Intra-annual growth and mortality of four <Emphasis Type="Italic">Populus</Emphasis> clones in pure and mixed plantings

Intra-annual growth rates were assessed during 3 years for four Populus clones grown in pure and mixed clonal stands at square spacings of 0.5, 1.0 and 1.5 m in western Washington, USA. Height growth rate peaked in August, except at the 0.5-m spacing where it peaked in July and June in years 2 and 3, respectively. Diameter growth rate generally peaked in June. Seasonal growth patterns in mixed clonal stands, relative to those in pure clonal stands, varied by clone. Following early season moisture stress in year 2, growth of a P. balsamifera ssp. trichocarpa clone declined significantly relative to three P. balsamifera ssp. trichocarpa × P. deltoides clones; this trend was most evident at the 0.5-m spacing. During this period of moisture stress, P. balsamifera ssp. trichocarpa had 11 and 36% mortality in pure and mixed stands, respectively, at the 0.5-m spacing; this clone had no mortality at wider spacings during the same period. Although height rankings among clones shifted during the first growing season, rankings at the end of year 1 were very similar to those at the end of year 3.     

Factors influencing tree species diversity and Betula alleghaniensis establishment in silvicultural openings

We examined the short-term effects of group-selection harvestingwith seed tree retention on the diversity, abundance and establishmentof tree seedlings in a northern hardwood forest in the UpperPeninsula of Michigan (49 openings, 20 closed canopy referencesites). Three opening sizes were examined – opening radius0.5 x canopy height (267 ± 62 m², n = 16), 0.75 x canopyheight (642 ± 85 m², n = 17) and 1.0 x canopy height(1192 ± 155 m², n = 16) (canopy height = 22 m). A singleyellow birch (Betula alleghaniensis Britt.) seed tree was retainedin the centre of each opening. Tree seedling density was significantlyhigher in the largest group-selection opening than at the closedcanopy reference sites (P < 0.05), the main factor for thiswas the increased proportion of yellow birch, red maple (Acerrubrum L.) and other minor species. Nevertheless, yellow birchwas still a minor component of the developing gap cohort, comprising5.9 per cent of the seedlings and 1.1 per cent of the saplings.Within openings, microsite variables, such as per cent coversof bare soil and coarse woody debris, were the best predictorsof yellow birch occurrence and density. Our results suggestthat microsite limitations and competing vegetation may greatlyreduce the efficacy of openings for ensuring the maintenanceof mid-tolerants.     

Overstorey density influence on the height of Picea abies regeneration in northern Sweden

The study aimed specifically at investigating if canopy opennesswas a better predictor of the height growth of Norway spruce(Picea abies (L.) Karst.) advance regeneration than overstoreybasal area or overstorey standing volume. In 1990, a field experimentwith 3 x 2 factorial design and two replications (blocks) wasestablished in an uneven-aged Norway spruce forest. Plots hada net plot area of 30 x 30 m, each with a 10-m-wide treatedbuffer zone. Three overstorey density levels retained approximately15, 40 and 70 per cent of the pre-harvest overstorey standingvolume and were allotted to the plots. Two types of thinningthat harvested smaller trees or harvested larger trees wererandomly allocated to each pair of overstorey density plots.In mid-June 2000, canopy openness was estimated from hemisphericalphotographs taken at five marked points in the centre of eachof the plots at 0.9 m from ground to the top of the ‘fish-eye’camera lens. Regression results showed that canopy opennesswas a better predictor of height increments of spruce seedlings(0.1< height < 0.5 m), saplings (0.5 height < 2.0m), and small trees (height 2.0 m, diameter at 1.3 m height< 5 cm) than with overstorey basal area (m² ha^–1) oroverstorey standing volume (m³ ha^–1). The height incrementof the spruce advance regeneration was not significantly correlatedto stand basal area or to standing volume. Overstorey basalarea in the net plots was significantly negative (P 0.05) withmean canopy openness estimates, and the r² value was 0.40. Resultsindicated that basal area was not linearly related to canopyopenness as it increased, which might explain the lack of predictivepower of retained basal area on spruce regeneration height indense stands in boreal Sweden.     

