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1.
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. 相似文献
2.
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. 相似文献
3.
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. 相似文献
4.
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. 相似文献
5.
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. 相似文献
6.
Long-term research plots in multi-aged stands managed with theplenter system were assessed to evaluate sustainability of theplenter system in Central Europe. Plots primarily consistedof Norway spruce (Picea abies (L.) Karst., silver fir (Abiesalba Mill.) or European beech (Fagus sylvatica L.) and weremeasured for seven to 16 measurement intervals over 60–91years. Sustainability was assessed with four types of criteria:stand density, tree species diversity, basal area increment,and stand structure. Comparable even-aged stands were also analysedto compare and evaluate the performance of the measures of sustainability.Measures of species diversity, increment and stand structuraldiversity generally experienced increasing trends over timein these even-aged stands. Basal area generally increased andtrees ha-1 decreased in multi-aged stands following similarpatterns as in even-aged stands. These results suggest thatthe plenter system is still evolving and is not the model ofsustainability often assumed. Many of the measures used havepotential as indicators of sustainability in multi-aged stands. 相似文献
7.
Diameter, height and volume increment of Scots pine (Pinus sylvestrisL.) and Norway spruce (Picea abies (L.) Karst.) stands wereinvestigated in long-term thinning experiments in southern Finland.The measurement period was on average 19 years, and thinningsconsisted of five different treatments: (1) unthinned; (2) selectivethinning from below where thinning intensity was determinedaccording to the number of stems; (3) selective thinning frombelow where thinning intensity was determined according to standbasal area; (4) systematic thinning where corridors were openedat regular intervals in the stand; and (5) half-systematic thinningwhere corridors were opened at regular intervals and the remainingstrips thinned from below, i.e. a combination of selective andsystematic thinning. The selective (basal area) thinning ofScots pine resulted in a volume growth reduction of about 12per cent, but in Norway spruce it resulted in no marked reductioncompared with the unthinned plots. In both tree species, volumeincrement in the half-systematic and selective (basal area)thinning differed only slightly from each other. The systematicthinning resulted in the lowest volume increment. In the systematicthinning, the total yield (m3 ha–1) somewhat decreasedwith increasing corridor width. In half-systematic thinning,on the other hand, the total yield was not clearly related tocorridor width. A corridor accelerated the diameter incrementof the edge trees. The edge effect progressively diminishedwhen moving deeper into the strip and ended at a distance ofabout 3–4 m from the corridor edge. After the thinning,the height increment first decreased, but later on it recovered.The unthinned plots had more dead trees than the other treatments,but there were no significant differences between the othertreatments. It can be concluded that the prevailing thinningmethod in the Nordic countries, i.e. half-systematic thinning,most probably results in no significant growth and yield losses. 相似文献
8.
Morecroft Michael D.; Stokes Victoria J.; Taylor Michele E.; Morison James I.L. 《Forestry》2008,81(1):59-74
Sycamore (Acer pseudoplatanus L.) is an invasive, non-nativespecies in Great Britain and its management in conservationareas is controversial. Climate change adds further uncertaintyto decision making. We investigated the role of management historyin determining present-day abundance and the effects of climaticvariability on growth, photosynthesis and phenology at WythamWoods, a UK Environmental Change Network (ECN) monitoring site.Relatively few sycamore trees were found in undisturbed ancient,semi-natural woodland and recent plantations, despite beingcommon in other areas of the site. Sycamore grew more slowlythan ash (Fraxinus excelsior L.), its principal competitor,but at a similar rate to pedunculate oak (Quercus robur L.)in the period 1993–2005. There were fewer sycamore thanash seedlings, regardless of which species dominated the canopy.Growth of sycamore was slower in dry periods than wet ones andlower photosynthetic rates were measured in canopy leaves underdry compared with wet soil conditions. This study thereforesuggests that sycamore does not present a serious threat toundisturbed ancient woodland on the site and that it may eventuallydecline in areas of the site where it competes with ash, inthe absence of disturbance. It may also decline under climatechange if summer droughts become more frequent. 相似文献
9.
