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1.
《山地科学学报》2020,17(8):1891-1900
Siberian silkmoth(SSM,Dendrolimus sibiricus Tschetv.) is the most important defoliator of Siberian pine(Pinus sibirica Du Tour) and fir(Abies sibirica Ledeb.) stands.Warming-induced SSM outbreaks are one of the major driving factors of successions within the taiga zone.It is suggested that climate change impacted the SSM range and life cycle.We analyzed the migration of alpine and northerly SSM outbreak boundaries in Siberia and the impact of the climate variables and topography on the outbreak dynamics.We used time-series scenes(multispectral data,and vegetation indexes EVI and NDII) in combination with field studies,climate variables,and GIS techniques.We found that SSM outbreaks in the area of alpine boundary shifted about 370 m uphill since the mid of 1950.The outbreak onset was promoted by increased dryness and active temperatures and decreased root zone moisture content in the spring-early summer period.The terrain topography strongly affected SSM outbreak onset and dynamics.Initially,the outbreak was located at the middle elevations on the gentle concave southeastern slopes,which are the favorable insect habitats between outbreaks.Then the outbreak expanded uphill and downhill,to steeper slopes,and both concave and convex terrains.Alongside with elevation range expansion,SSM surpassed its northern historical outbreak boundary:the potential outbreaks' boundary moved about 300 km northward.Climate warming contributes to SSM migration into former outbreak free conifer stands located in highlands and at northern latitudes.  相似文献   

2.
The phenomenon of tree waves(hedges and ribbons) formation within the alpine ecotone in Altai Mountains and its response to observed air temperature increase was considered. At the upper limit of tree growth Siberian pine(Pinus sibirica) forms hedges on windward slopes and ribbons on the leeward ones. Hedges were formed by prevailing winds and oriented along winds direction. Ribbons were formed by snow blowing and accumulating on the leeward slope and perpendicular to the prevailing winds, as well as to the elevation gradient. Hedges were always linked with microtopography features, whereas ribbons were not. Trees are migrating upward by waves and new ribbons and hedges are forming at or near tree line, whereas at lower elevations ribbons and hedges are being transformed into closed forests. Time series of high-resolution satellite scenes(from 1968 to 2010) indicated an upslope shift in the position ribbons averaged 155±26 m(or 3.7 m yr~(-1)) and crown closure increased(about 35%–90%). The hedges advance was limited by poor regeneration establishment and was negligible. Regeneration within the ribbon zone was approximately 2.5 times(5060 vs 2120 ha~(-1)) higherthen within the hedges zone. During the last four decades, Siberian pine in both hedges and ribbons strongly increased its growth increment, and recent tree growth rate for 50 year-old trees was about twice higher than those recorded for similarly-aged trees at the beginning of the 20~(th) century. Hedges and ribbons are phenomena that are widespread within the southern and northern Siberian Mountains.  相似文献   

3.
Siberian larch (Larix sibirica Ledeb.) forests cover the largest areas in the Eurasian boreal zone, but there are insufficient data on its root system including the structure and functional traits of ectomycorrhizas (EM). The aim of this research is to find out if the morphological parameters of Larix sibirica EMs responded to the changes in elevation and main ecological factors (soil humidity, soil richness, soil acidity and habitat illumination). Using light microscopy, we studied EM diameter, root diameter, mantle width, and mantle volume share, share of tannin cells layers, EM density and EM length of Larix sibirica in two main types of plant communities along the elevation gradient at the Northern and Subpolar Urals. Differences in the environment were traced using phytoindication approach and the Ellenberg ecological scales. All the studied traits depend on the elevation and studied ecological factors. The diversity of fungal mantles is low, and the proportion of unstructured and pseudoparenchymatous mantles is high in response to the deterioration of the humidity, soil nitrogen content and acidity at higher-altitude habitats. Results of EM quantitative parameters measurements confirmed this pattern. We found a decline in the EM linear dimensions accompanied by a compensatory growth of the EM density with the raised elevation and the deterioration of environmental conditions.  相似文献   

