首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 15 毫秒
1.
The aim of this study was to establish the sources of variation in maritime pine wood properties related to appearance and strength, because of the importance of this wood in the sawing industry in Galicia (NW Spain). Ten trees from each of ten plots of the species (i.e., 100 trees) growing in Galicia were felled and sawn to produce the structural planks required for studying the presence of external strength-reducing characteristics. The planks were sampled from the basal logs to 16 m height in the stems, yielding cross sections of target dimensions 100 × 40 mm to 200 × 200 mm. We propose a model in which individual tree height and dominant height are used to predict the knottiness of planks from trees in mature stands. The abundance of externally visible knots on faces and edges of sawn planks is therefore more dependent on the stand location than on the prior silvicultural treatment of the stand.  相似文献   

2.
Gene dispersion within a population was studied in a 2‐hectare stand of 74 seed trees and 1100 seedlings. Isozyme markers were used to determine the genetic relationships among parental trees, embryos and seedling progenies. Paternity exclusion analyses were used to study multilocus progeny genotypes from certain parents. Results demonstrate large variation between trees in their capacity to contribute their genes through natural regeneration. The proportion of all genes dispersed into a specific distance interval from the source was estimated. The estimation procedure took into account the background of seedlings where parenthood was not excluded, but where the seedlings turned out to be unrelated. We found little evidence for clusters of progeny seedlings surrounding their parental tree. Within 15 m from a tree, approximately 5 % of the genes originated from that tree and 95 % originated from other trees. We found no evidence for an increase in levels of inbreeding, or genetic substructuring in the seedling progeny stand relative to the parental seed trees. A mathematical model for pollen distribution was developed. According to this model, 90% of pollen was distributed more than 15 m from the source. It is concluded that the marker seed trees had a surprisingly low detectable genetic contribution to the regeneration. It seems likely that a considerable part of the new seedlings have parents among felled trees or from surrounding stands.  相似文献   

3.

• Introduction  

The objective of this work was to study how spacing and genetic entry and/or origin group affect radial growth (ring width and cumulative diameter development) and ring density from pith to bark in Scots pine (Pinus sylvestris L.) and in what sense their annual variability could be explained by the climatic variables. The spacing trial was located in central Finland, with current stand density range of 2,000–4,000 trees per hectare. All the six genetic entries had Kanerva pine (plus tree S1101) as a father tree, whereas the mother tree represented Finnish plus trees from southern, central and northern Finland.  相似文献   

4.

Context

Modulus of elasticity (MOE) is an important mechanical property determining the end-use and value of loblolly pine (Pinus taeda L.) lumber.

Aim

In this study, a model was developed to predict the within tree variation of MOE, from pith-to-bark and stump-to-tip, using data collected from a 21-year-old unthinned stand where trees were planted under seven initial stand density levels (746?C2,243 trees/hectare).

Methods

The study was laid out in a randomized complete block design, with seven levels of initial planting density, replicated three times. Seven trees were destructively sampled from each plot, and bolts were cut from each tree at heights of 2.4, 7.3, and 12.2?m. Static bending samples (of dimension 2.5?×?2.5?×?40.6?cm) representing pith-to-bark variation were cut from each bolt and MOE measured. A three-parameter logistic function was used to model the pith-to-bark variation in stiffness with distance from pith as an explanatory variable.

Results

Based on the final fitted model, it was found that the asymptotic parameter (maximum outerwood MOE?=?13.48?GPa) was not influenced by sampling height, initial planting density, and stem slenderness. However, the inflection and scale parameters were significantly influenced by these variables.

Conclusions

In summary, we found that initial planting density had a significant influence on the amount of corewood produced with higher initial planting densities producing a lower proportion of corewood as indicated by a linear decrease in inflection point with an increase in planting density.  相似文献   

5.
The effects of stand density, thinning and pruning on the quality of sawn timber of Scots pine (Pinus sylvestris L.) were studied based on a computer model. Procedures for the tree growth and crown structure produce a tree, whose properties in terms of location, dimensions and quality (living, dead) of branches are known for any moment of the selected rotation. Consequently, the size, quality (living, dead) and location of knots in sawn timber are recognizable allowing the grading of sawn pieces. The model computations showed that the natural dynamics of the crown system in narrowly‐spaced stands could yield sawn timber nearly of the same quality as resulted from pruning in widely‐spaced stands. Thinning increased the branch growth and the branchiness of the wood yielding lower grade for sawn pieces, respectively.  相似文献   