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. 相似文献
10.
Characteristics of lowland broadleaved woodland being restocked by natural regeneration 总被引：3，自引：0，他引：3
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. 相似文献
11.
Foliar nutrient imbalances, including the hyperaccumulation of manganese (Mn), are correlated with symptoms of declining health in sensitive tree species growing on acidic forest soils. The objectives of this study were to: (1) compare foliar nutrient accumulation patterns of six deciduous (sugar maple (Acer saccharum Marsh.), red maple (Acer rubrum L.), red oak (Quercus rubra L.), white oak (Quercus alba L.), black cherry (Prunus serotina Ehrh.) and white ash (Fraxinus americana L.)) and three evergreen (eastern hemlock (Tsuga canadensis L.), white pine (Pinus strobus L.) and white spruce (Picea glauca (Moench) Voss.)) tree species growing on acidic forest soils; and (2) examine how leaf phenology and other traits that distinguish evergreen and deciduous tree species influence foliar Mn accumulation rates and sensitivity to excess Mn. For the first objective, leaf samples of seedlings from five acidic, non-glaciated field sites on Pennsylvania's Allegheny Plateau were collected and analyzed for leaf element concentrations. In a second study, we examined growth and photosynthetic responses of seedlings exposed to excess Mn in sand culture. In field samples, Mn in deciduous foliage hyperaccumulated to concentrations more than twice as high as those found in evergreen needles. Among species, sugar maple was the most sensitive to excess Mn based on growth and photosynthetic measurements. Photosynthesis in red maple and red oak was also sensitive to excess Mn, whereas white oak, black cherry, white ash and the three evergreen species were tolerant of excess Mn. Among the nine species, relative rates of photosynthesis were negatively correlated with foliar Mn concentrations, suggesting that photosynthetic sensitivity to Mn is a function of its rate of accumulation in seedling foliage. 相似文献
12.
Tree growth was measured before, and 9 years after draining a boreal fen that supported a 50- to 60-year-old stand of tamarack
(Larix laricina (Du Roi) K. Koch) and black spruce (Picea mariana (Mill.) B.S.P.). Treatments consisted of a series of ditches spaced 30, 40 or 50 m apart, and an undrained control. Nine
years after drainage, the diameter, height, basal area, and volume growth of tamarack had increased by 2–5 times that on the
control site. Black spruce growth on the drained site was 1.6–5 times that on the control. Tamarack average volume growth
(1.20 m3 ha−1 year−1) on the drained site was superior to that of black spruce (0.21 m3 ha−1 year−1). In general for both species, there were no significant differences in growth between trees on the different ditch spacings.
This result was attributed to the water table being low enough that adequate aeration zones existed across the strips between
ditches on all spacings. Regeneration after treatment was greater on the drained than on the control plots, particularly in
the disturbed areas near the ditches where new tamarack seedlings reached densities between 9400 and 12,000 stems ha−1. There was no relationship between increased tree growth and tree distance from the ditches for both species, probably because
the water table had been lowered sufficiently so that inadequate substrate aeration was no longer a limiting factor. 相似文献
13.
Growth of regenerating trees in different light environments was studied for the mountainous, mixed-species forests in the Carpathian Mountains of Romania. The primary species in these mixtures were silver fir (Abies alba Mill.), European beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) Karst). Seedlings/saplings of these species were selected and measured in different stands from two different geographical locations. Regenerating trees were measured for height and diameter growth during the summer of 2002. For each seedling/sapling, percentage of above canopy light (PACL) and stand basal area (BA) were used to assess available and occupied growing space respectively. Regeneration growth was compared against these two variables and regression relationships were developed. Using these models, we predicted the dynamics of regeneration as both growth and species composition. Our results showed that in low-light environments (PACL<20–35%; BA>30 m2/ha), shade tolerant fir and beech clearly outcompeted the spruce. Therefore, in dense stands, spruce could be eliminated by the shade tolerant species. For intermediate levels of cover (PACL=35–70%; BA=15–35 m2/ha) the spruce grew at comparable rates as the beech and fir. All three species showed similar growth rates in open conditions (PACL>80–90%; BA<15–20 m2/ha) with the spruce having a tendency to outgrow the others. However, in terms of establishment, such conditions favor spruce and inhibit fir and beech. 相似文献
14.
