei Ulmus carpinifolia Gled.

Possible spread of »elm disease« in Ulmus carpinifolia Gled. through root grafts . In a stand of elms (Ulmus carpinifolia Gled.), nearly all the trees were joined in groups of various sizes by “connecting roots”.     

Frost Hardiness of Nothofagus procera and Nothofagus obliqua in Britain

The frost hardiness of four seedlots of Nothofagus proccra andsix seedlots of Nothofagus obliqua was measured experimentallyduring three winters. Shoots were taken from saplings growingat the Bush Estate in Scotland. All seedlots set buds in lateSeptember, hardened very slowly in the autumn, were damagedto some extent by temperatures below –14°C in mid-winter,and dehardened during frosty weather in February/March priorto budburst in mid to late April. The range of mid-winter temperaturesgiving 0%, 50% and 100% kill (LT₀, LT₅₀ and LT₁₀₀) were 8–14°C,13%20°C and 14–22°C, respectively. By contrast,British Fagus sylvatica hardened off rapidly in September, wasundamaged by frosts well below –20°C in mid-winter,and did not deharden until late April, prior to budburst atthe end of May. Nothofagus seedlots from Nuble in Chile (the most Equatorialsource) were the most frost susceptible: unfortunately, seedof this origin was supplied to many British nurseries between1976 and 1W9. Seedlots from Neuquen in Argentina, and from maturetrees of Malleco (Chile) origin growing in Britain, were themost host hardy. N. procera tended to be hardier than N. obliqua,and the trees became hardier with age. Past temperature records for Britain suggested that all theNothofagus seedlots had a high risk of suffering severe frostdamage at least once during a timkr rotation in all but mildcoastal regions. Spring and autumn frosts may be more damagingthan winter frosts. However, if it were possible to select individualswithin populations that were 3–6°C more frost hardythan the population means, such trees would be sufficientlyhardy to avoid frost damage in most lowland regions.     

Diversity and pathogenicity of Botryosphaeriaceae on declining Ostrya carpinifolia in Slovenia and Italy following extreme weather conditions

Unusual and extensive dieback of European hop hornbeam (Ostrya carpinifolia) has been observed in western Slovenia and northern Italy in recent years, when extreme drought and higher temperatures were recorded. A preliminary study identified Botryosphaeria dothidea as a potential causative agent of the dieback. Further characterization of intra- and interspecies diversity of Botryosphaeriaceae collected from O. carpinifolia and other tree species in the affected area was achieved based on anamorph morphology, sequence data from the ITS rDNA and EF1-??, PCR?CRFLP analysis and AFLP profiles. The majority of the isolates analyzed were identified as B. dothidea, and in vitro pathogenicity tests re-confirmed the fungus to be an important cause of the disease. Insight into the B. dothidea population, diversity based on AFLP markers indicates that the dieback observed in O. carpinifolia is probably associated with a heterogenous population of B. dothidea, which emerged from a latent state in response to changed climate conditions. Isolates with Dothiorella-like conidia were also identified during the survey, but these were collected more rarely and appear to represent undescribed species. Isolates from Dothiorella genus expressed low pathogenicity in pathogenicity tests and proved no impact on the pathogenic ability of B. dothidea.     

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.     

