Scale dependence of plant species richness and vegetation-environment relationship along a gradient of dune stabilization in Horqin Sandy Land, Northern China

Ecological patterns and processes in dune ecosystems have been a research focus in recent years, however the information on how dune stabilization influences the spatial scale dependence of plant diversity is still lacking. In this study, we measured the plant species richness, soil properties and altitude across four spatial scales （1, 10, 100 and 1,000 m2） at three different dune stabilization stages （mobile dune, semi-fixed dune and fixed dune） in Horqin Sandy Land, Northern China. We also examined the relationships between plant species richness, community composition and environmental factors along the gradient of dune stabilization. Our results showed that plant species richness increased with the increase of spatial scales in each dune stabilization stage, as well as with the increase of dune stabilization degrees. Canonical correspondence analysis （CCA） showed that plant distribu- tions in the processes of dune stabilization were determined by the combined environmental gradient in relation to soil organic carbon （SOC）, total nitrogen （TN）, carbon/nitrogen （C/N）, pH, electrical conductivity （EC）, soil water content （SWC）, fine sand （FS）, very fine sand （VFS）, silt and clay （SC）, and altitude. Plant species richness was significantly and positively correlated to SOC and TN in mobile dune, and significantly and positively correlated to SOC, TN, C/N, VFS and SC in semi-fixed dune. However, no significant correlation between plant species richness and environmental factors was observed in fixed dune. In addition, plant species richness in different dune stabili- zation stages was also determined by the combined gradient of soil properties and altitude. These results suggest that plant species richness has obvious scale dependence along the gradient of dune stabilization. Soil resources depending on dune habitats and environmental gradients caused by dune stabilization are important factors to de- termine the scale dependence of species diversity in sand dune ecosystems.

Evaluation of Land-Use Efficiency Based on Regional Scale——A Case Study in Zhanjiang,Guangdong Province

Evaluating land use efficiency is critical to the revision of general land use planning. An assessment indicator system for regional land use efficiency was established in this paper from the aspects of society,economy,ecology and environment. The weight of each indicator was defined by an analytical hierarchy process (AHP) and the entropy method (EM). Then,a case study in Zhanjiang was carried out to analyze the regional land use efficiency from 1996 to 2004 and its development by using the method of multifactor composite evaluation and an analytical model of the de-gree of coordination. The results indicate that land use efficiency with respect to society and the economy improved,whereas the ecological and environmental efficiencies were found to decrease. The degree of coordination in Zhanjiang is still at the status of basic coordination. Finally,measures for enhancing the ecological and environmental establish-ment are suggested in order to improve the regulations of land use structure and patterns,establish ecological forests for the public good and green corridors and prevent the soil erosion.

Response of CH_4 emission of paddy fields to land management practices at a microcosmic cultivation scale in China

The terrestrial ecosystem may be either a source or a sink of CH_4 in rice paddies, depending, to a great extent, on the change of ecosystem types and land use patterns. CH_4 emission fluxes from paddy fields under 4 cultivation patterns (conventional plain culture of rice(T1), no-tillage and ridge culture of rice(T2), no-tillage and ridge culture of rice and wheat (T3), and rice-wheat rotation(T4)) were measured with the closed chamber technique in 1996 and 1998 in Chongqing, China. The results showed that differences existed in CH_4 emission from paddy fields under these land management practices. In 1996 and 1998, CH_4 emission was 71 48% and 78 82%(T2), 65 93% and 57 18%(T3), and 61 53% and 34 22%(T4) of that in T1 during the rice growing season. During the non-rice growing season, CH_4 emission from rice fields was 76 23% in T2 and 38 69% in T1 The accumulated annual CH_4 emission in T2, T3 and T4 in 1996 decreased by 33 53%, 63 30% and 65 73%, respectively, as compared with that in T1 In 1998, the accumulated annual CH_4 emission in T1, T2, T3 and T4 was 116 96 g/m^2, 68 44 g/m^2, 19 70 g/m^2 and 11 80 g/m^2, respectively. Changes in soil physical and chemical properties, in thermal and moisture conditions in the soil and in rice plant growth induced by different land use patterns were the dominant causes for the difference in CH_4 emission observed. The relative contribution of various influencing factors to CH_4 emission from paddy fields differed significantly under different land use patterns. However, the general trend was that chlorophyll content in rice leaves, air temperature and temperature at the 5 cm soil layer play a major role in CH_4 emission from paddy fields and the effects of illumination, relative humidity and water layer depth in the paddy field and CH_4 concentration in the crop canopy were relatively non-significant. Such conservative land use patterns as no-tillage and ridge culture of rice with or without rotation with wheat are thought to be beneficial to reducing CH_4 emission from paddy fields and are, therefore, recommended as a significant solution to the problems of global(climatic) change.

