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.     

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

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

Regeneration and gene transformation systems of Robinia pseudoacacia ‘Idaho’ mediated by Agrobacterium tumefaciens

Robinia pseudoacacia ‘Idaho’ is one of several multi-purpose trees used in ornamental, soil and water conservation, fodder and nectar sources. Plant abiotic stress tolerance transformed by genes could meet the requirements for reclamation of arid or alkalid lands and vegetation restoration. For this paper, we studied the effects of auxin and cytokine on Idaho locust in vitro regeneration and the establishment of gene transformation systems for plants mediated by Agrobacterium tumefaciens. Results showed that the ratios of cytokinin and auxin were the major factors affecting adventitious bud differentiation on a MS medium; the concentration of 0.5 mg•L^–1 6-BA benefitted callus proliferation and 0.25 mg•L^–1 IBA promoted shoot rooting; however, a higher IBA concentration will inhibit rooting. The most effective antitoxin for screening transgenic Idaho locust shoots was G418 and the most sensitive concentra-tion of it was 8 mg•L^–1.     

A Study Undertaken in Southern Britain to Investigate the Late-Flushing of Hedgerow Ash in Spring 1987

Following the abnormally late flushing of many ash (Fraxinusexcelsior) in 1987 a study on their condition was initiated.An investigation of 19 trees at 12 sites in England and Waleswas carried out in June with a second inspection later in thesummer. For comparison, another full survey of the same treeswas undertaken the following year. Information collected onmore than 4000 bud positions showed that in 1987 significantlyfewer buds flushed to produce healthy shoots than in 1988 (18per cent compared with 34 per cent respectively). Although nodifference was detected between the two years in the numbersof buds killed or damaged by ash bud moth (Prays fraxinella)or invaded by fungi (principally Fusarium lateritium) therewere significantly more buds killed by unknown causes in 1987than in 1988 (13 per cent and 4 per cent respectively). Thetrees were fully recovered by mid-summer 1987 and went on tofoliate normally in 1988. There was thus no reason to considerthat the late flushing marked the onset of any serious dieback. Received 22 May 1990.     

Propagation of Prunus avium from Root Cuttings

In experiments with root cuttings of Prunus avium best resultswere obtained when cuttings were inserted with the proximal2–3 cm exposed to the air. All lengths and diameters ofroot cuttings were successful (i.e. produced at least one sucker),and all successful cuttings produced roots at their distal ends. Received 26 April 1990.     

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

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

Cold tolerance of Acacia karroo and A. nilotica, two tree species from South Africa, in Beijing

Fynbos plant communities developed under geographic and climatic conditions unique to South Africa. Acacia karroo is the most widespread tree species, well known for its drought tolerance. A. nilotica exudes a good quality gum which is edible and suitable for confectionery. The two species have been introduced to China but little is known about their adaptability under the new environmental conditions. For our present study, the growth potential and physiological and biochemical parameters of the two species in response to cold stress were investigated. The results, measured as seed qualities (purity, thousand seed weights, germination, etc.) show differences between A. karroo and A. nilotica. The seed germination rate was between 10% and 60%. Seedlings were established in fields, pots and plugs. Those in the field grew well during the growing season but completely died in the winter. Those in pots or plugs were moved to and managed in the greenhouse. The plants were green in winter. The electrical conductivity of cells, the contents of water soluble sugars, proteins, malondialdehyde (MDA) increased during eight hours of low temperature treatment at 4℃. The activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) decreased markedly during the eight hours of 4℃treatment. We conclude that A. karroo and A. nilotica have little adaptability to the cold winter weather and cannot survive in the outdoors in the Beijing area, but could grow well indoors as ornamentals.     

CONIFEROUS LITTER AMENDMENTS AND THE GROWTH OF SITKA SPRUCE

The growth of semi-checked Sitka spruce (Picea sitcbensis Carr.)on heathland has been stimulated to different degrees by theannual application of litter of Scots pine (Pinus sylvestrisL.), Corsican pine (P. nigra var. calabrica Schneid), Lodgepolepine (P. contorta Dougl.), Japanese larch (Larix leptolepisGord.), and Sitka spruce, at rates corresponding to normal plantationconditions, following an initial heavier rate. Foliar analysissuggests that the response is at least partially attributableto the influence of the litters on the nitrogen nutrition ofthe spruce and differences between litters appear to be largelydetermined by their total nitrogen contents. In this respect,Japanese larch, with an annual needle fall generally greaterthan that of the pines and a higher nitrogen content, offersthe best promise as a nurse species for spruce.     

