Nutrient Changes in Peaty Gley Soils after Clearfelling of Sitka Spruce Stands

The roots of second-rotation Sitka spruce (Picea sitchensis(Bong.) Carr.) planted on peaty gley sites are restricted tothe old litter (LFH) layer and are dependent on its decompositionfor availability of nutrients. A series of these sites of increasingage from felling were sampled to estimate changes in the nutrientcapital of the LFH horizon over time at Kielder Forest, Northumberland.Previous stand histories were reconstructed from stump data.Geographical, climatic, soil and mensurational data suggestedthat the use of a time series was justified. Nutrient capital in the LFH horizon generally declined overa 5 year period after clearfelling from approximately 997, 51and 83 kg ha^–1 to 676, 30 and 31 kg ha^–1 of N, Pand K, respectively. However, N concentration increased overa 5 year period from 11 mg g^–1 to 14 mg g^–1, P concentrationremained constant at about 0.6 mg g^–1, and K concentrationdecreased from 1.0 mg g^–1 to 0.7 mg g^–1. Nutrientconcentrations and contents of the LFH horizon were higher underthe brash (slash) swathes that resulted from the use of organizedfelling techniques than under clear strips devoid of brash. The patterned input of nutrient capital in brash as a resultof organized felling was also determined. Brash containing 219,20 and 71 kg ha^–1 of N, Pand K, respectively, was systematicallydistributed at a rate of 491 ha^–1 over 66 per cent ofthe site after harvesting. The needles and small branch fractionscontained 71 per cent of the N and 80 per cent of the P andK present in the brash.     

The Interaction of Green Spruce Aphid and Fertilizer Applications on the Growth of Sitka Spruce

In an 11-year-old stand of Sitka spruce (Picea sitchensis [Bong.]Carr.) application of nitrogen fertilizers, at a rate of 10kgN ha^–1 month^–1, increased mean diameter incrementby 12 per cent, while the further addition of phosphorus, at5 kg ha^–1 month^–1, resulted in a 23 per cent increase.An attack by the green spruce aphid (Elatobium albietinum Walker)occurred during the period of fertilizer addition. The mostseverely affected trees showed a reduction in diameter growthof 50 to 56 per cent but the severity of the attack betweentrees was unrelated to the treatments applied. However, fertilizerapplication did hasten the recovery of diameter growth afterdefoliation.     

Effects of Refertilization on Growth and Nutrition of Lodgepole Pine (Pinus contorta Dougl.) Planted on a Minerotrophic Peatland in Central Newfoundland, Canada

A plantation of lodgepole pine (Pinus contorta Dougl.), whichwas established in 1973 on a ditched minerotrophic fen at plantingspacings of 1.2 m, 1.8 m, and 2.4 m, was refertilized in 1985with control, P, PK and NPK treatments consisting of 60 kg ha^–1phosphorus, 100 kg ha^–1 potassium and 200 kg ha^–1nitrogen. Although each seedling had been spot-fertilized in1973 with a mixture of 71 g urea, 99 g ground rock phosphateand 41 g potassium sulphate, height and needle nutrient assessmentsof the plantation in 1984 indicated poor growth, low concentrationsof needle nitrogen (1.26 per cent) and possible deficiency levelsof needle phosphorus (0.10 per cent) and potassium (0.36 percent). Between 1985 and 1991, height and diameter growth increasedsignificantly in all refertilization treatments. Growth responsewas greatest in the PK treatment and least in the P treatment.Needle weights, determined from 1987 to 1991, did not responduniformly to any of the refertilization treatments. Needle concentrationsof phosphorus increased to levels between 0.20 per cent and0.23 per cent following refertilization with P, PK, and NPK,but by 1988 had decreased to about 0.14 per cent. Needle concentrationsof potassium also increased sharply to 0.60 per cent in 1985following refertilization with PK and NPK, but by 1988 had decreasedto levels between 0.35 per cent and 0.45 per cent. Similarly,needle nitrogen concentrations increased to 1.84 per cent in1985 following refertilization with NPK, then decreased to levelsbetween 1.20 per cent and 1.33 per cent in 1986 and remainedat those levels each year thereafter. Although needle nutrientlevels fell sharply following an initial peak after refertilization,height and diameter growth did not decrease significantly, especiallyin the PK treatment, suggesting that nutrient levels remainedadequate for optimum growth.     

