Variation of wood density and hydraulic properties of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) clones related to a heat and drought wave in France

Drought response of three Douglas-fir clones (slow, intermediate and fast growing) inhabiting two different climatic regimes in France was examined. We used the hydraulic conductivity and the percent loss of conductivity due to embolism from stems and branches as well as wood microdensity measurements to determine the role of genetics in the control of embolism in this species. Conductivity and tree-ring’s microdensity variables (ring width: RW, mean ring density: MRD, minimum ring density: MID and maximum ring density: MAD) were compared in growth rings in all three clones during a typical year (2002) vs. an extremely dry year (2003). A new method was developed in order to assess axial hydraulic specific conductivity (K_s) within tree rings. The results show that branches are more resistant to embolism than stems, and that there are significant differences in embolism resistance among the clones between the two sites. K_s varied between years, sites and clones but the site exerted the most significant effect. Lartimache (more humid site during 2003) trees showed substantially higher K_s than those inhabiting Chassenoix (strongly affected by the 2003 heat and drought wave site). Wood analysis showed a significant year effect for all ring variables and a significant clone effect for all ring variables except for MAD, while the site effect was significant for MRD and MAD. The existence of a genetic control for the study traits indicates that Douglas-fir populations introduced in France may have a selection potential to face extreme climate events like the 2003 heat and drought wave.     

Influence of initial planting spacing and genotype on microfibril angle,wood density,fibre properties and modulus of elasticity in Pinus radiata D. Don corewood

Pinus radiata D. Don trees from six clones, grown at initial spacings of 2500 stems ha⁻¹ and 833 stems ha⁻¹ were destructively harvested. For these trees wood properties were measured on radial slices sampled at a height of 1.4 m above the ground. Relative to wide spacing, close initial stand spacing significantly reduced microfibril angle (MFA) and ring width and significantly increased dynamic modulus of elasticity (MOE), fibre length, latewood percentage and cell wall thickness. Density and fibre width were not significantly different between spacing treatments. Examination of the influence of genetic population on wood properties indicated that genotype significantly influenced MFA, MOE and ring width. The key wood properties MFA, MOE and fibre length were regressed against tree diameter, height and stem slenderness. All three wood properties were most strongly correlated with stem slenderness. Multiple regression models developed for MFA, MOE and ring width accounted for respectively 62%, 81% and 58% of the variation in these variables. The following changes occurred in sampled properties with increasing ring number: MFA and ring width declined markedly; MOE and fibre length increased markedly; latewood percentage and cell wall thickness increased slightly; and density and fibre width did not show any radial trend.     

Optimum planting density for Japanese oak (Quercus mongolica var.grosseserrata) based on spacing experiment with systematic design

A spacing experiment for Japanese oak (Quercus mongolica var.grosseserrata) with Nelder's design have been studied at the Kyushu University Forest in Hokkaido, since 1975. The oak seedlings were planted according to systematic spacings which were 20 levels varying gradually from 40,816 to 1,086 seedlings per hectare with concentric circular arcs (22 in number) and spokes (41 in number). In 1992 when the planted oak seedlings were 18-year-old, DBH, crown diameter, total height and clear length of the survival trees were measured. Based on the results obtained from analyzing the relationships between planting density and the mean values of each block, the optimum planting density should be 7,241 seedlings per hectare. The title is tentative translation from the original Japanese title by the authors of this paper.     

Change in historic fire disturbance in a Garry oak (Quercus garryana) meadow and Douglas-fir (Pseudotsuga menziesii) mosaic,University of Victoria,British Columbia,Canada: A possible link with First Nations and Europeans

