Soil water regime under rotational fallow and alternating hedgerows on an Ultisol in southern Cameroon

Soil moisture depletion during dry seasons by planted hedgerows to lower levels than under natural fallow, would reduce drainage and nutrient losses in the following rainy season when food crops are grown. The volumetric water content of the 0–150 cm soil profile was measured under planted hedgerows (alternating Leucaena leucocephala and Gliricidia sepium) and natural fallow, both either annually cropped to sole maize or in a two-year crop/two-year fallow rotation, in the humid forest zone (annual rainfall 1700 mm) of southern Cameroon during the 1995–1996 and 1996–1997 dry seasons. Hedgerows were cut to 0.05 m height, largely eliminating trees’ water consumption during cropping phases. Differences in total soil water content at 0–150 cm depth, between systems, occurred only in the early phases of the 1996–1997 dry season. In both dry seasons, differences between systems in water content were found in some soil layers, all within 0–60 cm depth, yet, without consistent advantage of any system in exploiting the topsoil water resources. Soil water content was lower under L. leucocephala than G. sepium at 20–40 cm depth only. Below 60 cm depth, no differences in water regimes between systems were found. Under southern Cameroonian conditions it is unlikely that any of the systems has an advantage in accessing or recovering water and thus, if available, nutrients from the sub-soil. None of the systems examined was capable of delaying drainage and thus it appears unlikely that downward displacement of nutrients is delayed after the start of the rains.     

Above-Ground Biomass of Mountain Beech (Nothofagus solandri (Hook.f.) Oerst. var. cliffortioides (Hook.f.) Poole) in Different Stand Types Near Timberline in New Zealand

In the alpine timberline ecotone at 1350 m in the CraigieburnRange, New Zealand, four distinct mountain beech stand types(a pole, a coppice, a high forest and a shrublike stand) wereanalysed for stand biomass and leaf area by means of allomet-ricregressions based on stem diameter. Differences between stand types in terms of age, structure,biomass and leaf area are interpreted as development stagesafter stand breakdowns due to external impacts. Vegetative reproduction,mainly coppicing, plays an important part in stand regeneration. The young pole stand had 177 t ha^–1, the coppice stand272 t ha^–1, and the mature high forest stand 323 t ha^–1aboveground dry weight. A low mountain beech shrub stand withgnarled, windshaped dwarf trees had only 135 t ha^–1. Foliageaccounted for only 3–5% in all stands, the leaf area indexwas also low, at 3.0 in the shrub stand and 3.7–7.4 inthe forest stands. The low foliage proportion is consideredto be a response to the harsh environment.     

Conifer Plantations on Drained Peatlands in Britain: a Net Gain or Loss of Carbon?

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.     

Carbon pools and sequestration in forest ecosystems in Britain

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.     

Litter Production in Western Washington Douglas-Fir Stands

Litter production by Douglas-fir stands ranging in age from22 years old to 160 years old, is discussed. Typical leaf litterproduction was 2100 kg ha^–1 yr^–1 while total litterwas 2500 kg ha^–1 yr^–1. Annual fall of leaf litterincreases up to about 40 years of age and then becomes fairlyconstant while total litter continues to increase because ofwood production, although this increase may be quite irregular.Average nutrient returns to the forest floor are 21, 3, 7, 32,4, and 7 kg ha^–1 yr^–1 for N, P, K, Ca, Mg, and Mnrespectively.     

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.     

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.     

Denitrification of an Upland Forest Site

Rates of nitrogen loss through denitrification were monitoredfor standing forest and adjacent clear-felled areas locatedon a peaty-gley soil at Kershope Forest in the north of England,in two year-long studies. The rates of denitrification in soilcores brought back to the laboratory were determined using theacetylene (C₂H₂) block technique. An equation relating denitrificationto temperature was applied to derive an estimate for the monthlyloss of nitrogen via denitrification from the sites. In an additional study, half of the cores were incubated inthe absence of C₂H₂, so that an estimate of the ratio of emissionof N₂O/N₂ could be made. An annual loss of 1–3 kg N ha^–1 y^–1 was estimatedfor the standing forest while losses from the clearfelled siteswere estimated at 10–40 kg N ha^–1 y^–1 duringthe first 2 years after felling. This loss returned to pre-fellinglevels 4 years after felling. The results are discussed in relation to other studies of denitrificationin forest soils and to the rates of N₂O being lost to the atmosphereby UK forests.     

