Differential response of radial growth and δ^(13)C in Qinghai spruce(Picea crassifolia) to climate change on the southern and northern slopes of the Qilian Mountains in Northwest China

Tree radial growth can have significantly differ-ent responses to climate change depending on the environ-ment.To elucidate the effects of climate on radial growth and stable carbon isotope(δ^(13)C)fractionation of Qing-hai spruce(Picea crassifolia),a widely distributed native conifer in northwestern China in different environments,we developed chronologies for tree-ring widths and δ^(13)C in trees on the southern and northern slopes of the Qilian Mountains,and analysed the relationship between these tree-ring variables and major climatic factors.Tree-ring widths were strongly influenced by climatic factors early in the growing season,and the radial growth in trees on the northern slopes was more sensitive to climate than in trees on the southern.Tree-ring δ^(13)C was more sensitive to climate than radial growth.δ^(13)C fractionation was mainly influenced by summer temperature and precipitation early in the growing season.Stomatal conductance more strongly limited stable carbon isotope fractionation in tree rings than photosynthetic rate did.The response between tree rings and climate in mountains gradually weakened as climate warmed.Changes in radial growth and stable carbon isotope fractionation of P.crassifolia in response to climate in the Qilian Mountains may be further complicated by continued climate change.

Dieback of managed spruce stands in western Germany promotes beetle diversity

Biodiversity loss is a significant problem at a global scale and may be amplified by climate change.In recent years,coniferous forests have had substantial die-back across Europe due to drought and subsequent bark-beetle outbreaks.As many studies on the consequences of disturbance and subsequent management have focused on natural stands,management implications for managed spruce stands are not well understood,even though such stands are widespread throughout Europe.In this study,beetle taxonomy,conservation value,and community com-position are compared among spruce plantations and four post-disturbance management approaches:standing dead-wood,lying deadwood,clear cuts,and long-term succession.Diversity and community composition differed significantly among management categories,while different beetle fami-lies responded similarly.Intact spruce stands harbored the lowest beetle diversity while the highest taxonomic diver-sity and conservation value was on clear cuts and stands with lying or standing deadwood.The proportion of forest specialists was highest in successional forests.In summary,different forest management categories harbored distinct beetle communities at the family-,species-,and ecological guild levels.Therefore,post-disturbance management should consider the landscape scale and include different management types.This enhances landscape heterogeneity and thus overall biodiversity but could also mitigate negative impacts of natural disturbances on ecosystem services.

Radial growth in Qinghai spruce is most sensitive to severe drought in the Qilian Mountains of Northwest China

Global warming and frequent extreme drought events lead to tree death and extensive forest decline,but the underlying mechanism is not clear.In drought years,cambial development is more sensitive to climate change,but in different phenological stages,the response rela-tionship is nonlinear.Therefore,the dynamic relationship between tree radial growth and climatic/environmental fac-tors needs to be studied.We thus continuously monitored radial growth of Qinghai spruce(Picea crassifolia Kom.)and environmental factors from January 2021 to November 2022 using point dendrometers and portable meteorological weather stations in the central area of the Qilian Mountains.The relationship and stability between the radial growth of Qinghai spruce and environmental factors were compared for different levels of drought in 2021 and 2022.The year 2022 had higher temperatures and less precipitation and was drier than 2021.Compared with 2021,the growing period in 2022 for Qinghai spruce was 10 days shorter,maximum growth rate(Grmax)was 4.5μm·d^(-1) slower,and the initiation of growth was 6 days later.Growth of Qinghai spruce was always restricted by drought,and the stem radial increment(SRI)was more sensitive to precipitation and air relative humidity.Seasonal changes in cumulative radial growth were divided into four phenological stages according to the time of growth onset,cessation,and maximum growth rate(Grmax)of Qinghai spruce.Stability responses of SRI to climate change were stronger in Stage 3 and Stage 4 of 2021 and stronger in Stage 1(initiation growth stage)and Stage 3 of 2022.The results provide important information on the growth of the trees in response to drought and for specific managing forests as the climate warms.

