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1.
The phenology and frost hardiness of shoots of 15 provenancesof Alnus rubra growing in Scotland were measured over one autumn,winter and spring. Dates of budset (in September) and the onsetof rapid frost hardening (in October-November) occurred about2 days earlier for each degree latitude of origin northwards,except for an Idaho provenance. However, all provenances dehardenedat about the same time in March and burst their buds between8 and 14 April. Assuming that rapid frost hardening in the autumnwas triggered primarily by shortening daylengths, Alaskan provenancesof A. rubra seemed better adapted to British conditions thansouthern British Columbian provenances, which have been mostcommonly planted. However, even Alaskan provenances are proneto spring frost damage. Scottish A. glutinosa and Alaskan A.sinuata set buds and frost hardened 1–2 weeks before eventhe Alaskan A. rubra, and burst their buds 2–3 weeks laterin April-May. All three species were hardy to below –30°Cfrom December to mid-March. 相似文献
2.
Autumn Frost Damage on Young Picea sitchensis 2. Shoot Frost Hardening, and the Probability of Frost Damage in Scotland 总被引：3，自引：0，他引：3
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. 相似文献
3.
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. 相似文献
4.
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 (Bw) 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, Bw=10 t ha–1y–1, while for Populus, Bw= 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. 相似文献
5.
It is estimated that British peatlands, excluding lowland fens,contain about 3000 million tonnes of carbon, 76 per cent ofwhich is in deep peats (> 45 cm deep) and 9 per cent of whichhas been drained and planted with trees. Undisturbed peatlands emit CH4 but accumulate CO2-derived carbon.The net greenhouse effect may be near zero. Peatland drainagevirtually stops methane emission and increases CO2-carbon lossthrough aerobic decomposition, but can also increase CO2-carbonfixation by the peatland vegetation partly through microbialmineralization of nitrogen, resulting in either a net loss orgain in CO2-carbon. Planting conifer forests leads to an accumulation of CO2-derivedcarbon in the trees, wood products, litter and forest soil upto equilibrium values, totalling about 16.7 kg C m–2 forPicea sitchensis, Yield Class 12. Deep and shallow peats inthe British uplands contain about 0.47 and 0.80 kg C m–2per centimetre depth, respectively. Thus, the 16.7 kg C m–2that is stored by P. sitchensis (Yield Class 12) is equivalentto the carbon stored in about 35.5 cm of deep peat or 20.9 cmof shallow peat. If forests are planted on peats substantiallydeeper than this, there could be a net loss of CO2-carbon inthe long term. Scenarios are presented for the time course of CO2-carbon gainand loss when peatlands are drained and planted with conifers.If CO2 loss rates from drained peats are 50–100 g C m–2a–1 there is likely to be increased carbon storage inthe whole system for at least three rotations; but if CO2 lossrates are 200–300 g C m –2 a–1 increased storagemay be restricted to the first rotation, after which there isa net loss of carbon. 相似文献
6.
Seasonal Changes in the Frost Hardiness of Provenances of Picea sitchensis in Scotland 总被引：6，自引：0，他引：6
Changes in the natural level of frost hardiness of shoots offour provenances of Picea sitchensis were monitored over twogrowing seasons by detaching shoots from 7 to 10-year-old treesgrowing in a nursery in Scotland, and subjecting them to freezingtemperatures under conditions which simulated night frosts. Six seasonal phases of frost hardiness were identified (Fig.3).
- During each autumn, killing temperatures (the level of hardiness)decreased from –5°C to below –20°C, beginningseveral weeks after shoot elongation ceased. Alaskan provenanceshardened in September, apparently in response to shorteningday lengths alone, whereas an Oregon provenance did not hardenuntil November, after repeated frosts. Queen Charlotte Islandsprovenances were intermediate.
- From November to March allprovenances were hardy to below –20°C,which is adequateto prevent direct freezing injury at mostplantation sites.
- In March-April, several weeks before bud-burst, old shootsdehardenedto killing temperatures of about –10°Cin responseto warm temperatures, and southerly provenancesdid so beforenortherly ones.
- During bud-burst the newly-emergingshoots were hardy to only–3°C to –5°C untilthey were about 3.5 cmlong. All provenances burst bud at thesame time and were equallyfrost susceptible at this time.
- DuringMay-July the elongating shoots fluctuated in hardinessbetween–5°C and –10°C apparently in responsetofluctuating ambient temperatures.
- In August 1980 there wasa period of late summer dehardeningto killing temperaturesof about –3°C.
7.