Some Effects of Afforestation with Lodgepole Pine on Rates of Nitrogen Mineralization in Peat

Rates of mineral nitrogen production and carbon dioxide evolutionin incubated samples from the upper 300mm of peat beneath lodgepolepine (Pinus contorta Dougl.) have been compared with those foradjacent unplanted areas at each of six sites in the North ofScotland. Under both aerobic (moist) and anaerobic (water logged)conditions, rates of mineral nitrogen production at 30°Care strongly influenced by peatland type, sampling depth andafforestation. During the early stages of the incubation underaerobic conditions, samples of planted peat showed a more rapidaccumulation of mineral nitrogen than did samples from unplantedareas, the amounts after 17 days being 170ppm and 46ppm mineralN, respectively; after 62 days however, the difference was nolonger significant. The mean rate of CO₂ production averaged446µg CO₂ g^–1 day^–1 in planted as against728µg in unplanted peat. Under anaerobic conditions, amountsof mineral nitrogen accumulated were similar in planted andunplanted sites but a difference in accumulation between the0–150 and 150–300mm horizons in unplanted peat wassignificantly reduced beneath the trees.     

Carbon storage and sequestration in the forests of Northern Ireland

The rate of accumulation of carbon in forests and woodlandsin Northern Ireland was estimated using the record of forestplanting since 1900 and a model that calculated the flow ofcarbon from the atmosphere to trees, litter, soil, wood productsand back to the atmosphere. It was assumed that all coniferforests had the carbon accumulation characteristics of Piceasitchensis, and upper and lower estimates of carbon storagewere calculated assuming Yield Class 16 m³ha^–1 a^–1unthinned and Yield Class 14 m³ ha^–1 a^–1 thinned.Broadleaved woodlands were assume to have the carbon accumulationcharacteristics of Fagus sylvatica, Yield Class 6 m³ha^–1a^–1. Northern Ireland currently has about 78 300 ha offorest, 83 per cent of which is coniferous, 77 per cent state-owned,mostly planted since 1945, with peak planting in 1960–1975.In 1990, conifer forests contained 3–4 MtC (trees + litter)and broadleaved wdlands contained about 0.8 MtC (trees + litter+ new forest soil). In 1990, conifer forests were sequestering0.15–0.20 MtC a^–1 and broadleaved woodlands about0.025 MtC a^–1. To maintain these sink sizes, new coniferforests need to be planted at 1500–2000 ha a^–1,and new broadleaved woodland at100–150 ha a^–1 inaddition to full restocking. Current carbon sequestration byNorthern Ireland forests represents around 6.5–8.2 percent of the total for UK forests and is greater per hectar thanin Britain because the average forest age is younger in NorthernIreland     

Forest biomass estimated from MODIS and FIA data in the Lake States: MN, WI and MI, USA

This study linked the Moderate Resolution Imaging Spectrometerand USDA Forest Service, Forest Inventory and Analysis (FIA)data through empirical models established using high-resolutionLandsat Enhanced Thematic Mapper Plus observations to estimateaboveground biomass (AGB) in three Lake States in the north-centralUSA. While means obtained from larger sample sizes in FIA datasetscan be used as reference numbers over large scales, remote sensing(RS)-based observations have the ability to reflect spatialvariation of properties of interest within a given area. Thus,combining two national on-going datasets may improve our abilityto accurately estimate ecological properties across large scales.Using standard and consistent data sources can reduce uncertaintyand provide more comparable results at both temporal and spatialdimensions. We estimated total forest AGB in the region was1479 T_g (10¹² g, dry weight) in 2001 with mean AGB value of95 mg ha^–1 ranging from 4 to 411 mg ha^–1 (within95 per cent percentiles). Mixed forests featured 66 per centof the total AGB while deciduous and evergreen forests contained32 and 2 per cent of the total AGB, respectively, at 1-km pixelresolution. Spatially, AGB values increased from north-westto south-east in general. The RS-based estimates indicated agreater range in AGB variations than the FIA data. Deciduousforests were more variable (both in absolute and relative terms)than evergreen forests. The standard deviation of AGB for deciduousforests was 137 mg ha^–1, or a coefficient of variationof 92 per cent, that for evergreen forests was 24 mg ha^–1,or a coefficient of variation of 37 per cent.     