4.
Within Karakoram Himalaya, Hunza River Basin(study area) is unique for a number of reasons: 1) potential impacts of highly concentrated highpitched mountains and glacial ice; 2) the glaciated portions have higher mean altitude as compared to other glaciated landscapes in the Karakoram; 3) this basin occupies varieties of both clean and debriscovered glaciers and/or ice. Therefore, it is imperative to understand the stability of topographic surface and potential implications of fluctuating glacial-ice causing variations in the movement of material from higher to lower elevations. This paper advocates landscape-level hypsometric investigations of glaciated landscape lies between 2280–7850 m elevation above sea level and non-glaciated landscape between 1461–7570 m. An attempt is made to understand intermediate elevations, which disguise the characteristics of glaciated hypsometries that are highly correlated with the Equilibrium Line Altitude(ELA). However, due to data scarcity for high altitude regions especially above 5000 m elevation, literature values for climatic conditions are used to create a relationship between hypsometry and variations in climate and ELA. The largest glaciated area(29.22%) between 5047 to 5555 m lies in the vertical regime of direct snow-accumulation zone and in the horizontal regime of net-accumulation zone(low velocity, net freezing, and no-sliding). In both landscapes, the hypsometric curves are ‘slow beginning' followed by ‘steep progress' and finally reaching a ‘plateau', reflecting the rapid altitudinal changes and the dominance of fluvial transport resulting in the denudation of land-dwelling and the transport of rock/debris from higher to lower altitudes. Reported slight differences in the average normalized bin altitudes against the cumulative normalized area between glaciated and non-glaciated landscapes are an indicator of slightly different land-forms and landform changes.  相似文献   

5.
Compared to burn interiors, edges exhibit distinct biotic and abiotic conditions that include microclimate, wind speed, sunlight levels, soil composition, moisture content, nutrient availability, population density, and species diversity. This study characterized the landscapes in which burned forest edges formed in Samcheok, Korea. Over the study area, 500-m2 grid cells were generated to capture landscape characteristics. Grid cells intersecting burn boundary lines were designated as edge, while cells without these lines were classified as the interior of burned areas. Topographic variables including slope, elevation, topographic wetness index, solar radiation index, and proportions of fuel and land use types within grid cells were computed in a geographical information system （GIS）. Correlation analysis with modified t-test and regression tree analysis were performed to explore the influences of landscape variables on edge formation with avoiding spatial autocorrelation problems. The results indicated that edges formed at low elevations with mild slopes, high topographic wetness, and low solar radiation. Edges were unlikely to form in areas dominated by Japanese red pines at low elevations. Moreover, heterogeneous land use/cover types contributed significantly to edge formation. Different forest management strategies for different landscape conditions can be more effective for enhancing resilience of forests to fire. Reducing susceptible fuel types might be effective at low elevations, while enhancing forest heterogeneity might be more effective at high elevations.  相似文献   

6.
Topographic feature points and lines are the framework of topography, and their spatial distance relationship is an breakthrough in the study of topographical geometry, internal structure and development level. Proximity distance(PD) is an indicator to describe the distance between the gully source point(GSP) and the watershed boundary. In the upstream catchment area, PDs can be expressed by the streamline proximity distance(SPD), as well as by the horizontal proximity distance(HPD) and the vertical proximity distance(VPD) in the horizontal and vertical dimensions, respectively. The series of indicators(e.g., SPD, HPD and VPD) are important for quantifying the geomorphological development process of a loess basin because of the headward erosion of loess gullies. In this study, the digital elevation model data with 5 m resolution and a digital topographic analysis method are used for the statistical analyses of the SPD, VPD and HPD in 50 sample areas of 6 geomorphic types in the Loess Plateau of northern Shaanxi. The spatial characteristics and the influencing factors are also analysed. Results show that: 1) Central tendencies for the HPDs and the VPDs for the whole study area and the six typical loess landforms are evident. 2) Spatial patterns of the HPDs and the VPDs exhibit evident trends and zonal distributions over the whole study area. 3) The HPDs have a strong positive correlation with gully density(GD) and hypsometric integral. The VPDs also correlates with GD to an extent. Vegetation cover, mean annual precipitation and loess thickness have stronger effects on the VPD than on the HPD.  相似文献   