Autumn Frost Damage on Young Picea sitchensis 1. Occurrence of Autumn Frosts in Scotland compared with Western North America 总被引：1，自引：0，他引：1
Dates of first autumn air frosts (in Stevenson screens) of –2.5°Cand 4.5°C were obtained for 42 meteorological stations innorthern Britain with runs of 18 to 116 years. Frequency distributionsof first frost dates were approximately normal. Altitude, distancefrom the sea, latitude and distance from the NWSE axis of Britaintogether accounted for 75% and 81% of the variation in datesof first –2.5°C and –4.5°C frosts, respectively,at the 42 stations. The variance in dates of first frosts decreasedfrom lowland coastal to upland inland sites. Multiple regressionswere used to produce maps of first frost dates in 20 x 20 kmgrid squares of Scotland. Dates of first 28°F (–2.2°C) and 24°F (–4.4°C)frosts were obtained for 20 sites in western North America,spanning the natural range of P. sitchensis. Mean dates wereearlier, and variances decreased, from south to north. Upland sites like Eskdalemuir and Kielder Castle experience–2.5°C and –4.5°C frosts earlier in theautumn than all coastal stations in western North America southof about latitude 58°N (between Cordova and Sitka), andabout 4 weeks earlier than at Masset on the Queen CharlotteIslands. Thus, P. sitchensis from Q.C.I. and further south mayoften experience autumn frosts in Scotland before the treeshave experienced the cool/short days that they require to inducefrost hardening. 相似文献
8.
Needle Damage in Sitka Spruce Caused by Early Autumn Frosts 总被引：2，自引：0，他引：2
Autumn frosts preceded by warm weather cause distinctive needlebrowning symptoms on young Sitka spruce trees which have completedshoot elongation. Damage is invariably confined to needles ofthe current year and typically consists of pink or reddish-brownpatches in the centres of needles. Needles clustered aroundthe apical buds are usually unaffected but in extreme casesall current year's needles may be entirely reddish-brown. Thesesymptoms were reproduced on young plants by experimentally freezingthem in a programmed chamber. Widespread damage was observed in the field in October 1971,September 1972 and September 1979 and assessments of field trialsshowed that damage was most severe on southerly provenancesand on trees deficient in phosphorus. 相似文献
9.
Carbon pools and sequestration in forest ecosystems in Britain 总被引：1，自引：0，他引：1
British vegetation is estimated to contain 113.8 million tC,80 per cent of which is in forests and woodlands (91.9 milliontC). Sitka spruce plantations, although covering 21.4 per centof the forest/woodland area, contain only 8.2 per cent of theforest/woodland carbon, because the plantations are young andhave an average of only 14.1 tC ha–1. Broadleaved woodlandsin Britain have an average of 61.9 tC ha–1 and contain46.8 per cent of the total carbon in all vegetation. A breakdownis given of the carbon density (tC ha–1) and content ofdifferent tree species. A carbon density map of Britain highlightsthe concentration of carbon in the broadleaved woodlands insouthern England and in the large conifer plantations in southernScotland and northern England. Carbon storage in the trees, products, litter and soil can beevaluated in terms of long-term equilibrium storage or short-termrate of storage. These two components vary among forest typesin Britain and globally. Plantations harvested at the time ofmaximum mean annual increment (MAI) will not store as much carbonas mature, old-growth forests on the same site unless they havelong-lasting products and/or are very fast growing. Maximumequilibrium carbon storage is generally achieved by harvestingat the time of maximum MAI when the lifetime of products exceedsthe time to maximum MAI. Undisturbed peatlands sequester CO2and emit CH4, and may be greenhouse neutral. When peatlandsare drained and planted with trees, they stop emitting CH4 andstore carbon in the trees, forest litter, forest soil and woodproducts. However, these greenhouse gas ‘gains’are offset by the oxidation to CO2 of the peat, and the gainsare exceeded by CO2 losses when 20–40 cm depth of peathas been oxidized. Forests in Britain are currently sequestering1.5–1.7 million tC a–1 in trees, 0.3–0.5 tCa–1 in litter and 0.5 million tC a–1 in wood products,totalling about 2.5 million tC, equivalent to about 1.5 percent of the carbon currently emitted by burning fossil fuelsin the UK. In order to maintain the current forest carbon sink,the forest area needs to continue to expand at about 25 000ha a–1 of upland conifers or 10 000 ha a–1 of poplarson good land. 相似文献
10.
EFFECT OF PLOUGHING AND DIRECT DRILLING ON SOIL NITRATE CONTENT 总被引：4，自引：0，他引：4
The concentration of nitrate-N at 30 cm depth in a clay soil was 2–5 times greater (p<.05) after ploughing than after direct drilling during the winter and spring of 1972–3. However, by early May no significant differences could be detected between cultivation treatments. It is concluded that decreased mineralization of soil nitrogen in the direct-drilled soil is the main factor responsible for the differences observed. 相似文献