We investigated late Holocene vegetation and fire changes on southeast Vancouver Island, British Columbia, through high-resolution analysis of pollen, spores and charcoal contained within a forest soil. Located in the Mystic Vale Endowment lands, University of Victoria campus, the site occurs adjacent to Garry oak (Quercus garryana) meadows within a Douglas-fir (Pseudotsuga menziesii) forest regionally influenced by First Nations burning. The age of the sequence is estimated from the occurrence of non-native plantain (Plantago spp.) pollen, between the early 19th century and the present. Prior to the 1850s, the Mystic Vale supported a Douglas-fir forest with a sword fern (Polystichum munitum) understory. Low-intensity fires may have burned either at or near the site, but did not destroy the stand. From the time of European settlement (ca. 1850s to 1872) to the early 20th century, Douglas-fir forests with a sword fern understory persisted but with more openings than in the past. Adjacent forests were cleared leading to successional stands of red alder (Alnus rubra). The site may have supported more grasses near or after 1872 because of adjacent cultivation and the introduction of livestock. Local establishment of Garry oaks at the margin of a field adjacent to the deposition site may have occurred at this time. The strong charcoal signal may be attributable to clearing and local fires of European settlers. Exotic weedy species such as plantain arrived during this time. From about the mid 20th century to the present a closed canopy Douglas-fir forest returned. Pre-European charcoal concentrations were significantly greater than modern-day charcoal concentrations. Peak charcoal concentrations coincided with the onset of European settlement in the area, a period in which land-clearing is thought to have been aided by the use of fire. This study suggests that the observed changes in charcoal concentrations in pre- and post-European contact time may be linked with a switch from aboriginal to European ignition sources. The study provides a historical impetus to consider partially restoring parts of southeast Vancouver Island by re-introducing fire via the application of controlled burns.     

Family variation for fall cold hardiness in two Washington populations of coastal Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco)

In order to assess the genetics of fall cold hardiness in coastal Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco), shoot cuttings were collected in October from saplings (9-year-old trees) of open-pollinated families in two progeny tests in each of two breeding zones in Washington, one in the Coast range (80 families) and one on the west slope of the Cascade Mountains (89 families). Samples from over 5500 trees were subjected to artificial freezing and visually evaluated for needle, stem and bud tissue injury. The extent to which cold injury is genetically related to tree height and shoot phenology (timing of bud burst and bud set) was also evaluated.

Significant family variation was found for all cold hardiness traits; however, individual heritability estimates were relatively low (ranging from 0.09 to 0.22). Significant family-by-test site interaction was detected for needle injury in the Cascade breeding zone, but not in the coastal zone. Genetic correlations (r_A) among needle, stem and bud tissues for cold damage were weak (0.16 ≤ r_A ≤ 0.58) indicating that genes controlling fall hardening are somewhat different for different tissues. Timing of bud burst and bud set were only weakly correlated with cold injury (r_A ≤ 0.49). Thus, bud phenology is a poor predictor of fall cold hardiness in this species. There was no consistent relationship between tree height and cold injury in the coastal zone. In the Cascade zone, taller trees appeared to be more susceptible to cold injury, but the association was weak (mean r_A = 0.38, range 0.20 – 0.72).     

Effect of spacing on growth and quality parameters in sessile oak (Quercus petraea) stands in central Poland: results 7 years after planting

We examined the growth and quality of young oaks in stands established at three different spacings. The three densities were the traditional level, that is, 8000?seedlings?ha^?1 (1.5?×?0.85?m) plus two where the initial density was decreased by 50% and 70%, achieved by increasing the distance between the rows from 1.5 to 3 or 4.5?m. The experiment was located in central Poland on a moderately fertile site. In the two wider spacings, the intention was to use natural regeneration occurring between oak rows as a replacement of intraspecific competition for oaks. The mean height was only affected in the third and the fourth year after establishment. Subsequently, the differences between spacings with respect to both growth and quality traits were insignificant and small. At lower densities, natural regeneration of willow and aspen was abundant and inter-species competition replaced intra-species competition, thus explaining the absence of a spacing effect on growth and quality properties. In the study period, the wider spacings were economically beneficial compared to traditional densities. A strong competition affecting height growth caused by natural regeneration necessitated extensive tendings. More tendings are likely to be needed in the future and they might reduce the initial economical superiority of wider spacing. The study indicates that it is possible to decrease the initial spacing in oak plantations and simultaneously support good growing conditions by means of natural processes, for example, natural regeneration. However, economic efficiency of the method has to be studied in a longer perspective.     

Carbon accumulation along a stand development sequence of Nothofagus antarctica forests across a gradient in site quality in Southern Patagonia

