Species diversity and its relation with soil factors under different site conditions in a desert-oasis ecotone

Vegetation and soil surveys were conducted under different site conditions in 2007-2011 to study species diversity using richness, evenness and diversity indices, in the middle portion of the Heihe River Basin. The relationship between species distribution and soil environmental factors was also studied by Canonical Correspondence Analysis （CCA）. Results show that vegetation coverage and species diversity were the highest in the interdune lowland, and the lowest in the mobile dime. Results of the Hill＇s index （di- versity ordering） shows that species diversity is reduced along decreasing soil water content, and the order of species diversity was interdune lowland, flat slope, fixed dune, semifixed dune and mobile dune. The influence degree of soil factors on vegetation dis- tribution was soil water content 〉 pH 〉 total K 〉 organic matter 〉 available N 〉 total N 〉 available K 〉 total P 〉 saline content 〉 available P. Soil water content and pH were important factors significantly affecting spatial distribution difference of vegetation, the environmental explanation was 98%.

Study on Ecological Landscape Pattern Change of Desert Sewage Discharge Area in Desert-Oasis Ecotone on the Southern Edge of Junggar Basin,Xinjiang

In order to understand the change characteristics of ecological landscape pattern of desert sewage discharge area in the desert-oasis ecotone on the southern edge of Junggar Basin,Xinjiang,based on the remote sensing images of 13 scenes GF1 and GF2 from 2013 to 2019,through image preprocessing,classification interpretation,GIS spatial analysis and landscape pattern index,the conclusions were as follows.From 2013 to 2019,the landscape area of sparse shrub forest land,grassland and saline alkali land increased,while the area of sandy bare land and pond surface increased.The mutual transformation among various types of landscapes was more active,among which the mutual transfer between sandy bare land and sparse shrub forest land was the most frequent.Various landscape dynamics changed significantly with time.All kinds of landscapes and the overall landscape showed the trend of fragmentation,discretization and complexity,and the overall landscape showed the trend of balanced distribution.The above results hoped to provide basic data and technical basis for eco-environmental protection,restoration and treatmen on the southern edge of Junggar Basin,and fill the current research gap.

The effect of hydrologic process changes on NDVI in the desert-oasis ecotone of the Hexi Corridor

In the arid inland river basins of northwestern China,human activities control almost all the surface hydrologic processes.The potential effects of these altered hydrologic processes are gradually becoming clear,especially since the 2000 implementation of the integrated water resources management projects in the Shiyang River,the Heihe River,the Tarim River,and the Shuler River.While the appearance of these eco-hydrology changes and consequent environmental effects in the oasis has attracted broad attention,related research is still lacking.Eco-hydrological process changes in the desert-oasis ecotone were investigated in the Pingchuan irrigation district in the middle reaches of the Heihe River.The results showed that the annual average amount of surface water irrigation during the past 20 years has decreased by 1.498×107 m3,while the annual average amount of well irrigation has increased by 1.457×107 m3,since 2000,when the State Council of China approved the water diversion scheme for the Heihe River Basin.The groundwater depth before the water diversion scheme generally varied between2.44–3.19 m(average 2.73±0.24 m),while that after the water diversion scheme has varied between 3.08–4.01 m(average3.79±0.62 m).The distribution area of<3 m groundwater depth decreased from 3612 to 394 hm2;while the distribution area of>3 m groundwater depth increased from 853 to 3843 hm2.However,although the hydrologic processes changed dramatically,no significant effects on vegetation productivity in the desert-oasis ecotone were detected during the study period.