Characteristics of lowland broadleaved woodland being restocked by natural regeneration

A survey of 78 sites in southern England with approved managementplans for restocking by natural regeneration was made duringthe summers of 1993 and 1994. The following features were recorded:species, stocking, canopy cover and seed-bearing potential oftrees present in the overstorey; species and canopy cover ofthe understorey; ground cover; species, browsing damage, numberand heights of tree seedlings. In general, sites were poorlystocked with overstorey trees having an average of 135 stemsha^–1 and a mean canopy cover of 36 per cent. Similarly,the understoreys were poorly developed with an average coverof only 23 per cent. Twenty-nine species of tree were foundin the overstorey, Quercus spp. and Fraxinus excelsior werethe most common. Many of the stems present had poor seed-bearingpotential. Cover of the ground flora often exceeded 75 per cent.Seedlings were present on most sites, with F. excelsior andBetula pendula being most abundant with mean seedling densitiesexceeding 10000 ha^–1. Most seedlings were >20 cm tall,few exceeded 120 cm. About 30 per cent of seedlings were browsed.The results are related to current guidance and the future prospectsfor use of natural regeneration.     

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.     

Changes in Amount and Distribution of Stem Growth in Pole-Stage Corsican Pine Following Application of Nitrogen Fertilizer

Ring-width measurements on trees felled in a nitrogen-deficientpole-stage crop of Corsican pine on the sand dunes of Culbinforest (Morayshire) showed that, in addition to a growth checkascribed to the low nitrogen content of the soil, there wasevidence for decreasing site quality, tree growth decliningprogressively with time. This feature is ascribed to the continuingimmobilization of the limited nitrogen capital in the newlydeveloping mor humus layer. Ammonium sulphate, at rates equivalentto 84, 168, 336, and 504 kg elemental nitrogen ha^–1, wasapplied to this crop when it was 36 years old, and the treatmentsrepeated for a further 2 years. Nitrogen levels in the foliagerose from 0.9 per cent to as high as 20 per cent in the firstyear, increasing to 2.6 per cent after the third year of application.Response in terms of basal area appeared in the year after firstapplication but was not accompanied by any changes in the patternof growth throughout the season, nor was there a significanteffect of tree size on the proportional change in relative basalarea growth induced by the fertilizer, except for a slightlyreduced response by the smallest trees to the lower rates ofapplication. A similar low response by the smallest trees wasfound for height, but, in addition, height growth after treatmentwas greatest for the middle-sized trees, despite the fact thatthese had been growing significantly more slowly than the largesttrees prior to application of the fertilizer. Form factor remainedunaltered by the treatments but taper changed slightly. Heightand basal area showed very different response patterns to thetreatments. Thus, whereas maximum height growth occurred atthe 168 kg N ha^–1 treatment rate (2.41 m over 7 years,1.4 times the control growth) maximum basal area growth occurredat the 504 kg N ha^–1 rate, the highest rate used (13.0m² ha^–1 over seven years, 2.4 times the control growth);volume growth was maximum at the 336 kg N ha^–1 rate (126m³ ha^–1 over 7 years, 2.6 times the control growth). Whenrelated to levels of foliar nitrogen in the previous year, annualheight growth was maximum at 1.6 per cent with maximum basalarea growth occurring nearer 2.2 per cent. It is estimated thatvolume growth would be maximised at just over 20 per cent nitrogen.     

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.     

Nitrogen critical loads for spruce plantations in Wales: is there too much nitrogen?

We have used the mass balance approach for calculating nitrogencritical loads (CL(N)) to avoid eutrophication for Sitka spruceplantation forestry in Wales. The various approaches for assigningvalues to the parameters in the mass balance equation are discussedwith particular reference to the soil nitrogen immobilizationvalue. A CL(N) value of 11 kgN ha^–1 a^–1 was calculatedfor an intensively studied site in Wales of Yield Class 14 ona freely draining acid soil. If this site is assumed to representa typical spruce stand, application of the CL(N) value meansthat 97 per cent of the area of coniferous forest in Wales,which is predominantly Sitka spruce, is currently receivingnitrogen deposition in excess of the CL(N). The area of coniferousforest at risk is reduced to 72 per cent if the proposed empiricalCL(N) for managed acidic coniferous forests to prevent ecologicalchanges (10–20 kgN ha^–1 a^–1) is applied andto 45 per cent if the empirical CL(N) to prevent nitrogen saturation,nitrate leaching and depletion of soil base cations is applied(10^–25kgN ha^–1 a^–1). Irrespective of the choiceof CL(N) values, the implications of critical load exceedanceneed urgent investigation. Available information at presentindicates that the main known consequence of chronic atmosphericnitrogen deposition to coniferous forest ecosystems is enhancednitrate and associated aluminium leaching to freshwaters. Thereis insufficient information regarding the potential adverseeffects of eutrophication of soils and waters and of impactson tree health and production.     

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.     