6.
Abstract

This study focused on the amount of sapwood and its variation by means of computed tomographic (CT) imaging. Twenty-four trees were selected from four Norway spruce [Picea abies (L.) Karst.] stands in north-eastern France, varying in age, density and fertility. In each stand, sampled trees represented the dominant, co-dominant and suppressed strata. The heartwood/sapwood boundary was detected from the CT images, and the heartwood and sapwood amount and their variations were then evaluated. At the within-tree level sapwood width was relatively constant along the tree stem above the butt swelling and below the living crown. The between-tree sapwood width variations were partially explained by the total cross-sectional area of living branches. This result opens up the possibility of investigating within-tree allometric relationships. Sapwood width was found to be highly correlated with tree slendemess (tree height/breast height diameter) and with the relative height of the crown. This suggests that sapwood width could be readily predicted from conventional forest inventory measurements. The number of sapwood rings within the stem was largely dependent on cambial age, and could be determined dynamically using the concept of mean lifetime of sapwood rings.  相似文献   

7.
SIMPSON  H. L.; DENNE  M. P. 《Forestry》1997,70(1):31-45
The aim of this work was to quantify patterns of change in ringwidth and specific gravity within trees of Picea sitchensiswith ring number across juvenile and mature wood, in relationto height in tree, original spacing, and crown dimensions. Fivetrees were sampled from each of three plots on a 52-year-oldunthinned spacing trial at Clocaenog, North Wales. The ring width of wood produced in early decades of the plantationwas most strongly correlated with original spacing, while thatproduced in later decades was more strongly correlated withbranch diameters of the upper crown. In later decades, treesoriginally at the widest spacing had higher specific gravitythan those originally at closer spacing, presumably associatedwith self-thinning of the narrower-spaced unthinned plots. Differencesin amount of juvenile wood between spacing plots were less markedthan those reported from the same plots when harvested 7 yearsearlier; it is suggested that as trees surviving after self-thinningare likely to be those with a competitive advantage from anearly stage, differences between plots in amounts of juvenilewood may become less apparent in trees harvested later in therotation than in those sampled earlier. Underlying patterns of variation in ring width and specificgravity across the tree were found to be modified by a progressivedrift with height in the tree. Linear regressions between specificgravity and ring width also varied in a systematic way; theintercept and slope of these regressions tended to increasewith ring number from the pith, and with height in tree at aspecified ring number. Equations are given as a basis for quantifyingthese trends, but more data are needed from other sites to determinethe extent to which these equations represent trends inherentto cambial and apical ageing, as distinct from influence ofchanging environment around the trees.  相似文献   

8.
Mountain pine beetle, Dendroctonus ponderosae Hopkins can cause extensive tree mortality in ponderosa pine, Pinus ponderosa Dougl. ex Laws., forests in the Black Hills of South Dakota and Wyoming. Most studies that have examined stand susceptibility to mountain pine beetle have been conducted in even-aged stands. Land managers increasingly practice uneven-aged management. We established 84 clusters of four plots, one where bark beetle-caused mortality was present and three uninfested plots. For all plot trees we recorded species, tree diameter, and crown position and for ponderosa pine whether they were killed or infested by mountain pine beetle. Elevation, slope, and aspect were also recorded. We used classification trees to model the likelihood of bark beetle attack based on plot and site variables. The probability of individual tree attack within the infested plots was estimated using logistic regression. Basal area of ponderosa pine in trees ≥25.4 cm in diameter at breast height (dbh) and ponderosa pine stand density index were correlated with mountain pine beetle attack. Regression trees and linear regression indicated that the amount of observed tree mortality was associated with initial ponderosa pine basal area and ponderosa pine stand density index. Infested stands had higher total and ponderosa pine basal area, total and ponderosa pine stand density index, and ponderosa pine basal area in trees ≥25.4 cm dbh. The probability of individual tree attack within infested plots was positively correlated with tree diameter with ponderosa pine stand density index modifying the relationship. A tree of a given size was more likely to be attacked in a denser stand. We conclude that stands with higher ponderosa pine basal area in trees >25.4 cm and ponderosa pine stand density index are correlated with an increased likelihood of mountain pine beetle bark beetle attack. Information form this study will help forest managers in the identification of uneven-aged stands with a higher likelihood of bark beetle attack and expected levels of tree mortality.  相似文献   