Near-surface wind field characteristics of the desert-oasis transition zone in Dunhuang,China

The desert-oasis transition zone(DOTZ)serves as a buffer area between the desert and oasis.Understanding its wind field characteristics is of great significance for the prevention and control of aeolian disasters in the oasis.In this study,we used meteorological data during 2013–2019 from the portable meteorological stations at five sites(site A on the edge of the oasis,sites B,C,and D in the DOTZ,and site O in the desert)in Dunhuang,China to analyze the near-surface wind field characteristics and their causes,as well as to reveal the key role of the DOTZ in oasis protection.The results showed that the mean wind speed,frequency of sand-driving wind,and directional variability of wind decreased from west to east within the DOTZ,and wind speed was significantly affected by air temperature.The terrain influenced the prevailing winds in the region,mainly from northeast and southwest.Only some areas adjacent to the oasis were controlled by southeasterly wind.This indicated that the near-surface wind field characteristics of the DOTZ were caused by the combined effects of local terrain and surface hydrothermal difference.At site D,the annual drift potential(DP)was 24.95 vector units(VU),indicating a low wind energy environment,and the resultant drift direction(RDD)showed obvious seasonal differences.Additionally,the DOTZ played an important buffering role between the desert and oasis.Compared with the desert,the mean wind speed in the oasis decreased by 64.98%,and the prevailing wind direction was more concentrated.The results of this study will be useful in interpreting the aeolian activity of the DOTZ in Dunhuang.

生态交错带（Ecotone）理论研究进展

生态交错带（Ｅｃｏｔｏｎｅ）理论研究进展高洪文（东北师范大学草地研究所，长春１３００２４）ＡｄｖａｎｃｅｍｅｎｔｏｆＴｂｅｏｒｅｔｉｃａｌＲｅｓｅａｒｃｈｉｎＥｃｏｔｏｎｅ．￥ＧａｏＨｏｎｇｗｅｎ（ＩｎｓｔｉｔｕｔｅｏｆＧｒａｓｓｌａｎｄＲｅ－ｓｅａ...

生态环境脆弱带ECOTONE的基础判定

ECOTONE为国际生态界最近重新定义的基本概念之一。本文在诠释生态环境脆弱带的定义之后,对其实质及其空间属性作了较全面的逻辑归纳。在进一步研究的基础上,对于生态环境脆弱带作出了独立的函数表达,并且就生态环境脆弱带的宽度指标、重迭度指标、脆弱度指标、综合性指标,提出了较严格的表述形式。它们吸收了生态界面理论,并把系统生态学中的非稳定性理论,广延为辨识“全球变化”的基本手段,从而在生态学理论与应用两个方面,体现了研究的意义和价值。

蒙古栎群落交错带(ecotone)的研究

通过群落学的样地法对蒙古栎 (Quercusmongolica)群落和核桃楸 (Juglansmandshurica)群落、蒙古栎群落和长白落叶松 (Larixolgensis)群落、蒙古栎群落和杂灌丛群落及其交错带进行了研究 ,分析了在三个地点的几种群落结构和物种组成方面的差异 ,计算了各群落的物种丰富度指数 (dGl)、Simpson物种多样性指数 (D)、Shannon_Weiner物种多样性指数 (H′)及Pielou均匀度指数 (J)。研究发现在通化和大青沟两个地区群落交错带的物种丰富度及Shannnon多样性指数最高 ;而在桦甸群落交错带的物种丰富度和物种多样性指数要比核桃楸群落低 ,比蒙古栎群落高 ,没有表现出特别强烈的边缘效应。本文也分析了群落乔木层、灌木层和草本层盖度之间的关系。

Current Situation and Development Countermeasures on Grassland Resource in Farming-pasturing Ecotone in West Jilin Province

Upon the current degradation situation of grassland in west Jilin Province,I analyzed the effects of natural factors and human activities on the degradation of grassland,and further purposefully put forward countermeasures on the remediation and development of grassland.As a conclusion,scientifically utilizing and protecting the grassland resources could suppress grassland degradation,promoting the sustainable development of regional economy.

