Response of tree-ring growth to climate at treeline ecotones in the Qilian Mountains,northwestern China

Climate constitutes the main limiting factor for tree-ring growth in high-elevation forests, and the relationship between tree-ring growth and climate is complex. Based on tree-ring chronology and meteorological data, the influence of precipitation, mean temperature and mean minimum temperature at yearly, seasonal and monthly scales on the tree-ring growth of Picea crossifolia was studied at treeline ecotones in the Qilian Mountains, northwestern China. The results show that growing season temperatures of previous and current years are important limiting factors on tree-ring growth, particularly June mean temperature and mean minimum temperature of current year. The precipitations in the previous winter and current spring have a positive correlation, and in the current fall has a negative correlation with tree-ring growth, but these correlations are not significant. Our results suggest that temperature controls tree-ring growth more strongly than precipitation at treeline ecotones in the Qilian Mountains.

Degradation problems of the land/water ecotones in China and their ecological impact to water systems

Degradation of land/water ecotones in China is a serious problem and it is often neglected by people. The types of ecotone degradation are described and analyzed. The degradation of land/water ecotones enhanced the water quality reduction, bank erosion, desasters such as landslide, flood and drought, biodiversity reduction, lost of fertilized lands, decrease of the resource value of water scenic beauty and many others. The paper analyzes how these problems are related with each other.

Biomass distribution patterns of ecotones between forest andswamp in Changbai Mountaion

This paper studied the biomass distribution patterns of Lanix olgensis/swamp ecotones and Betula platyphlla/swamp ecotones in Changbai Mountain so as to provide theory foundation for the management of these nature resources, by setting up sample belts, investigating initial data along the environmental gradients change, and establishing regression models. By means of regression models, the biomass of communities, layers, tree species and organs was calculated. In this system, it was found that the community biomass inreased gradually along the environmental gradients change from swamp to forest in Changbai Mountain. Furthermore, the ecotoneal biomass distributed mainly over tree layer. The tree biomass distributed mainly in two or three dominate tree species.

Examples of Ecotones and Paragenese in the Vegetation Cover of the Baikalian Siberia

Changes in vegetation structure in environments contact community characterize the ecotones and paragenese inside zonal vegetation site or altitude belt as of concrete environments while differences of cenotic structures of communities between zones or between altitude belts as well. The aim of this work was research of structural-dynamic organization of phytocenoses forming under the conditions of environments contact and mountain tundra, forests (zonal taiga) and extrazonal steppes, zonal forest steppes of some areas at the Baikalian Siberia, Eastern Siberia of Russia.

Current vegetation dynamics of the “forest-mountain tundra” ecotones of Lake Baikal coastal ranges

During last decades, new trends appeared in the ecotones of the upper boundary of forests at the ridges surroundingLakeBaikal(Khamar-Daban and Baikal’sky Ridge): ones to advance of wood species (Pinus sibirica Du Tour, Abies sibirica Ledeb., Larix sibirica Ledeb., Larix dahurica Lawson) out of timber stands into the area of subgoltsy with Pinus pumila (Pallas) Regel. up to mountain tundras. In average, this is from 100 to 200 - 300 meters (maximum up to500 m) in linear distance from the margin of dense timber stand. A burst of forests renewal occurred in 1989-1995, it resulted probably from a high productivity of the seeds of wood species due to warmer winters in 1980ies-1990ies which favoured the formation of favourable climate-edaphic conditions for the development of forest communities above the forests boundary on the ridges surrounding Lake Baikal.

What can natural edges of gallery forests teach us about woody community performance in sharp ecotones?