9.
This study focuses on two rarely studied aspects of oak decline: relations with site characteristics and effects on tree growth. The study was carried out in a 5.5 ha stand in Hungary which is strongly affected by oak decline. The nearly pure sessile oak (Quercus petraea) stand of mostly coppice origin was 90 years old at the beginning of the study. Within-stand site heterogeneity was described by the herbaceous vegetation. Four ecological site types were distinguished by the species composition of herbs, and characterized by the ecological indicator values of the species. Tree growth between 1987 and 1993 was measured, and tree vigour was estimated from visual characteristics five times between 1987 and 1993. Potential volume increment of declining trees was estimated with the growth rates of healthy trees of the same size. Volume increment loss caused by oak decline was also assessed. Significant positive relationships were found between tree vigour and tree size and between tree vigour and tree growth. The growth of seriously declining trees dropped to almost one-half of that of healthy ones. Growth reduction of living trees at the stand level amounted to 5.4%, whereas growth reduction of all trees, including those that died during the observation period, amounted to 19.9% of the potential growth. Tree size and growth were greater on better sites. A strong relationship was also found between tree vigour and site type, but sessile oak was more susceptible to decline at better sites.  相似文献   

10.
The development of tree allometric equations is crucial to accurate forest carbon assessment. However, very few allometric equations exist for sub-Saharan Africa and as a result generalized allometric equations, often established for forests in other continents, are used by default. The objectives of this study were (1) to propose a sampling methodology and calculation procedures to assess biomass for tropical tree species of contrasted tree shapes in Africa, (2) to identify factors affecting within and between trees wood density, (3) to propose an allometric model that integrates these factors and (4) to evaluate the reliability of using generalized allometric equations in this type of forests. Models were developed to predict wood density and phytomass of the trees based on the harvesting of 42 trees from 16 species, representing three guild status in the wet evergreen forest of Boi Tano in Ghana. Results indicated that the wood density was highly influenced by the tree species, guild status, size of the tree and pith to bark distance. Dry mass of a tree was influenced by diameter at breast height, crown diameter and wood density. The wood density depends on the position of the wood within the tree and the guild status considered. The use of generalized allometric models in literature is limited by the specific climate zone, the consideration of tree height and species specific wood density. In considering those factors, using generalized allometric equations could result in an error of 3%. Further research should better consider the bigger trees and the influence of the topography and ecosystem history.  相似文献   

11.
马尾松人工林管胞长度的株间和株内变异   总被引：1，自引：1，他引：1       下载免费PDF全文
林木株间变异和株内变异是木材的两个主要变异来源,由于木材性状具有较强的遗传性以及育林措施对木材的可塑性,人们可以培育出材质优异的木材,然而因变异的存在,在如何充分利用木材时却遇到了许多困难。林学家的一个主要目的就是在充分掌握木材变异规律的基础上,采用有效方法提高材质的均匀性。  相似文献   

12.
Growth behaviour of the relatively shade-intolerant species Eucalyptus dunnii and the rather more shade-tolerant Corymbia citriodora was considered during several growth periods over 8–14 years of age in experimental plantation monoculture in subtropical New South Wales. Larger trees dominated growth in any stand; this was consistent with the principle that inter-tree competition in such forests is for light and is asymmetric in that larger trees shade smaller trees but the reverse does not occur. Once competition was established, competition-induced mortality of C. citriodora was less than that of E. dunnii. A model relating tree diameter growth rate to tree diameter, competitive position in the stand and stand basal area was developed. The model showed that smaller, hence partially shaded, trees in stands of C. citriodora were better able to maintain their growth rates than equivalent trees in stands of E. dunnii. It is hypothesised that this reflects the greater shade tolerance of C. citriodora. This pattern of growth led to a more even distribution of tree size classes across the stand in the more shade-tolerant species.  相似文献   