In this study, the supply and input–output balances of phosphorus (P) were investigated for a 10-year-period at 85 long-term
monitoring sites in German forest ecosystems under the European Level II programme. These sites encompass 23 European beech
(Fagus sylvatica L.) stands, 9 oak stands comprised of common oak (Quercus robur L.) and/or sessile oak (Quercus petraea Liebl.), 20 Scots pine (Pinus sylvestris L.) and 33 Norway spruce (Picea abies H.Karst.) stands. We quantified P concentrations in needles and leaves, P inputs from the atmosphere, P outputs through leaching
and harvesting, and total P in the soil and humus layers. The P concentrations in European beech leaves from two sites (>1 mg P g−1 dry weight), and in Norway spruce needles from four sites (>1.2 mg P g−1 dry weight), were deficient over several years. In contrast, the oak and Scots pine sites were well supplied with P. When
P removal through harvesting was disregarded, P balances were positive or stable (median 0.21 kg P ha−1 a−1). With harvesting, balances were mostly negative (median −0.35 kg P ha−1 a−1), with long-term P removal from the forest ecosystems. 相似文献
15.
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• Construction cost (g glucose g−1), chemical composition and morphology of leaves of beech (Fagus sylvatica L.) and two co-occurring valuable broadleaved species (sycamore maple — Acer pseudoplatanus L. — and ash — Fraxinus excelsior L.) were investigated along a horizontal light gradient (3–60% of above canopy radiation) and from top to bottom within the
crowns in a fairly even-aged mixed-species thicket established by natural regeneration beneath a patchy shelterwood canopy. 相似文献
16.
Aurelio Guevara-Escobar Peter D. Kemp Alec D. Mackay John Hodgson 《Agroforestry Systems》2007,69(3):199-213
Traditionally, poplar (Populus spp.) have been planted to control erosion on New Zealand’s hill-slopes because of their capacity to dry out and bind together
the soil. Two systems: (1) widely spaced, planted poplar for soil conservation, and (2) non-eroded open pasture were compared
to determine the relative effect of the poplar–pasture system on the production, nutritive value and species composition of
the pasture, and on the water balance. Measurements were made at three sites with mature poplar (>29 years and 37–40 stems ha−1) and at a replicated experiment with young poplar (5 years, 50–100 stems ha−1). Soil water relations did not suggest strong competition for water between poplar and pasture. Pasture accumulation under
mature poplar was 40% less than in the open pasture, but under young poplar was similar to that in the open pasture. Chemical
composition of pasture suggested that feed quality of pasture in the open was better than under the poplar canopy, except
during spring, when most chemical components were similar. At the most, in vitro digestibility of pasture dry matter was 8.9%
lower and metabolisable energy of pasture dry matter was 1.5 MJ kg lower under the poplar canopy than in the open pasture.
Shade tolerant species were not dominant in the plant community under the poplar canopy with grasses such as browntop (Agrostis capillaris, L.) and ryegrass (Lolium perenne, L.) being a high proportion of the plant community. Differences in chemical composition were related to differences in the
botanical composition between the open pasture and the poplar understorey. It was concluded that the greatest effect of poplar
was on pasture production due to shading, and that management of this silvopastoral system needs to focus on control of the
tree canopy to lessen the decrease in pasture production. 相似文献
17.