Early response of understory vegetation to the mass dieback of Norway spruce in the European lowland temperate forest

Spruce-dominated forests are commonly exposed to disturbances associated with mass occurrences of bark beetles.The dieback of trees triggers many physical and chemical processes in the ecosystem resulting in rapid changes in the vegetation of the lower forest layers.We aimed to determine the response of non-tree understory vegetation to the mass dieback of Norway spruce(Picea abies)in the first years after the disturbance caused by the European spruce bark beetle(Ips typographus)outbreak.Our study area was the Białowieża Biosphere Reserve covering the Polish part of the emblematic Białowieża Forest,in total 597km^(2).The main data source comprised 3,900 phytosociological relevés(combined spring and summer campaigns)collected from 1,300 systematically distributed forest sites in 2016–2018–the peak years of the bark beetle outbreak.We found that the understory responded immediately to mass spruce dieback,with the most pronounced changes observed in the year of the disturbance and the subsequent year.Shade-tolerant forest species declined in the initial years following the mass spruce dieback,while hemicryptophytes,therophytes,light-demanding species associated with non-forest seminatural communities,as well as water-demanding forest species,expanded.Oxalis acetosella,the most common understory species in the Białowieża Forest,showed a distinct fluctuation pattern,with strong short-term expansion right after spruce dieback,followed by a gradual decline over the next 3–4 years to a cover level 5 percentage points lower than before the disturbance.Thus,our study revealed that mass spruce dieback selectively affects individual herb species,and their responses can be directional and non-directional(fluctuation).Furthermore,we demonstrated that the mass dieback of spruce temporarily increases plant species diversity(α-diversity).

Photosynthetic acclimation to long-term high temperature and soil drought stress in two spruce species (Picea crassifolia and P. wilsonii) used for afforestation

Picea crassifolia and P.wilsonii,commonly used for afforestation in northern China,are increasingly likely to be subjected to high temperatures and soil drought stress as a result of global warming.However,little is known about the effects of these stresses on foliar photosynthesis in the two species.To investigate how photosynthetic characteristics and sensitivity respond to prolonged high temperatures and soil drought,foliar gas exchange and other closely related parameters were recorded from four-year-old seedlings of both species.Seedlings were grown under two temperature treatments(25/15 and 35/25 °C) and four soil water regimes [80,60,40 and 20% of maximum field capacity(FC)] for 4 months.Although all treatments significantly reduced photosynthetic rates(Pn) of both species,P.crassifolia exhibited greater photosynthetic acclimation than P.wilsonii.Differences in photosynthetic acclimation were mainly related to variations in stomatal conductance(Cond) and the maximum quantum yield of PSII(Fv/Fm) between treatments.Indeed,higher Cond and Fv/Fmin all treatments were shown for P.crassifolia than for P.wilsonii.Moreover,photosynthesis in P.crassifolia exhibited inherently lower temperature sensitivities(broader span for the temperature response curves; lower b) and higher thermostability(invariable b between treatments).Further,severe drought stress(20% FC) limited the survival of P.wilsonii.Our results indicate that P.wilsonii is more susceptible to high temperatures and soil drought stress.Planting P.crassifolia would be more expected to survive these conditions and hence be of greater benefit to forest stability if predicted increases in drought and temperature in northern China occur.

Spatial and temporal patterns of the sensitivity of radial growth response by Picea schrenkiana to regional climate change in the Tianshan Mountains

Climate change significantly impacts forest ecosystems in arid and semi-arid regions.However,spatiotemporal patterns of climate-sensitive changes in individual tree growth under increased climate warming and precipitation in north-west China is unclear.The dendrochronological method was used to study climate response sensitivity of radial growth of Picea schrenkiana from 158 trees at six sites during 1990-2020.The results show that climate warming and increased precipitation significantly promoted the growth of trees.The response to temperature first increased,then decreased.However,the response to increased precipitation and the self-calibrating Palmer Drought Severity Index(scPDSI)increased significantly.In most areas of the Tianshan Mountains,the proportion of trees under increased precipitation and scPDSI positive response was relatively high.Over time,small-diameter trees were strongly affected by drought stress.It is predicted that under continuous warming and increased precipitation,trees in most areas of the Tianshan Mountains,especially those with small diameters,will be more affected by precipitation.