7.
Local temperature changes in mountain areas are significantly affected by the uplifted mountain terrains. Understanding how temperature increase with mountain terrains is an important component in accurately modeling the spatial distribution of temperature. The study, after minimizing the effect of elevation and latitude, quantitatively simulated the temperature increase in the uplifted mountain terrains, described the characteristics in the spatial distribution of warming areas with different magnitudes, and identified the correlated indices of mountain bodies for warming. Selecting Yunnan Province in southwest China as the study area, we simulated the warming field on a baseline surface at the average elevation of 2000 m and average latitude of 24.96°. The results indicated that the warming magnitudes in different local areas varied with the change in the spatial locations, and the warming process concentrated in the mountainous regions. Throughout the entire study area, the warming field presented a general pattern of three terraces from the regions of high mountains to middle mountains and then low mountains. The areasof high warming magnitude mainly surrounded large mountain bodies and were distributed on the upper part. The areas of low warming magnitude clustered in the valleys and basins of the middle mountain region, mostly on the lower part of the large mountain bodies and its branches. The areas with zero warming magnitude occurred in the low mountains and broad valleys, which were distributed largely on the lower parts of the middle mountains and in most of the valleys. Quantified sampling analysis demonstrated good positive correlation between the warming magnitudes in uplifted mountain terrains and the volume index of the mountain body, as well as elevation difference, with the coefficients corresponding to 0.82 and 0.91, respectively.  相似文献   

8.
为了充分了解“一带一路”国家和地区百年的干旱变化规律和趋势,探索其干湿变化情况,本文利用标准化降水蒸散指数SPEI（Standardized Precipitation Evaporation Index）1901-2013年12个月和3个月尺度的0.5°×0.5°数据,结合线性趋势、PCA主成分分析、Mann-Kenndall非参数检验和小波分析等方法研究多时间尺度下干旱趋势和周期变化特征。结果表明,研究区百年尺度内（1901-2013）干旱指数和面积呈现波动上升趋势,但干旱化进程缓慢,60%以上地区呈现缓慢变湿趋势,SPEI指数发生显著上升地区面积百分比为25.38%,发生显著下降地区面积仅占12.02%。MK检验和PCA分析均显示15°~35°N的中低纬度地区干旱化程度最为严重,主要地区为北非及阿拉伯半岛、伊朗高原,常年呈现显著干旱状态,而俄罗斯、哈萨克斯坦、印度半岛以及中国和蒙古两国干湿变化季节性特征明显。基于Morlet小波分析的周期分析显示,年际和季节SPEI指数的周期特征既具有相似性,又存在一定的差异性,尺度越小干湿变化交替越明显,尺度越大虽有全局特征但所展示的周期不能通过显著性检验,最终得到可用显著周期年际SPEI变化显著尺度为2~4 a,干旱特征在此尺度的周期中时间变化显著。  相似文献   

9.
The relationship between species richness and elevation is a hot issue in ecology and has been documented extensively. It is widely accepted that area size can significantly affect this relationship and thus mask the effects of other predictors. Despite the importance of the relationship between species richness and elevation while accounting for the area effect, it is insufficiently studied. Here, we evaluated area-corrected species richness patterns of all vascular plants as well as six vascular plant subgroups (seed plants, ferns, trees, shrubs, herbs and vines) along a tropical elevational gradient (Hainan Island, China). If assessed in equal-elevation bands, uncorrected species richness showed bell-shaped curves, while area-corrected species richness assessed in equal-area bands appeared to increase monotonically due to the small proportion of highlands on Hainan Island. The mid-domain effect (MDE) was significantly correlated with both uncorrected and area-corrected species richness. On Hainan Island, the use of equal-area elevational bands increased the explanatory power of MDE. These findings provide useful insights to adjust for the area effect and highligh t the need to use equalarea bands along the elevational gradient.  相似文献   

