黄土丘陵沟壑区乔灌草植物空间优化配置——以甘肃省定西地区为例

黄土丘陵沟壑区水土流失的影响因素有气候、植被、土壤、地形等,而乔灌草植物在空间上的不合理配置是造成该区水土流失严重的主要原因之一。本文选择研究区内限制植物生长与分布的4个关键环境因子 (高程、坡度、坡向和降雨量),利用多属性决策分析(MCDA)的方法,探讨乔灌草植物在空间上的优化配置,将整个研究区划分为5类乔灌草植物空间优化配置主模式和18类乔灌草植物空间优化配置子模式;同时,应用GIS聚类分析与统计分析方法,对所划分的乔灌草植物空间优化配置模式进行空间布局分析。结果显示:农民赖以生存的经济林/农林复合配置模式和农田/庭院经济配置模式是研究区的主要配置模式,占配置模式总面积的76.02％。     

Land degradation in the subtropical hilly andmountain regions of South China

1BackgroundSoutilChinaistilemostdevelopedandmostdenselypopulatedpaltofChina--oneofthecounts'smostimportantgrainproducingareas.ItissitUatedintropicalandsubtropicalhumidzones.andannualdownfallringesfrom950nuninthenorthto1700nuninthesouth.Landdegradahoncausedbywatererosionisne\'ertllelessveryseverehere,secondonlytotheLoessPlateau.SeverewatererosioncausesgreatlossofsoilandnutrienLdrashcreduchoninbiologicalandeconolnjcproduchvityandheaVygUllingoflandulhmatelyleadingtodesert-linelandscape,so-cal…     

Modelling the runoff-sediment yield relationship using a proportional function in hilly areas of the Loess Plateau, North China

Based on data observed at the 12 small watersheds in hilly areas of the Loess Plateau, North China, the relationship between event runoff volume and sediment yield is examined. The results reveal that the runoff-sediment yield relationship at the inter-event timescale is mainly determined by the runoff-sediment concentration relationship at the intra-event timescale. In the study area, the sediment concentration tends to be stable when the flow discharge exceeds a certain critical value. Many factors that are important for determining the characteristics of low-magnitude events, such as flow discharge, particle size of fluvial sediment, and accumulation of loose material on land surfaces prior to a rainstorm, appear to have little importance for high-magnitude events. Consequently, mean sediment concentration tends to be stable for large flood events, suggesting a strong similarity between the two flow-sediment relationships at inter-and intra-event temporal scales. Furthermore, a proportional function is proposed to predict event sediment yield, and the correspondence between the predicted and observed sediment yields is examined. The performance of the model is good for high-magnitude events, especially extreme events. The applicability of the proposed model at the annual timescale is also discussed.     

Salinity tolerance in Schinopsis quebracho colorado: Seed germination, growth, ion relations and metabolic responses

Soil salinity is a major abiotic stress influencing plant productivity worldwide. Schinopsis quebracho colorado is one of the most important woody species in the Gran Chaco, an arid and salt-prone subtropical biome of South America. To gain a better understanding of the physiological mechanisms that allow plant establishment under salt conditions, germination and seedling growth of S. quebracho colorado were examined under treatment with a range of NaCl solutions (germination: 0–300 mmol l⁻¹ NaCl; seedling growth: 0–200 mmol l⁻¹ NaCl). The aim was to test the hypothesis that S. quebracho colorado is a glycophite that shows different salt tolerance responses with development stage. Proline content, total soluble carbohydrates and Na⁺, K⁺ and Cl⁻ concentrations in leaves and roots of seedlings, and the chlorophyll concentration and relative water content of leaves were measured. Germination was not affected by 100 mmol l⁻¹ NaCl, but decreased at a concentration of 200 mmol l⁻¹. At 300 mmol l⁻¹ NaCl, germination did not occur. Seedling growth decreased drastically with increasing salinity. An increase in NaCl from 0 to 100 mmol l⁻¹ also significantly reduced the leaf relative water content by 22% and increased the proline concentration by 60% in roots. In contrast, total soluble carbohydrates were not significantly affected by salinity. Seedlings showed a sodium exclusion capacity, and there was an inverse correlation between Cl⁻ concentration and the total chlorophyll concentration. S. quebracho colorado was more tolerant to salinity during germination than in the seedling phase. The results suggest that this increased tolerance during germination might, in part, be the result of lower sensitivity to high tissue Na⁺ concentrations. The significant increment of proline in the roots suggests the positive role of this amino acid as a compatible solute in balancing the accumulation of Na⁺ and Cl⁻ as a result of salinity. These results help clarify the physiological mechanisms that allow establishment of S. quebracho colorado on salt-affected soils in arid and semi-arid Gran Chaco.     