Productivity of Closely-spaced Young Poplar on Agricultural Soils in Britain

Recent ideas on ‘silage’ and ‘fuel’forestry call for more information on the total harvestablewoody dry matter produced by hardwoods grown at very close spacingsin fertile soils and coppiced every few years. Yields of oven-driedstems and branches (S and B) are presented here for Populustrichocarpa Torr. and Gray, clone ‘Fritzi Pauley’.Plantings in Bedfordshire at 21 600 trees ha^–1 had a meanannual increment (M.A.I._SB) of 5.2 t ha^–1 y^–1 overfive years, and plantings in the Cambridgeshire fens at 1480trees ha^–1 produced 4.8 t ha^–1 y^–1 over sixyears. Fan-shaped spacing experiments, established in Midlothianby inserting cuttings through black polythene into nursery soilwith added fertilizers, gave 4.6 t ha^–1 y^–1 at theend of the first year and about 7 t ha^–1 y^–1 oneyear after coppicing, but only with over 250 000 stems ha^–1producing closed canopies with leaf area indices of about 4.Similar spacing experiments planted without fertilizer on farmlandin Gloucestershire, Suffolk, Argyll and Midlothian gave averageM.A.I._SB values of 6.5–7.0 t ha^–1 y^–1 afterthree years with over 25 000 trees ha^–1 and similar valuesafter five years with over 10 000 trees ha^–1. Peak currentannual increments (C.A.I._SB) averaged 10–12 t ha^–1y^–1. The maximum M.A.I._SB, attained in Gloucestershire,was 10.0 t ha^–1 y^–1 at age 5 with over 20 000 treesha^–1, with maximum C.A.I._SB values of about 14 t ha^–1y^–1 at age 4; M.A.I._SB values of about 11.5 t ha^–1y^–1 were anticipated at this site by age 6–8. Equivalentstem volumes are given. As expected, trees subjected to competitionaccumulated greater proportions of their woody biomass in stemsrather than branches. Biomass yields of fully-stocked young hardwood stands are independentof planting density. In Britain, M.A.I._SB values of 6–8t ha^–1 y^–1 can be obtained over 1 or 25 years byplanting 250 000 or 2000 trees ha^–1, using vigorous Populusspp, Salix spp or Nothofagus procera on good sites. Advantages and problems of ‘silage’ forestry arediscussed, and it is considered that hardwood fuel coppicescould not meet more than about 2% of national energy needs. The reciprocals of individual tree weights were linearly relatedto planting density.     

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.     

First report on the Dutch elm disease pathogen Ophiostoma novo‐ulmi from Latvia

During 2017, Dutch elm disease was investigated on 67 Ulmus glabra and 29 Ulmus laevis samples from 28 sites in Latvia. The presence of Ophiostoma novo‐ulmi was detected in 61.2% of the samples from U. glabra and in 34.5% of the samples from U. laevis. In 11% of cases, hybrids between subsp. novo‐ulmi and subsp. americana were identified, particularly in the sites in the southern part of Latvia. This study presents the first verified record of Ophiostoma novo‐ulmi and its subspecies in Latvia.     

Oviposition preference and larval performance of Aeolesthes sarta (Coleoptera: Cerambycidae) in six hardwood tree species

Sarta longhorned beetle (SLB), Aeolesthes sarta Solsky, is an economically important pest of fruit and shade trees in central and east Asia. Choice, no-choice, and larval insertion experiments were conducted to determine SLB oviposition preference and larval host suitability on six hardwood tree species including Ulmus carpinifolia Borkh., Ulmus carpinifolia var. umbraculifera Rehd., Platanus orientalis L., Populus alba L., Salix alba L., and Fraxinus rotundifolia Miller subsp. persica (Boiss.), under laboratory conditions. In the choice and no-choice experiments, significantly greater numbers of eggs and living larvae, and greater mass of living larvae were found on U. carpinifolia and U. carpinifolia var. umbraculifera compared to those on the other tree species. In the choice experiment, oviposition did not occur on F. rotundifolia subsp. persica. There were a few eggs on P. alba but no living larvae. The mean mass of living larvae was lowest on P. orientalis. In addition, in the no-choice experiment significantly fewer numbers and mass of living larvae were found in P. alba and F. rotundifolia subsp. persica. In the larval insertion experiment, more larvae survived on U. carpinifolia and U. carpinifolia var. umbraculifera compared to the other trees. Larvae recovered from U. carpinifolia and U. carpinifolia var. umbraculifera weighed significantly more than larvae from the other trees. These results suggest that U. carpinifolia and U. carpinifolia var. umbraculifera are the most preferred and suitable hosts for SLB adults and larvae. Salix alba is an acceptable host for adult oviposition and a potentially suitable host for larval development. Platanus orientalis and P. alba are less suitable, and F. rotundifolia subsp. persica appeared to be unsuitable as a host for SLB.     