Above- and below-ground C pools were measured in pure even-aged stands of Nothofagusantarctica (Forster f.) Oersted at different ages (5–220 years), crown and site classes in the Patagonian region. Mean tissue C concentration varied from 46.3% in medium sized roots of dominant trees to 56.1% in rotten wood for trees grown in low quality sites. Total C concentration was in the order of: heartwood > rotten wood > sapwood > bark > small branches > coarse roots > leaves > medium roots > fine roots. Sigmoid functions were fitted for total C accumulation and C root/shoot ratio of individual trees against age. Total C accumulated by mature dominant trees was six times greater than suppressed trees in the same stands, and total C accumulated by mature dominant trees grown on the best site quality was doubled that of those on the lowest site quality. Crown classes and site quality also affected the moment of maximum C accumulation, e.g. dominant trees growing on the worse site quality sequestered 0.73 kg C tree⁻¹ year⁻¹ at 139 years compared to the best site where 1.44 kg C tree⁻¹ year⁻¹ at 116 years was sequestered. C root/shoot ratio decreased over time from a maximum value of 1.3–2.2 at 5 years to a steady-state asymptote of 0.3–0.7 beyond 60 years of age depending on site quality. Thus, root C accumulation was greater during the regeneration phase and for trees growing on the poorest sites. The equations developed for individual trees have been used to estimate stand C accumulation from forest inventory data. Total stand C content ranged from 128.0 to 350.9 Mg C ha⁻¹, where the soil C pool represented 52–73% of total ecosystem C depending on age and site quality. Proposed equations can be used for practical purposes such as estimating the impact of silvicultural practices (e.g. thinning or silvopastoral systems) on forest C storage or evaluating the development of both above- and below-ground C over the forest life cycle for different site qualities for accurate quantification of C pools at regional scale.     

无性系和株行距对杨树人工林生长和树冠结构的影响

【目的】探索无性系、株行距及两者交互作用对杨树人工林的林木生长和树冠结构的影响。【方法】采用双因素随机试验设计,通过调查36块13年生杨树样地胸径、树高、活枝下高和冠幅等指标,以综合指数法构建3个林分综合指数(生长指数、冠形指数、干冠协调指数)。【结果】南林95杨和南林895杨的胸径、树高和生长指数显著高于南林797杨(P <0.05)。南林797杨的冠幅、树冠体积和树冠圆满度显著高于南林895杨,与南林95杨差异不显著(P> 0.05)。株行距为6 m×6 m和4.5 m×8 m的林分胸径、冠形指数和生长指数均显著高于5 m×5 m和3 m×8 m林分,不同密度林分对树高影响不显著(P> 0.05)。在相同密度条件下,正方形和长方形配置对东西和南北冠幅有显著影响,较大株行距促进树冠生长,但对胸径、树高和平均冠幅等影响不显著(P> 0.05)。无性系和株行距对冠长、活冠比、树冠表面积和干冠协调指数影响均不显著,且无性系和株行距对林木生长和树冠结构均无显著交互作用(P> 0.05)。【结论】杨树无性系对林木胸径、树高和树冠结构的影响大于株行距。综合考虑林木生长和树冠结构等两个方面,在类似的立地条件上,相比于其它无性系和配置方式,以南林95杨在种植株行距为6 m×6 m(278株/hm^2)时具有培育大胸径林木的潜力,适于培育速生、优质大径材。     

Density-dependent effects of northern hardwood competition on selected environmental resources and young white spruce (Picea glauca) plantation growth, mineral nutrition, and stand structural development – a 5-year study

The effects of competition from red raspberry (Rubus idaeus L.) and northern hardwood tree species on white spruce (Picea glauca (Moench) Voss) seedlings were examined on a clearcut site of the boreal mixedwood forest of the Bas-Saint-Laurent region of Quebec, Canada. A controlled experiment involving a gradient of five vegetation densities on the basis of the leaf area index (LAI) was established in a completely randomized plot design with six replications. Each of the five levels of vegetation cover (including vegetation-free plots) were examined to evaluate how they affected environmental factors (quantity and quality of light reaching the spruce seedlings, and soil temperature), spruce growth (height, basal diameter, volume index, and above-ground biomass), spruce mortality, browsing damage, spruce foliar mineral nutrition, as well as the stand structural development, during the first 5 years after seedling planting.

Each spruce growth variable analyzed in this study, according to a RMANOVA procedure, followed a negative hyperbolic form of density dependence of competitive effects. Loss of growth in young white spruce plantations in competition with northern hardwoods is likely to occur with the first few competitors. In cases where higher levels of competing vegetation were maintained over time, loss of spruce growth was extremely severe, to an extent where the exponential growth character of the young trees has been lost. At the end of the fifth year, spruce growing with no interference were larger in mean total above-ground biomass by a factor of 9.7 than those growing with the highest level of vegetation cover. Spruce did not develop a strategy of shade avoidance by increasing tree height, on the contrary. Spruce mortality differed among treatments only in the fifth year, indicating that early evaluation of spruce survival is not a strong indicator of competitive effects, when compared to diameter growth. Spruce foliar N and Ca contents were significantly reduced by the first level of competing vegetation cover, while K increased with the density of the vegetation cover, and P and Mg were not affected. Nitrogen nutrition of young white spruce planted on recently disturbed sites is discussed in relation to the potential root discrimination of this species against soil nitrate, a reaction observed by Kronzucker et al. [Kronzucker, H.J., Siddiqi, M.Y., Glass, A.D.M., 1997. Conifer root discrimination against soil nitrate and the ecology of forest succession. Nature London 385, 59–61]. The effects of hardwood competition indicate a prevalence of competition for light over a competition for nutrients, as revealed by the substantial increase in the h/d ratio of white spruce. Two indicators, h/d ratio and the quantity of light received at the tree seedling level, are suggested as a basis for the management of hardwood competition in a white spruce plantation.