Sweet chestnut: silviculture, timber quality and yield in the Forest of Dean

The silviculture, performance and value of sweet chestnut (Castaneasativa Miller) are reviewed in the light of experience in theForest of Dean in Gloucestershire. The many advantages of includingthe species within broadleaved woodland include its ease ofestablishment, fast growth rate, and the high value of its timber.Veneer and first quality planking material fetch premium prices.That it is not more widely planted is mainly due to the widelyheld view that it is difficult or impossible to grow chestnutlogs that are not shaken. Shake is shown to be mainly a problemof overmature trees. Ink disease (Phytophthora sp.) is not regardedas a major limitation, especially in new plantings. Guidanceis given on the conversion of chestnut coppice to high forest.Yield tables are presented which may be applied to chestnuthigh forest of coppice origin in the Forest of Dean, and withcaution elsewhere in southern England. The data for the bettersites in the Forest of Dean indicate possible yields of up to11 m³ ha^–1 a^–1, and a dominant diameter incrementof up to 1 cm a^–1.     

High Productivity in a Polestage Sitka Spruce Stand and its Relation to Canopy Structure

1. The net annual above ground dry matter production of a 17 yearplantation of Sitka spruce in Scotland was 26.7 t ha^–1y^–1.Total annual production which includes estimates for roots,was 35 t ha^–1y^–1, one of the highest values reportedfor coniferous forest in the temperate zone.
2. When comparedwith other forests with high rates of net productionthis standhad the highest foliage and branch biomass and lowestrate ofproduction per unit of foliage.
3. Gross foliage increment tothe canopy declined following thetime of maximum stand basalarea increment, which coincidedwith the onset of competitionbetween individual trees. Thesechanges in canopy and standstructure are discussed in relationto the decline in net productionwhich has been observed inpolestage conifer plantations.
4. Foliageand branch production were greatest in the top 6 whorlsof thecanopy; over the period studied new foliage became concentratednearer to the top of the trees. Significant branch wood incrementceased below the height where needle death balances needle production.
5. New needles produced at increasing depth in a canopy weighedless per unit needle area. Generally needles lost weight asthey aged. All needles survived for three years, the greatestmortality was of 5-year-old needles but some survived for 8years.
6. Needle area index was 10–11 at age 16, 7–8at age18. Branch area index was 3.6 and the ratio of main stembarksurface area to ground area was 0.4 at age 16.

     

The effect of geographical variation of planting rate on the uptake of carbon by new forests of Great Britain

The planting rates from 1921 to 1996 of new coniferous and broadleavedforests for 11 regions of Great Britain were assembled for thestate and private sectors. Over that period new planting totalled231 kha of conifers and 132 kha of broadleaves in England, 141kha of conifers and 16 kha of broadleaves in Wales and 881 khaof conifers and 52 kha of broadleaves in Scotland. These time series and regional values of Yield Class were usedas input data for an accounting model of carbon in the trees,litter, soils and products to produce estimates of their netuptake of carbon by the forests from the atmosphere (i.e. increasein the carbon pools). On the assumption that conifer and broadleafplanting could be represented by Sitka spruce and beech treesrespectively, litter and forest soil in Great Britain were accumulatingcarbon at 2.42 Mt a^–1 in 1995–96. Coniferous forestaccounted for 89 per cent of this uptake. Scottish conifer andbroadleaf forests took up 68 per cent and mapping the uptakeshowed that the greatest rate occurred in western Scotland.The pool of carbon in wood products increased in 1995–96by 0.31 Mt a_–1. The estimated uptake rates were sensitive to the relative amountsof conifer and broadleaf forest planted (particularly in relationto increases in the pool of carbon in wood products) but notto regional differences in Yield Class. Use of any single YieldClass in the range 10–16 m³ ha^–1 a^–1 for allSitka spruce planting produced estimates of uptake rate in GreatBritain to trees, litter and soil within ±10 per centof that, assuming yield varied across the country. Lack of preciseknowledge on the parameters of the model was estimated to introducean uncertainty of ±30–70 per cent into estimatesof carbon uptake.     

Biomass production and allometric above- and below-ground relations for young birch stands planted at four spacings on abandoned farmland