Seed predation and moisture limit germination of recalcitrant Dobera glabra (Salvadoraceae) seeds in the Afar rangelands, Ethiopia

We studied current recruitment failure of Dobera glabra, an important famine-food throughout the dryland parts of the Horn of Africa. The species has previously been found to have recalcitrant seeds, a strategy not common for plants in dryland areas. We experimentally tested (1) how germination capacity of D. glabra is affected by seed form, storage period and moisture under nursery conditions, and (2) how seed predation by vertebrate herbivore and seed exposure at germination site affect germination under field conditions in northern Afar rangelands, Ethiopia. D. glabra seeds that received either mulching or supplementary watering (3 days/week) had a higher germination success than controls. The seeds are probably desiccation sensitive since stored seeds had poor germination performance compared to fresh seeds. Seeds in the rangeland plots protected from herbivores had significantly higher germination success compared to open plots. Our findings demonstrate that seed predation and moisture limitation highly reduced the germinability of the recalcitrant D. glabra seeds, indicating that the species might have persisted due to past wetter periods and low herbivore density in dry environments.     

Evaluating the soil quality of newly created farmland in the hilly and gully region on the Loess Plateau,China

Journal of Geographical Sciences - In order to better understand the quality of newly created farmland (NF) as well as slope and check-dam farmland (CF) soil quality, two typical traditional...     

Hydrological responses and soil erosion potential of abandoned cropland in the Loess Plateau, China

Recent changes in hydrological processes and soil erosion in the Loess Plateau, China, are immediate responses to cropland abandonment for revegetation, which lead to a long-term decrease in runoff generation and soil erosion. However, detailed hydrological responses and soil erosion changes have not been clearly evaluated. In this study, two issues were focused on the plot scale. The first issue relates to changes in vegetation cover and soil properties during the early stages of revegetation. Given the occurrence of soil compaction, it was hypothesized that runoff increased during this period and the soil erosion did not significantly decline, even though vegetation increased. The second issue is the effect of scale on runoff and soil erosion. Three plot groups of three vegetation types and two restoration stages were established for comparative experiments. The results from these experiments confirmed that the soil compaction occurred during revegetation in this region. Greater runoff was produced in plot group that experienced both a longer restoration time and with higher vegetation cover (such as Groups 2 and 3 in this study) than that with a shorter restoration time and lower vegetation cover (Group 1). In addition, the total soil loss rates of all plot groups were rather low and did not significantly differ from each other. This indicates that a reduction in runoff generation and soil erosion, as a result of revegetation, was limited in the early stages of restoration following the cropland abandonment. With increasing plot area, the runoff coefficient decreased for the plot group with a longer revegetation time (Groups 2 and 3), but gently increased for the one with a shorter restoration time (Group 1). In Groups 2 and 3, soil loss rate decreased when plot area enlarged. In Group 1, it decreased before a plot area threshold of 18 m² was exceeded. However, the increase occurred when plot area crossed the threshold value. In conclusion, the high vegetation cover alone did not lead to reduction in the runoff coefficient during the early stages of revegetation. When evaluating hydrological and soil erosion responses to revegetation, the soil compaction processes should be considered. Additionally, the effect of scale on runoff and soil erosion was found to be dependent on restoration extent, and thus on restoration time.     

Spatial and temporal variability of soil properties under Caragana microphylla shrubs in the northwestern Shanxi Loess Plateau, China