The tolerance of young trees to applications of clopyralid alone and in mixture with foliar-acting herbicides

The selective herbicide clopyralid is often used to controlcompeting Cirsium arvense in newly planted woodlands. When appliedas an overall spray at different dates in the spring (at 0.2kg acid equivalent (a.e.) ha^–1) to 10 tree species (Fraxinusexcelsior, Prunus avium, Quercus robur, Acer pseudoplatanus,Populus x canadensis cv. ‘Ghoy’, Pseudotsuga menziesii,Pinus nigra ssp. laricio, Larix kaempferi, Picea abies and Piceasitchensis) it did not reduce survival, and had little effecton growth. However, some species showed distortion of the youngestsprayed leaves or needles for several weeks after treatment,particularly F. excelsior, L. kaempferi and P. x canadensis.Sequential applications of clopyralid (first at 0.1 kg a.e.ha^–1 followed by 0.2 kg a.e. ha^–1 after 3 weeks),which are often required to control C. arvense, did not leadto increased leaf damage or growth reduction. Mixtures of clopyralidwith selective graminicides (cycloxydim at 0.45 kg active ingredient(a.i.) ha^–1; fluazifop-p-butyl at 0.38 kg a.i. ha^–1and propaquizafop at 0.15 kg a.i. ha^–1) did not causesignificant adverse effects on survival or growth of any species.If herbicides are required to control mixed stands of susceptibleproblem weeds such as C. arvense and grasses which are overtoppingyoung trees, these herbicide mixtures, applied as overall sprays,are less likely to cause damage to trees than attempts to usedirected applications of broad-spectrum foliar-acting herbicides.     

Biomass production by two-year-old poplar clones on floodplain sites in the Lower Midwest, USA

Four Populus clones were grown for two years at 1×1 m spacing for study of total biomass production and carbon sequestration capacity on floodplain sites previously in forage grasses under climatic conditions of the lower Midwest, U.S.A. Total biomass (above-and below-ground) in the first year ranged from 3.9 Mg ha^–1 in a Populus deltoides x P. nigra clone (I45/51) to 1.9 Mg ha^–1 for a local-source Populus deltoides clone (2059). Second year total biomass production was substantially higher, ranging from 13.9 Mg ha^–1 in I45/51 to 7.4 Mg ha^–1 in P. deltoides clone 26C6R51. Second-year leaf area index (LAI) values for I45/51 plants reached 4 during mid-season, indicating essentially complete canopy closure in this clone by the second year after planting. In contrast, maximum mid-season, second-year LAI was significantly lower in P. deltoides clones ( 2.4). There was some evidence for differential allocation to roots and shoots among Populus clones, with 26C6R51 showing relatively more allocation to root biomass than other clones. Second-year growth in Populus deltoides clone 2059 accelerated substantially, and this genotype exhibited two-year biomass accumulation nearly equal to that of I45/51 despite having less leaf area. This result suggested a higher photosynthetic capacity or assimilation efficiency in the former. This revised version was published online in August 2006 with corrections to the Cover Date.     

Sap flow of irrigated <Emphasis Type="Italic">Populus alba</Emphasis> var. <Emphasis Type="Italic">pyramidalis</Emphasis> and its relationship with environmental factors and leaf area index in an arid region of Northwest China

Populus alba L. var. pyramidalis Bge. (Populus) is a main tree of the farmland shelter-belt system in the arid region of Northwest China. However, soil moisture cannot satisfy the water requirements of normal Populus growth under local natural conditions, thus studying the transpiration characteristics of irrigated Populus and its relationship with the environmental factors and growth parameters is very important to the growth of the trees in this region. In this study, the sap flow of two irrigated Populus trees was measured during May to September from 2005 to 2008 using the heat-pulse technique. The results show that the maximum and minimum daily sap fluxes in Populus were 15.7–24.0 and 3.0–4.0 L day⁻¹, respectively. And the sum of sap fluxes from June to August accounted for approximately 63–69% of the total sap flux during May to September (almost the whole growing season). The order of the meteorological factors affecting the daily sap flux of Populus was: vapor pressure deficit > solar radiation > mean air temperature > wind speed. Furthermore, a highly linear relationship between the ratio of daily sap flux to the reference evapotranspiration (SF/ET₀) and the amount of soil water in the 0–2.0 m layer was found, indicating that the amount of soil water at this layer was quite important to the growth of Populus in this region. Especially, the amount of soil water in the 0.5–1.0 m soil layer contributed to most of the plant transpiration as the highest coefficient of determination at this layer. Based on the environmental factors and leaf area index influencing sap flux, an empirical transpiration model was constructed to estimate daily transpiration.     

