共查询到20条相似文献,搜索用时 31 毫秒
1.
Correlations between canopy gaps and species diversity in broad-leaved and Korean pine mixed forests
Regeneration of tree species associated with canopy gaps in broad-leaved Korean pine forests was investigated. Species diversity
in gaps and under closed canopy was compared, the relationship between biodiversity and gap structure was analyzed. Results
indicate that there were significant differences between tree species diversity in gaps and that under canopy (p<0.01). In terms of Shannon-Wiener index, evenness index, and abundance index, the biodiversity in gap community were higher
than those under forest canopy in regeneration layer. In terms of Simpson’s dominance index, the dominance of certain species
in the regeneration layer increased from gaps to closed canopy (p<0.01). In contrast, trends of biodiversity changes of succession layer in gaps and under closed canopy were opposite. Tree
species diversity of different layers reacted directly to the change of gap size class. For example, Shannon-Wiener index
and abundance index is higher and Simpson’s dominance index is the lowest in succession layer of medium-size gap (100–250
m2) in the broad-leaved Korean pine forest of Changbai Mountains. Shannon-Wiener index reached the highest in a size of ≥250
m2 and <100 m2, reached the lowest in a size of 200–250 m2 in the regeneration layer. Simpson’s dominance index reached its maximum when the gap size was between 200 and 250 m2. Generally, species of different layers reacted differently to the changes of gap size classes. The gap size class with more
seedlings did not correspond to size class containing more medium-size trees. Tree species diversity indices in the two layers
behaved reciprocally during the development process of forest gaps.
__________
Translated from Chinese Journal of Applied Ecology, 2005, 16(12): 2,236–2,240 [译自: 应用生态学报, 2005, 16(12): 2,236–2,240] 相似文献
2.
The oak (Quercus robur L.) regeneration intensity was assessed in the core area of the Białowieża National Park (BNP) in Poland with respect to
the selected ecological factors. The emphasis was placed on the response of oak regeneration to disturbances, including the
large-scale dieback of spruce stands. Defining their effect could help predicting the role of oak in naturally developing
lowland forest ecosystems in the European hemiboreal zone. The results of the study challenge the opinion that the ‘lime-oak-hornbeam
forest’ is a ‘climax’ community, confirming a very poor regeneration represented by only two saplings taller than 0.5 m per
hectare. By contrast, in spruce-dominated communities, from 49 to 848 taller saplings per hectare were found. The occurrence
of saplings was associated with discontinuous canopy of late seral stage of stands, as well as with large gaps. Most of the
best quality grown-up oak saplings developed in the immediate neighbourhood of spruce logs. The results of the research indicate
that ‘lime-oak-hornbeam forest’ (Tilio-Carpinetum) should be rather perceived as a transient community, evolved from relict, culturally modified, oak woodlands. Because spruce
had become a dominating species only after abandoning in mid-1800s the historical regime of anthropogenic disturbances (involving
frequent forest fires), the observed phenomena related to the disintegration of spruce stands had probably no precedent over
the last 500 years. To confirm whether the massive decline of spruce stands will finally result in the successful establishment
of the new canopy oak generation, both in Białowieża and other forests of hemiboreal zone, further research is needed. 相似文献
3.
Zhongling Guo Qingkang Li Jinping Zheng Wande Liu Chunnan Fan Yuandan Ma Guirui Yu Shijie Han 《Frontiers of Forestry in China》2007,2(1):47-54
From 2001 to 2003, the litter decomposition dynamics of dominant tree species were conducted using a litterbag burying method
in the broadleaf-Korean pine forest, spruce-fir forest and Ermans birch forest, which represents three altitudinal belts in
Changbai Mountain, northeast China. The spatial and temporal dynamics of litter decomposition and the effects of litter properties
were examined. Furthermore, the decomposition trend of different species was simulated by the Olson model, and results showed
that annual mass loss rates increased over time, but was not significantly correlated. Leaf decomposition rates increased
after decomposing for 638 days (1.75 years), and the order of dry weight remaining rates of leaf litter for different species
is: Asian white birch (Betula platyphylla) (24.56%) < Amur linden (Tilia amurensis) (24.81%) < Korean pine (Pinus koraiensis) (38.48%) < spruce (Picea jezoensis var. microsperma) (41.15%) < Ermans birch (Betula ermanii) (41.53%) < fir (Abies nephrolepis) (42.62%). The dry weight remaining rates of twig litter was smaller than that of leaf litter, and followed the order of
Amur linden (44.98%) < fir (64.62%) < Korean pine (72.07%) < spruce (73.51%) < Asian white birch (77.37%) < Ermans birch (80.35%).