13.
Rockfall is a major threat to settlements and transportation routes in many places. Consequently, the protective function of mountain forests has recently gained particular interest. However, much is still unknown about the ideal properties of protective forest stands. Therefore the present paper discusses a method for the inventory and analysis of tree injuries in a rockfall-damaged forest stand. With this method, the interrelation between stand geometry and rockfall injuries in a subalpine Polygalo chamaebuxi-Piceetum was examined. The study site of 0.3 Ha is located in the transit zone of frequently passing, small rockfall fragments (~10 cm in diameter) causing healable tree injuries. Tree and injury parameters were recorded and analysed as to injury number, height and size. The spatial distribution of the 157 trees (diameter at breast height dbh>5 cm) in the stand as well as of the 1,704 identified rockfall injuries showed a very uneven pattern. As expected, number, height and size of the injuries generally declined with increasing distance from the cliff as well as due to higher stem densities. In contrast, results indicated that the dbh of trees has no significant influence on the number of injuries per tree. However, this study showed a clear interrelation between tree and injury distribution: in general, large trees close to the cliff and smaller trees with a high density further down the slope seem to be favourable for good protection. At least an uneven-aged, multilayered stand should be sustained. Overall, the combined analysis of stand geometry and injury parameters provides information on the spatial distribution of rockfall and on the influence of tree arrangements.  相似文献   

14.
This study considered the effects of thinning on the development of compression wood in stems of 35-year-old stand of Corsican pine (Pinus nigra L.). Part of the stand had been thinned at 5-yearly intervals and part left unthinned. Twenty trees each from the thinned and unthinned stands were randomly selected and felled. Measurements were made on tree height, stem diameter, stem slenderness and canopy depth. Wood samples were removed from the central part of the main log and cross-sectional measurements made on ring width, basic density and compression wood content. Cross-sectional area of compression wood was found to be three time higher in stems from the unthinned trees in comparison with those from the thinned trees. No significant differences in mean radial ring width or basic density were found between treatments. Correlations indicated that, with increasing in stem diameter, compression wood content increased in the unthinned trees, while a decline in compression was observed in the thinned trees. Tree height was also positively correlated with compression wood content in unthinned trees, while no equivalent relationship was observed in thinned trees. Observations from this study, while not conclusive, suggest that phototropic stimulus may be producing stem inclinations in the unthinned stand as trees compete for space in the canopy, whereas crown competition has been largely eliminated in the thinned stand; and that this is responsible for compression wood levels recorded in this study.  相似文献   

15.
The occurrence of Heterobasidion annosum in stumps and growing trees was investigated on 15 forest sites in southern Finland where the previous tree stand had been Norway spruce (Picea abies) infected by H. annosum, and the present stand was either Scots pine (Pinus sylvestris), lodgepole pine (Pinus contorta), Siberian larch (Larix siberica), silver birch (Betula pendula) or Norway spruce 8–53 years old. Out of 712 spruce stumps investigated of the previous tree stand, 26.3% were infected by the S group and 0.3% by the P group of H. annosum. The fungus was alive and the fruit bodies were active even in stumps cut 46 years ago. In the subsequent stand, the proportion of trees with root rot increased in spruce stands and decreased in stands of other tree species. On average, one S type genet spreading from an old spruce stump had infected 3.0 trees in the following spruce stand, 0.5 trees in lodgepole pine, 0.3 trees in Siberian larch, 0.05 trees in Scots pine and 0.03 trees in silver birch stand. Although silver birch generally was highly resistant to the S type of H. annosum, infected trees were found on one site that was planted with birch of a very northern provenance.  相似文献   

16.
To elucidate the development of heartwood,bark,sapwood,pith and specific gravity of wood in fastgrowing teak(Tectona grandis)plantations in Costa Rica,we sampled three trees in each of 55 plantations and modelled each variable with age,site and different tree heights.Age and stand density of plantations were significant correlated with stem diameter at breast height and total height of the tree.Formation of heartwood was initiated at the age of 4-year-old and increased in direct proportion with age.The age of plantation had a significant relationship with stem diameter at breast height,heartwood percentage,sapwood thickness,sapwood percentage,percentage of bark,pith diameter and percentage,and specify gravity.The model for these tree parameters was model with these parameters as dependent variable and in relation to age as independent variable.  相似文献   