The effect of nitrogen supply on root growth and development in sycamore and Sitka spruce trees

Sycamore (Acer pseudoplatanus L.) and Sitka spruce (Picea sitchensis(Bong.) Carr.) were grown in sand culture in glasshouses withtwo levels of N supplied with irrigation 1.0 (deficient) and6.0 (sufficient) molNm^–3, all as NH₄NO₃. Providing trees with a sufficient N supply increased both theirabove ground growth and N content compared with the N deficientplants. Provision of the generous N supply also altered thedistribution of growth between leaves and roots, with the N-deficientplants having a higher root:leaf or root:needle ratio than thewell fertilized trees. Provision of a generous N supply stimulatedroot growth, especially at the later harvests, which was reflectedmainly in growth of the tap root in sycamore. There was an increasein both root mass and root diameter with N supply. When thegrowth of white roots was monitored using a borescope, it wasshown that there were significantly more new roots producedby the well-fertilized trees. The borescope data also showeddetail of the bimodal seasonal pattern of root growth underhigh N in Sitka spruce which related to trends in nitrogen uptake.     

The effect of roots and litter of Calamagrostis canadensis on root sucker regeneration of Populus tremuloides

Marsh reed grass (Calamagrostis canadensis (Michx.) Beauv.)is a common, highly competitive grass native to the boreal mixedwoodforest. This grass increases in abundance after clear-cut loggingbut little is known about its effects on trembling aspen (Populustremuloides Michx.) sucker regeneration. The effects of Calamagrostissod and its litter on aspen regeneration were studied in twoseparate greenhouse studies. Calamagrostis sod did not affectthe initiation of suckers, but resulted in 30 per cent fewersuckers emerging above the soil that were smaller and had 40per cent less leaf area. Calamagrostis litter had little effecton the initiation and number of emerged suckers; however, itdelayed emergence by 10 days. The physical barrier by rootsand litter of Calamagrostis reduced or delayed the expansionof suckers and therefore prolonged their dependence on rootreserves. By the time the suckers reached the surface, theyhad to compete for light with Calamagrostis shoots that hademerged a week earlier. This, coupled with low soil temperaturesassociated with Calamagrostis in other experiments, will significantlyreduce the number and growth of suckers. Any reduction and delayin sucker emergence will decrease aspen regeneration and productivitysince the growing season in the boreal forest region is short.     

The Influence of Shelter and Weeds on Early Growth of Sitka Spruce and Lodgepole Pine

An experiment in Helmsdale Forest (Highland Region, Scotland)examined the effects of shelter and weed competition on Sitkaspruce (Picea sitchensis (Bong.) Can.) and lodgepole pine (Pinuscontorta Douglas ex Loudon). Different levels of shelter fromwind were achieved by using netting and were measured usingtatter flags. Three treatments compared weed competition byremoving no vegetation, heather (Calluna vulgaris L.) only orall ground vegetation respectively. Results indicate a definiterelationship between material lost from tatter flags and treedry weight at five years. Even the smallest increase in shelterresulted in increased growth of Sitka spruce and the beneficialeffect of shelter became most apparent 4 to 5 years after planting.Tree dry weight was found to be correlated with root collardiameter and height but not fifth year height increment. Resultsfrom weeding treatments were unclear and differed between species.This was because bird damage interacted with weeding, the completelyweeded plots being most heavily damaged; and because the methodof hand weeding (pulling out the whole plant including roots)damaged fine tree roots. Bird damage was prevented by nettingbut in unnetted plots it was found impossible to separate birddamage from other factors although it was clearly more seriouson lodgepole pine.     