Forecast of the Scale of Urban Construction Land in Chongqing Municipality during the Period 2010-2014

With the rapid development of China's modern cities,the scale of urban construction land has experienced dramatic changes.The forecast of urban construction land is the important content of urban construction development,and guarantee for healthy,rapid and intensive development of cities,therefore,we must reasonably determine the scale of urban construction land.Based on the status quo of construction land in Chongqing Municipality during the period 2000-2009,this article selects GM(1,1) model,linear model and non-linear model,to forecast the scale of construction land and each type of land subordinate to it in Chongqing Municipality during the period 2010-2014,respectively.The results show that the construction land in Chongqing Municipality will increase substantially during the period 2010-2014,and the area of each type of land subordinate to construction land will also increase to varying degrees,therefore the land contradictions will become more prominent.

Land Breeze and Thermals: A Scale Threshold to Distinguish Their Effects

Land breeze is a type of mesoscale circulation developed due to thermal forcing over a heterogeneous landscape. It can contribute to atmospheric dynamic and hydrologic processes through affecting heat and water fluxes on the land-atmosphere interface and generating shallow convective precipitation. If the scale of the landscape heterogeneity is smaller than a certain size, however, the resulting land breeze becomes weak and becomes mixed up with other thermal convections like thermals. This study seeks to identify a scale threshold to distinguish the effects between land breeze and thermals. Two-dimensional simulations were performed with the Regional Atmospheric Modeling System （RAMS） to simulate thermals and land breeze. Their horizontal scale features were analyzed using the wavelet transform. The thermals developed over a homogeneous landscape under dry or wet conditions have an initial scale of 2-5 km during their early stage of development. The scale jumps to 10-15 km when condensation occurs. The solution of an analytical model indicates that the reduced degree of atmospheric instability due to the release of condensation potential heat could be one of the contributing factors for the increase in scale. The land breeze, on the other hand, has a major scale identical to the size of the landscape heterogeneity throughout various stages of development. The results suggest that the effects of land breeze can be clearly distinguished from those of thermals only if the size of the landscape heterogeneity is larger than the scale threshold of about 5 km for dry atmospheric processes or about 15 km for moist ones.

County scale spatial differential characteristics of cultivated land use grade: A case of Binchuan County

Land resource is the material foundation of human survival and economic development, and the cultivated land is the essence of land resources. This paper takes the county scale, by using the method of GIS spatial analysis and statistical analysis unifies, to explore the quality of cultivated land in Binchuan County using level, and explain the utilization level of county cultivated land quality spatial differentiation characteristics. The results showed that:(1) in the quantity of cultivated land quality and utilization level, the average utilization of paddy land was greater than that of dry land, and the comprehensive utilization of cultivated land and so on. Among them, the paddy land ranged from grade 6 to 15, the average utilization was grade 11.6; dry land ranged from grade 2 to 11, the average utilization was grade 5.9; comprehensive range of cultivated land is grade 2 to 15, the average utilization was grade 8.1;(2) the quality of cultivated land utilization spatial differentiation. Paddy field, dry land and cultivated land and large value distribution in the central and southern, inverted V shape distribution; the smaller the value distribution in the East and West, a dumbbell shaped distribution. Among them, they don't use a larger value of paddy land distributed in the central, South and southwest, the maximum value is 14.3, the smaller the value distribution in the West and East, the minimum value is grade 7; the larger the value distribution by the dry land in the South and West, the maximum value is grade 10.2, the smaller the value distribution in the West and East. The minimum value is grade 2.3; the comprehensive utilization of cultivated land don't distributed larger value in the central, South and south-west, the maximum value is grade 12.7, the smaller the value distribution in the West and East, the minimum value is grade 3.5. This paper can provide scientific basis for the dynamic monitoring of cultivated land quality, the transformation of low yield farmland and the early warning of cultivated land pressure.