Predicting Potential Distribution of Tibetan Spruce (Picea smithiana) in Qomolangma (Mount Everest) National Nature Preserve Using Maximum Entropy Niche-based Model

Tibetan spruce (Picea smithiana) is an endemic species of the Himalayas,and it distributes only in a re-stricted area with very low number.To address the lack of detailed distributional information,we used maximum en-tropy (Maxent) niche-based model to predict the species' potential distribution from limited occurrence-only records.The location data of P.smithiana,relative bioclimatic variables,vegetation data,digital elevation model (DEM),and the derived data were analyzed in Maxent.The receiver operating characteristic (ROC) curve was applied to assess the prediction accuracy.The Maxent jackknife test was performed to quantify the training gains from data layers and the response of P.smithiana distribution to four typical environmental variables was analyzed.Results show that the model performs well at the regional scale.There is a potential for continued expansion of P.smithiana population numbers and distribution in China.P.smithiana potentially distributes in the lower reaches of Gyirong Zangbo and Poiqu rivers in Gyirong and Nyalam counties in Qomolangma (Mount Everest) National Nature Preserve (QNNP),China.The species prefers warm temperate climate in mountain area and mainly distributes in needle-leaved evergreen closed to open forest and mixed forest along the river valley at relatively low altitudes of about 2000-3000 m.Model simulations suggest that distribution patterns of rare species with few species numbers can be well predicted by Max-ent.

基于红皮云杉(Picea koraiensis)重建大兴安岭南麓历史径流量

基于红皮云杉(Picea koraiensis)年轮宽度标准化年表重建了大兴安岭南麓贡格尔河流域1845—2016年历史径流量序列。结果表明:(1)贡格尔河流域在过去172 a共经历1853—1855年、2000—2010年2个枯水期和1869—1873年、1911—1918年、1952—1958年3个丰水期,丰水年及枯水年占比分别为17.4%和10.5%。(2)重建序列存在显著的3 a、7~12 a、15~22 a及30 a周期,研究区水文变化受全球大尺度气候环流活动的影响。丰、枯水期与该地区历史典籍记载的自然灾害高度重合,与附近其他重建结果相关性显著,重建方程稳定可靠。研究结果丰富了大兴安岭地区树木年轮数据库,为区域长历史时期水文变化的研究提供参考。

Essential Oil from Ether-Containing Plants of Juniper (<i>Juniperus</i>) and Spruce (<i>Picea</i>) Leaves by Distillation

This article is investigating the preparation of essential oil from the ether-containing plants of Juniper (Juniperus) and spruce (Picea) leaves by using the simple water distillation equipment. This water distillation method forms an essential oil with water vapor from plants of Juniper (Juniperus) and spruce (Picea) leaves based on Dalton’s law of partial pressure, applicable for plants containing a large amount of ether oil where distillation temperature is not affecting product quality. Obtained essential oils are widely used in medicine, perfumery, cosmetics, and food industry. In addition, these essential oils possess different activities including antimicrobial, antiviral, and anti-inflammatory, which have different effects such as adaptogenic, antidepressive, disinfection, and wound healing, diuretic, and antipyretic.

Studies on Refinement of Container Size and Potting Mixture for Production of Quality Seedlings in Spruce (<i>Picea Smithiana</i>Wall. Boiss)