Analysis of the stand structural development indicates that spruce height distribution was affected only by moderate or dense cover of vegetation, while diameter distribution, when compared to competing vegetation-free plots, was affected by the lowest level of vegetation cover. This study shows that competition influenced the stand structural development in the same way as genetic and micro-site factors by aggravating the amplitude of size inequality. The impact of hardwood competition is discussed in view of reaching an equilibrium between optimal spruce plantation growth and benefits from further silvicultural treatments, and maintaining hardwood species known to improve long term site quality, within a white spruce plantation.     

Estimation of the self-thinning boundary line within even-aged Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) stands: Onset of self-thinning

The trajectory of self-thinning was studied using data from Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) stands measured 17 times over 26 years to elucidate the relationship between the maximum average stem volume (dm³) and the stand density (stems/ha). The study examined five initial density levels (2 m × 3 m, 2 m × 1.5 m, 2 m × 1 m, 1 m × 1.5 m, and 1 m × 1 m) with three replications at each level, but only 10 plots were used in the final analysis. Subsets of the data were constructed using 0-67%, 2-67%, 5-67%, 10-67%, 15-67%, 20-67%, 23-67%, 25-67% and 30-67% mortality rate classes. Ordinary least squares and reduced major axis (RMA) regression techniques were employed to obtain self-thinning parameters for each mortality rate class subset. The RMA method combined with jackknife estimation (RMA + jackknife) was the most appropriate regression method based on standard error estimations. The self-thinning exponent with a mortality rate class of 2-67% adequately represented the maximum volume-density relationship. The self-thinning exponents changed systematically with the mortality rate classes, and −1.5 was a transitory value in the course of self-thinning. It is also concluded that self-thinning in closed Chinese fir stands may occur when the ratio of the live crown length to tree height approaches 0.3.     

Influence of mulching and tree shelters on 4-year survival and growth of zeen oak (Quercus canariensis) seedlings

We assessed the effect of mulching and tree shelters on the establishment and early growth of zeen oak(Quercus canariensis Willd.) during the first 4 years after planting in Northwestern Tunisia. Five mulch types(Italian Stone Pine(Pinus pinea L.), Lentisk(Pistacia lentiscus L.),and a combination of Italian Stone Pine and Lentisk(organic mulches), gravel(inorganic mulch) and control), and three tree shelter types(non-vented and vented tree shelters, and control) were tested. An increase in the number of internodes occurred under the gravel mulch, while a reduction in survival was found for the lentisk mulch. Tree shelters had no effect on survival, but increased mean height growth and reduced mean diameter growth during the 4 years(excepting a non-significant effect for vented tree shelter at year four). Comparison of the annual shoots and growth units(GU) between sheltered and unsheltered plants according to year of formation revealed two growth phases. In first phase, shoots were totally or partially inside the shelters; mean length of annual shoots and GU were greater for sheltered plants. The second phase was characterized by shoots emerging from shelters; mean length of annual shoots and GU were similar for all plants, with or without tree shelters. Results suggest that the use of tree shelters, particularly vented shelters, could contribute to the improvement of the artificial regeneration of zeen oak.The use of mulching alone or in combination with tree shelters did not improve zeen oak performance in the field.     

Effects of clonal selection on biomass production and quality in Robinia pseudoacacia var. monophylla Carr.