10.
Evapotranspiration(ET) is a crucial part of the global hydrological cycle, and quantifying ET components is significant for understanding the global water cycle and energy balance. However, there is no consensus on the value of ET components, especially in topographic abrupt change zone, such as eastern margin of the Qinghai-Tibet Platea, where values of ET changes along the altitudinal gradients. Our aim is to explore the influencing factors in partitioning evapotranspiration and how ET components change with increasing elevations. A novel approach was proposed to estimate ET components by adding net solar radiation(Rn) instead of the vapor pressure deficit(VPD) into the underlying water use efficiency(u WUE) model based on one-year continuous measurements of flux data along the elevation gradient on Mount Gongga. Correlation analysis shows that the u WUE model's performance can be improved significantly by considering Rn instead of VPD, with correlation coefficients increasing by 35%-64%. The ratios of transpiration(T) to ET(T/ET) were 0.47, 0.48, 0.50 and 0.35 for the deciduous broadleaf forest(BF), mixed coniferous and deciduous broadleaf forest(MF), evergreen needle forest(ENF) and shrub land(SL), respectively. Leaf area index(LAI) and air temperature(Ta) were the two main controlling factors in determining T/ET during the growing season and at an annual scale, while Rn and Ta played more important roles during the dormant season. This study highlights the importance of incorporating Rn in partitioning evapotranspiration by using the water use efficiency(WUE) method in a humid mountainous region, which can improve the estimation of T/ET on a global scale.  相似文献   

11.
Elevation is one of key factors to affect changes in the environment, particularly changes in conditions of light, water and heat. Studying the soil physicochemical properties and vegetation structure along an elevation gradient is important for understanding the responses of alpine plants andtheir growing environment to climate change. In this study, we studied plant coverage, plant height, species richness, soil water-holding capacity, soil organic carbon(SOC) and total nitrogen(N) on the northern slopes of the Qilian Mountains at elevations from2124 to 3665 m. The following conclusions were drawn:(1) With the increase of elevation, plant coverage and species richness first increased and then decreased, with the maximum values being at 3177 m.Plant height was significantly and negatively correlated with elevation(r=–0.97, P0.01), and the ratio of decrease with elevation was 0.82 cm·100 m-1.(2) Both soil water-holding capacity and soil porosity increased on the northern slopes of the Qilian Mountains with the increase of elevation. The soil saturated water content at the 0-40 cm depth first increased and then stabilized with a further increase of elevation, and the average ratio of increase was2.44 mm·100 m-1. With the increase of elevation, the average bulk density at the 0-40 cm depth first decreased and then stabilized at 0.89 g/cm3.(3) With the increase of elevation, the average SOC content at the 0-40 cm depths first increased and then decreased,and the average total N content at the 0-40 cm depth first increased and then stabilized. The correlation between average SOC content and average total N content reached significant level. According to the results of this study, the distribution of plants showed a mono-peak curve with increasing elevation on the northern slopes of the Qilian Mountains. The limiting factor for plant growth at the high elevation areas was not soil physicochemical properties, and therefore,global warming will likely facilitate the development of plant at high elevation areas in the Qilian Mountains.  相似文献   

12.
The typically sparse or lacking distribution of meteorological stations in mountainous areas inadequately resolves temperature elevation variability. This study presented the diurnal and seasonal variations of the elevation gradient of air temperature in the northern flank of the western Qinling Mountain range,which has not been thoroughly evaluated. The measurements were conducted at 9 different elevations between 1710 and 2500 m from August 2014 to August 2015 with HOBO Data loggers. The results showed that the annual temperature lapse rates(TLRs) for Tmean,Tmin and Tmax were 0.45?C/100 m,0.44?C/100 m and 0.40?C/100 m,respectively,which are substantially smaller than the often used value of 0.60°C/100 m to 0.65°C/100 m. The TLRs showed no obvious seasonal variations,except for the maximum temperature lapse rate,which was steeper in winter and shallower in spring. Additionally,the TLRs showed significant diurnal variations,with the steepest TLR in forenoon and the shallowest in early morning or late-afternoon,and the TLRs changed more severely during the daytime than night time. The accumulated temperature above 0°C,5°C and 10°C(AT0,AT5 and AT10) decreased at a lapse rate of 112.8?C days/100 m,104.5?C days/100 m and 137.0?C days/100 m,respectively. The monthly and annual mean diurnal range of temperatures(MDRT and ADRT) demonstrated unimodal curves along the elevation gradients,while the annual range of temperature(ART) showed no significant elevation differences. Our results strongly suggest that the extrapolated regional TLR may not be a good representative for an individual mountainside,in particular,where there are only sparse meteorological stations at high elevations.  相似文献   