Incidence and Severity of Bean Rust (Uromyces appendiculatus) in Alleys between Leucaena Hedgerows in Kenya

The effects of inter-row spacing of Leucaena leucocephala (Lam.) de Wit in an alley cropping system on the incidence and severity of rust (Uromyces appendiculatus (Pers.) Unger) on intercropped beans (Phaseolus vulgaris L.) and their yield were examined over 2 years (1993 and 1994) at Chepkoilel Campus in Kenya. Each experiment consisted of three randomized blocks with treatments of three alley widths (2 m, 4 m and 8 m) and a treeless control with two intra-row spacings of Leucaena (0.5 m and 1.0 m). Hedgerows were coppiced at 1.0 m height and pruned subsequently at 2–3 months intervals. No fertilizer was applied but Leucaena loppings were incorporated as green leaf manure. Rust on beans was assessed at three growth stages in each season, using the Centro International de Agricultura Tropical (CIAT) scales. Microclimate was monitored in treatments, in 1994. Bean growth and yield were also measured. Rust increased with increasing alley width and was less severe in bean rows adjacent to hedgerows. Bean yield was highest in the treeless control plots and declined with decreasing alley width. Beans in 2 m alleys had significantly lower (p < 0.05) yields than 8 m alleys and treeless control plots. Bean growth was greatly modified in 2 m alleys and close to hedgerows. Light availability and diurnal temperature increased with alley width but relative humidity and leaf wetness duration decreased. Proximity to hedgerows also had marked effect on microclimate. The changes in yield, rust incidence and severity were examined in relation to microclimate, inoculum survival and dispersal.     

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.     

Hybrid poplars: present status and potential in Britain

Past and potential future use of hybrid poplars for wood productionin Britain is considered, and preliminary results of trialswith new clones imported from Belgium in 1985 are given. A seriesof nine field experiments established in 1991, to a common protocol,was analysed using stepwise multiple regression. The superiorvigour of ‘Beaupré’ compared with ‘Ghoy’,‘Robusta’ and ‘Trichobel’ was clearin almost every case. For ‘Beaupré’ (Populustrichocarpa x P. deltoides) altitude emerged as the variableexplaining most variation in tree height after six growing seasons,height declining with increasing altitude. The four best siteswere characterized by low elevation and low rainfall. At the two older sites planted in 1987, at Ampthill and Bedgebury,the ‘interamerican’ hybrids (P. trichocarpa x P.deltoides) were the most vigorous, and the clones ‘Unal’and ‘Raspalje’, which were thought to be too rustsusceptible to release for commercial use in 1990, achievedsimilar stem sizes to those of ‘Beaupré’and ‘Bolelare’. The General Yield Class (based ona reference spacing of 8 x 8 m) calculated for ‘Beaupré’was 8 at Ampthill and 24 at Bedgebury. Future prospects for poplar planting are considered in relationto possible reform of the Common Agricultural Policy.     

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.     

The carbon sink provided by plantation forests and their products in Britain

The rate of accumulation of carbon in forest plantations inBritain is estimated using the record of forest planting since1925 and a model that calculates the flow of carbon from theatmosphere to trees, litter, soil, wood products and back tothe atmosphere. It is assumed that all trees planted so farhave the carbon accumulation characteristics of P. sitchensis,Yield Class 14 m³ ha^-1 a^-1, but that future planting could includeF. sylvatica Yield Class 6 and Populus Yield Class 12. It isfurther assumed that conifer plantings increase surface litter,but not soil organic matter, whereas broadleaved tree plantings(on mineral soils) increase both. Because the current forest estate is relatively young, it isestimated to be accumulating about 2.5 million tonnes of carbonper year (1990), and to be still increasing in carbon density(tonnes C ha^-1). In order to maintain this rate of carbon removalfrom the atmosphere, planting would need to continue at a rateof 25–30 thousand ha of conifers or (theoretically) 10thousand ha of poplars per year (on good mineral soils). Itis noted that 2.5 million tonnes C is about 1.5 percent of theUK carbon emission, and may be similar to the natural carbonsink in Britain represented by wetlands and rivers.     

