渭北黄土高原刺槐林—草地景观界面土壤水分影响域及其动态变化规律研究

对渭北黄土高原刺槐林—草地景观界面土壤水分影响域及其时空动态变化规律进行了研究。采用移动窗口法分析得出刺槐林—草地景观界面土壤水分影响域为林内4 m到林外12 m之间,宽度16 m,为渐变型界面,由此可将刺槐林—草地景观划分为3个区域：草地区、界面区和刺槐林区。经典统计分析表明,历经3个区域,不同层次的土壤水分在水平方向上随着水平距离梯度的变化表现出不同的上升或下降的趋势,在界面区域土壤含水量变化最为显著。基于标准差和变异系数两个指标,可将草地和林地区域土壤剖面水分垂直变化划分为4层,界面区域划分为3层。3个区域土壤含水量的季节变化表现为基本一致的“高-低-高”规律,可以划分为3个时期,4～5月中旬为土壤水分贮存期,6～7月中旬为土壤水分消耗期,8～10月中旬土壤水分恢复期。水分在时间和空间上的这种变化主要受植被类型、根系分布、降水资源再分配的影响。

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.

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.

Ecological Consequences of Land Use Change: Forest Structure and Regeneration across the Forest-grassland Ecotone in Mountain Pastures in Nepal

The ecotone, the spatial transition zone between two vegetation communities, is claimed to have more species than the adjoining communities. However, empirical studies do not always confirm higher richness at the ecotone. The ecotone position and structure are dynamic over time and space and it is driven by the changes in climate, land use or their interaction. In this context, we assessed the forest- grassland ecotone of temperate mountains in central Nepal by i） comparing species composition and richness across the ecotone, ii） analyzing if the forestgrassland ecotone is shifting towards the grassland center by colonizing them with trees, and iii） discussing the consequence of changed disturbance regime in the dynamics of this ecotone and the surrounding grasslands. We analyzed vegetation data sampled from belt transects laid across the forest- grassland ecotone in semi-natural grassland patches. Vegetation data consisting of species richness and composition, and size structure and regeneration of the two most dominant tree species, namely Rhododendron arboreum and Abies spectabilis, from the transects, were used to analyze the trend of the forest-grassland ecotone. Forest and grasslands were different in terms of floristic composition and diversity. Vascular plant speciesrichness linearly increased while moving from forest interior to grassland center. Spatial pattern of tree size structure and regeneration infers that forest boundary is advancing towards the grasslands at the expense of the grassland area, and tree establishment in the grasslands is part of a suceessional process. Temporally, tree establishment in grasslands started following the gradual decline in disturbance. We argue that local processes in terms of changed land use may best explain the phenomenon of ecotone shift and consequent forest expansion in these grasslands. We underpin the need for further research on the mechanism, rate and spatial extent of ecotone shift by using advaneed tools to understand the process indepth.

黄土丘陵区林草景观界面雨后土壤水分空间变异规律

对黄土丘陵区刺槐林-草地景观界面上雨后土壤表层(0～10 cm)和亚表层(10～20 cm)水分的空间变异规律进行了研究.经典统计学分析表明,草地两层的土壤含水量分别高于林地;林草界面两层的土壤含水量均为弱变异程度,并具有明显的生态梯度.移动窗口法分析表明,林草界面对土壤表层和亚表层的水分影响范围为边界两侧4 m、3 m,影响域分别为8 m、6 m.地统计学分析表明,草地两层土壤含水量空间分布均表现为纯块金效应,林地两层均可拟合成线性模型,而林草界面两层均可拟合成球状模型;林草界面土壤表层、亚表层水分空间依赖性和空间自相关较强,其空间结构异质性明显高于林地和草地.克立格制图描述的林草界面土壤水分的空间分布格局为从边界处向两侧的一定距离范围内,土壤含水量呈条带状分布,而在较远的距离,水分的空间分布呈现出几个明显的斑块状.

黄土丘陵区林草景观界面土壤养分分布特征和空间变异性研究

通过对泾河流域林草景观界面的土壤养分测定,分析比较界面中养分的分布特征及空间变异性。结果表明:该流域内的土壤养分分布不平衡,除钾素含量(22.977～25.183 g.k-g1)富足外,其他养分含量都很低;林地内养分含量高于草地(有机质含量高16.310%;水解氮含量高19.570%),在界面上养分变化较大,林内和草地内养分变化较小;界面上养分时空差异不明显,而层次之间差异显著。无论是林地还是草地,土壤各养分的变化是确定性变异和随机性变异共同作用的结果,且确定性的变化规律往往控制一定范围内土壤养分的变化和分布。

Soil Carbon Stock and Flux in Plantation Forest and Grassland Ecosystems in Loess Plateau, China

Carbon sequestration occurs when cultivated soils are re-vegetated. In the hilly area of the Loess Plateau, China, black locust （Robinia pseudoacacia） plantation forest and grassland were the two main vegetation types used to mitigate soil and water loss after cultivation abandonment. The purpose of this study was to compare the soil carbon stock and flux of these two types of vegetation which restored for 25 years. The experiment was conducted in Yangjuangou catchment in Yah＇an City, Shaanxi Province, China. Two adjacent slopes were chosen for this study. Six sample sites were spaced every 35-45 m from summit to toe slope along the hill slope, and each sample site contained three sampling plots. Soil organic carbon and related physicochemical properties in the surface soil layer （0-10 cm and 10-20 cm） were measured based on soil sampling and laboratory analysis, and the soil carbon dioxide （CO2） emissions and environmental factors were measured in the same sample sites simultaneously. Results indicated that in general, a higher soil carbon stock was found in the black locust plantation forest than that in grassland throughout the hill slope. Meanwhile, significant differences in the soil carbon stock were observed between these two vegetation types in the upper slope at soil depth 0-10 cm and lower slope at soil depth 10-20 cm. The average daily values of the soil CO2 emissions were 1.27 μmol/（m2·s） and 1.39 μmol/（m2·s） for forest and grassland, respectively. The soil carbon flux in forest covered areas was higher in spring and less variation was detected between different seasons, while the highest carbon flux was found in grassland in summer, which was about three times higher than that in autumn and spring. From the carbon sequestration point of view, black locust plantation forest on hill slopes might be better than grassland because of a higher soil carbon stock and lower carbon flux.