The simulation results by the Olson model showed that, in leaf, the 95%-decomposition rates ranged from 4.5 to 8.0 years,
and annual decomposition rate (k) followed the order of Amur linden (0.686) > Asian white birch (0.624) > Korean pine (0.441) > spruce (0.406) > fir (0.397)
> Ermans birch (0.385); in twig, it ranged from 7.8 to 29.3 years, and k follows the order: Amur linden (0.391) > fir (0.204) > Korean pine (0.176) > spruce (0.157) > Asian white birch (0.148) >
Ermans birch (0.102). In general, the differences of decomposition rate are evident between leaf and twig litter and among
species, and were higher in broad-leaved species compared with coniferous species at the same elevation, and decreased with
the ascending of elevation.
__________
Translated from Acta Ecologica Sinica, 2006, 26(4): 1,037–1,046 [译自: 生态学报] 相似文献
4.
Natural regeneration measurements are the main silvicultural objective in overaged protective forests of the Bavarian Limestone
Alps. While manifold problems with these stands, especially the impact of browsing, are widely recognised, the regeneration
niches of Norway spruce (Picea abies [L.] Karst.) are insufficiently known. The purpose of this study was to determine favourable combinations of site factors
for the development of spruce in small, unfenced canopy gaps, located on Aposerido-Fagetum caricetosum albae forest sites. We recorded the occurrence of spruce saplings (as dependent variable) and of six site factors (as independent
variables) on 480 0.5 m2-subplots. In addition, we estimated the coverage of six acid adapted plant species to determine correlations with the humus
depth. A binary logistic regression analysis was used to predict the probability of the occurrence of a spruce sapling in
dependency of the different site factors. Supported by other studies, we assumed that the supply of solar radiation was adequate
for the sufficient regeneration of spruce within the canopy gaps. Other site factors significantly determined the regeneration
niches of spruce saplings. More spruce saplings were found near hindrances and on rough surfaces than would be expected from
a random occurrence of saplings. These microsite types may have characteristics, especially protection against snow gliding
that promotes spruce establishment. A calculated “hindrance index”, which accounted for the number, and the distance of surrounding
hindrances might be a good specific value to describe the influence of hindrances on steep slopes. The sapling establishment
decreased on thin humus layers. Our assumption for the sites was that thick organic layers might represent a good seedbed
for spruce. Decayed dead wood was scarce, but was exceedingly favoured by spruce saplings. Results obtained suggest that the
natural regeneration establishment of spruce on steep slopes can be successfully influenced by site factors which inhibit
the influence of snow gliding. According to a “positive microsite” concept, we recommend for artificial regeneration measurements
with spruce, microsites close to hindrances (e.g. stumps, downed trees) and Vaccinium myrtillus as a predictor for thick, acid humus layers. 相似文献
5.
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
6.
通过对不同结构青海云杉林天然更新情况的调查分析,结果表明:不同生境条件下青海云杉林的树种组成、林分结构、生长状况和更新状况都有较大的差别;青海云杉的径级和高度决定着青海云杉林内不同树木个体间的竞争和分异状况,决定着不同高度级内的株数分布比例;青海云杉纯林中林分结构单一,更新良好;青海云杉+白桦混交林林分结构复杂,更新不良;青海云杉纯林下,拥有丰富的云杉种源,云杉种子饱满,保存云杉幼树数量多且生长状况好,能维持云杉种群的更新连续性和相对稳定性;林冠郁闭度为0.4时,更新情况最好;当郁闭度为0.7时,更新情况差。 相似文献
7.