In this paper, the results of the effects of clonal selection on biomass production and quality in monophylla black locust (Robinia pseudoacacia var. monophylla Carr.) were studied. The genetic material included seedlings of open pollinated families, ramets of selected clones within them and seedlings of common black locust (Robinia pseudoacacia L.) as a control. Both seedlings and ramets were planted in the field in April 1994. At the end of the first and the subsequent growing seasons (1994–2002) all of them were cut at 20 cm aboveground. Measurements were done at the end of October–beginning of November and included height and oven-dry weight of saplings, stem number, leaf/stem ratio of oven-dry weight and length of the longest thorn. It was found that height and oven-dry weight were increased in the first three years but they declined thereafter both in clones and families. Overall, however, clones were superior to families. Stem number was increased with age more in families than in clones. Leaf/stem ratio of oven-dry weight declined with time but clones were superior to families. Thorn length, finally, increased over the years but clones had significantly lower values than families. The results showed that the most productive clones were also better in quality characteristics (leaf/stem ratio of oven-dry weight and thorn length) than most families and the control. It is concluded that clonal selection can result in significant increase of biomass quantity and improvement of its quality.     

Effects of light and intraspecific competition on growth and crown morphology of two size classes of understory balsam fir saplings

This paper characterizes the growth and crown morphology of young balsam fir saplings naturally regenerated under a gradient of understory light environments and intraspecific competition densities for two size classes (50–100 cm and 100–200 cm). Most growth and crown morphological parameters investigated were strongly related to the natural light gradient investigated (3–83% full sunlight), but the relationship tended to plateau at around 25% full sunlight. The relationships were generally better for the larger size class. Intraspecific competition did not significantly affect growth and crown morphology of saplings receiving less than 25% full sunlight, but it affected relative height growth, relative radial growth and the apical dominance ratio for those receiving more than 25% full sunlight (R²=0.506; p<0.001; R²=0.403; p<0.002; R²=0.348; p<0.001, respectively). These results suggest that live crown ratio, apical dominance ratio and the number of internodal branches can provide, alone or in combination, useful indicators of vigour for understory fir. Such a study provides the basic data inputs required for the development of empirically-derived mechanistic models that can predict understory tree growth and survival.     

Effects of wide spacing and thinning strategies on wood quality in Norway spruce (Picea abies) stands in southern Sweden

Abstract

The initial density of a stand influences both the prethinning growth and the quality of the harvested trees. This study investigated the effects of different square spacings (2.0, 2.5 and 3.0 m) with thinning from above and thinning from below on stand development and tree characteristics in a 33-year-old Norway spruce [Picea abies (L.) Karst.] plantation in southern Sweden. Before thinning the total standing volume was not significantly different between treatments. Diameter at breast height (dbh) and diameter of the thickest branch were positively correlated. Before thinning, dbh of the trees and their thickest branches were significantly higher in the stands with 3.0 m spacing. After thinning, the dbh and the diameter of the thickest branch did not significantly differ between the 3.0 m spacing with thinning from above and 2.0 and 2.5 m spacing with thinning from below. Spacing did not significantly influence the presence or size of spike knots. The results suggest that a combination of wide spacing with thinning from above may yield timber of similar quality to denser spacing with thinning from below.     

Effect of site preparation on survival and growth of Douglas-fir (Pseudotsuga menziessi Mirb. Franco.) seedlings

The performance (survival and growth) of Douglas-fir (Pseudotsuga menziesii Mirb. Franco.) seedlings planted in minimally disturbed, scalped, and bedded soils, both with and without herbicidal control of weeds, were compared. Douglas-fir growing for 3 years in bedded soils treated with herbicide were heavier, taller, and had deeper root systems than trees growing in other preparations. Scalping did not improve seedling performance when compared to minimally disturbed soils. Soils rich in organic matter benefited tree growth. Competing vegetation in raised beds was detrimental to seedling performance.     

水分胁迫对毛红椿幼苗生长和生物量分配的影响

以我国亚热带落叶阔叶优势树种毛红椿的1年生幼苗为试验材料,设置4个水分胁迫处理,模拟研究不同水分胁迫强度下毛红椿幼苗生长和生物量分配规律。结果表明:水分胁迫对毛红椿幼苗根系生长的限制作用明显大于对苗高生长的限制作用,对地径生长限制作用不明显;随着水分胁迫程度增加,根质量比表现出先增大后减小的趋势;叶质量比在处理初期和中期增大,在处理后期和末期降低;在整个处理阶段,茎质量比始终保持增加趋势;根系平均直径在处理中期和后期逐渐减小,处理末期则有所上升;细根/总根长比值则在处理中期和后期逐渐增大,处理末期则有所降低;不同水分胁迫程度导致根尖数量差异显著。在整个处理阶段,水分首先保证苗高和叶片生长,根系生长受到限制;随着水分胁迫程度增加,通过落叶和根系二次生长来保障根系的水分需求和提高水分吸收效率,以此来缓解水分胁迫对生存的胁迫。     