A Reappraisal of Canker and Dieback of European Larch

Evidence from the assessment of two large European larch (Larixdecidua Mill.) provenance experiments replicated on a numberof sites in England, Wales, and Scotland, and from other observations,suggested that: (a) Larch canker was not caused by frost, butwas probably due to primary infection by the fungus Trichoscyphellawillkommii (Hart.) Nannf. (b) Scottish provenances of Europeanlarch were more susceptible to canker and dieback than wereCarpathian provenances, (c) Canker and epidemic dieback of Europeanlarch were unrelated phenomena, although the relative susceptibilityof the provenances examined was similar for both conditions.     

Influence of nurse birch and Scots pine seedlings on early aerial development of European beech seedlings in an open-field plantation of Central France

Beech woodland can be restored by direct planting of beech (Fagussylvatica L.) seedlings in abandoned areas, but this methodis generally avoided in forestry because of the growth difficultiesof beech in full-light conditions. This study tested a methodthat consists of planting beech seedlings in full-light conditionswith silver birch (Betula pendula Roth.) or Scots pine (Pinussylvestris L.) as nurse trees. A total of 65 two-year-old beechseedlings surrounded by either 3, 4, 5 or 6 pine or birch seedlingsor without competitors were planted in bare-soil open-fieldconditions in Central France. Tree growth and light availabilitywere monitored at the end of each of the following 3 years,and soil moisture was also measured the last year. At the endof the experiment, aerial biomass measurements were made onthe beeches. Results showed that relative beech growth in termsof diameter was significantly reduced by the local neighbouringtrees and that this reduction was particularly noticeable inthe pine treatments where there was extensive pine seedlingdevelopment. In contrast, relative beech height did not exhibitany significant variations among the treatments. Light availabilitywas decreased by the neighbouring trees, especially in the pinetreatments. Light reduction was more pronounced in the last2 years and in the middle or lower parts of the canopy of thesubject beech. Soil water content was lower under the pine canopiesthan under the birch canopies, and was positively correlatedto beech relative diameter growth. Specific leaf area, height-to-diameterratio and crown length-to-crown width ratio weakly but significantlyincreased with competition from the neighbours. Beech biomasspartitioning was only weakly affected by the treatments. Thisstudy showed that nurse trees tend to reduce beech growth butimprove form although effects remained weak due to the insufficientlength of the experiment. Further studies are also needed toquantify the effects of the neighbourhood on the growth of competitiveherbaceous vegetation and on changes in the microclimatic conditions.     

Early regeneration of Fraxinus rhynchophylla in the understorey of Larix kaempferi stands in response to thinning

The effects of thinning were investigated on naturally regeneratedFraxinus rhynchophylla Hance (Korean ash) grown in the understoreyof a Larix kaempferi (Lamb.) Carr. plantation, established ona site that previously supported old growth hardwood forests.The regeneration characteristics were evaluated after thinningof the plantation (about 60 per cent of relative density wasremoved). In the naturally regenerated and mixed stands, Quercusmongolica Fisch. was the most abundant tree species in the overstorey,but the understorey of the thinned plantations was dominatedby F. rhynchophylla with six other minor tree species. Fraxinusrhynchophylla was regenerated by four propagation types includingnatural seedling, stump sprout, root sprout and layering. Beforethinning, the difference of average height growth for each regenerationtype was insignificant. One year after thinning, the stump sproutsshowed the fastest growth among the regeneration types. Heightgrowth of advance regeneration was slow in the year followingthinning but then increased rapidly surpassing the other regenerationtypes 5 years after thinning. Thinning had an effect on thecomposition of regenerated trees also by seedling, stump sprout,root sprout and layering in the understorey. Advance regenerationsoccupied the upper understorey at 5 years after thinning. Alarge number of stump sprouts emerged in the plots 1 year afterthinning, while at 5 years after thinning the occupation ofstump sprouts decreased. Root sprouts and layers faded away.Considering the early growth and the composition of understoreyF. rhynchophylla, its advance regeneration has a high potentialto develop into overstorey trees at this site.     