AN INSIGHT ON DRIVERS OF LAND USE CHANGE AT REGIONAL SCALE

The studies of driving forces of regional land use change (LUC) are to reveal the real motivation behind the LUC and its interacting mechanism, so as to simulate and predict the process of LUC. Presently, studies rooting from different natural and socio-economic backgrounds and from different scales have deepened the people’s understanding and cognition to driving forces of regional LUC. Biophysical driving forces are relatively stable, and have the cumulating effects. Human driving forces are relatively active, and are main driving forces of short-term regional LUC. Existing regional LUC models can answer the three main problems: which contribution (why), which location (where) and what rate (when). But, regional land use system is defined as the self-organized system, usually affected by the cri- tical value area and sudden change, and controlled by different stages. To reduce the impact of critical threshold and break on land use system, the studies of LUC driving forces will aim at following priority areas: data linkage between remote sensing and no-remote sensing data; underlying driving force identification; driving factor quantification; driving factor scale dependence; and driving process integration simulation.

粮食主产区的新型城镇化与粮食安全——基于土地规模化经营中介效应检验

在新时代发展背景下,新型城镇化成为粮食主产区城乡二元结构变革和农业生产方式转型的关键。论文基于2007—2021年我国13个粮食主产区的省级面板数据,从产业链视角利用熵值法测度粮食安全水平,基于新型城镇化内涵构建包含人口、经济、社会、空间的多维度指标体系并测度新型城镇化水平,探究新型城镇化对粮食安全的影响,并以土地规模化经营为中介变量,分析新型城镇化及其各维度影响粮食安全的作用机制。结果表明:1)粮食主产区的新型城镇化对粮食安全有显著的促进作用,并且土地规模化经营在新型城镇化对粮食安全的作用过程中存在中介效应;2)分维度异质性分析表明,人口城镇化与空间城镇化对粮食安全产生显著的正向影响,且土地规模化经营在其中发挥部分或完全的中介效应。为此,提出积极推进新型城镇化、鼓励土地规模化经营并从人口、经济、社会、空间城镇化多个维度因地制宜调整粮食发展战略是粮食主产区发展的长远之策。

Study of Urban and Rural Construction Land Change Based on Small Scale in Dafang

This paper is to examine the urban and rural construction land data of Dafang between basic year and final year based on country scale and spatial econometrics,and analyze its spatial pattern and change feature. According to the results,the construction lands in all the villages of Dafang County showed strong spatial autocorrelation and significant spatial cluster. After the analysis of local Moran's I,the construction lands in 381 villages of 36 counties presented strong activity. The original small-scale villages were gradually enlarging,which will not only gradually benefit local development,but also be in accordance with the strategy of " one city,one district,eight parks".

Effects of Finer Scale Soil Survey and Land-Use Classification on SWAT Hydrological Modelling Accuracy in Data-Poor Study Areas

The limited availability of high-quality spatial data often limits the development of hydrological modelling in developing countries. Hydrological models with data at different scales may generate large uncertainties in modelling outputs. This study analysed the accuracy of four SWAT built models that combine soil and land use/land cover (LULC) data at the scale of 1:250,000 and 1:100,000 in a basin of Mexico. SWAT model allowed determining that large-scale maps produced better results than data from small-scale. Sensitivity analysis with different soil data was less than LULC data. However, the small-scale can be used for exploratory purposes when testing SWAT performance.

规模经营与农业绿色发展——基于农业绿色全要素生产率的观察

规模化经营与绿色化发展是实现农业高质量发展的题中之义。明晰规模经营与农业绿色发展的关系具有重要的理论与现实意义。运用SBM-GML指数测算并刻画出我国农业绿色全要素生产率的时空演变趋势,基于2008-2021年中国省级面板数据,使用固定效应模型实证研究了土地规模经营与服务规模经营对农业绿色全要素生产率的影响及作用路径。研究发现:我国省域农业绿色全要素生产率与规模经营在研究期内整体均呈上升趋势;土地规模经营与服务规模经营对农业绿色全要素生产率影响存在先扩大后缩小的倒“U”型非线性关系,两种规模经营和农业绿色全要素生产率之间均存在适度规模效应;农业机械化水平在规模经营对农业绿色全要素生产率的影响中发挥作用。两种规模经营对不同地区农业绿色全要素生产率的影响具有异质性。因此,应促进农业适度规模经营、提高农业机械化水平、因地制宜发展规模经营。