Changes in size of soil seed bank in Robinia pseudoacacia L. (Leguminosae), an exotic tall tree species in Japan: Impacts of stand growth and apicultural utilization

This study examined the factors that influence the size of a soil seed bank in Robinia pseudoacacia stands. We proposed two hypotheses: the amount of buried seeds of R. pseudoacacia is proportional to stand biomass rather than stand age, and apicultural utilization influences the size of the soil seed bank. R. pseudoacacia generally produces seeds with various degrees of physical dormancy. In addition, this tree is short-lived, and fecundity declines after 30–40 years in relation to tree vigor. However, R. pseudoacacia is intensively used in apiculture as an important honey source, and supply of honeybees by beekeepers could influence seed crops. We investigated 25 plantations in Hokkaido (Central, Hidaka, and Oshima) and in Nagano, Japan, where many naturally regenerated R. pseudoacacia stands occur. We found great variation in the size of the soil seed bank among stands, ranging from 13,757 to 6.4 seeds m⁻² per plot. A generalized linear mixed model revealed that both basal area (BA_Rp) and apicultural utilization best explained the size of the soil seed bank. Both the positive effect of BA_Rp and small contribution of stand age to the model implied that the soil seed bank is transitory, and will not persist for very long time. The large contribution of apicultural utilization to the size of the soil seed bank implied pollinator limitation under natural conditions. R. pseudoacacia often has large flower crops, and native pollinators can not keep up with the demand for pollination. Thus, the supply of honeybees by beekeepers should improve the pollination success of R. pseudoacacia. From these results, we conclude that we must consider stand history with respect to apicultural utilization if the land is harvested or a stand declines.     

Seed spacing and seedling biomass: Effect on root growth potential of loblolly pine (Pinus taeda)

Results from three studies conducted in bare-root nurseries indicate a positive linear relationship between seed spacing and root growth potential of Pinus taeda L. seedlings. However, root growth potential was also correlated with several morphological variables, including seedling weight, root collar diameter, root weight, root volume, foliage weight and stem weight. Because seedlings grown at wider spacings were larger in diameter and biomass, covariate analyses (using either root collar diameter or foliage ovendry weight) were also conducted. These analyses indicate that differences in root growth potential between seed spacings can be accounted for by differences in seedling size.     

Effects of the lateral growth rate on wood quality parameters of Eucalyptus grandis from different latitudes in Brazil and Argentina

Climate change resulting from increased atmospheric carbon dioxide (CO₂) and shortages of fossil fuels such as petroleum are major problems worldwide. Under these conditions, demand for woody biomass resources is increasing. We investigated the feasibility of using fast-growing Eucalyptus grandis for material production. Samples of E. grandis were collected from four plantations in different latitude divisions, including tropical and subtropical Brazil and subtropical Argentina. Various xylem qualities were measured and related to the lateral growth rate. Lateral growth rate did not significantly affect the longitudinal released strain of the surface growth stresses or the xylem density at any of the sampling sites. Higher lateral growth rate, higher values of xylem density, and lower absolute values of the released strain were observed in plantations closer to the equator. Higher growth rates in tropical climate promote longer fiber length. In subtropical plantations, smaller diameter trees will produce tension wood with smaller microfibril angles. Planting E. grandis closer to the equator thus produces higher quality wood than in plantations at lower latitudes.     

不同翻地深度和栽植密度对华北落叶松早期生长的影响

通过不同翻地深度和不同栽植密度的造林试验,对河北省查字龙头山种苗场的华北落叶松早期生长性状进行了研究。栽植5a后,调查结果表明:深翻15cm可促进华北落叶松树高与胸径生长,深翻15cm比深翻40cm和对照的树高生长量分别提高5cm、16cm,胸径生长量分别提高0.12cm、0.23cm;造林密度2.0m×2.0m的比密度1.5m×1.5m的树高生长量低4cm、胸径高0.07cm;华北落叶松在一年中的7、8月份生长量最大,深翻15cm和40cm树高生长量分别达到年生长量的46.60%和43.71%、胸径生长量分别达到年生长量的38.52%和40.65%,造林密度2.0m×2.0m和密度1.5m×1.5m的树高生长量分别达到年生长量的38.23%和40.43%、胸径生长量分别达到年生长量的44.93%和40.45%。因此,通过适宜深度翻耕与合理的栽植密度造林可提高华北落叶松早期生长量。