17.
《Southern Forests》2013,75(4):311-318
Average wood density of 38-year-old Cariniana legalis (Mart.) Kuntze, a Brazilian native forest species, was found to increase with faster growth and lower stocking, while decreasing from pith to bark. A complete randomised block design was planted with five blocks. Ten trees were harvested in each of three spacing treatments. We hypothesised that the stand stemwood production would not significantly differ depending on tree spacing. However, tree growth would be higher in the wider spacing and wood density would be higher in the narrower spacing. The diameter growth of trees was higher at 3 m × 2.5 m than at 3 m × 2 m and 3 m × 1.5 m. Nevertheless, this higher individual tree growth at 3 m × 2.5 m did not compensate for the greater tree stock density at 3 m × 1.5 m with stand stemwood production at 38 years of 530 m3 ha?1 and 649 m3 ha?1, respectively. These results suggest that C. legalis, which can produce up to 17 m3 ha?1 y?1 of medium-to high-density timber – about 800 kg m?3 – is a promising native species for forest plantations in Brazil.  相似文献   

18.
Abstract

Untreated Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) samples were exposed above ground in a durability test for 6 years. The samples consisted of three pieces of wood, 22×95×500 mm, screwed together; two pieces lengthwise with a third piece overlapping. Weight was measured, to calculate moisture content (MC), and samples checked regularly for cracks and fungal growth. Parameters investigated were heartwood/sapwood (pine), annual ring orientation (spruce), stand site, annual ring width and density. Stand site, annual ring width and density had no influence on MC or fungal growth for either pine or spruce. Spruce samples with vertical annual rings had fewer cracks than samples with horizontal annual rings. Pine sapwood samples had a high MC and a large amount of rot fungi, while heartwood had a lower MC and no rot. Most spruce samples were similar to pine heartwood, except from a few samples that had high MC and fungal growth. Those were all sawn from the outer part of the log. Therefore, it can be stated that spruce sawn from the inner part has almost the same properties as pine heartwood, while spruce from the outer part of the log has similar properties to pine sapwood.  相似文献   

19.
以内蒙古根河林业局潮查林场境内的在20世纪80年代初主伐利用后形成的兴安落叶松过伐林为研究对象,利用兴安落叶松林8块标准地每木定位数据,分析林木分布格局和样方(5 m×5 m)林木株数对枯立木株数影响,探讨了林分大树和更新幼树位置与枯立木位置的关系,阐明了枯立木分布格局形成机制。结果表明:1)各树种枯立木比例,随树种组成成数增加而增大。枯立木主要在更新幼树阶段形成,径级分布集中在4径阶以下,其株数占总数的比例平均达82.2%。在更新幼树(含枯立木)中,生成枯立木的比例平均达8.8%。2)枯立木分布格局为聚集分布。林木分布格局、样方林木株数和更新株数与枯立木株数有显著正相关关系,林木分布格局对枯立木分布格局无显著影响。林木聚集度越大,形成枯立木的可能性越大,数量也就越多。3)枯立木位置与更新幼树和大树位置有显著相关关系。主要表现为落叶松和白桦相互关系。枯立木出现位置主要在大树和更新幼树集聚区域。大树对枯立木形成影响较更新幼树大,而且均以落叶松较白桦明显。白桦更新幼树对落叶松枯立木的形成,无显著影响。受影响的枯立木主要是枯立木株数中所占比例和树种组成成数较高的树种。影响枯立木位置的林木主要取决于其样方内位置和林木株数。  相似文献   

20.

Tree resistance to the pathogenic blue-stain fungus Ceratocystis polonica was studied in a monoclonal stand of Norway spruce [ Picea abies (L.) Karst.] in relation to tree social status and diameter at breast height (DBH). The DBH distribution of the 33-yr-old stand ranged from 5 to 35 cm. There were clear differences in tree height between the suppressed (DBH 7.4-10.3 cm), codominant (DBH 11.8-17.4 cm) and dominant (DBH 18.6-23.9 cm) tree classes. The resistance was tested by mass inoculating trees with a low (400 inoculations m -2 , 60 cm inoculation belt) or high (400 inoculations m -2 , 120 cm inoculation belt) dosage. The small, suppressed trees were more susceptible to inoculation than the codominant and dominant trees, based on the amount of blue-stained and occluded sapwood, lesion length and dead cambium/phloem. A threshold in tree social status or tree size may be important in the overall resistance to fungal infection.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号