Study on Over-urbanization of the Ecotone between Mount Tai and Tai'an City

By investigating the ecotone between Mount Tai Scenic Area and downtown area of Tai'an City,the characteristics of such an ecotone are analyzed,serious problems brought by the over-urbanization to local natural environment,such as destruction of eco-environment,aggravated pollution and degradation of mountainous landscape resources are studied.Then countermeasures for the harmonious development of the ecotone are proposed to better promote the coordinated development of cities and mountainous scenic areas.

Vegetation landscape structure and dynamics in sandy forest-steppe ecotone

Sandy forest-steppe ecotone in Baiyinaobao Natural Reserve of Inner Mongolia Autonomous Region of China is one of the special landscape types in forest-steppe vegetation zone in China. Vegetation landscape types, landscape patches, and patch size were measured by the field investigation, forest photograph, and airscape. The structure of landscape patches in sandy forest-steppe ecotone, including composition structure, and size structure, was studied and the dynamics and transformation of landscape patches were analyzed. The data obtained in this study could provide theoretical basis for the research on vegetation landscape in forest-steppe ecotones and other vegetation types.

Research Progress on Ecological Safety Assessment of the Farming-pastoral Ecotone in China

[Objective] The study was conducted to overview the farming-pastoral ecotone research progress in China.[Methods] Started from the influences on soil,precipitation and water conservation,climate and mulching of different land use types,the paper summarized the current research situation on several hot issues and proposed suggestions for future study.[Results] Researches on farming-pastoral ectone in China have achieved great progress,but still require more deep and comprehensive studies.Suggestions：Current studies should focus on solutions for degradation of farmland and grassland;Conduct deeper analysis on the relatively weaker aspects in a multi-domain fusion type;Implement the study results on eco-environmental recovery,production improvement and other practical activities;Lift the research of ecotone to a national or even global level,and make them far more comprehensive.[Conclusion] Provide theoretical basis for ecological protection of farming-pastoral ecotone in our country.

Quantification of driving factors on NDVI in oasis-desert ecotone using geographical detector method

Within oasis-desert ecotone regions,the normalized difference vegetation index(NDVI)is an important parameter for evaluating the growth of vegetation.An accurate quantitative study between NDVI and environmental and anthropogenic factors is critical for understand the driving factors of vegetation growth in oasis-desert ecotone.In 2016,four periods Landsat 8 OLI_TIRS images,relevant climatological parameters data(air temperature,air relative humidity,wind velocity and accumulated temperature),land cover type data and soil data were selected as proxies.In order to quantify the explanatory power for NDVI spatial and temporal distribution in the southern edge of Dunhuang City and northern side of the Mingsha Mountain,the geographical detector model was used to explain the potential influences of factors versus the spatial distribution of NDVI,and each explanatory variable's relative importance can be calculated.The factor detector results disclose that the spatial distribution of NDVI is primarily dominated by land cover type.The risk detector results show that,high NDVI region is located within woodland.The mean value of NDVI displays an increase and then decrease trend with air temperature increase.With the increase of wind velocity and decrease of air relative humidity,the NDVI value shows a decrease trend.The interactive q values between the two factors are higher than any q value of separated factors.Results also indicate that the strongest interactive effects of NDVI are different in distinct seasons.Consequently,anthropogenic activity is more important than environmental factors on NDVI in oasis-desert ecotone.We also demonstrate that air relative humidity rather than air temperature have played a greater role in NDVI spatial distribution.

Soil properties and herbaceous characteristics in an age sequence of Haloxylon ammodendron plantations in an oasis-desert ecotone of northwestern China