13.
At 5:39 am on June 24, 2017, a landslide occurred in the village of Xinmo in Maoxian County, Aba Tibet and Qiang Autonomous Prefecture(Sichuan Province, Southwest China). On June 25, aerial images were acquired from an unmanned aerial vehicle(UAV), and a digital elevation model(DEM) was processed. Landslide geometrical features were then analyzed. These are the front and rear edge elevation, accumulation area and horizontal sliding distance. Then, the volume and the spatial distribution of the thickness of the deposit were calculated from the difference between the DEM available before the landslide, and the UAV-derived DEM collected after the landslide. Also, the disaster was assessed using high-resolution satellite images acquired before the landslide. These include Quick Bird, Pleiades-1 and GF-2 images with spatial resolutions of 0.65 m, 0.70 m, and 0.80 m, respectively, and the aerial images acquired from the UAV after the landslide with a spatial resolution of 0.1 m. According to the analysis, the area of the landslide was 1.62 km2, and the volume of the landslide was 7.70 ± 1.46 million m3. The average thickness of the landslide accumulation was approximately 8 m. The landslide destroyed a total of 103 buildings. The area of destroyed farmlands was 2.53 ha, and the orchard area was reduced by 28.67 ha. A 2-km section of Songpinggou River was blocked and a 2.1-km section of township road No. 104 was buried. Constrained by the terrain conditions, densely populated and more economically developed areas in the upper reaches of the Minjiang River basin are mainly located in the bottom of the valleys. This is a dangerous area regarding landslide, debris flow and flash flood events Therefore, in mountainous, high-risk disaster areas, it is important to carefully select residential sites to avoid a large number of casualties.  相似文献   

14.
This study addressed the floral component traits and biomass allocation patterns of Gentiana hexaphylla as well as the relationships of these parameters along an elevation gradient (approximately 3700 m, 3800 m, 3900 m, and 4000 m) on the eastern Qinghai-Tibet Plateau. The plant height, floral characteristics, and biomass allocation of G. hexaphylla were measured at different altitudes after field sampling, sorting, and drying. Plant height was significantly greater at 3700 m than that at other elevations. Flower length was significantly greater at 4000 m than that at other elevations, whereas the flower length at low elevations showed no significant differences. Corolla diameter increased with altitude, although the difference was not significant between 3800 m and 3900 m. Variations in biomass accumulation, including the aboveground, photosynthetic organ, flower and belowground biomasses, showed non-linear responses to changes in altitude. The aboveground and photosynthetic organ biomasses reached their lowest values at 4000 m, whereas the belowground and flower biomass reached minimum values at 3700 m. The sexual reproductive allocation of G. hexaphylla also increased with altitude, with a maximum observed at 4000 m. These results suggest that external environmental factors and altitudinal gradients as well as the biomass accumulation and allocation of G. hexaphylla play crucial roles in plant traits and significantly affect the ability of this species to adapt to harsh environments. The decreased number of flowers observed at higher altitudes may indicate a compensatory response for the lack of pollinators at high elevations, which is also suggested by the deformed flower shapes at high altitudes. In addition, the individual plant biomass (i.e., plant size) had significantly effect on flower length and corolla diameter. Based on the organ biomass results, the optimal altitude for G. hexaphylla in the eastern Qinghai-Tibet Plateau is 3800 m, where the plant exhibits minimum propagule biomass and asexual reproductive allocation.  相似文献   