Spruce (Picea Smithiana) is an evergreen tree and distributed through the temperate Himalaya at the elevation of 2000 - 3500 m. Natural regeneration of spruce (Picea smithiana) is generally slow and almost negligible due to a number of factors e.g. presence of un decomposed raw humus on forest floor low germinative capacity of seed and infrequent good seed years. In order to supplement natural regeneration through artificial means, nursery raising assumes significance. The present study aimed at optimizing the root trainer container size and the potting mixture ingredients and their proportion for the production of quality nursery stock of Picea smithiana. Nine combinations of potting mixture ingredients (Forest Soil, Garden Soil, Sand, FYM and Lake weed) were tested in various ratios for the optimization of potty mixture in different root trainer sizes. Simultaneously, three different volumes (150cc, 250cc and 300cc) of root trainers were tested for suitability of container size. Chemical and physical analysis of potting mixture ingredients was carried out for better understanding of nutrient status. The best seedling growth at seven month age in terms of height (5.53 cm), Collar diameter (1.57 mm), fresh shoot weight (0.34 g), dry shoot weight (0.10 g), fresh root weight (0.27 g) , dry root weight (0.03 g), root shoot ratio(2:52), and total fresh biomass (0.61 g) were observed when seedlings were raised in root trainer container size (300cc) filled with potting mixture of (M8) Soil:Sand:FYM (1:1:2) and the lowest growth parameters were observed in root trainer container size (150cc) filled with forest soil only. Plantable quality seedlings can be recovered within a period of 7 months using potting mixture of Soil, Sand and FYM (1:1:2) and Soil, Sand and Lake weed (1:1:2) ratios in root trainer container size 300cc.

Spatiotemporal evidence of tree-growth resilience to climate variations for Yezo spruce(Picea jezoensis var. komarovii) on Changbai Mountain, Northeast China

Global warming-induced changes in tree-growth resilience to climate variations have been widely reported for mid-and high-latitude regions around the world. Most studies have focused on the spatial variability of trees in radial growth-climate relationships on Changbai Mountain in Northeast China, but little is known about temporal changes in tree growth in response to climate. We explored the stability of effect of climate variables on radial growth of Yezo spruce [Picea jezoensis Carr. var. komarovii(V.Vassil.) Cheng et L.K.Fu] at 1200, 1400, and 1600 m above sea level, representing low, middle, and upper ranges of the spruce-fir mixed forest on Changbai Mountain. The results showed that the relation between tree growth and climate did not vary with altitude, but the stability of the tree-growth-climate relationship did vary with altitude as the climate changed. Radial growth of Yezo spruce at allthree elevations was influenced primarily by maximum temperature during May(Tmax5) and mean minimum temperature from January to March(Tmin1-3). More specifically, the relationship strengthened significantly at lower elevations, but weakened significantly at higher elevation, and fluctuated at mid elevations since 1980.Increase in Tmin1-3 and decrease in Tmax5 were the main reasons for the decrease in the radial growth at three altitudes. The findings of this study clarified that the decrease in radial growth on Changbai Mountain is not a “divergence problem” of an unexpected decrease in tree growth in response to an increase in mean temperature and provides a reference for using tree-ring data to reconstruct climate patterns and/or predict the growth of trees under various climate change scenarios.

Spatial patterns of Picea crassifolia driven by environmental heterogeneity and intraspecifi c interactions

Research on the spatial patterns of tree populations is critical for understanding the structure and dynamic processes of forests.However,little is known about how the underlying drivers shape these patterns and species interactions in forest systems.In this study,spatial point pattern analysis investigated the combined eff ects of intraspecifi c interactions and environmental heterogeneity on the spatial structure and internal maintenance mechanisms of Picea crassifolia in the Qilian Mountain National Nature Reserve,China.Data were obtained from a 10.2-ha dynamic monitoring plot(DMP)and sixteen 0.04-ha elevation gradient plots(EGPs).Under complete spatial randomness,both mature trees and saplings in the DMP demonstratedlarge-scale aggregation with negative correlations.In EGPs,saplings were clustered in small mesoscales,mature trees were randomly distributed,and the interactions of saplingstrees at all elevations were not correlated.By eliminating the interference of environmental heterogeneity through the inhomogeneous Poisson process,saplings in the DMP and EGPs were clustered in small scales and trees randomly distributed.Intraspecifi c associations were negatively correlated,in the DMP and at low elevations,and no correlations in high elevations of EGPs.In the vertical scale,saplings showed a small-scale aggregation pattern with increase in elevation,and the aggregation degree fi rst decreased and then increased.The interactions of saplings-trees and saplings–saplings showed inhibitions at small scales,with the degree of inhibition gradually decreasing.Spatial patterns and associations of adults–adults did not change signifi-cantly.The results revealed that intraspecifi c interactions and environmental heterogeneity regulated the spatial patterns of P.crassifolia at small and large scales,respectively.Environmental heterogeneity might be the most decisive factor aff ecting the spatial patterns of saplings,while trees were more aff ected by intraspecifi c interactions.Moreover,competition between trees in this area could be more common than facilitation for the growth and development of individuals.