Haloxylon ammodendron, a typical desert shrub with C4 pathway of photosynthesis, possessing a strong ability to adapt to an extreme drought environment, has a rapid growth rate in sandy lands and is widely used in sand-fixing shelter-forest systems in oasis-desert ecotones. To assess the effects of H. ammodendron plantation on the soil, we measured soil properties and herbaceous characteristics along a nearly 40-year chronosequence after H. ammodendron was planted in shifting sand dunes in an oasis-desert ecotone. Results showed that silt and clay fractions increased significantly in the topsoil. The accumulation rates of soil organic carbon （SOC）, total nitrogen （TN） and total phosphorus （TP） were faster in the early stages （0-9 years） and slower in the late stages （9-39 years）. The soil pH and electrical conductivity （EC） were higher than those in the non-vegetation dunes. Moreover, the soil properties in the topsoil （0-5 cm） showed larger variation scope than those in the deeper soil layers （5-20 cm）. The significant relationships of the soil silt＋clay content with the chemical properties mainly appeared in the topsoil. The wind erosion susceptibility of the soil, evaluated by erodible fraction （EF）, decreased significantly with increasing H. ammodendron plantation age. Additionally, the annual pioneer herb, Agriophyllum squarrosum, was gradually substituted by the annual salt-tolerant herb, Bassia dasyphylla, with increasing plantation age. These results showed beneficial effects of H. ammodendron plantation on improving soil conditions. However, the dynamics of the herbaceous species also reminded us that the long- term effects of H. ammodendron plantation, especially on changes in vegetation composition, still need further evaluation.

Desert vegetation distribution and species-environment relationships in an oasis-desert ecotone of northwestern China

Environmental heterogeneity significantly affects the structure of ecological communities.Exploring vegetation distribution and its relationship with environmental factors is essential to understanding the abiotic mechanism(s)driving vegetation succession,especially in the ecologically fragile areas.In this study,based on the quantitative analysis of plant community and environmental factors in 68 plots at 10 different transects in the Minqin oasis-desert ecotone(ODE)of northwestern China,we investigated desert vegetation distribution and species-environment relationships using multivariate analysis.Two-way indicator species analysis(TWINSPAN),detrended correspondence analysis(DCA),and canonical correspondence analysis(CCA)methods were used.A total of 28 species,belonging to 27 genera in 8 families,were identified.Chenopodiaceae,Zygophyllaceae,Gramineae,and Leguminosae were the largest families.Annual and perennial herbs accounted for 28.60%of the total number of plants,while shrubs(42.90%)were the most dominant.Nitraria tangutorum was the constructive species of the desert plant community.We divided the 68 plots surveyed in this study into 7 community types,according to the results of TWINSPAN.The distribution of these 7 communities in the DCA ordination graph showed that species with a similar ecotype were clustered together.Results of CCA indicated that groundwater was the dominant factor influencing vegetation distribution,while distance between plot and oasis(Dis)and soil electrical conductivity(EC)were the local second-order factors.Our study suggests that optimizing the utilization of groundwater in oases is key to controlling the degradation of desert vegetation.The favorable topographic conditions of sand dunes should be fully utilized for vegetal dune stabilization,and the influence of soil salinity on the selection of afforestation tree species should be considered.

Changes in soil carbon stocks and related soil properties along a 50-year grassland-to-cropland conversion chronosequence in an agro-pastoral ecotone of Inner Mongolia,China

Land use change significantly influences soil properties. There is little information available on the long-term effects of post-reclamation from grassland to cropland on soil properties. We compared soil carbon （C） and nitrogen （N） storage and related soil properties in a 50-year cultivation chronosequence of grassland in the agro-pastoral ecotone of Inner Mongolia. Field surveys on land use changes during the period of 1955-2002 were conducted to build a chronosequence of cropland of different ages since the conversion from grassland. The results showed that soil C and N storage, soil texture, and soil nutrient contents varied with land use types and cropland ages （P〈0.01）. In the 0-30 cm soil layer, the soil organic carbon （SOC） density was significantly lower in the crop- lands （3.28 kg C/m2 for C50 soil） than in the grasslands （6.32 kg C/m2）. After 5, 10, 15, 20, 35, and 50 years of crop planting （years since the onset of cultivation）, the SOC losses were 17%, 12%, 19%, 47%, 46%, and 48%, respec- tively, compared with the grasslands. The soil total nitrogen （TN） density of the grasslands was 65 g N/m2, and TN density of the cropland soil was 35 g N/m2 after 50 years of crop planting. Both the SOC and TN densities could be quantitatively determined by a negative exponential function of cropland age （P〈0.0001, R2=0.8528; P〈0.0001, R2=0.9637）. The dissolved organic carbon （DOC） content, pH value were decreased; and the soil bulk density and soil available potassium （AK） content, clay content, and sand content were increased since the conversion of grassland into cropland during the 50-year period. Our results show soil nutrients were higher in grassland than in cropland. The conversion of grasslands to croplands induced a loss of soil C storage and changes of related soil properties. The reclamation time of cultivated soil （cropland age） had significant effects on soil properties in the study area.