Shrub-induced spatial and temporal heterogeneity of soil properties is common in arid and semiarid ecosystems, and it facilitates the development of plant species diversity. We selected 5-, 10-, 20-, 30-, and 40-year-old Caragana microphylla shrubs in the Shanxi Loess Plateau to evaluate the spatial and temporal heterogeneity of soil properties under and outside the shrub canopy. In addition, the presence of adventitious plant species was investigated to assess the development of herbaceous species diversity. Soil samples were collected from two depths (0-5 cm and 5-10 cm). The establishment and development of shrubs promoted temporal variation, improved soil texture, enhanced soil organic matter (SOM), total nitrogen (TN), and cation exchange capacity (CEC), and decreased pH, bulk density (BD), and soil water content (SWC). The results further confirmed that SOM, TN, and CEC were significantly higher at the center than at the outside of the shrub canopies (P < 0.05) and were higher at the 0-5 cm depth than at the 5-10 cm depth. Moreover, the differences in SOM, TN, and CEC from the center to the outside of shrub canopies were greater under 30- and 40-year-old shrubs than under 10- and 5-year-old shrubs. Furthermore, the spatiotemporal heterogeneity of the soil properties facilitated the development of herbaceous species diversity.     

西南丘陵山地区土地整理与区域生态安全研究

开展土地整理是实现土地可持续利用的重要途径,不同区域土地整理的目标、任务侧重点各不相同。对于生态脆弱、生态区位非常重要的西南地区而言,其丘陵山地区土地整理的目标必须与区域生态安全的目标相一致。本文从国际国内土地整理的发展趋势以及土地整理目标区域分工的角度,论述西南丘陵山地区土地整理与区域生态安全之间的关系,提出西南丘陵山地区土地整理的首要目标是确保区域生态安全,小流域土地整理是实现该区域生态安全的典型模式。     

Factors influencing seed germination of Cyperus capitatus, inhabiting the moving sand dunes in southern Europe

Cyperus capitatus Vandelli (Cyperaceae) is distributed in coastal sandy habitats and mobile dunes of south Europe. Its seed germination ecology is not known, despite its potential to be used in re-vegetation projects. Laboratory experiments were conduced to assess the effects of salinity, light regime, cold stratification and burial on seed germination of this species. Overall, increasing salinity delayed germination, increased seed dormancy and mean time to germination (MTG), and reduced final germination percentage, inhibiting it completely above 1% of salinity; although it did not affect seed viability. C. capitatus seeds exhibited their greatest germination at levels between 0 and 1% in non-stratified seeds, and between 0 and 0.5% for stratified seeds. Thus, the effect of salt was greater for stratified seeds at 5 °C. Germination in light/darkness conditions was similar to that in full darkness. Finally, burial in sand of C. capitatus seeds appeared to have a significant effect on cumulative percentage of germination. Seeds buried at depths greater than 2 and 3 cm showed a lower germination success than those on sand surface or buried at shallower depths. Burial also affected the beginning and speed of seed germination.     

Microclimate, freezing tolerance, and cold acclimation along an elevation gradient for seedlings of the Great Basin Desert shrub, Artemisia tridentata

Vegetation, microclimate, seedling frequency, freezing tolerance, and cold acclimation were compared for seedlings of Artemisia tridentata collected from 1775, 2175, and 2575 m elevation in the eastern Sierra Nevada, California. Data were used to test the hypothesis that ecotypic differences in stress physiology are important for seedling survival along gradients from desert to montane ecosystems. The vegetation canopy cover and A. tridentata seedling frequency were greatest at 2575 m, compared to 1775 and 2175 m. Snow cover ameliorated temperatures near the soil surface for part of the winter and depth varied across elevations. Freezing tolerance was compared for seedlings maintained in growth chambers at day/night air temperatures of 25°C/15°C. The temperature at which electrolyte leakage and Photosystem II function (F_V/F_M) from leaves were half-maximum was approximately −13·5°C for leaves of seedlings from all three elevations. Shifting day/night air temperatures from 25°C/15°C to 15°C/5°C initiated about 1·5° of acclimation by plants from all three altitudes, with seedlings from the highest elevation exhibiting the greatest acclimation change. Measurements of ambient air and canopy temperatures at the three elevations indicated that wintertime average low temperatures were consistent with the measured degree of freezing tolerance. At small spatial scales used in this study, pollen and seed dispersal between study sites may have precluded resolution of ecotypic differences. Patterns of freezing tolerance and cold acclimation may depend on a combination of mesoclimate and microclimate temperatures, canopy cover, snow depth, and snow melt patterns.     