GPR Survey for Fir(Abies alba)and Spruce(Picea abies)Root Systems in Different Locations in the Western Carpathians Mts.(Poland)

The aim of the GPR research was a non-invasive inspection of the root systems arrangement of selected trees(fir Abies alba and spruce Picea abies),in the Silesian Beskids Landscaped Park and Zywiec Beskids Landscaped Park(Carpathian Mountains,Poland).Field research has been done using RAMAC/GPR with 800 MHz shielded antennas.The survey was conducted by linear profiling to a depth of 2 m.The survey was carried out around the designated trees in 6 meters×6 meters grids.Base points for X(S-N)and Y(W-E)axis were set in corners of each grid.Parallel GPR traverses were conducted within each study area,at intervals of 0.20 m.The maps of the research areas show existing trees and stumps within the GPR sections,with ±1 m error.GPR data analysis was carried out in 2D and 3D systems.Major findings from the GPR survey concluded that the firs(Abies alba),have a "vertical" root system type(with the roots dominant at depths of 0.2-0.8 meters),concentrically away from the tree trunk at a distance of about 1 m to about 2 m,and the spruces(Picea abies),have a "cloud" root system type(at a depth of 10-100 cm),with a few clear,thicker roots extending from the trunk.

Behavior of Decayed Spruce (Picea abies) during Kraft Pulping

This study indicated that by applying an improved classification system to decayed large-diameter Norway spruce(Picea abies)wood,its use as raw material for kraft pulping without loss of pulp quality could be essentially increased.This is based on the fact that although the cooking yield of decayed spruce material which has been sorted according to these new recommendations is somewhat lower and Kappa number higher than those of sound wood material,the greatest part of the decayed stem(the outer part of the stem)contains long-fiber wood material which produces pulp of good quality.Therefore,large-diameter spruce logs can also be separately used,for example,in the manufacture of reinforcement pulp.

Divergent responses of Picea crassifolia Kom.in different forest patches to climate change in the northeastern Tibetan Plateau

Global climate changes have significantly affected tree growth and forest structures and functions in some arid and semi-arid regions,which are becoming warmer and wetter.Due to natural factors such as climate and terrain,some tree species may form different forest patches at the edges of their distribution areas.However,how forest patches of various sizes respond to climate change is unclear.In this study,we collected 203 tree cores from six different sizes of forest patches at the edge of the distribution area of Picea crassifolia Kom.in the northeast Tibetan Plateau.And we used the dendrochronology method to study the response of tree growth and resilience in different forest patches to climate change from 1961 to 2020.We simultaneously measured the contents of nonstructural carbohydrates(NSC),total nitrogen and total phosphorus of tree needles.Our results showed that the growth of trees in small-and medium-size forest patches(0.8–18.6 ha)has increased significantly.The early growing season(May–July)minimum temperature was the most important climate factor driving the growth of small-and medium-sized patch trees.The early growing season maximum temperature was the most important climate factor that inhibited the growth of trees in the largest patches(362.8 ha).The growth of individual trees in medium forest patches was better and the correlation with annual minimum temperature,maximum temperature,precipitation,actual evapotranspiration,and palmer drought severity index was stronger.The higher NSC content,stronger photosynthesis,and higher nitrogen utilization efficiency in leaves might be one of the reasons for the better growth of trees in moderate forest patches.In extreme drought years,as the forest patch area increased,the overall trend of tree growth resistance showed a unimodal pattern,with the highest at a forest patch area of 7.1 ha,while the overall trend of tree growth recovery was opposite.Therefore,we should strengthen the management of trees in large forest patches to cope with climate change.