The objective of the study was to quantify above- and below-stumpbiomass of silver (Betula pendula Roth) and downy (Betula pubescensEhrh.) birches planted at four spacing intervals and growingon two soil types on an area of farmland. The 12-year-old bircheshad been grown at four spacings (1.3, 1.5, 1.8 and 2.6 m) ontwo sites: one on medium clay soil and the other on fine sandsoil. The dry weight of the stem, branches, leaves, stumps androots was estimated by drying and weighing sub-samples. Theprojected leaf area (PLA) m^–2 of trees, leaf area indexof stands and basic density (kg m^–3)of stems were alsoestimated. A significant greater dry weight of stem, branches,stump and roots and species and spacing for pendula birch werefound. The root length of silver birch was significantly greaterthan that for downy birch and for both species the root lengthwas greatest at the widest spacing (2.6 m). There was also asignificant difference between leaf weights of birch of thesame species growing on the two soil types. Significant differenceswere also found between PLA and species, and for both species,between PLA spacing. Basic density of stems was significantlydifferent between soil types. Equations for estimating the above-groundbiomass and root biomass from diameter at breast height weredeveloped for birches growing on fine sand and on medium claysoils. The total biomass production per hectare on fine sandwas higher for silver birch (19.9–65.9 tonnes ha^–1),than for downy birch (13.0–48.3 tonnes ha^–1). Onmedium clay soil, total biomass production for silver and downybirches was 30.8–52.8 and 16.8–42.8 tonnes ha^–1,respectively.     

The dynamics of biomass production in relation to foliar and root traits in a grey alder (Alnus incana (L.) Moench) plantation on abandoned agricultural land

The dynamics of the above-ground biomass production of a greyalder plantation on abandoned farmland was investigated during11 years after establishment. In the 12-year-old stand, thetotal biomass of the above-ground part of the stand was 68.8t dry matter (DM) ha^–1 and the current annual production(CAP) was 14.0 t DM ha^–1 year^–1. The predicted meanannual increment (MAI) reached is maximum at the age of 16 years,which indicates bulk maturity (the stand age when CAI = MAI)and appropriate rotation time for obtaining maximum biomassproduction. In the case of short-rotation forestry, initialstand density should not be higher than 6500–6000 treesper hectare. Below-ground biomass accounted for 18 and 16 percent of total stand biomass at a stand age of 5 and 10 years,respectively. The biomass of the nodules was estimated at 155± 63 kg DM ha^–1 and the biomass of the fine rootswas estimated at 870 ± 130 kg DM ha^–1 in the 10-year-oldgrey alder stand. Of the fine roots, 80 per cent and almostall nodules were located in the upper 0–20 cm soil layerin both the 5-year-old and the 10-year-old stand. The valueof leaf area index increased with stand age, ranging between1.38 and 5.43 m² m^–2 during the development of the stand.Specific leaf area varied in different years from 11.1 to 13.5m² kg^–1.     

UK conifer forests may be growing faster in response to increased N deposition, atmospheric CO2 and temperature

Site studies have shown that conifer plantations in northernBritain have increased in General Yield Class (GYC) by 1 m³ha^–1 a^–1 per decade or more (20–40 per cent)since the 1930s. Large increases in forest productivity havealso occurred in many other regions of Europe. Are these increasesdue to improved silvicultural practices or to increases in Ndeposition, CO₂ and temperature? Two process-based mathematicalmodels of forest growth were used to simulate the responsesof conifer forests growing in the Scottish southern uplandsto increases in atmospheric N deposition, CO₂ concentrationand temperature, during this century and next century. The modelsdiffered substantially in the ways in which underlying processeswere represented: one simulated a managed plantation, the othera natural forest. Nevertheless, both showed that: (1) increasesin N deposition, CO₂ and temperature together might accountfor up to half of the observed increase in GYC this century;(2) increased N deposition and CO₂, considered separately, probablyincreased forest productivity by a modest amount (7–14per cent), but their combined effect has been approximatelyadditive; (3) increased temperature, even when combined withincreasing CO₂ concentrations, promoted growth less than expectedfrom site studies relating GYC to temperature; and (4) substantialfurther increases in productivity, GYC, leaf area index andstanding biomass are forecast during the next century as a resultof increasing CO₂ concentrations and continued N deposition,with or without climatic warming. The predicted increases inGYC could be large enough to have profound effects on the forestindustry.     

The Application of Fertilizers to Drained Peat 1. Nutrient Losses in Drainage

An experiment to follow the fate of applied fertiliser was installedon a newly-drained raised bog near Edinburgh. Sixteen lysimeters(2.25 m²) were constructed to isolate blocks of peat to 0.8m depth and were allocated to four treatments; untreated control,+ 50 kg P ha^–1 (as rock phosphate), + 100 kg K ha^–1(as KCl), P and K together at these same rates. Fertiliserswere applied in May 1977 and for the following three years drainagewas collected weekly for chemical analysis. The hydrologicalbehaviour of the lysimeters was checked by monitoring run-offfrom an enclosed 2.5 ha catchment. Losses of K in drainage were rapid but declined over the perioduntil they were only slightly greater than control values; lossesof P began after 24 weeks and were greatest in winter with noapparent decline; Ca was not leached and no significant releaseof N was detected. Control lysimeters showed a net loss of Nand P following drainage. When K and P were applied separatelylosses were 39 and 16 per cent respectively but in combinationthe losses were reduced to 26 and 7 per cent. Concentrationsof dissolved P in leachates exceeded 1.0 mgl^–1 on occasionand K fertiliser initially reduced water pH.     