Dendroclimatic response of Abies spectabilis at treeline ecotone of Barun Valley, eastern Nepal Himalaya

A dendroclimatic study was conducted in the treeline ecotone of Barun Valley, eastern Nepal, to determine the tree-ring climate response and ring width trend of Abies spectabilis. A 160-year-old chronology, from 1850 to 2010, was developed from 38 tree-ring samples. No higher growth in recent decades was observed in tree-ring width in this area. The mean temperature of the current year in February and in the combined winter months of December, January, and February showed significant positive correlation with tree-ring width, although no significant correlation was found between tree-ring width and the precipitation pattern of the region. This tree-ring climate response result is different from that in other studies in Nepal, which could be attributed to location and elevation.

Vertical and temporal distribution of nitrogen and phosphorus and relationship with their influencing factors in aquatic-terrestrial ecotone:a case study in Taihu Lake,China

Vertical and temporal distributions of N and P in soil solution in aquatic-terrestrial ecotone （ATE） of Taihu Lake were investigated, and the relations among N, P, ORP （oxidation reduction potential）, TOC, root system biomass and microorganism were studied. As a whole, significant declines in TN, NO3^--N, DON （dissolved organic nitrogen） and TP concentration in soil solution have occurred with increase of the depth, and reached their minima at 60 cm depth, except for NH4^＋-N, which increased with depth. The concentration of TP increased gradually from spring to winter in the topsoil, the maximum 0.08 mg/L presented in the winter while the minimum 0.03 mg/L in spring. In the deeper layer, the concentration value of TP fluctuated little. As for the NO3^--N, its seasonal variation was significant at 20 cm depth, its concentration increased gradually from spring to autumn, and decreased markedly in winter. Vertical and temporal distribution of DON is contrary to that of NO3^--N. The results also show that the variation of N and P in the percolate between adjacent layers is obviously different. The vertical variation ofTN, TP, NO3^--N, NH4^＋-N and DON is significant, of which the variation coefficient of NO3^--N along the depth reaches 100.23%, the highest; while the variation coefficient of DON is 41.14%, the smallest. The results of correlation analysis show that the concentration of nitrogen and phosphorus correlate significantly with TOC, ORP, root biomass and counts of nitrifying bacteria. Most nutrients altered much from 20 to 40 cm along the depth. However, DON changed more between 60 and 80 cm. Results show that soil of 0-60 cm depth is active rhizoplane, with strong capability to remove the nitrogen and phosphorus in ATE. It may suggest that there exists the optimum ecological efficiency in the depth of above 60 cm in reed wetland. This will be very significant for ecological restoration and reestablishment.

