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981.
Plant diversity of secondary forests in response to anthropogenic disturbance levels in montane regions of northeastern China 总被引:4,自引:0,他引:4
The effects of anthropogenic disturbances on forest structure and plant diversity of secondary forest ecosystems were evaluated
based on the classification by site factors in the montane regions of northeastern China. Forty-five sample plots containing
720 sub-plots of overstory species (8 m × 8 m), 1,440 quadrats of understory species (2 m × 2 m), and 1,440 quadrats of herbaceous
layer species (1 m × 1 m) were clustered into five groups (G1, G2, G3, G4 and G5) by site variables with Hierarchical Cluster
Analysis. Meanwhile, the disturbance levels corresponding to the five groups were determined according to the factors influencing
human disturbances (D0-G2, D1-G1, D2-G3, D3-G5, and D4-G4). Species diversities of overstory, understory, herbaceous layer
and overall species were evaluated using species number, Margalef index, Pielou index, Shannon–Wiener index, and Simpson index;
and β-diversities (Whittaker index, Cody index). Basal area of stands exhibited a decreasing trend along the disturbance level
due to a gradual increase in the extraction of timber by the human disturbances. The indices of species diversity suggested
that overstory and understory species were distributed evenly among the groups or disturbance levels. There were no absolutely
dominant tree species in the secondary forest ecosystems. The differences in site factors and the current disturbance intensities
were not intense enough to lead to loose changes in overstory and understory species. The species diversity indices exhibited
the maximum values at D3 (G5) for herbaceous layer species; this may suggest that the current disturbance intensities were
intense enough to lead the changes of herbaceous layer species. Three rare and endangered species (Juglans mandshurica, Fraxinus mandshurica and Acanthopanax senticosus) were found within the secondary forests. These rare and endangered species appeared in each clustered group or disturbance
level, which suggested that the current disturbance intensity in the study area was not strong enough to influence the distribution
of rare and endangered species. The current disturbances in the secondary forests may not lead to a decrease in stability
and complexity of the overstory and understory species, but the higher disturbance level may be intense enough to change the
habitat fitness for the herbaceous species.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized authors. 相似文献
982.
Based on paper of “Theoretical derivation of risk-ratios for assessing wind damage in coastal forest“,wind damage in the pine coasteal forest,which was thinned at four levels in December of 1997,was investigated for four successive growing seasons.Besides wind damage,the wind profiles outside and inside the coastal forest stand and the distributions of optical stratification porosity (OSP) were also observed.Based on these data,risk-ratios of wind damage for both individual trees and stands were estimated according to the methods developed in “Theoretical derivation of risk-ratios for assessing wind damage in a coastal forest“.The results showed that risk-ratios of wind damage,which were calculated from the meen height and diameter only and from the combination of wind and stand sructure profiles,accurately predicted wind damage in the plantation.Relationships between different thinning ratios and incidence of wind damage showed that stand stability decreased soon after the thinning.This was due to the immediate effects of thinning on increasing the canopy roughness and wind load,and on decreasing the sheltering effects from surrounding trees.However,thinning strategies could improve the stability by long-term effects on growthand development of trees against extreme wind.Only canopy damage was recorded during the experimental period,no stem damage was found,even though the maximum 10-min wind speed outside the coastal forest attained 30.2m s^-1.The results obtained in this study indicate that thinning is the most effective silvicultural strategy available for managing coastal forest despite the increased probability of wind damage soon after thinning. 相似文献
983.
The effect of tool angles on the shapes of chips generated by parallel-to-grain and end-grain milling was explored for China
fir and maple under fixed spindle and feed speeds and cutting depth. The milling path was up-milling by straight router-bits
with a diameter of 12 mm. The chip shapes could be distinguished as five types: spiral, splinter, flow, thin, and granules
or powder. The flow and thin chips were generated most often (on a weight percentage basis) for all tool angles investigated
for parallel-to-grain and end-grain milling of China fir and maple. More granule chips were produced with parallel-to-grain
milling than with end-grain milling for both woods. The measured chip thickness (t′) was thicker than the calculated thickness (t
max). Thicker and longer maple chips were produced by end-grain milling than by parallel-to-grain milling. The tool geometries
of 40°/15° (sharpness of the angle–rake angle), 50°/15°, and 60°/15° for China fir and 40°/25°, 50°/5°, and 60°/5° for maple
produced relatively more flow chips with parallel-to-grain milling. Furthermore, the tool geometries of 40°/5°, 50°/15° and
60°/25° produced more flow chips (weight percentage) by end-grain milling of China fir and maple.