The Continuing Effects of Aluminium Smelter Emissions on Coniferous Forest Growth

Industrial emissions have a detrimental effect on forests. Theeffects of an isolated aluminium smelter's emissions, particularlyfluoride, upon the surrounding coniferous forest is suggestedas the most likely cause for the measured decrease in growth. Permanent sample plots were established in 1974 in three intensitiesof fume - inner, outer and surround and in a control area. Theywere remeasured in 1979 and 1984. Increment cores were collectedfrom sample trees. Annual ring width and density were measuredwith an X-ray densitometer. Tree growth prior to establishmentof the smelter in 1954 provided another control. The growthreduction was quantified per unit area, extended to estimatethe total loss of growth for the whole forest and its valueappraised. The estimated volumes lost were 2800 m³y^–1for the period 1954–73, 920m³y^–1 1974–78 and753m³y^–1, 1979–83. The value of wood lost in thelast period, 1979–83, was $13,750. At the lowest levelof fumigation, the emissions appear to have a stimulating effecton forest growth.     

Methane and CO2 exchange over peatland and the effects of afforestation

The exchange of CH₄ and CO₂ over extensive tracts of peatlandhas recently been measured using micrometeorological methods.Fluxes of CH₄ measured in Caithness (UK) during May and June1994 using eddy covariance yielded fluxes in the range –70to +170 µmol CH₄ m^–2 h^–1 with a mean fluxof 39 µmol CH₄ m^–2 h^–1 Landscape emissions of CH₄ from peatland are shown to vary withwater table and temperature, increasing from 25 µmol CH₄m^–2 h^–1 at 5 per cent area to 50 µmol CH₄m^–2 h^–1 with 30 per cent within the footprint occupiedby pool. A positive temperature response of 4.9 µmol CH₄m^–2 h^{–1 {ring}} C^– in the temperature range6–12^{ring}C was also observed The mean day time fluxes of CO₂ during May and June 1994, of—3.6 mmol m^–2 h^–1 were two orders of magnitudelarger than the emission of CH₄ of 40 µmol m^–2 h^–1,while at night (when net radiation is negative) the respirationflux of CO₂ averaged +2.2 mmol m^–2 h^–1approximatelytwo orders of magnitude larger than night-time CH₄ emissionsof 30 µmol m^–2 h^–1.     

Nitrogen Transformations and Decomposition in Litter and Humus from beneath Closed-Canopy Sitka Spruce

Samples of litter and humus from beneath 10 m tall, closed-canopySitka spruce planted on a brown forest soil were incubated underboth field and laboratory conditions to measure mineral nitrogenproduction and carbon dioxide evolution. Mineral nitrogen productionin enclosed samples over 12 months was equivalent to 50 and17 kg N ha^–1 in litter and humus, respectively. Applicationsof fertilizer NPK (200 kg N ha^–1 as ammonium nitrate,100 kg P ha^–1 as unground rock phosphate and 150 kg Kha^–1 as potassium chloride), 18 months previously, decreasedthese values slightly, but stimulated the production of nitratein both litter and humus. Compared with samples kept under laboratoryconditions at 10°C, those incubated in the field at a similarmean temperature released less carbon dioxide and, in the caseof fertilized humus produced smaller amounts of mineral nitrogen.     

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 Development of Stain in Wounded Sitka Spruce Stems

In order to investigate the severity of staining in woundedSitka spruce stems, the vertical extent of two categories ofstain (based on colour and termed ‘light’ and ‘heavy’)was measured in stems at two sites in south Scotland. Data wereobtained from 98 wounds most of which were between 8 and 14years old and most of which had been caused by Red deer. Theupward extent of stain and its rate of upward spread were positivelycorrelated with wound surface area and length. Most stain wasof the light type which, although it was associated with nearlyall wounds, usually constituted an insignificant defect anddid not commonly extend for more than 1 m ahve wounds. Heavystain occurred above less than half of all wounds studied butwas common above wounds exceeding 300 cm² surface area. Forall wounds, the mean value for the upward extent of heavy stainwas 16.1 cm with a mean rate of spread of 1.9 cm y^–1.However, for wounds exceeding 300 cm² surface area, the valueswere 51.7 cm and 5.5 cm y^–1. These results suggest that,although there is an important effect of wound size on the typeand extent of stain, wounds of the type studied are unlikelyto lead to severe stain and decay in Sitka spruce over a periodof 8–14 years. The results are discussed in relation toother studies on wound staining in conifers.