Expression of Genes Associated with Nickel Resistance in White Spruce (<i>Picea glauca</i>) under Nickel Stress: Analysis of AT2G16800 and <i>NRAMP</i>Genes

Heavy metals such nickel (Ni) can cause toxicity by 1) displacing essential components in the biomolecules, 2) blocking the functional group of molecules, or 3) modifying enzymes, proteins, the plasma membrane, and membrane transporters. The main objective of the present study was to investigate the effect of nickel (Ni) on gene expression of nitrate on gene expression with a focus on the genes coding for the high affinity Ni transporter family protein AT2G16800, and natural resistance-associated macrophage protein (NRAMP). Ni toxicity was assessed by treating seedlings with an aqueous solution of nickel nitrate salt [Ni(NO3)2] at the concentrations of 150 mg, 800 mg, and 1600 mg of nickel per 1 kg of dry soil. RT-qPCR was used to measure the expression of AT2G16800, and NRAMP genes in samples treated with nickel nitrates and controls. The results revealed that P. glauca is resistant to Ni based on lack of plant damage at all nickel concentrations. Ni has no effect on the expression of the AT2G16800 gene in needles or roots. However, it induced an upregulation of the NRAMP genes in roots at all the doses tested (150 mg/kg, 800 mg/kg, and 1600 mg/kg). On the other hand, Ni has no effect on the expression of the NRAMP gene in needle but the lowest dose of potassium (150 mg/kg) upregulated this gene in needle tissues.

天山北坡中段雪岭云杉人工林碳汇随林龄的动态变化

人工林是森林固碳增汇的重要组成部分,其碳汇动态随林龄的增长存在较大差异.以天山林区广泛分布的单一人工林雪岭云杉(Picea schrenkiana)为研究对象,选取未抚育的各龄级人工林样地并以无林地为对照,通过样地调查与取样,计算植被地上、植被地下、枯落物和土壤碳密度,采用空间代替时间的方法量化了人工林碳汇量和造林后固碳量特征随林龄的变化规律.结果表明:1)不同龄组雪岭云杉人工林植被地上碳密度为1.82~119.34 t·hm^(-2),植被地下碳密度为1.26~27.77 t·hm^(-2),树干累积了植被46.4%~62.0%的碳,随林龄增加,碳密度(造林固碳量)呈现明显的异速增长,碳汇量则表现为先升高后降低的趋势.2)凋落物碳密度介于0.42~1.74 t·hm^(-2)之间,碳汇量在各龄组间差异不大,发挥了0.23~0.42 t·hm^(-2)·10 a的碳汇功能,造林后固碳量随林龄成线性增长趋势.3)造林前期,土壤深层碳密度显著增大;造林后期,表层土壤碳在凋落物分解输入作用下逐渐累积,显著大于10~60 cm;造林能够有效提高土壤碳汇,平均碳汇量达51.66 t·hm^(-2)·10 a;造林后土壤固碳量与无林地相比提升较明显,21~30 a林龄时达最大值101.83t·hm^(-2),固碳量随林龄表现为先增后降的二项式分布.4)雪岭云杉人工林总碳汇呈非匀速增长趋势,其中60 a人工林碳汇潜力较高,总碳汇累积量可达488.60 t·hm^(-2);雪岭云杉人工林植被地上部和地下部碳汇在生态系统总碳汇的占比不断增加,由10~20 a林龄的4.6%增加至51~60 a林龄的67.7%,同时土壤碳汇在生态系统总碳汇的占比不断降低.