TVDI与土壤湿度关系的多时间尺度分析与旱情监测

[目的]揭示不同时间尺度的TVDI与土壤湿度的关联关系,确定反映土壤湿度的最佳时间尺度,以更为准确地获取土壤湿度信息,精准监测旱情。[方法]以3种不同时间尺度(8 d,16 d和月)的遥感地表温度、反射率数据以及山东省31个地面观测站土壤湿度数据为基础,分析不同时间尺度下植被指数-温度空间特征,建立不同时段不同时间尺度温度植被干旱指数(TVDI)的热边和冷边函数,研究TVDI与土壤湿度之间的关联性随时间尺度的变化规律,确定了区域土壤墒情监测的时间尺度,反演了区域土壤湿度,监测旱情。[结果]植被指数-温度二维空间形状呈三角形,但随时间发生改变;二维空间中植被指数与最大、最小温度之间有明显的线性关系,湿边并非理想的与坐标轴平行的直线;TVDI与土壤湿度线性相关,但两者之间的紧密程度随时间尺度而变,8 d尺度的TVDI与土壤湿度有更高的相关系数;山东省冬小麦旱情与降水高度一致。[结论]短时间尺度的TVDI更适于区域的旱情监测,尽管人工灌溉有效降低了对降水的需求,但降水的多寡仍是影响区域小麦旱情的主要因素。

我国农业劳动力质量对农户土地规模经营的影响

农业劳动力高质量发展是支撑农业发展的基石之一,随着城镇化进程加快,我国农业劳动质量及其对于土地规模经营的影响值得深入研究。首先通过K-means聚类分析的方法,测定出我国农业劳动力质量的基本特征,然后利用CHARLS2011-2018年四期面板数据分析农业劳动力质量对农户土地规模经营的影响。研究发现:①我国有26.31%的高水平农业劳动力,这是发展土地规模经营的职业农民主力军。②农业劳动力质量对于0~0.087hm²的小规模土地经营的影响并不显著;对于0.087~0.536hm²的土地、0.536hm²以上的农户,农业劳动力质量每降低1%,会使得农户的土地规模经营分别下降4.5%、5.9%。③农业劳动力质量通过影响农户土地转入行为以及改变农业生产投入的方式,对土地规模经营产生影响。政府应针对不同类型的农业劳动力分类施策,加强职业农民的培养,在保障农户权益的情况下,以农业劳动力高质量发展推动农业现代化进展。

土地流转、农业规模经营与农业碳排放——基于土地流转政策的准自然实验

土地流转是解决农村土地问题、实现我国农业现代化发展的重大农业变革。在“碳达峰、碳中和”的碳排放格局下,土地流转政策被视为推动农业低碳绿色发展的重要举措。现有研究指出土地流转已具备提升农业绿色效益的潜力,但并未深入探究土地流转政策实施对农业碳排放产生的影响。基于2007−2020年中国省级面板数据,通过构建准自然实验,实证分析土地流转政策实施对农业碳排放的影响机制及中介路径。研究表明:(1)基于连续型DID模型的估计结果表明,土地流转政策对农业碳排放具有一定抑制性作用;(2)影响机制分析表明,农业规模经营在政策实施过程中承担部分中介作用,能够有效实现农业减排目标;(3)地区异质性分析表明,不同地区间土地流转政策的实施结果存在差异,其中,东北、中部以及西部地区的碳减排效果均较为明显,而东部地区缺乏显著减排效应。为此,应持续支持并推广土地流转,进一步推进农业规模化经营,采取不同地方性流转政策满足各地差异化需求。

从经营方式演化看中国农业现代化的前沿问题

在对家庭联产承包责任制改革确立农户主体地位及土地流转和规模化过程进行梳理的基础上,研究了正在蓬勃发展的几种有代表性的农业组织形式的特点和现代农业演化趋势,针对租佃高成本、超大规模垄断性经营和政府补贴等方面的问题,提出了相应的政策建议。

