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.     

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.     

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.     

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.     

The Amount and Nutrient Content of Litter Fall under Sitka Spruce on Poorly Drained Soils

Litter fall was collected every three months for four yearsfrom twenty-one vigorous (Yield Class 18–20 m³ ha^–1y^–1) and sixteen less vigorous (Yield Class 10–12)plots of Sitka spruce on gleyed soils in Northern Ireland. Forty-fourper cent of all litter fell in the June-August quarter, andlitter fall was heaviest in years when there was green spruceaphis attack. Beneath YC 10–12 crops, both rate and quantityof litter fall was less and nutrient concentrations were lower,than under YC 18–20 crops. As the pool of organic matterand nutrients on the forest floor was greater under trees ofYC 10–12, poor growth was associated with a slow organicmatter and nutrient turnover.     

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.     

Carbon stocks and sequestration in plantation forests in the Republic of Ireland

The United Nations Framework Convention on Climate Change andits Kyoto Protocol (KP) have created a clear need for methodsthat enable accurate accounting of carbon (C) stocks and stockchanges in forest ecosystems. The rate of accumulation of Cin plantation forests in the Republic of Ireland was estimatedfor the period 1906–2002 using the record of afforestationand a dynamic C accounting model (C-flow). Projections for theperiod 2003–2012 were made using different afforestationrates. It was assumed that Sitka spruce planted in the period1906–1989 was Yield Class (YC) 16 m³ ha^–1 year^–1and that after 1990 this increased to 20 m³ ha^–1 year^–1.All other conifers were assumed to have the growth characteristicsof YC 8 m³ ha^–1 year^–1 lodgepole pine. Broadleaveswere assumed to have the growth characteristics of YC 6 m³ ha^–1year^–1 beech. In 2002, the total forest C stock was 37.7Mt C representing an increase of 14.8 Mt C since 1990. In 2002,the rate of increase in trees, products, litter and soil was0.7, 0.1, 0.1 and 0.5 Mt C, respectively. Under a business-as-usualscenario, afforestation since 1990 is estimated to create anannual average C sink of 0.9 Mt C year^–1 during the period2008–2012. This accounts for 22 per cent of Ireland'sreduction commitment under the KP. Afforestation on peat soilswas found to reduce the net C sink, although the extent to whichit does so is highly dependent on assumptions regarding therate of peat C loss.     

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.     

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.     

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.     

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.     

Estimating net primary productivity of Chinese pine forests based on forest inventory data

Forest inventory data (FID) include forest resources informationat large spatial scale and long temporal scale. They are importantdata sources for estimating forest net primary productivity(NPP) and carbon budget at landscape and regional scales. Inthis study, more than 100 datasets of biomass, volume, NPP andstand age for Chinese pine forests (Pinus tabulaeformis) fromthe literature were synthesized to develop regression equationsbetween biomass and volume, and between NPP and biomass as wellas stand age. Using these regression equations and the fourthFID surveyed by the Forestry Ministry China from 1989 to 1993,NPP values of Chinese pine forests were estimated. The meanNPP of Chinese pine forests was 4.35 Mg ha^–1 yr^–1.NPP varied widely among provinces, ranging from 1.5 (Neimenggu)to 13.73 Mg ha^–1 yr^–1 (Guizhou). Total NPP of Chinesepine was 10.87 Tg yr^–1 (1 Tg = 10¹² g). NPP values ofChinese pine forests were not distributed evenly across differentprovinces in China. This study may be useful not only for estimatingforest carbon of other forest types but also for evaluatingterrestrial carbon balance at regional and global levels.     

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.     

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.     

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.     

The tolerance of newly emerged broadleaved tree seedlings to the herbicides clopyralid, cycloxydim and metazachlor

In direct-seeded woodlands and nursery seed-beds, weeds canrapidly invade newly sown areas, leading to death or suppressionof tree seedlings. Hand weeding is usually expensive, and thesafe use of broad-spectrum contact herbicides is seldom possible.Hence in the work reported here, the tolerance of young treeseedlings to the potentially more selective, post-emergenceherbicides clopyralid, cycloxydim and metazachlor, was tested.Seedlings of Fraxinus excelsior L. (ash) with two to four expandedtrue leaves (2–4 ETL), Fagus sylvatica L. (beech) (2–4ETL), Acer pseudoplatanus L. (sycamore) (4–6 ETL), Prunusavium L. (cherry) (6–8 ETL) and Quercus robur L. (oak)(6–8 ETL) appeared to tolerate applications of cycloxydimat a rate of 0.45 kg a.i. ha^–1. Applications of 0.2 kga.i. ha^–1 clopyralid or 1.25 kg a.i. ha^–1 metazachloralso appeared to be generally tolerated, but did cause somesuppression of annual growth increment in Q. robur, P. avium,F. sylvatica and A. pseudoplatanus, particularly where repeatapplications were made to the earliest growth stages. Seedlingsurvival was unaffected by any herbicide treatment. Mixturesof all three herbicides were no more damaging than the sameherbicides applied separately. Therefore, depending on treespecies and growth stage, it appears that clopyralid could potentiallybe safely used to control a range of herbaceous weed species,metazachlor a variety of seedling or germinating weeds and cycloxydima range of established grass weed species, in direct sown woodlandsor nursery seed-beds, although further research is advisableto confirm crop safety.     

Litter production, seasonal pattern and nutrient return in seven natural forests compared with a plantation in southern China

The amount and pattern of litterfall and its nutrient returnwere studied in seven natural forests of Schima superba Gardn.and Champ. (SCS), Castanopsis fabri Hance (CAF), Tsoongiodendronodorum Chun (TSO), Cinnamomum chekiangense Nakai (CIC), Altingiagracilipes Hemsl. (ALG), Castanopsis carlesii (Hemsl.) Hayata(CAC) and Pinus massoniana D. Don (PIM), and compared with thatof an adjacent 29-year-old plantation of Chinese fir (Cunninghamialanceolata Lamb.) (CUL) in Jianou, Fujian, China. Mean annualtotal litterfall over 3 years of observations varied from 4.63Mg ha^–1 in the CUL to 8.85 Mg ha^–1 in the PIM; ofthis litterfall, the leaf contribution ranged from 62 to 73per cent. Litterfall in the CAF, ALG and CAC showed an unimodaldistribution pattern, while for the five other forests, thelitterfall pattern was multi-peak. The rank order of the eightforests, according to nutrient return mass with the exceptionof P, was different from the order when rank was according tototal mass of litterfall. The highest annual N, K and Ca returnsfrom total litterfall were noticed in the TSO, the CAF and theCUL, respectively. The amounts of P and Mg potentially returnedto the soil were the highest in the PIM. The leaf fraction providedgreater potential returns of N, P, K, Ca and Mg to the soilthan other litter fractions. The results of this study demonstratethat natural forests have a greater capability for maintainingsite productivity than the monoculture coniferous plantation,due to higher amount of above-ground litter coupled with greaternutrient returns; therefore conservation of natural forestsis recommended as a practical measure in forest management torealize sustainable development of forestry in mountainous areasof southern China.     

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.

     

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.