Kewu Cheng Runguo Zang Xiaofang Zhou Weiyin Zhang Zhiqiang Bai 《Frontiers of Forestry in China》2007,2(1):66-71
The riparian forests along the Ergis River, west China, composed mainly of Salicaceae species, play an important role in eco-environment
protection and sustainable development of local agriculture, stockbreeding, and social economy of the northern desert region
of Xinjiang Uygur Autonomous Region. The study of the influence of floods on the natural riparian forests is imperative for
the understanding of the successional process and the acceleration of conservation and restoration of forests. By investigating
the relationship between floods and dispersal of seeds, sprouting, natural regeneration, the structure of the forests, and
their current distribution, we conclude that: 1) the ripening and dispersal periods of Salicaceae species seeds overlap largely
with flood occurrence periods, and the sprouting and natural regeneration of seeds depend greatly on flood events; 2) floods
supply soil water and increase groundwater level of riparian land through flood irrigation and horizontal infiltration to
maintain the normal growth of the riparian forests; 3) floods have a decisive influence on the structure, composition, and
distribution pattern of riparian forests, and any disturbance in the water flow has a profound effect on these characteristics.
Given these facts, some management measures for conservation and restoration of the riparian forests are proposed, including
the establishment of riparian forest buffer belt, bank stabilization measures, and maintenance of flood protection.
__________
Translated from Journal of Beijing Forestry University, 2006, 28(2): 46–51 [译自: 北京林业大学学报] 相似文献
8.
《Scandinavian Journal of Forest Research》2012,27(1-4):364-369
In single‐tree selection, trees removed by harvest or lost through mortality are replaced by ingrowth from the seedling/sapling bank. Because the level of ingrowth is governed not only by the recruitment rate of new seedlings, but also by mortality and growth rates within the seedling/sapling stratum, knowledge of how these processes are related to the tree stratum is important for successful application of single‐tree selection. Therefore, Norway spruce (Picea abies (L.) Karst.) regeneration (0.1 m ≤ height ≤ 2.0 m) was measured on seventy 100 m2 circular subplots at each of two sites in central and northern Sweden. Both sites had previously been selectively logged, but the time elapsed since the last harvest was at least 30 yrs. Basal area of trees of at least 2 m height within three different radii from the subplot centres was measured. Measurements on regeneration included height and leader length. Influence of local stand basal area on density and growth of regeneration was analysed by ordinary least‐squares linear regression for each of four height intervals. Regeneration was significantly aggregated at both sites, but number of Norway spruce seedlings and saplings per circular subplot was not correlated to local stand basal area. Out of 36 regressions, only eight showed a significantly (p < 0.05) negative correlation between seedling and sapling height growth and local stand basal area. In five of these cases, removal of one point (subplot) made p > 0.05. The results suggest that density and growth of Norway spruce regeneration in selectively logged uneven‐aged Norway spruce stands is affected more by ground conditions than by local stand basal area. 相似文献
9.
《Scandinavian Journal of Forest Research》2012,27(1-4):215-225
A general model for comparing the profitability of natural regeneration in beech (Fagus sylvatica L.) with planting of Norway spruce (Picea abies L.) is developed. The model is basically a method of comparing a series of net present values. An example of using the model is given: BEECH (90–110) denotes a cyclic regime in which regeneration is initiated at age 90 of a stand, and the canopy trees are cleared at age 110. This regime is compared with the alternative of planting Norway spruce. Economic data used for the comparison are representative of the southeastern regions of Denmark. The conclusion of the comparison is as follows: BEECH (90–110) is superior to planting of Norway spruce for required real rates of return up to 3–4%. For higher required rates of return planting of Norway spruce is preferable. 相似文献
10.