Growth characteristics and allometry of <Emphasis Type="Italic">Robinia pseudoacacia</Emphasis> as a silvopastoral system component

Demand for goat (Capra hircus) meat in the southeastern USA is steadily increasing as a result of preferences exhibited by ethnic communities. Feeding systems that include fodder trees can be developed to take advantage of the natural preference of goats for browse. Data were collected for 2 years on a 5-year old stand of Robinia pseudoacacia L. to evaluate growth characteristics for goat browse and to develop allometric relationships in a randomized complete block design (intra-row spacing 0.5 or 1 m and coppice height 0.25 or 0.50 m) replicated six times. Allometric equations were derived from destructive harvests of 68 trees. Main branch size was not affected by intra-row spacing when trees were coppiced at 0.25 m; however, when coppiced at 0.5 m, trees spaced at 1 m had more and larger branches (P < 0.05) than trees spaced at 0.5 m. Intra-row spacing did not influence tree herbage biomass when trees were spaced at 0.5 m whereas trees coppiced at 0.25 m and spaced at 1 m produced less woody and herbaceous biomass than trees spaced at 0.5 m (P < 0.05). A strong relationship (P < 0.0001) was found between tree herbage biomass and the number of main branches greater than 0.01 m (r ² = 0.80). The results, based on growth characteristics and tree herbage biomass production, suggest that Robinia pseudoacacia L. would be an excellent candidate as a silvopastoral component in the southeastern USA.     

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.     

Poplar leaf biomass distribution and nitrogen dynamics in a poplar-barley intercropped system in southern Ontario, Canada

The effect of hybrid poplar (Populus spp. clone DN 177) leaf biomass distribution on soil nitrification was investigated in two experiments during the 1993, 1994 and 1995 growing seasons in a poplar-barley (Hordeum vulgare cv. OAC Kippen) intercropping experiment established at Guelph, Ontario, Canada. In experiment 1, poplar was intercropped with barley during all three years and the poplar leaves shed during the fall season were removed from the soil surface during 1993 and 1994. In experiment 2, poplar was intercropped with barley in 1993 and with corn (Zea mays cv. Pioneer 3917) in 1994 an 1995, respectively, and the shed poplar leaves were not removed. In experiment 1, the nitrification rates were lower during 1994 and 1995 when the dropped leaves were removed from the field. The total above-ground biomass of barley within 2.5 m of the tree row was 517, 500 and 450 g×m⁻², respectively during the three years, whereas in the middle of the crop row (4–11 m), the corresponding figures were 491, 484 and 464 g×m–2. Mean nitrification rates, N availability and carbon content were higher in soils close to the poplar tree rows (2.5 m) compared to the corresponding values in the middle of the crop alley (4–11 m from the tree row). In experiment 2, where poplar leaves were not removed from the field, nitrification rates in soils within 2.5 m distance from the poplar row were fairly constant (range 100 to 128 μg 100 g⁻¹ dry soil day⁻¹) during the three years. Results suggest that soil nitrification rates, soil carbon content and plant N uptake adjacent to the poplar tree rows are influenced by poplar leaf biomass input in the preceding year. This revised version was published online in June 2006 with corrections to the Cover Date.     

Silvicultural Characteristics of Abies equi-trojani Aschers-Sinten and Growth Relationships between Pinus nigra Arnold var. pallasiana Endl and Abies equi-trojani in Mixed Natural Forests of Turkey

Pinus nigra Arnold var. pallasiana Endl. and Abies equi-trojaniAschers-Sinten are indigenous species of Turkey. The area ofPinus nigra is very large (more than 2 million hectares) occurringin the west, south and north of Turkey. However, Abies equi-trojanioccurs only in the west of Turkey in the Ida Mountains (Kazdagi)and is of limited area (5500 ha).These two species naturallyform both mixed stands and pure stands in the Ida Mountains. When mixed stands of Pinus nigra and Abies equi-trojani areregenerated, if the seedlings of these two species regeneratesimultaneously, the Pinus nigra will be eliminated from thestand in 15 to 25 years because of the rapid growth of Abiesequi-trojani. In different site conditions, Abies equi-trojanireaches 22–30 m in height and 40–65 cm in diameterin 70 years, whereas Pinus nigra reaches 17–22 m in heightand 25–40cm in diameter in the same period in the sameforest sites.     