Community Structure and Seasonal Variation of Soil Arthropods in the Forest-Steppe Ecotone of the Mountainous Region in Northern Hebei,China

Soil fauna have been receiving more and more attention because they play an important role in nutrient cycling.However,there is a lack of information on soil arthropods in the forest-steppe ecotone in the mountainous region of northern Hebei,which makes it difficult to meet the need of protecting biodiversity in this area.Soil arthropod communities were investigated in the forest-steppe ecotone in northern Hebei province to provide basic information on changes in mountain soil fertility,which could promote the development of soil arthropod communities in mountain ecotones.From the preliminary identification,a total of 7994 individual soil arthropods were collected,which belonged to 25 groups,6 classes and 24 orders.Acarina,Hymenoptera and Collembola were the dominant groups in the ecotone.The number of Acarina was higher than Collembola,and this phenomenon was obviously different from other areas in the same climate zone.The increased abundance of rare groups in the Forest zone with the richer vegetation,higher arthropod abundance and more substantial litter depth,could be interpreted as a reaction to the suitable soil environment and food supply.And these rare groups were sensitive to environmental changes,which could be regarded as biotic indicators for evaluating soil quality.The analysis of community diversity showed that the abundance index (d),the Shannon-Wiener index (H'),the evenness index (J) and the density-group index (DG) were significantly higher in the forest zone,lower in the forest-steppe zone,and lowest in the meadow-steppe zone.Seasonal variations in community composition correlated with changes in average air temperature and precipitation in this ecotone.Groups and individuals of soil arthropod communities in the three zones were present in greater numbers in the middle of the rainy season than in the early or late periods of the rainy season as a whole.At the same time,seasonal changes in soil arthropod communities from different plots were also influenced by habitat condition.

Effects of land use change on the spatiotemporal variability of soil organic carbon in an urban-rural ecotone of Beijing,China

Understanding the effects of land use changes on the spatiotemporal variation of soil organic carbon （SOC） can provide guidance for low carbon and sustainable agriculture. In this paper, based on the large-scale datasets of soil surveys in 1982 and 2009 for Pinggu District -- an urban-rural ecotone of Beijing, China, the effects of land use and land use changes on both temporal variation and spatial variation of SOC were analyzed. Results showed that from 1982 to 2009 in Pinggu District, the following land use change mainly occurred： Grain cropland converted to orchard or vegetable land, and grassland converted to forestland. The SOC content decreased in region where the land use type changed to grain cropland （e.g., vegetable land to grain cropland decreased by 0.7 g kg-1; orchard to grain cropland decreased by 0.2 g kg-l）. In contrast, the SOC content increased in region where the land use type changed to either orchard （excluding forestland） or forestland （e.g., grain cropland to orchard and forestland increased by 2.7 and 2.4 g kg-1, respectively; grassland to orchard and forestland increased by 4.8 and 4.9 g kg-1, respectively）. The organic carbon accumulation capacity per unit mass of the soil increased in the following order： grain cropland soil〈vegetable land/grassland soil〈orchard soil〈forestland soil. Therefore, to both secure supply of agricultural products and develop low carbon agriculture in a modern city, orchard has proven to be a good choice for land using.

Soil N Pools and Transformation Rates Under Different Land Uses in a Subalpine Forest-Grassland Ecotone

Soil nitrogen pools (NP), denitrification (DN), gross nitrification (GN), N2O and CO2 flux rates with their responses to temperature increases were determined under five different land uses and managements in a subalpine forest-grassland ecotone of the eastern Tibetan Plateau. Land uses consisted of 1) sparse woodland, 2) shrub-land, 3) natural pasture, 4)fenced pasture, and 5) tilled pasture mimicking a gradient degenerating ecosystem under grazing impacts. The NO3--N content was higher than the NH4+-N content. Comparing tilled pasture with fenced pasture showed that higher intensive management (tillage) led to a significant decrease of soil organic matter (SOM) (P ＜ 0.05) in the soils, which was in contrast to the significant increases (P ＜0.05) of DN, GN, N2O and CO2 flux rates. GN (excluding tilled pasture) and CO2 flux rates increased with a temperature rise, but DN and N2O flux rates normally reached their maximum values at 12-14 ℃ with tilled pasture (the highest management intensity) being very sensitive to temperature increases. There was a difference between net nitrification and GN, with GN being a betterindicator of soil nitrification.