Jiří Kamler Miloslav Homolka Miroslava Barančeková Jarmila Krojerová-Prokešová 《European Journal of Forest Research》2010,129(2):155-162
Browsing of overabundant free-living herbivores often limits the natural as well as artificial regeneration of forest in Central-European
Mountains. The aim of the study was to assess the efficiency of the extensive reductions of herbivore populations for protection
of forest regeneration in preferred areas. We analysed the relationship between the intensity of shoot browsing and relative
density of herbivores in viewpoint of natural regeneration of secondary mountain spruce stands with low proportion of broadleaved
trees in Králicky Sněžník Reserve (Czech Republic). The distribution of seasonally migrating herbivores was established by
counting faecal pellet groups (standing crop method) in growing season. The intensity of browsing of spruce, beech and rowan
was assessed using the proportion of browsed shoots on individual tree sapling. Density of red deer was re-counted from the
number of pellet groups and it was 15–56 individual/km2. The intensity of spruce browsing was low in the whole area in all seasons. In general, the intensity of rowan and beech
shoot browsing was high in the whole area. There were no correlations between deer density and browsing intensity of rowan
(browsing was severe in all plots). We conclude that the natural regeneration of attractive trees and shrubs is nearly impossible
in habitats where proportion of these food items is too small, even when the density of herbivores is low. Reduction of herbivores
density is useful for protecting spruce and other tree species with low preference by herbivores. Forest managers should take
into account the high palatability of deciduous tree species and distribution of herbivores on localities. Preference of localities
is often based on grasses in the food supply. Regeneration of highly palatable tree species requires both low density of herbivores
and sufficient protection of saplings. 相似文献
11.
The effect of seed water content (WC) (2–3, 5–6 and 22–25%, on a fresh weight basis), storage temperature (+4, −20, −80 and
−196°C) and storage duration (6, 12, 24, 48 and 60 months) on the germination of white spruce (Picea glauca (Moench) Voss), black spruce (Picea mariana (Mill.) B.S.P.) and lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) seed was investigated. Germination of white spruce control (untreated) seeds and seeds adjusted to 2–3% and 5–6%
WC declined after 48 months of storage at −80 and −196°C, with a further decline at 60 months at −20, −80, −196°C. Germination
remained high when control white spruce seeds and seeds with 2–3, 5–6% WC were stored at +4°C, over all storage durations.
Generally, black spruce and lodgepole pine exhibited high germination at all storage temperatures at 2–3% and 5–6% WC as well
as the control (untreated) seed, for up to 60 months in storage. Germination declined for all three species when seed was
conditioned to 22–25% WC. This loss in germination was partially recovered in white spruce seed stored at +4, −20 and −80°C
after storage durations of 24, 12 and 48 months, respectively, and in black spruce seeds stored at −20 and −196°C after storage
durations of 24 months. Mean germination time (MGT) was relatively constant for all species, under all conditions, except
for seed conditioned to 22–25% WC, where MGT increased for white spruce seed stored 48 months at −80 and −196°C, and for black
spruce seed stored 24 months at +4 and −80°C and 60 months at −196°C. These results show that the optimal storage temperatures
are 4°C for white spruce, and 4, −20, −80, and −196°C for black spruce and lodgepole pine, and 2–6% water content is optimal
for all 3 species at these temperatures. 相似文献
12.