Received: May 23, 2001 / Accepted: June 28, 2002
Acknowledgment This study was supported by a grant from the National Council of Science, Taiwan (NSC89-2313-B-415-011). 相似文献
984.
农田防护林主要间距离的确定——基于林带结构与风速降低的关系 总被引:3,自引:0,他引:3
Relative windspeed reduction was measured behind nine relatively narrow, homogenous tree windbreaks with porosities between
0.13–0.33, and behind 28 combinations of model stubble barriers representing 25 different optical porosities (0.00–0.80).
The optimum porosities observed were 0.25 and 0.13 for tree windbreaks and stubble barriers respectively. Based on the relationship
between windbreak structure (optical porosity) and wind reduction, the chief indices for determining spacing interval, i.e.,
the windbreak structure index (δ) and the parameter of microclimate, represented by the problem wind (L
rp
), were determined. Additionally, investigations on shelterbelt trees were carried out, and stem-analysis techniques were
used, to develop a method for determining the mature height of tree windbreaks (H
0). Optimal spacing intervals between windbreaks could be predicted from the indices of a given windbreak structure, percentage
of reduction of windspeed desired and tree growth model. A hypothetical example for determining the spacing interval of principal
poplar windbreaks is given at the end of this paper. The results can be applied not only to tree windbreak design but also
to other plant materials and artificial barriers for wind protection.
Foundation item: This study was supported by Innovation Research Project of Chinese Academy of Sciences
Biography: ZHU Jiao-jun (1965-), male, Ph. Doctor, PhD advisor. Professor of Institute of Applied Ecology, the Chinese Academy of Sciences,
China, Scholar researcher of Faculty of Agriculture, Niigata University, Japan.
Responsible editor: Song Funan 相似文献
985.
986.
987.
988.
989.
分析引自澳大利亚东部的桃金娘科(Myrtaceae)伞房属(Corymbia) 4个树种/亚种在广东省乐昌试验点的早期生长表现,结果表明:10 a生时,4个树种/亚种生长量最大的是大叶斑皮桉(Corymbia henryi),其次是斑皮柠檬桉(Corymbia citriodora ssp. variegata)、柠檬桉(Corymbia citriodora ssp. citriodora)和斑皮桉(Corymbia maculata),平均单株材积分别为0067 4、0059 0、0054 1和0034 1 m3;与8 a生时比较,4个树种/亚种在10 a生时仍保持较快的增长速度,材积增长均在67%以上,其中斑皮桉的材积增长率高达1450%。方差分析结果表明:在试验组Ⅰ,柠檬桉和大叶斑皮桉3个生长性状在家系间差异极显著(P<001),种源间胸径差异达极显著水平(P<001),树高差异达显著水平(P<005),单株材积差异不显著;在试验组Ⅱ,斑皮柠檬桉和斑皮桉3个生长性状在种源、家系间差异极显著(P<001)。以单株材积高于对照为选择目标,选出大叶斑皮桉2个种源2个家系,斑皮柠檬桉5个种源11个家系,共计7个种源13个家系,分别占参试种源和家系总数的389%和140%。 相似文献
990.
微贮牧草对山羊生产性能、饲粮养分消化率和消化道微生物数量的影响 总被引:1,自引:0,他引:1
试验使用黑曲霉、乳酸菌、酵母菌3种微生物的固体菌剂以及尿素作为微生态制剂青贮(微贮)高丹草和牛鞭草,并对64只黑山羊进行30 d饲养对比试验,研究高丹草和牛鞭草青贮对山羊生产性能、饲粮养分消化率和消化道微生物数量的影响。试验结果为,相比于普通青贮(普贮),微贮高丹草酵母菌、黑曲霉、乳酸菌数量分别增加了475.61%、290.65%和513.37%;微贮牛鞭草酵母菌、黑曲霉、乳酸菌数量分别增加了466.67%、762.07%和486.05%;微贮组羊瘤胃中的酵母菌、黑曲霉和乳酸菌数量均极显著增加(P0.01);微贮组羊粪中的酵母菌、黑曲霉和乳酸菌数量显著或极显著增加(P0.05),大肠杆菌数量极显著降低(P0.001);微贮组饲粮除中性洗涤纤维的表观消化率极显著高于普贮组(P0.01),其余均显著高于普贮组(P0.05);微贮组平均日增重和饲料转化率显著高于普贮组(P0.05)。综上所述,微生态制剂青贮不仅可增加瘤胃和粪中酵母菌、黑曲霉和乳酸菌数量,减少粪中大肠杆菌的数量,还能提高山羊饲粮表观消化率和生长性能。 相似文献