北美黄杉和云杉-松木-冷杉平行弦木桁架承载性能比较

【目的】对比不同腹杆角度下北美黄杉和云杉-松木-冷杉(SPF)华伦式平行弦木桁架的承载性能,探究腹杆角度和结构用材对华伦式平行弦木桁架承载性能的影响规律,为平行弦木桁架结构设计提供理论依据。【方法】以承载力和稳定性为验算指标,利用Smsolver结构力学求解器对平行弦木桁架各杆件的内力变化及其变形情况进行定量分析,得到平行弦木桁架腹杆角度的上、下临界角度和最优腹杆角度;采用ABAQUS有限元软件对3种腹杆角度的北美黄杉和SPF平行弦木桁架进行有限元模型分析与验证,获得不同基材平行弦木桁架在不同腹杆角度情况下的内力变化规律,判断其可能的破坏形式和受力机理;以SPF和北美黄杉为基材分别制作3种腹杆角度的平行弦木桁架,进行抗弯承载性能静力试验,探究平行弦木桁架的极限荷载、应力分布及主要破坏形式,并与有限元模拟结果进行对比,验证平行弦木桁架有限元模型分析的准确性和适用性。【结果】1)华伦式平行弦木桁架的最优腹杆角度为47°,下临界角度为34°,上临界角度为60°;2)北美黄杉平行弦木桁架的极限荷载范围为26.53~40.83 kN,跨中挠度范围为30.57~31.01 mm,SPF平行弦木桁架的极限荷载范围为23.48~34.16 kN,跨中挠度范围为31.85~32.05 mm;3)腹杆角度34°、47°、60°的北美黄杉和SPF平行弦木桁架极限荷载分别为26.53和23.48 kN、35.10和30.06 kN、40.83和34.16 kN,对应跨中挠度分别为31.85和31.01 mm、30.72和32.05 mm、30.57和31.97 mm;4)北美黄杉平行弦木桁架的破坏形式主要表现为靠近桁架支座处的腹杆出现裂纹以及桁架端部或荷载施加点处齿板拔出,SPF平行弦木桁架的破坏形式主要表现为桁架端部和荷载施加点处齿板拔出;5)ABAQUS有限元模拟和试验验证发现,2种平行弦木桁架跨中处弦杆轴力最大,往两边逐次递减,桁架跨中处腹杆轴力最小,往两边逐次递增,且弦杆轴力大于腹杆。【结论】北美黄杉平行弦木桁架承载性能优于SPF平行弦木桁架;平行弦木桁架的承载性能随腹杆角度增加而增加;2种平行弦木桁架的薄弱点均为桁架端部和荷载施加点处的齿板连接节点;ABAQUS有限元模型能有效反映出平行弦木桁架受力分布和整体结构变形趋势。

利用半球图像反演祁连山区青海云杉(Picea crassifolia)林盖度

青海云杉是祁连山森林生态系统的主要建群种,具有重要的生态水文功能。冠层盖度是评估生态环境的一个重要参数,但目前缺乏有效评估手段。半球摄影技术在估算林冠盖度方面已显示出潜在优势,但它受到环境条件例如天气的影响仍然没有报道。在祁连山排露沟流域利用半球摄影技术反演冠层盖度,界定不同天气条件对阈值的影响,评估与传统方法估算林冠盖度的差别,结果表明:分类阈值受天气状况的影响较大,阴天的最佳阈值为118,晴天的最佳阈值为149;另外传统观测与半球图像法获得的林冠盖度有一定的差异,其中最大差值17.88%,最小差值5.34%。该项研究对青海云杉林盖度估算提供新的方法,为生态水文过程模型提供有价值的输入参数。

青海云杉(Picea crassifolia)种群格局的分形特征及其影响因素

应用计盒维数、信息维数和关联维数对祁连山主要森林类型青海云杉（Picea crassifolia）种群空间格局进行的研究表明：青海云杉种群格局计盒维数在0.992～1.938之间,平均值为1.716,信息维数在0.996～1.860之间,平均值为1.632,关联维数在1.418～1.759之间,平均值为1.568。计盒维数与样地海拔和土壤水分含量呈显著的负相关,与样地坡向呈显著的正相关,信息维数与样地海拔呈显著负相关而与坡向呈显著的正相关,关联维数与样地坡度呈显著的负相关,主成分分析表明,海拔和土壤含水量是影响青海云杉种群格局分形维数第一主成分,坡向是第二主成分,坡度是第三主成分,这3个主成分累计解释率为87.6%。