LIU Zu-gen ZHU Jiao-jun HU Li-le WANG He-xin MAO Zhi-hong LI Xiu-fen ZHANG Li-jun 《林业研究》2005,16(3):193-199
In order to understand the effects of thinning on microsite conditions and natural regeneration in the larch plantation, thinning experiment was conducted in a 40-year-old Larix olgensis plantation in Qingyuan County in eastern Liaoning Province, China in 2003-2004 Five thinning treatments (0%, 10.2%, 19.8%, 29.7% and 40.3% thinned) were designed on the same site. After thinning, canopy openness and the microsite conditions such as photosynthetic photon flux density (PPFD), soil moisture content, and soil temperature were measured in one growing season. Meanwhile, the investigation of natural regeneration was conducted at the end of the growing season. The results showed that the canopy openness increased with the increase of thinning intensities. PPFD and soil temperature and soil moisture content in different soil layers were positively relative with canopy openness after thinning. The richness of regenerating tree species did not significantly increase (p=0.30) after one growing season since thinning, but the regeneration density and frequency of tree species increased significantly (p〈0.05). In addition, the number of regenerating tree species increased, and the increment was correlated with the characteristics of iudividual tree species. The increasing percentage of regenerating seedlings of the shade-intolerant tree species was more than that of shade-tolerant tree species. Among the investigated regeneration species, the biggest response of seedling emergency to the canopy openness was Phellodendron amurense. This paper confirmed the following conclusions: after thinning, the variety of regenerating tree species was correlative with the characteristics of regenerating tree species, and the distribution of unthinned trees and the site conditions in the investigated larch plantation were the additional factors influencing, the regeneration. 相似文献
13.
Jan Holeksa Milan Saniga Jerzy Szwagrzyk Tomasz Dziedzic Stanisław Ferenc Maciej Wodka 《European Journal of Forest Research》2007,126(2):303-313
The structure of natural subalpine spruce forest in the Zadná Pol’ana massif of the Western Carpathians was analysed. We focused
on the variability of different aspects of stand structure, tree decay and regeneration processes in altitudinal gradient.
We used systematic sampling, covering an area of 2 km2, to detect even subtle changes in stand structure within one forest type over a range of less than 200 m in elevation. Mean
stand density was 290 trees (>7 cm DBH) per hectare, average basal area was 41 m2 ha−1, and the volume accumulation in living trees amounted to 500 m3/ha−1. Stand volume decreased by more than 50% between 1,260 and 1,434 m a.s.l. This means for an increase of altitude of 100 m
that stand volume decreased by nearly 200 m3. Neither stand density nor basal area was related to elevation. Maximum tree height was strongly correlated to elevation,
and it decreased on average by 6 m for each 100 m increment of altitude. No significant changes in the maximum spruce diameter
were recorded in relation to the elevation gradient. Spatial distribution of trees was biased toward regularity at lower altitudes.
Tree clustering increased with increasing altitude. The stock of coarse woody debris (CWD) decreased slightly along the altitudinal
gradient, but changes were not significant. Density of spruce saplings and their number growing on CWD significantly increased
across the elevation gradient. Despite the fact that the analysed forest tract was relatively large, highly variable in respect
to environmental factors, and that stand volume, spatial structure, and tree height displayed strong variability along the
elevation gradient, the diameter structure of stands and regeneration measures were uniform. Our results suggest that the
recruitment of new trees in the Zadná Pol’ana subalpine spruce forest is not temporally continuous even at a scale of several
square kilometres. 相似文献
14.
Daniel C. Dey Martin A. Spetich Dale R. Weigel Paul S. Johnson David L. Graney John M. Kabrick 《New Forests》2009,37(2):123-135
Research on oak (Quercus L.) regeneration has generally consisted of small-scale studies of treatments designed to favor oak, including consideration
of site quality and topographic effects on oak regeneration. However, these experiments have not consistently factored in
broader-scale ecological differences found in the eastern United States. Oak regeneration experiments should be replicated
at appropriate ecological scales to address the similarities and differences in regeneration following prescribed silvicultural
treatments among ecological units. Patterns in oak regeneration can be better understood in an ecological context by considering
how oak species interact in the differing physical environments and are able to maintain dominance in changing complexes of
competing vegetation among the selected eco-units. Our understanding of oak regeneration response to specific silvicultural
practices and our ability to model regeneration is improved when we use replication, blocking, or factorial deployment of
relatively small-scale (0.5–1.0 ha) treatment plots within an ecological classification system. We present an example of this
approach to understanding oak regeneration dynamics in a synthesis of research to regenerate northern red oak (Quercus rubra L.) by underplanting shelterwoods in Arkansas, Missouri and Indiana. We summarize important considerations to guide the design
of future research in oak regeneration.