内蒙古羊草草原优势物种生产力对气候变化响应的动态模拟

气候变暖影响植物生产力,进而影响群落的结构和演化。本文提出在不同的温度年变化率条件下内蒙古锡林郭勒盟锡林河流域羊草草原主要物种演化的动力学模型,模拟了近几十年来4个主要物种羊草、大针茅、变蒿和西伯利亚羽茅的地上初级生产力对气候变暖的响应过程。模拟和预测结果表明,在气温升高幅度不大的情况下,这4个物种的优势顺序不会发生改变,当温度年变化率高于0.06℃时,竞争能力相近物种的优势顺序发生了转换,即第一、三奇数优势物种羊草和变蒿退化为第二、四偶数优势物种,原来的偶数优势物种第二、四大针茅和西伯利亚羽茅进化为第一、第三奇数优势物种,出现的物种优势顺序为大针茅、羊草、西伯利亚羽茅和变蒿。如果温度年变化率达到0.17℃,物种的强弱顺序将重新组合,变为大针茅、西伯利亚羽茅、羊草和变蒿。现有的观测资料初步验证了这种变化的可能性。研究结果为该区羊草草原群落动态预测和草原管理提供依据。     

黄土高原半干旱区天然锦鸡儿灌丛对土壤水分的影响

本文选择黄土高原半干旱区定西地区的一种地带性植被,天然甘蒙锦鸡儿灌丛,将其0～99m深的土壤水分含量与人工柠条锦鸡儿灌丛、人工杏树林、天然草地、放牧荒坡和农地的土壤水分含量进行了比较。结果发现,天然锦鸡儿灌丛在1m以下土壤各层的水分含量均高于人工柠条灌丛和人工杏树林,而与放牧荒坡和农地的土壤湿度接近,略低于农地。天然锦鸡儿灌丛4m以上土层的土壤湿度还明显高于天然草地;天然锦鸡儿灌丛形成的难效—无效水层深度在2m土层以上,而人工柠条灌丛形成的难效无效水层则深达56m,人工杏树林42m,天然草地、放牧荒坡分别为36m和33m,农地1m。     

西南丘陵山地区农村居民点土地整理模式——以重庆渝北区为例

通过对样本区域农村居民点布局及土地利用特点的研究 ,从丘陵山地区的自然环境条件和社会经济发展水平的实际出发 ,提出两种土地整理模式 :一是农林综合开发整理模式 ,即居民点闲置土地的复垦利用与抛荒地利用结合 ,与山地区退耕还林等生态建设工程结合 ,进行退宅还林 ;二是新村建设整理模式 ,即由政府对新村统一规划 ,供给道路等基础设施 ,引导农民集中建房的“政府引导型”农村居民点整理模式 ,并对重庆市渝北区新春村的新村建设的运作和效益进行了实证分析。     

黄土高原森林植被景观的特征分析

用1∶50万森林类型图为信息源,以G IS为手段,对黄土高原地区森林景观类型斑块的大小、形状以及空间特征进行了分析。结果表明:黄土高原地区27类森林总面积仅64 980.7 km2,共有斑块数5 890个,林斑平均面积较小,且分布不均,森林景观破碎化程度较高。森林景观以华北落叶松林、山杨林、油松林、辽东栎林等为优势类型。黄土高原森林景观类型的形状指数值都比较大,说明森林斑块的形状明显偏离于圆形和方形,多为狭长的不规则形,其斑块的边界率都比较高。不同类型森林分维数变化较大,这也表明黄土高原森林景观破碎化程度较高,景观异质性较大。     

The influence of rainfall and land use patterns on soil erosion in multi-scale watersheds: A case study in the hilly and gully area on the Loess Plateau,China

Soil erosion has become a major global environmental problem and is particularly acute on the Loess Plateau (LP), China. It is therefore highly important to control this process in order to improve ecosystems, protect ecological security, and maintain the harmonious relationship between humans and nature. We compared the effects of rainfall and land use (LU) patterns on soil erosion in different LP watersheds in this study in order to augment and improve soil erosion models. As most research on this theme has so far been focused on individual study areas, limited analyses of rainfall and LU patterns on soil erosion within different- scale watersheds has so far been performed, a discrepancy which might influence the simulation accuracies of soil erosion models. We therefore developed rainfall and LU pattern indices in this study using the soil erosion evaluation index as a reference and applied them to predict the extent of this process in different-scale watersheds, an approach which is likely to play a crucial role in enabling the comprehensive management of this phenomenon as well as the optimized design of LU patterns. The areas considered in this study included the Qingjian, Fenchuan, Yanhe, and Dali river watersheds. Results showed that the rainfall erosivity factor (R) tended to increase in these areas from 2006 to 2012, while the vegetation cover and management factor (C) tended to decrease. Results showed that as watershed area increased, the effect of rainfall pattern on soil erosion gradually decreased while patterns in LU trended in the opposite direction, as the relative proportion of woodland decreased and the different forms of steep slope vegetation cover became more homogenous. As watershed area increased, loose soil and craggy terrain properties led to additional gravitational erosion and enhanced the effects of both soil and topography.     