There is a need for selective foliar-acting herbicides for transplantlines in forestry nurseries and new forestry plantings. Toleranceof 2-year-old pot-grown trees of beech, birch, sycamore, ash,cherry, oak, red alder, Japanese larch and Sitka spruce to contactherbicides applied at different dates in the growing seasonwas investigated.Clopyralid was safe to use on all species apartfrom some fresh weight reduction in Japanese larch. Bentazoneand phenmedipham caused initial necrosis on most species tested;however, most trees outgrew the effect of phenmedipham in thefollowing season. Bentazone, generally, had a long-term inhibitoryeffect on growth of alder and at the highest dose tested (5.2kg ha–1 ) also affected ash and beech.Metsulfuron-methyland tribenuron-methyl were safe on most species tested.However,fresh weight reductions were caused by metsulfuron-methyl inash and cherry and by tribenuron-methyl in alder. Mecoprop damagedall species, apart from Sitka spruce. 相似文献
18.
This study investigated the effects of clear-cutting and several other commonly used silvicultural systems on regeneration at seven sites in the Appalachian Mountains of Virginia and West Virginia. These even-aged oak dominated stands ranged in age from 63 to 100 yr and were located on medium quality oak sites (site indices from 18 to 23 m, base age 50). The treatments evaluated included a clear-cut, commercial harvest, shelterwood, leave-tree, group selection, preharvest herbicide, and control. Mixed model ANOVA was used to analyze treatment response in five species groups: (a) oak (Quercus spp.); (b) maple (Acer spp.); (c) black cherry (Prunus serotina Ehrh.), and yellow-poplar (Liriodendron tulipifera L.); (d) miscellaneous overstory hardwoods; and (e) midstory species that typically do not occupy main canopy positions in mature stands. Response variables included stem density, importance value, average height for all regeneration, and the tallest 365 stems ha?1. Comparisons were made among treatments, species groups, and between regeneration of sprout and seedling origin. Alternative systems with residual trees reduced the regenerations overall mean height growth compared to the clear-cut by 0.34 to 0.74 m. Current conditions indicate oak will be a lesser component of the future stand, represented mostly through stump sprouting, and maple will likely increase in proportion among all treatments. 相似文献
19.
Anthony S. Davis Douglass F. Jacobs Kevyn E. Wightman Zonda K. D. Birge 《New Forests》2006,31(2):293-303
Bareroot hardwood seedling production involves intensive soil management. To increase soil organic matter (OM), nurseries
commonly grow a cover crop for 1 year after every 1–2 year of seedling production. Raising soil OM levels can also be achieved
through addition of soil amendments. We studied the influence of chicken manure (CM) and composted leaf, tree, and lawn trimmings
(Cp) on soil properties and morphology of green ash (Fraxinus pennsylvanica Marsh.) and northern red oak (Quercus rubra L.) seedlings. CM was applied at 725, 1450, or 2900 kg ha−1 (CM725, CM1450, and CM2900, respectively) and Cp was applied at 200 m3 ha−1. Addition of CM and Cp significantly raised soil OM levels and altered soil chemical properties compared to the control (Ctrl).
Root-collar diameter increased with addition of CM1450, CM2900, or Cp compared to CM725 or Ctrl plots for northern red oak,
but was largest in soils amended with CM2900 for green ash. Conversely, height was greatest with addition of CM725 for northern
red oak, but green ash seedlings were shorter in Ctrl plots than in all amendments except for CM725. Root volume of green
ash and northern red oak seedlings was positively influenced by addition of CM or Cp. Seedling responses to nursery soil amendments
vary with different forms and amounts of OM. Benefits to seedling growth through application of appropriate materials in the
proper balance can improve seedling morphological quality and positively influence soil chemical properties. 相似文献
20.
Biomass production and allometric above- and below-ground relations for young birch stands planted at four spacings on abandoned farmland 总被引：4，自引：0，他引：4
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. 相似文献
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