Paul S. Johnson and David L. Graney—Retired U.S. Forest Service scientists. 相似文献
15.
Li-zhi Wang 《林业研究》2009,20(1):87-90
This paper reports three newly recorded species, Diphascon modestum Binda, Pilato and Dastych, 1984, Diphascon nobilei Binda, 1969, and Diphascon triodon Maucci, 1996, of the genus Diphascon (Tardigrada; Hypsibiidae) from China. Five specimens of Diphascon modestum were collected from Taibai Mt. (34°18′N, 107°42tpE) at 2,500 m above the sea level (a.s.l.), two specimens of Diphascon nobilei were collected from Tonggu County, Jiangxi Province (28°31’N, 114°26′E) at 900 m a.s.l, and one specimen of Diphascon triodon was collected from Linzhi County, Tibet (29°40′N, 94°23′E) at 3,500 m a.s.l. All specimens are deposited at the College of
Life Sciences, Shaanxi Normal University, China. A key to the Chinese species of Diphascon was also given.
Foundation project: This study was supported by scientific research foundation project of Shaanxi Institute of Education (No.
07KJ37Q) 相似文献
16.
Newly recorded species of the genus Isohypsibius (Tardigrada; Hypsibiidae) from China 总被引:9,自引:0,他引:9
This paper reports two newly recorded species, lsohypsibius lunulatus Iharos, 1966 and lsohypsibiusprosostomus Thulin, 1928, of the genus lsohypsibius (Tardigrada; Hypsibiidae) from China. The specimens of lsohysibius lunulatus were collected from Taibai Mt (34°18′N, 107°42′E) at 2,500 m a.s.1, and those oflsohypsibius prosostomus from Taibai Mt (34°10′N, 107°35′E) at 2,000 m above sea level. All specimens are deposited at the College of Life Sciences, Shaanxi Normal University, China. A key to the Chinese species of lsohypsibius was also given. 相似文献
17.
This study presents empirical data on regeneration and growth of understory trees and constructs simple models for predicting
these characteristics at various stand structure and post-thinning standing volume levels. The field experiment was established
on a grass/herb mineral soil site in central Finland. Regeneration and understory tree growth data were collected from 24
Norway spruce (Picea abies L.)-dominated mixed substands. Seedlings with heights from 5 to 130 cm were measured in 1996 and 2007. In addition, the annual
height growth of Norway spruce seedlings was measured in 2007. The spatial pattern of the substands varied from clustered
to regular with a decreasing standing volume. Stand complexity was uniform across the range of standing volume. In the 2007
survey, the amount of Norway spruce regeneration increased from approximately 400 to 5,000 seedlings ha−1 when the post-thinning standing volume level was reduced from 230 to 90 m3 ha−1, respectively. Nearly no seedlings were found when the standing volume was over 300 m3 ha−1. The annual diameter increment in Norway spruce understory (dbh < 5 cm) trees decreased, on the average, from 2.3 to 0.3 mm
with an increase in the standing volume level from 90 to 340 m3 ha−1, respectively; their height growth showed also a decreasing trend when the standing volume increased. The results indicated
that a post-thinning standing volume lower than 150 m3 ha−1 with a regular overstory spatial structure provides a suitable environment for regeneration and growth of Norway spruce understory
trees in the studied forest type. 相似文献
18.