15.
Development and Applications of Dome A-DEM in Antarctic Ice Sheet   总被引：1，自引：0，他引：1  
Dome A, the highest dome of East Antarctic Ice Sheet, is being an area focused by international Antarctic community after Chinese Antarctic Expedition finally reached there in 2005, and with the ongoing International Polar Year (IPY) during August 2007. In this paper two data processing methods are used together to generate two 100-m cell size digital elevation models (DEMs) of the Dome A region (Dome A-DEM) by using Cokriging method to interpolate the ICESat GLAS data, with Ihde-DEM as a constraint. It provides fundamental data to glaciological and geophysical investigation in this area. The Dome A-DEM was applied to determining the ice-sheet surface elevations and coordinates of the south and north summits, defining boundaries of basins and ice flowlines, deducing subglacial topography, and mapping surface slope and aspect in Dome A region. The DEM shows there are two (north and south) summits in Dome A region. The coordinate and the surface elevation of the highest point (the north summit) are 80°21′29.86″S, 77°21′50.29″E and 4092.71±1.43m, respectively. The ice thickness and sub-ice bedrock elevation at north summit are 2420m and 1672m, respectively. Dome A region contains four drainage basins that meet together near the south summit. Ice flowlines, slope and aspect in detail are also derived using the DEM.  相似文献   

16.
In this paper,the quantitative relationship between the wild fruit communities and direct environmental factors is discussed on the basis of detailed data on landscape scale habitats obtained through field vegetation investigation.The results from TWINSPAN and DCCA showed that:1) In the distribution sections of the wild fruit forest in the Keguqin Mountain region,the basic patterns characteristic of the different habitats are due to topographic factors,nutrients and moisture conditions;2) The elevation affected the most basic differentiation of plant communities in the study area,indicating that the elevation condition was the most important factor restricting the distribution of the wild fruit communities in the study area;3) The close relationship between the moisture content in the upper soil layer and the elevation reflected the influence of moisture conditions on both wild fruit and herb-layer communities;4) Nutrient differences not only indicated that the habitat conditions were different in themselves but also showed that the present nutrient conditions of the habitats were seriously affected by human activities.In summary,under complicated mountainous topographic conditions,the habitat conditions for the communities differed very significantly,and the combination of elevation,soil moisture content,total nitrogen,slope aspect,and pH value influenced and controlled the formation of community distribution patterns in the study area.  相似文献   

17.
Effect of the Zagros Mountains on the spatial distribution of precipitation   总被引：4，自引：0，他引：4  
In order to examine the effect of the Zagros Mountains on precipitation, first, the annual and Seasonal rainfall indices （rain days frequency, rain amount, daily rainfall intensity, and heavy rains） from 43 stations in 1995 - 2004 between the 30° N to 35° N parallels over the mountain range were analyzed. Second, the effect of the Zagros Mountains was studied through the computation of the spatial correlations between the precipitation parameters and the topographic indices （station site elevation, station mean elevation within a radius of 2.5 km, mean elevation of 9 blocks along each of the eight Cartesian directions, and the elevation differences of these 9 blocks from the station mean elevation）. The results showed that in the cold season the maximal rainfall occurs on the upper range of west slope, while in warm season it spreads over the study area. The correlations between precipitation and elevation indices were positive on the north of the stations and negative on the south of the stations, that is, the higher elevations of the stations to the north force the uplifting of the moist air masses and increase rainfall at the stations, while the lower elevations to their south lead the movement of the moist air masses to the stations. This is due to the fact that these stations or slopes are exposed to the moist air masses coming from the Mediterranean Sea and the Persian Gulf. The heavy rain days and the summer sporadic rain events do not show significant correlations with the topographic indices. The findings indicate that the Zagros Mountains intensify the cold period frontal rains especially over the west slope and block the moist air masses from entering the interior parts of the country. Moreover, these mountains play a secondary role in creating rain days. But they are very important in the production of precipitation in the area. Therefore, their absence will decrease the amount of rainfall to their west and, in return, expand the dry climates of their west and east.  相似文献   