Diffusivity Models and Greenhouse Gases Fluxes from a Forest,Pasture,Grassland and Corn Field in Northern Hokkaido,Japan

Information on the most influential factors determining gas flux from soils is needed in predictive models for greenhouse gases emissions. We conducted an intensive soil and air sampling along a 2 000 m transect extending from a forest, pasture, grassland and corn field in Shizunai, Hokkaido （Japan）, measured CO2, CH4, N20 and NO fluxes and calculated soil bulk density （Pb）, air-filled porosity （fa） and total porosity （Ф）. Using diffusivity models based on either fa alone or on a combination of fa and 4, we predicted two pore space indices： the relative gas diffusion coefficient （Ds/Do） and the pore tortuosity factor （T）. The relationships between pore space indices （Ds/Do and T） and C02, CH4, N2O and NO fluxes were also studied. Results showed that the grassland had the highest Pb while fa and Ф were the highest in the forest. CO2, CH4, N20 and NO fluxes were the highest in the grassland while N20 dominated in the corn field. Few correlations existed between fa, Ф, Pb and gases fluxes while all models predicted that Ds/Do and T significantly correlated with CO2 and CH4 with correlation coefficient （r） ranging from 0.20 to 0.80. Overall, diffusivity models based on fa alone gave higher Ds/Do, lower τ, and higher R2 and better explained the relationship between pore space indices （Ds/Do and τ） and gases fluxes. Inclusion of Ds/Do and τ in predictive models will improve our understanding of the dynamics of greenhouse gas fluxes from soils. Ds/Do and τ can be easily obtained by measurements of soil air and water and existing diffusivity models.

Research on the Patterns and Evolution of Ecosystem Service Consumption in the “Belt and Road”

With great significance in ecosystem protection and sustainable development,the study of ecosystem service consumption(ESC)has become a hot topic in ecological research.Based on FAOSTAT data,in this study the patterns,composition and evolution of ESC and ecosystem service consumption patterns(ESCP)in the“Belt and Road"were revealed on the total and regional scales,taking consumed-biomass as a main indicator.Three main conclusions were reached.1)The total ESC was mainly contributed from farmland ecosystems along the"Belt and Road",followed by grassland ecosystems.The ESC indicators on the whole system scale fluctuated,but increased from year 2000 to year 2016.The total ESC increased from 12911.89 Tg yr_1 to 16810.00 Tg yr^1,and the annual per capita consumption of ecosystem services increased from 3.3228 million g p_1 yr'1 to 3.6392 million g p_1 yr'1.2)The ESC,composition and evolution varied significantly among countries,zones and ecosystems.The annual per capita ESC was highest in Mongolia on the national scale,and highest in Central and Eastern Europe and lowest in Southeast Asia on zone scale,which represented the results from the joint effects of regional resource endowments,consumption habits,levels of productive forces,and other factors.3)Higher farmland ESC was the dominant ESCP,which accounted for about 76.7%of the total area along the"Belt and Road",followed by higher farmland+higher grassland ESC,which accounted for about 19.0%of the total area.The other consumption patterns(i.e.,those of higher grassland ESC,higher forestland ESC or higher farmland+higher forest+higher grassland ESC)were found in only a few countries.The ESCP may be related to higher regional population density or the higher proportions of developing countries.Therefore,to realize sustainable social,economic and ecological development,and to improve people's well-being,countries along the,lBelt and Road"should take advantage of their own resources in developing industries,actively expand trade,achieve mutual benefits and win-win situations,and adjust and optimize consumption patterns of ecosystem services.This study can provide data support for further research on the mechanism of ESCP formation this area.

Assessing Threats and Setting Conservation Priorities for Plant Species between Forest and Meadow Ecotone in Sanjiangyuan Nature Reserve, China

In order to understand the pattern and status of plant species in the forest-meadow ecotonein Sanjiangyuan Nature Reserve, this study was undertaken through expert consultation, literaturesurvey and fieldwork in various parts of the ecotone during 2002-2004. Based on 3 important systems,i.e. threatened status, genetic loss effect and use value, the list of threatened and prioritized plants wasestablished. In this paper, the threatened coefficient was defined as the criteria of category for threatenedplants, the conservation priorities coefficient summed by threatened coefficient, genetic coefficient anduse value coefficient was defined as the criteria of prioritized plants. In addition, 10 indicators toevaluate threatened grading and conservation priorities sequence were included in the 3 importantsystems. The weights of 3 systems and 10 indicators were given through expert consultation andanalytic hierarchy process. Ten indicators were given scores based on the subcriteria, respectively, andall the scores of the 3 systems were summed up for each species, then contrasted to the criteria ofthreatened grading and conservation priorities for plant species. The status of endangerment andconservation priorities of plant species were analyzed, and the results showed that the number ofendangered species was 2, vulnerable species 37, near threatened species 140, safe species 767; the firstconcern category had 4 species, the second concern category 18, the third concern category 150 and theleast concern category 774.