黄土高原泥流灾害成因及特征

黄土泥流是戴土地区一类重要的灾害地貌过程,是泥石流的一个特殊类型,是水土流失的一种特殊形式,也是山地环境恶化、水土流失极严重的标志。本文在对黄土泥流这一黄土高原特有的严重水土流失现象的分布、成因、物质组成、动静力学性质、堆积形态等全面系统研究的基础上,对其和一般泥石流与高含沙水流做了初步对比和分析,揭示了黄土泥流灾害的形成规律、运动机制和沉积特征。     

黄土丘陵沟壑区坡面产流能力及影响因素研究

坡面是黄土高原土壤侵蚀的重要来源,本文以团山沟流域的7个径流场9年的降雨－径流事件,对不同坡面和降雨特征下径流系数随坡面的变化进行了研究。结果表明,研究区存在降雨强度大、持续时间短的A型雨、降雨强度小持续时间长的C型雨以及居于二者之间的B型雨。不同雨型下坡面产流能力大小为A型雨>B型雨>C型雨,而产流尺度效应则为C型雨>B型雨>A型雨。坡度一定,A型雨下随着坡面长度增加产流能力先增加后减小,径流系数峰值出现在坡长为40m的坡面上,B型和C型雨坡面产流能力随坡面长度的增加而增加;坡长一定,峁坡区坡面产流能力随着坡度的增加而增加;A型雨下沟坡产流能力最小,而在B型和C型雨下,坡面产流能力相对有所提高。     

黄土丘陵区雨强对水流含沙量的影响

To study the effects of changes in the rainfall intensity on sediment concentrations in the Loess Plateau,the observed rainfall intensities and sediment concentrations from three typical small watersheds were used to analyze the relationship between these parameters.The results showed that the sediment concentration generally increased with the increasing rainfall intensity on slope scale.However,at watershed scale,a significant threshold phenomenon was observed for the effects of the rainfall intensity on the sediment concentration.When the rainfall intensity exceeds the threshold,the flood sediment concentration will no longer increase with the increase in the rainfall intensity.The rainfall intensity threshold increased with increasing vegetation coverage.The rainfall intensity threshold was 10–15 mm/h during 1956–1969,reached 20 mm/h from 1990 to 1997 and is approximately 40 mm/h at present.Due to a rainfall intensity of 10–15 mm/h almost happened every year,the vegetation did not change much from the 1950s to 1980s.Sediment yield mainly depends on soil erosion caused by surface flow,but the surface flow speed does not increase indefinitely with the increase in the flow discharge.Thus,the annual maximum sediment concentration of the tributaries in the loess area has been basically stable before the 1990s.     

Grazing as a driver for Populus euphratica woodland degradation in the semi-arid Aibi Hu region, northwestern China

The endangered river plain woodlands of semi-arid Central Asia provide numerous ecosystem services. Previous studies have focused mainly on changes in water supply and salinity as the underlying mechanisms of Populus euphratica woodland’s decline. We tested whether vegetative regeneration of P. euphratica serves as an alternative pathway to propagation from seeds for reproduction in a degraded tree steppe in northwestern China and whether this method also works on grazed sites. We measured the effects of different grazing pressures on tree growth, survival, and vegetative regeneration. When subjected to high or moderate grazing pressure, P. euphratica populations failed to regenerate vegetatively, indicating recruitment limitation. A 25% increase of grazing pressure decreased the ramet density to 50% and the ramet height to 25%, as well as reducing the average age of ramets to one year. As overgrazing seriously limits the potential of natural recovery of P. euphratica a balance between livestock grazing and the regeneration of the Tugai forests is needed to sustain positive effects of increasing water tables and floods on tree vitality and regeneration. To restore population structure, and to support early vegetative regeneration long-term livestock management interventions to exclude livestock from degraded and recovered land need to be developed.