18.
This study addressed the floral component traits and biomass allocation patterns of Gentiana hexaphylla as well as the relationships of these parameters along an elevation gradient(approximately 3700 m, 3800 m, 3900 m, and 4000 m) on the eastern Qinghai-Tibet Plateau. The plant height, floral characteristics, and biomass allocation of G. hexaphylla were measured at different altitudes after field sampling, sorting, and drying. Plant height was significantly greater at 3700 m than that at other elevations. Flower length was significantly greater at 4000 m than that at other elevations, whereas the flower length at low elevations showed no significant differences. Corolla diameter increased with altitude, although the difference was not significant between 3800 m and 3900 m. Variations in biomass accumulation, including the aboveground, photosynthetic organ, flower and belowground biomasses, showed non-linear responses to changes in altitude. The aboveground and photosynthetic organ biomasses reached their lowest values at 4000 m, whereas the belowground and flower biomassreached minimum values at 3700 m. The sexual reproductive allocation of G. hexaphylla also increased with altitude, with a maximum observed at 4000 m. These results suggest that external environmental factors and altitudinal gradients as well as the biomass accumulation and allocation of G. hexaphylla play crucial roles in plant traits and significantly affect the ability of this species to adapt to harsh environments. The decreased number of flowers observed at higher altitudes may indicate a compensatory response for the lack of pollinators at high elevations, which is also suggested by the deformed flower shapes at high altitudes. In addition, the individual plant biomass(i.e., plant size) had significantly effect on flower length and corolla diameter. Based on the organ biomass results, the optimal altitude for G. hexaphylla in the eastern Qinghai-Tibet Plateau is 3800 m, where the plant exhibits minimum propagule biomass and asexual reproductive allocation.  相似文献   

19.
To identify impact factors on the distribution and characters of natural plants community in reclamation area, with survey data from 67 plant quadrats in July 2009, soil properties data from 216 sampling points in April 2009, and TM (30 m) data in 2006, the composition and characteristics of natural plants community in different time of the Fengxian area in the Changjiang (Yangtze) River estuary were analyzed with two-way indicator species analysis (TWINSPAN), multivariate analysis of variance (MANOVA), detrended canonical correspondence analysis (DCCA) and canonical correspondence analysis (CCA). The results show that: 1) The plant communities in the reclaimed area are mainly mesophytes and helophytic-mesophytic transitional communities, showing a gradient distribution trend with the change in reclamation years. Species richness (MA), species diversity (H) and above-ground biomass also increase with the increase of reclamation years. Nevertheless, they appear to decline slightly in the middle and late reclamation period (> 30 years). 2) With the rise in land use levels, the changes in species richness and species diversity tend to increase at first and then decrease; species dominance (D), however, tends to decline; and above-ground biomass increases slightly. 3) The distribution of the plant community is mainly influenced by the following factors: land use levels (R = 0.55, p < 0.05), soil moisture (R = 0.53, p < 0.05), soil salinity (R = 0.43, p < 0.05) and reclamation time (R = 0.40, p < 0.05).  相似文献   

20.
Climate affects Picea crassifolia growth and climate change will lead to changes in the climate–growth relationship (i.e., the “divergence” phenomenon). However, standardization methods can also change the understanding of such a relationship. We tested the stability of this relationship by considering several variables: 1) two periods (1952–1980 and 1981–2009), 2) three elevations (2700, 3000, and 3300 m), and 3) chronologies detrended using cubic splines with two different flexibilities. With increasing elevation, the climatic factor limiting the radial growth of Picea crassifolia shifted from precipitation to temperature. At the elevation of 2700 m, the relationship between radial growth and mean temperature of the previous December changed so that the more flexible spline had a greater precipitation signal. At the elevation of 3000 m, positive correlation of radial growth with mean temperature and precipitation in September of the previous year became more significant. At the elevation of 3300 m, positive correlation between radial growth and precipitation of the current summer and the previous spring and autumn was no longer significant, whereas the positive correlation between radial growth and temperature of the current spring and summer strengthened. The detrending with the most flexible spline enhanced the precipitation signal at 2700 m, while that with the least flexible spline enhanced the temperature signal at 3300 m. All results indicated that the divergence phenomenon was affected by the climatic signals in the chronologies and that it was most dependent on the detrending method. This suggests it is necessary to select a suitable spline bootstrap for studies of growth divergence phenomena.  相似文献   

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