Aims The diversity and structure of forest edges are a central issue in ecology.However,most studies have focused on anthropogenic for-est edges,being natural ones least understood.We studied the com-munities of shrubs and trees in natural edges of gallery forests with the main goal of learning what are the main factors that shape the structure and diversity of these natural sharp ecotones.Methods We evaluated 10 gallery forest sites,allocating in each of them three 15×20 m plots.The plots were laid out in relatively rectilinear stretches of forest edges,respecting a minimal distance of 10 m between each plot.As they are permanent plots and meant to study eventual fluctuations in the forest-grasslands limits,we allocated the plots with their longest side parallel to the forest edge and covering perpendicularly 5 m of the grassland and 10 m of forest.Inside the plots we identified,mapped and measured all shrub and tree individuals with diameter at breast height(DBH)≥1 cm.Important Findings Although many differences exist among the communities in terms of density and basal area,all of them were highly dense and had relatively low basal areas.In addition,both the number of individu-als and the basal area increased rapidly towards the forest interior.Our results also revealed that the edge communities are composed mainly by small individuals that demand a great amount of light.Both the vertical stratification and the proportion of the functional groups are similar among the sites yet change quickly in the first 10 m of the forest edge.However,the floristic similarities were low among the communities mainly due to the species turnover within each area.Therefore,although the overall structure is constant in the studied edges,the low floristic similarity among them possibly indicates that the species within the same functional groups are sub-stituting each other across the sites.Despite older and seemingly stable,our results showed the gallery forest edges are quite similar to the anthropogenic edges or recent clearings.This points out that,independent of the age,those characteristics are possibly permanent in edges.

Species richness and similarity of the flora on four lajedos in Boa Nova, Bahia, Brazil

The municipality of Boa Nova,in northeastern Brazil,is in an ecotone zone between the Caatinga and Atlantic Forest phytogeographic domains.The transition phytophysiognomy is seasonal forest and known locally as mata de cipó.In these phytophysiognomies there are lajedos,which are rock outcrops colonized by vegetation welladapted to extreme microclimatic variation and vegetation diversity is affected by the vegetation types of the surrounding areas.Due to the singularity of these environments and the relevance of floristic studies for conservation,this work aimed to identify the species richness and compare the similarity of the flora on four rock outcrops in Boa Nova.The flora was surveyed during exploratory walks along lajedos between 2016 and 2019.In total,162 species were identified on the Boa Nova outcrops.The flora has a composition and structure similar to semiarid outcrops,as well as endemic species that also occur in surrounding phytophysiomies.Despite the proximity,a similarity index revealed there is floristic dissimilarity between the areas.Nine new occurrences were recorded for the region,five species are threatened with extinction(Aosa gilgiana,Ficus cyclophylla,Hippeastrum stigmovittatum,Pleroma caatingae and Trixis pruskii),and 43 species are common in anthropogenic areas.This reinforces the importance of actions to conserve these areas.

Agricultural Vulnerability to Drought in China's Agro-pastoral Ecotone:A Case Study of Yulin City,Shaanxi Province

Agro-pastoral ecotone of northern China is the prominent area for agricultural production,but it is also the most typical ecological fragile area with frequent drought disasters.Taking Yulin City at Shaanxi Province in China as the case area,the paper aims to investigate the spatio-temporal changes of agricultural vulnerability to drought in China’s agro-pastoral ecotone in the period 2000 to2020.The results show that:1)the agricultural vulnerability to drought in Yulin City has shifted from high vulnerability in the period2000–2010 to low vulnerability in the period 2011–2020.2)There exist obvious spatio-temporal differences of the agricultural vulnerability to drought in Yulin City during the research period.3)Four sensitive events and 14 resilient events were identified in the research and the crops of Yulin had become more resilient to drought.Finally,the paper put forward with policy implications to make adaptive strategies of agriculture to climate change in China’s agro-pastoral ecotone in the future,e.g.,carrying out agricultural zoning based on agricultural production conditions,intensifying the construction of disaster prevention and relief system,and integrating with modern agricultural technology to develop new type agriculture.

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...

生态型城镇化:生态脆弱区城镇化道路的必然选择

在全面建设小康社会中 ,生态脆弱区 (ECOTONE)面临脱贫与现代化建设的双重任务 ,大力提高城镇化水平既是实现双重任务的手段也是现代化建设的目标。生态脆弱区的城镇化必须考虑生态脆弱性和特殊的人地关系。在分析城市现代化发展的趋势和生态脆弱区城镇化的具体实际的基础上 ,根据生态城市理论、生态学理论、城市地区理论和新城市主义的观点 ,参照国内外成功的实践经验 ,生态型城镇化是生态脆弱区城市化道路的必然选择 ,“大分散、小集中”是脆弱生态区城镇化可行的区域性策略。

泰山与泰安城区交错带过度城市化问题研究(英文)

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.