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

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

Sitka Spruce and Douglas fir Seedlings in the Nursery and in Cold Storage: Root Growth Potential, Carbohydrate Content, Dormancy, Frost Hardiness and Mitotic Index

Seedlings (transplants) of 2+1 Sitka spruce (Picea sitchensis(Bong.) Carr.) and 1 + 1 Douglas fir (Pseudotsuga menziesii(Mirb.) Franco) were grown in a nursery at the Bush Estate,Scotland. Batches were lifted and cold stored at 0.5°C inNovember, December and January. Changes in growth, shoot apicalmitotic index, root growth potential (RGP), carbohydrate content,bud dormancy and shoot frost hardiness were monitored throughoutthe winter by taking samples at intervals from the nursery andfrom cold storage. Frost hardening occurred during the later stages of bud development(as mitotic indices decreased); autumn hardening was arrestedwhen seedlings were put in cold store, and some dehardeningoccurred in cold storage, especially in spring. Bud dormancystarted, and was greatest, just after bud growth (mitotic activity)virtually ceased; chilling in cold store was almost as effectivein releasing dormancy as natural chilling. The concentrationof total nonstructural carbohydrates stayed more or less constantat 100–150mg g^–1 from September to April in thenursery; in cold storage carbohydrates were depleted at 0.4–0.6mgg^–1 d^–1 (corresponding to respiration at 0.03–0.05mgCO₂ g^–1 h^–1) until there was only 40–50mgg^–1. Root growth potentials in the nursery increased in December,once the buds ceased growth, became dormant and had receivedsome chilling. Sitka spruce was ‘storable’ in November,before RGPs increased, but they then failed to achieve maximalfrost hardiness or ROP. Winter RGPs were high in Sitka spruceand were increased or maintained in cold storage, whereas RGPswere low in Douglas fir and decreased immediately after storage(except when stored in January). By the end of April, the RGPof cold stored Sitka spruce was much higher than that of directlifted plants. ROP changes in the nursery and in cold storagewere not consistently related to changes in seedling carbohydratecontents, shoot frost hardiness or bud dormancy. In practical terms, it was concluded that (1) the optimum dateto start lifting bare- rooted conifer transplants in the autumnis when their shoot apical mitotic indices have decreased tonear zero, and their RGPs have risen sharply; (2) high RGPsmay depend as much on the morphology of the roots (e.g. numberof undamaged root apices) as on the physiology of the shoots(e.g. carbohydrate status, dormancy and frost hardiness); and(3) in spring, transplants kept in cold storage since November,December or January are more frost hardy, slightly more dormant,and (in May) have higher RGPs than transplants lifted from thenursery.     

THIRTY YEARS' DEVELOPMENT OF AFFORESTATION TECHNIQUES ON DIFFICULT GROUND TYPES IN SOUTH-WEST SCOTLAND

The development of ploughing, draining, planting, and the useof turfs and of phosphate is considered in detail for each oftwo main types. For Molinia lands, the 1952 technique securesadequate drainage and a very considerable turnover of turf,and here the spruces Picea abies Karst. and P. sitcbensis Carr.remain the first choice. For Calluna lands, the developmentof methods and the choice of species is more difficult. Thespruces refuse to grow pure and unnursed on the poorer Callunatypes and the use of Scots pine (Pinus sylvestris L.), P. contortaDoug., the Mountain pine (P. uncinata Ramond), Japanese larch(Larix leptolepis Gord.), and Douglas fir (Pseudotsuga taxifoliaBrit.) is discussed. The main requirements for successful afforestationof these ground types are summarized.     

Cross Breeding of Populus and Its Hybrids for Cold Resistance

Populus tomento a was crossed with P. tremuloidis, P grandiden ata, P. lba × P. grandidentata and P. alba × Ulmus s . ta pumila in order to maintain its rapid growth and high wood quality and improve its resistance to cold. Two methods were used to increase the germination rate from 1.5% to 41.1% and the remaining rate from 1.7% to 44.2%. Forty crossing combinations were conducted and 2 744 hybrid seedlings were obtained. MX. t4 × P grandiden ata (G-1-58), MX3 × P. tremuloidis (T-44-60), MX2 × P. tremuloidis (l-13-87-37) and MX2 × (P. alba × P. grandidentata) were regarded as superior combinations after analysis and selection. Thirty seedlings of these combinations and 11 triploid seedlings identified by counting their chromosomes were selected as super plants.