Larch(Larix olgensis), Manchurian ash(Fraxinus mandshurica), Korean pine(Pinus koraiensis) and White birch(Betula platyphylla) are the major planting species in northeast China. The samples of forest litters were collected from the stands of the above
4 species in Laoyeling and Jianlagou experiment stations of Maorshan Exp. Forest Farm (45°12′–45°30′N, 127°30′–127°48′E),
Northeast Forestry University, in early October 2002. Quantitative analysis and qualitative analysis were carried out on the
organic acids existing in freshly fallen litters (L layer) and hemi-decomposed litters (F layer) of the four forest species
by using Gas Chromatogram system. A wide variety of organic acids were identified, including oxalic, malonic, fumaric, succinic,
maleic, malic, citric, C16:O, C18:O, C18:1, C18:2, C18:3 and C20:O acids. In respect of L litters of all samples, the oxalic acid content (over 30 mg/g) was the highest of the seven low-molecular-weight
organic acids identified, while the content of oleic or linoleic (above 40mg/g) was found to be highest among the six high
aliphatic acids identified. As to F litters, oxalic acid content was also the highest, followed by linoleic and oleic. For
the same tree species or the same forest, the kinds and contents of organic acids in L litters were more abundant than that
in F litters.
Foundation item: This paper is supported by National Natural Science Foundation of China (30170768)
Biography: SONG Jin-feng (1976-), female, doctor postgraduate, Harbin 150040, P. R. China.
Responsible editor: Chai Ruihai 相似文献
19.
Identification of anisotropic vibrational properties of Padauk wood with interlocked grain 总被引:1,自引:0,他引:1
Iris Brémaud Pierre Cabrolier Joseph Gril Bruno Clair Jean Gérard Kazuya Minato Bernard Thibaut 《Wood Science and Technology》2010,44(3):355-367
Grain deviations and high extractives content are common features of many tropical woods. This study aimed at clarifying their
respective impact on vibrational properties, referring to African Padauk (Pterocarpus soyauxii Taub.), a species selected for its interlocked grain, high extractives content and uses in xylophones. Specimens were cut
parallel to the trunk axis (L), and local variations in grain angle (GA), microfibril angle (MFA), specific Young’s modulus
(E′
L
/ρ, where ρ stands for the density) and damping coefficient (tanδL) were measured. GA dependence was analysed by a mechanical model which allowed to identify the specific Young’s modulus (E′3/ρ) and shear modulus (G′/ρ) along the grain (3) as well as their corresponding damping coefficients (tanδ3, tanδG). This analysis was done for native and then for extracted wood. Interlocked grain resulted in 0–25° GA and in variations
of a factor 2 in E′L/ρ and tanδL. Along the grain, Padauk wood was characterized, when compared to typical hardwoods, by a somewhat lower E′3/ρ and elastic anisotropy (E′/G′), due to a wide microfibril angle plus a small weight effect of extracts, and a very low tanδ3 and moderate damping anisotropy (tanδG/tanδ3). Extraction affected mechanical parameters in the order: tanδ3 ≈ tanδG > G′/ρ > > E′3/ρ. That is, extractives’ effects were nearly isotropic on damping but clearly anisotropic on storage moduli. 相似文献
20.
Morphology and vertical distribution patterns of spruce and beech live fine roots (diameter ≤2 mm) were studied using a soil
core method in three comparable mature stands in the Solling: (1) pure beech, (2) pure spruce and (3) mixed spruce–beech.
This study was aimed at determining the effects of interspecific competition on fine root structure and spatial fine root
distribution of both species. A vertical stratification of beech and spruce fine root systems was found in the mixed stand
due to a shift in beech fine roots from upper to lower soil layers. Moreover, compared to pure beech, a significantly higher
specific root length (SRL, P<0.05) and specific surface area (SSA, P<0.05) were found for beech admixed with spruce (pure beech/mixed beech SRL 16.1–23.4 m g−1, SSA 286–367 cm2 g−1). Both indicate a flexible ‘foraging’ strategy of beech tending to increase soil exploitation and space sequestration efficiency
in soil layers less occupied by competitors. Spruce, in contrast, followed a more conservative strategy keeping the shallow
vertical rooting and the root morphology quite constant in both pure and mixed stands (pure spruce/mixed spruce SRL 9.6/7.7 m g−1, P>0.10; SSA 225/212 cm2 g−1, P>0.10). Symmetric competition belowground between mixed beech and spruce was observed since live fine roots of both species
were under-represented compared to pure stand. However, the higher space sequestration efficiency suggests a higher competitive
ability of beech belowground. 相似文献