生态环境脆弱带对全球变化研究的特殊意义

生态环境脆弱带对全球变化响应具有独特性 ,能及时、灵敏地反映全球变化 ,体现全球变化的早期信号 ,且将变化过程记录在系统物质环境中 ,对生态环境脆弱带的研究在全球变化研究中具有特殊的意义。文章以农牧交错带对全球变化响应为例 ,分析响应的自然基础、响应过程及特点 。

The tropical-subtropical evergreen forest transition in East Asia:An exploration

The transition from tropical to subtropical(warm temperate)evergreen forests is more clearly apparent in East Asia,fromNepal to the western Pacific coast,than elsewhere in the tropics.We review the nature of this transition and hypothesize the physical,ultimately climatic,factors thatmay maintain it,with a special focus on how the increasing instability and warming of climates will affect these forests.A primary climatic mediator of the transition is proposed,thereby offering a testable hypothesis for the climateeforest transition relationship.What is known of this transition is summarized in context of the primary climatic mediators of elevational zonation of forest formations in equatorial Asia to the tree line,in the Himalaya at the India-Indo-Burma northern tropical margin,and as both elevational and latitudinal zonation in southern China.Consequent secondary edaphic and other physical changes are described for the Himalaya,and hypothesized for southern China.The forest ecotones are seen to be primarily defined by tree floristic change,on which account changes in structure and physiognomy are determined.The montane tropical-subtropical transition in the Himalaya is narrowand observed to correlate with an as yet ill-defined frost line.A distinct tropical-subtropical transition forest is recognized in the southwest Chinamountains.There is a total change in canopy species at the Himalayan ecotone,but subcanopy tropical species persist along an elevational decline of c.400 m.The latitudinal transition in South China is analogous,but here the tropical subcanopy component extends north over ten degrees latitude,albeit in decline.The tropical-subtropical transition is uniquely clear in East Asia because here alone a tropical wet summer-dry winter monsoon extends to 35
north latitude,encompassing the subtropical evergreen forest,whereas subtropical evergreen forests elsewhere exist under drier temperate summer climate regimes.

Impacts of soil fauna on nitrogen and phosphorus release during litter decomposition were differently controlled by plant species and ecosystem type

The dynamics of litter nitrogen (N) and phosphorus (P) release could be affected by soil fauna and environmental conditions. The objective of the present study was to investigate the effects of soil fauna on the dynamics of N and P during foliar litter decomposition in three types of ecosystems (i.e., montane forest, ecotone, and dry valley) along an elevation gradient. A field experiment using litterbags with two different mesh sizes (0.04 and 3 mm) was conducted from November 2013 to October 2014. Nitrogen and P release rates in decomposing foliar litter from fir (Abies faxoniana) and birch (Betula albosinensis) in montane forest, oak (Quercus baronii) and cypress (Cupressus chengiana) in ecotone, and cypress and clovershrub (Campylotropis macrocarpa) in dry valley were investigated in the upper reaches of the Yangtze River. Soil fauna strongly affected N and P release across different decomposition periods and ecosystem types. The average release rate of N mediated by soil fauna across the entire year was higher in the dry valley (15.6–37.3%) than in the montane forest (0.5–6.4%) and the ecotone (- 3.7–4.9%). The effects of soil fauna on P release rate were manifest in both the montane forest and the dry valley. Moreover, the impacts of soil fauna can vary substantially among different decomposition periods. Our results indicated that soil fauna can significantly affect N and P release during litter decomposition. The N release rate mediated by fauna was likely to be more sensitive to the effects of plant species (i.e., initial litter chemical traits), while the P release rate mediated by soil fauna might be subject to the effects of local-scale environmental factors (e.g., temperature) to a greater extent.

Changes of landscape pattern and its influence on environment in Dongling District，Shenyang City，China

Dongling District of Shenyang City is an ecotone between city and countryside. Human disturbance causes serious changes of the landscape pattern studed by using indices of landscape pattern: proportion in land cover types,average area and number of patches,fractal dimension of patches,indices of diversity, dominance and contagion and index of human disturbance.There are many changes of the landscape pattern of Dongling District for the last 30 years.The landscape pattern is breaking, the diversity is increasing and the dominance is decreasing.There are different fractal dimension and contagion in distinct geomorphological unit.The changes of landscape pattern bring some beneficial results but causes deterioration of ecological environment.

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.

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.

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.

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.

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.