Productivity of Sitka Spruce in Northern Britain 2. Prediction from Site Factors

Productivity and site data from 187 temporary sample plots wereanalysed by multiple regression analysis to derive models inwhich site variables accounted for 78–86 per cent of thevariation in Sitka spruce productivity (General Yield Class,GYC). Climatic variables (accumulated temperature and windiness)extrapolated from meteorological data and tatter flag resultsaccounted for up to 78 per cent of the variation, the contributionof edaphic factors being small. The best regression models wereassociated with confidence limits of about ± 2.5 m³ ha^–1y^–1 and the mean error for predicting GYC for a forestblock (acquisition) was calculated to be ±1 m³ ha^–1y^–1 These figures were confirmed by the results of a validationsurvey and the application to field prediction of productivityis described.     

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.     

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.     

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.     

Changes in the Ground Flora of a Broadleaved Wood within a Clear Fell, Group Fells and a Coppiced Block

Changes in the ground flora, relative to undisturbed woodland,were measured in permanent (100 m² quadrats in a clear fell,group fells and a coppice area in Sheephouse Wood (Buckinghamshire)from 1984 to 1988. Species numbers rose rapidly in the clearand group fells to about twice that in the undisturbed woodland.Species indicative of higher light, moisture and nutrient conditionsappeared after felling or coppicing and the flora shifted fromone dominated by stress-tolerant species to a flora with morecompetitive and ruderal species. After two years, in both clearand group fells, the ground flora covered 90–100 per centof the quadrats (compared with 30–75 per cent in the undisturbedwoodland), but species richness started to decline. This wasprobably because of increased competition associated with thespread of grasses and rushes (Agrostis stolonifera, Deschampsiacespitosa, Holcus mollis and Juncus spp.). Species richnessdid not increase as much in the coppice area, and bramble (Rubusfruticosus), rather than grasses, became dominant. The subsequentdecline in species richness was more gradual in the coppicearea than in the clear fells. During this period there wereno significant changes in the species richness, total coveror species composition within the undisturbed woodland.     

Growth Changes in 20-year-old Sitka Spruce Picea sitchensis after Attack by the Green Spruce Aphid Elatobium abietinum

Following a severe attack by Elatobium abietinum (Walker) in1979–80, annual observations were made for 5 years on320 pole-size Sitka spruce in a nitrogen and phosphate experimentlaid out on oligotrophic blanket bog. Leader length was reduced by 25.5 per cent in 1980–81compared with the 3 previous years. This reduction was highlycorrelated with defoliation, being 39.4 per cent for trees thatlost all 1977–79 needles and 8.4 per cent in trees thatlost no needles. There were strong interactions with fertilizertreatment. Defoliated trees continued to grow less well duringthe 5 years of observations and were more likely to go intogrowth check. Early flushing trees suffered significantly less growth reductionfollowing defoliation. The same trees consistently broke budearly over 4 years of observations. Early bud burst was notcorrelated with height, girth or defoliation. No reattack by aphids was observed in the experiment until 1985–86and in this minor infestation the trees previously colonizedwere found to be significantly more likely to be recolonized. A novel measuring-rod for tree height is described.     

Stem volume equations and basic density for grey alder and common alder in Sweden

The objective was to determine stem volume models for grey andcommon alders and, based on the models, stand volume for naturallyregenerated grey and common alder stands was summarized. Basicdensity for grey and common alders and mean annual growth forstands was estimated. Net volume accretion data were collectedfrom 24 stands of grey alder (Alnus incana (L.) Moench) and31 stands of common alder (Alnus glutinosa (L.) Gaertner) inSweden. The stands ranged in latitude from 58 to 64° N andfrom 56 to 62° N for grey and common alder, respectively.The mean age of grey and common alder stands was 41 years and48 years, respectively, the mean stand density 1726 stems ha^–1and 1078 stems ha^–1, and the mean diameter at breast height(over bark) was 20 cm and 21 cm. Stem volume equations weredeveloped for grey and common alders. The adopted model forgrey alder was based on diameter at breast height and height.For common alder, crown height was added to diameter and height.Mean standing volume (over bark) for grey and common alder standswas 428 and 374 m³ ha^–1. Mean annual growth for grey andcommon alder stands was 12.0 m³ and 8.4 m³ a^–1 ha^–1,respectively. Basic density (under bark), for grey and commonalder stems was 359 and 427 kg m^–3, respectively. Thebasic density (under bark) for the lowest twigs in the crownand in the lateral part of the crown was 415 and 421 kg m^–3for grey alder and 423 and 423 kg m^–3 for common alder.     

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.