Light Use Efficiency and Woody Biomass Production of Poplar and Willow

Stands of clonal Salix viminalis (in 1985) and Populus trichocarpa(in 1986) were grown for one growing season from cuttings incontainers, at 0.3 m spacing, supplied with trickle irrigationand nutrients. Woody biomass production (B_w) in the first yearwas analysed as the product of the proportion of dry matterpartitioned to wood ({macron}), the seasonal mean efficiencywith which intercepted light was used to produce dry matter({macron}), the mean fraction of incident light interceptedby the canopies (f{macron}), and the amount of incoming solarradiation over the season (A). Thus, Bw = {macron}f{macron}{macron}A. For Salix, B_w=10 t ha^–1y^–1, while for Populus, B_w= 5 t ha^–1y^–1, mainly because of differences in{macron} and f{macron}. The Populus partitioned more dry matterto roots (and correspondingly less to stems) and interceptedless light over the growing season. The Salix and Populus cloneshad surprisingly similar ({macron}) values, namely 1. 58 and1. 50 g MJ^–1, respectively (based on total dry matterand total solar radiation), which are very like the {macron}values measured on C₃ agricultural crops in Britain. Also, theSalix and Populus clones produced canopies with similar lightextinction coefficients and hence similar relationships betweenfractional interception and leaf area index.     

Pedunculate and Sessile Oak (Quercus robur L. and Quercus petraea (Mattuschka) Liebl.): A Review of the Hybrid Controversy

Early nineteenth-century studies of variation in the genus QuercusL., particularly those relating to Pedunculate and Sessile oakby Lasch and Greville, illustrate the confused situation thatawaited the forest botanist. Attempts of that period and laterto explain this condition led to the general acceptance of atheory of unlimited hybridization and introgression betweenthe two species. Experimentation and observations between thethirties and fifties of the present century by Dengler, Høeg,Jones, and others demonstrate the weakness of this popular concept—hence the controversy. More recent investigations by Johnssonand Krahl-Urban, supported by the biometric research of Cousens,Carlisle, and Brown, have helped in the production of a moreaccurate picture of the form and extent of hybridization. Agreat deal still remains to be done to elucidate the naturalfrequency of F₁ hybrids, and backcrossea in different regions.The karyotypes of both species and hybrids have still to bedefined.     

Shading Reduces both Visible and Invisible Frost Damage to Norway Spruce Seedlings in the Field

Two-year-old cuttings of Norway spruce were subjected to nightfrosts in spring on an exposed site in southern Sweden. Shadingwas used to assess the influence of sunlight on the extent ofdamage resulting from night frost. Chlorophyll fluorescencewas measured in needles in flushing shoots, and in shoots atthe stage of bud burst. The F_v:F_m ratio was significantly lowerfor plants exposed to light, compared with shaded plants onthe days following the night frost (minimum temperature –6°C).The effect was similar both in 1-year-old and current year needles.The low F_v:F_m ratios indicate damage to photosystem H, causedby an interaction between sub freezing temperatures and highlight intensity. Shading also increased the survival of flushingshoots. It is suggested that regeneration of Norway spruce onsites exposed to frost should be carried out in partial shade,for example under a shelterwood.     

Effects of nitrogen fertilization and temperature on frost hardiness of Aleppo pine (Pinus halepensis Mill.) seedlings assessed by chlorophyll fluorescence

In a 14-week study, 1-year-old Aleppo pine seedlings were grownin two growth chambers. Seedlings were artificially hardenedby decreasing photoperiod and temperature. In each chamber halfof the seedlings were fertilized with nitrogen (8.4 mg seedling^–1).In order to determine the relative importance of the hardeningenvironment versus fertilization, each chamber was programmedto decrease night temperatures down to a low of 8 or 4°C.Chlorophyll fluorescence and frost hardiness was measured fivetimes during the experiment. A sample of seedlings from eachtreatment was exposed to an artificial frost at –5°Cand the freezing effects were assessed by measurements of chlorophyllfluorescence and visual evaluation of needle damage. Seedlingsincreased their frost hardiness during the experiment in allthe treatments but the ratio of variable to maximal chlorophyllfluorescence (F_v/F_m) measured before freezing did not vary duringthe experiment. This indicates that Aleppo pine maintains itsphotosynthetic ability during hardening in contrast to otherconiferous species from colder climates. The effect of nitrogenfertilization on frost hardiness was small in comparison withchamber effect. Nitrogen fertilization slightly delayed theacquisition of hardening in the coldest chamber. Seedlings inthe warmest chamber did not become fully resistant to –5°C,but in the coldest chamber, where night temperature reached4°C, all the seedlings were resistant to the frost. Severedamage caused by frost could be related to a rapid rise of minimalfluorescence (F₀) but the best index of damage was the dropof F_v/F_m after freezing.     

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.