耕地经营规模对农户水稻生产生态效率的影响——以常德市为例

提高水稻生产生态效率是协同实现保障粮食产量稳增长与减少粮食生产环境损耗双目标的关键路径,耕地作为农业生产活动最基本的生产资料之一,探索耕地经营规模对农户水稻生产生态效率的影响对促进农业适度规模化经营和耕地可持续利用具有重要意义。本文基于粮食生产微观主体——农户的视角,从理论上揭示耕地经营规模对农户水稻生产生态效率的影响,并利用常德市416份农户问卷调查数据,运用随机前沿分析法构建效率测算模型和影响模型进行实证检验。研究表明:农户耕地规模化水平和水稻生产生态效率均有待提升,样本农户中较小规模农户数量最多,占总样本的94.95%,较小规模农户仍是农业生产的主力;农户水稻生产生态效率均值为0.830,还存在0.170的提升空间。耕地经营规模对农户水稻生产生态效率有显著影响,二者并非简单线性关系而是呈“倒U型”关系,且拐点所在区间为1.2~1.4 hm2;农户水稻生产生态效率还受到户主受教育程度、抚养比、农业收入占比的显著正向影响和户主年龄的显著负向影响。因此,应在尊重较小规模农户将长期存在这一现实的基础上,进一步推进耕地适度规模经营并培育新型农户,以促进水稻生产生态效率提高。

代际差异视角下农户土地承包权退出意愿与补偿方式选择——基于全国11省(区)1012份农户问卷调查

引导农户根据自身情况自愿有偿退出土地承包权,有助于推进以适度规模化生产为目标的农业现代化经营。基于全国11个省(区)18个县区的1012个农户微观调查数据,分析农户代际差异对农户土地承包权退出意愿和退出补偿方式选择的影响。研究发现:不同代际农户在土地承包权退出意愿上存在着明显的差异,老一代农户土地承包权退出意愿较低,而新生代农户土地承包权退出意愿则较高;大多数农户都会选择“以承包地换现金补偿”的退出补偿方式,但不同代际农户在其他退出补偿方式选择上存在着明显的差异,新生代农户更倾向于选择“以承包地换城镇住房就业”,而老一代农户和中生代农户更倾向于选择“以承包地换社保或股份”的退出补偿方式。因此,优化我国农村土地承包权当前的退出模式,还应考虑不同代际农户土地承包权退出意愿的差异,并构建差异化的退出补偿机制,使不同群体农户退出土地承包权之后都有合理的价值预期,从而促进土地的适度规模化经营。

基于“三生用地”的四川丘陵区乡村生态系统服务价值及其供需格局评估

科学评估乡镇尺度生态系统服务价值(ESV)是乡村生态系统生产总值(GEP)定量核算以及镇域国土空间规划的重要前提。以四川丘陵区215个典型乡镇为研究对象,基于乡村生产-生活-生态用地(“三生用地”)分类系统和单位面积价值当量因子法,定量评估了乡镇尺度生态系统服务价值的空间分布及供需格局特征,并引入和弦图清晰表达了生态系统服务之间的权衡与协同关系。研究结果表明:(1)研究区乡村ESV空间分布存在明显的空间异质性和聚集特征,总体上南部和西南部丘陵区ESV高于北部和中部,中部地区ESV最低同时,ESV热点主要集中于西部和南部,冷点主要分布于中部和东北。(2)2015年,研究区ESV为62705元·hm^(-2),以调节服务为主(75.69%),其次为食物生产(9.07%)和生境服务(6.45%)。以农业生产用地为主导的乡村“三生用地”格局很大程度上导致了四川丘陵区ESV偏低,提升生态用地的数量与质量是改善区域生态系统服务的关键。对ESV的贡献率较高的“三生用地”类型为:乔木林地(41.25%)、河流湿地(22.95%)、水田(15.08%)、旱地(12.13)。(3)生态系统供给服务与其他三类服务均存在权衡关系,而调节、文化和生境服务之间为协同关系。随着人类对食物与水资源获取能力的增强,可能导致研究区大部分生态系统服务的下降。(4)研究区生态系统服务供需失衡较为明显,供需模式以L-H(39.98%)和H-L(35.92%)为主,呈现两极分化的趋势。同时,H-H模式“三生用地”结构合理,经济生态效益协调,是乡镇尺度可持续发展的代表模板。本文研究结果可为四川盆地乡村振兴空间布局优化以及长江上游生态环境保护提供科学依据。