Disease incidence and severity on beans in alleys between Leucaena hedgerows in Kenya

The effects of inter-row spacing of Leucaena leucocephala in an alley cropping system on the incidence and severity of diseases on intercropped beans (Phaseolus vulgaris L.) and their yield were examined over two years (1993 and 1994) at Chepkoilel Campus in Kenya. Each experiment consisted of three randomized blocks with treatments of three alley widths (2 m,4 m and 8 m) and a treeless control with two intra-row spacings of Leucaena (0.5 m and 1.0 m). Hedgerows were coppiced at 1.0 m height and pruned subsequently at two-to-three months intervals. No fertilizer was applied but Leucaena loppings were incorporated as green leaf manure. Incidence of angular leaf spot (Phaeoisariopsis griseola) and anthracnose (Colletotrichum lindemuthianum) on beans were assessed at three growth stages in each season, using the Centro International de Agricultura Tropical (CIAT) scales. Microclimate was monitored in treatments, in 1994. Angular leaf spot and anthracnose decreased with increasing alley width and were more severe in bean rows adjacent to hedgerows. Light availability and diurnal temperaturereaching the bean canopy increased with alley width but relative humidity and leaf wetness duration decreased. Proximity to hedgerows also had markedly reduced light levels, lower temperatures and higher relative humidity. Higher incidence and severity of angular leaf spot and anthracnose on beans in alleys than on beans in treeless plots were examined in relation to microclimate, inoculum survival and dispersal. The pattern of the diseases was best explained by microclimate changes induced by Leucaena hedgerows, especially effects of humidity. This revised version was published online in June 2006 with corrections to the Cover Date.     

Establishing forest tree species on peatland in a reflooded area of the Huleh Valley, Israel

The study evaluates the establishment performance of four treespecies (Ficus carica, Fraxinus syriaca, Salix acmophylla, Platanusorientalis) 3 years after planting in the peatland in the HulehValley. To develop good tree establishment and avoid uprooting,two types of soils were tested as alternatives for the rhizosphere.For each tree 6 m³ of soil (2 x 2 x 1.5 m) were replaced withriver bed alluvium or terra-rossa, in which the tree was planted.Control trees were planted directly in the peat. Changing therhizosphere soil type to river bed alluvium significantly improvedthe establishment and performance of Salix acmophylla and Fraxinussyriaca (survival, height, diameter and canopy shade area).Ficus carica was not affected by changing the soil in the rhizosphere,while Platanus orientalis was affected mainly in canopy shadearea. Terra-rossa improved establishment only of Salix acmophylla;it did not affect the other species.     

六个杨树无性系苗木生长、生物量和光合作用的研究*

六个杨树无性系苗木（２年生根１年生于）叶面积、苗高和地径的季生长用Ｒｉｃｈａｒｄｓ方程模拟，根据模拟参数分别计算最大绝对生长速率，平均绝对生长速率，生长期和拐点。结果为：六个无性系之间在生长速率、拐点和生长期方面均有明显的差异；最好的欧美杨６４号生长季末的总生物量是赤峰杨３４号的六倍多；六个无性系的总生物量与它们的总叶面积、平均单个叶片的面积、叶面积的平均生长速率和每株树的日净光合总量等呈正相关，而与单位叶面积的日净光合总量呈负相关；总生物量生产依赖于叶面积、苗高、直径的生长速率及其生长期。     

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.     

Hybrid poplar (<Emphasis Type="Italic">Populus</Emphasis> ssp.) selections for arid and semi-arid intermountain regions of the western United States

The rapid growth rates of hybrid poplar (Populus spp.) enable rotations of 3–6 years for biofuels or 10–15 years to obtain merchantable timber, but many clones are susceptible to nutrient deficiencies when grown in alkaline soils. A 1995 Oregon study demonstrated that clone OP-367 (P. deltoides × P. nigra) was the only clone tested that performed well on alkaline soils. Tests in Colorado and New Mexico confirmed the adaptation of this clone. A multi-clonal trial was established in 2003 at Farmington, New Mexico and Ontario, Oregon in order to screen a larger number of clones for adaptability to alkaline soils. Trees were planted at 1.5 × 1.5 m spacing and irrigated by surface drip irrigation. Diameter at breast height (DBH) and tree height were recorded annually (2003–2006); wood volumes (WVol) and total aboveground biomass (TAB) were calculated from these measurements. Of the 25 clones tested, 19 were common to both sites. Mean height was greater at the Ontario site through the first 3 years (2003–2005). By the end of four seasons, the tallest Farmington entry was OP-367 at 9.4 m with 177 Mg ha⁻¹ TAB while the tallest Ontario entry was Malheur-3 at 8.9 m with 195 Mg ha⁻¹ TAB and several other clones had statistically similar production. Given the growth and productivity range at these two sites, it is difficult to make generalizations across wide areas, but it appears feasible to identify clones suited to alkaline soils in arid and semi-arid regions.