北洛河流域植被恢复的支撑体系

北洛河流域自实行退耕还林政策以来取得了显著成效,但是实践证明植被恢复不是简单的种树种草,必须要根据生态学原则合理种植,既要有技术支撑,还必须考虑到退耕后农民的生存问题,也就是粮食与能源的问题,并要保证农民有一定的经济收入,最后指出要解决好以上问题,必须靠国家政策的支撑。     

Soil nitrogen and denitrification potential as affected by land use and stand age following agricultural abandonment in a headwater catchment

Changes in vegetation and soil properties because of agricultural abandonment may affect soil nitrogen (N) and associated processes. We investigated soil N (total N: TN, inorganic N: NH₄–N and NO₃–N) and denitrification potential in cropland, pine plantations and abandoned agricultural land along a secondary succession sequence (grassland→shrubland→secondary forest) in a headwater catchment in the Qinling Mountains, northwest China. The results show that the soil denitrification potential differed significantly among the five land‐use types with the highest potential in the secondary forest, followed by grassland, shrubland, cropland and plantations. The denitrification potential of the 20‐ to 40‐cm layer was significantly lower compared with the topsoil (0–20 cm) across all land‐use types. TN, soil organic matter (SOM) and NH₄–N increased significantly with stand age, whereas there was an opposite trend in soil pH. However, the denitrification potential did not relate to stand age in a linear manner. We conclude that changes in soil TN, SOM and pH during vegetation succession following agricultural abandonment are critical controls on the denitrification potential.     

次强降雨下不同植被类型产流产沙对比分析

设置径流观测场,观测次强降雨下不同植被恢复5年后产流、产沙特征。结果表明,苦竹＋牛鞭草植被类型在此次强降雨106.3mm下,产流、产沙量占其全年的15.24%和17.07%,调节降雨和抑制土壤侵蚀的能力最强;农耕地产流、产沙量占其全年的22.05%和31.65%,其中产沙量达其他3种植被类型的4.6～13.3倍,水土保持能力最弱;桦木＋牛鞭草、杂交竹＋牛鞭草植被类型因桦木生长和杂交竹间歇性采伐的原因水土保持能力居于中等水平。对比农耕地来说,3种植被恢复后土壤侵蚀得到了有效控制,但此次强降雨下地表径流控制程度还较弱,需继续加强对土壤和植被的培育。     

玉米叶片高光谱特征及与叶绿素、类胡萝卜素相关性的研究

测定了不同品种类型、不同株型、不同发育期的春玉米叶片及其它器官、不同叶位叶片及叶片不同部位的高光谱反射率和叶片的叶绿素、类胡萝卜素含量。结果表明,玉米不同鲜器官的反射率随波长的变化趋势相似,但数值存在较大差异;不同叶位的叶片、不同品种同一叶位的叶片、叶片的不同部位的光谱反射率有差异;叶片光谱反射率随含水率减少而升高,它们的变化趋势相似;叶片叶绿素和类胡萝卜素浓度与光谱植被指数R800/R550、R673/R640、PSSRa、PSNDa、RCh、CARI、λred、Dλred和Sred具有极显著相关。说明可以通过光谱方法来监测玉米长势和估算叶绿素、类胡萝卜素含量。     

基于无人机多光谱遥感的冬小麦冠层叶绿素含量估测研究

为探讨利用无人机多光谱影像监测冬小麦叶绿素含量的可行性,基于北京市大兴区中国水科院试验基地的2019年冬小麦无人机多光谱影像和田间实测冠层叶绿素含量数据,选取16种光谱植被指数,确定对冬小麦冠层叶绿素含量显著相关的植被指数,采用一元二次线性回归和逐步回归分析方法建立各生育时期及全生育期的SPAD值估测模型,通过精度检验确定对冬小麦冠层叶绿素含量监测的最优模型。结果表明,两种分析方法中逐步回归建模效果最佳。拔节期选取4个植被指数(MSR、CARI、NGBDI、TVI)建模效果最好,模型率定的决定系数(r~2)为0.73,模型验证的r~2、相对误差(RE)和均方根误差(RMSE)分别为0.63、2.83%、1.68;抽穗期选取3个植被指数(GNDVI、GOSAVI、CARI)建模效果最好,模型率定的r~2为0.81,模型验证的r~2、RE、RMSE分别为0.63、2.83%、1.68;灌浆期选取2个植被指数(MSR、NGBDI)建模效果最好,模型率定的r~2为0.67,模型验证的r~2、RE、RMSE分别为0.65、2.83%、1.88。因此,无人机多光谱影像结合逐步回归模型可以很好地监测冬小麦SPAD值动态变化。     

Impact of land degradation on soil respiration in a steppe (Stipa tenacissima L.) semi-arid ecosystem in the SE of Spain

Climate change scenarios predict increases in temperature, changes in precipitation patterns, and longer drought periods in most semi-arid regions of the world. Ecosystems in these regions are prone to land degradation, which may be aggravated by climate change. Soil respiration is one of the main processes responsible for organic carbon losses from arid and semi-arid ecosystems. We measured soil respiration over one year in two steppe ecosystems having different degrees of land degradation under three ground-covers: with vegetation, bare soil, and an intermediate situation between plants and bare soil.The largest differences in soil respiration rates between the sites were observed in spring, coinciding with the highest level of plant activity. The degraded site had drier and hotter soils with less soil water availability and a longer drought period. As a result, vegetation on the degraded site did not respond to spring rainfall events. Soil respiration showed a strong seasonal variability, with average annual rates of 1.1 and 0.8 μmol CO₂ m⁻² s⁻¹ in the natural and degraded sites, respectively. We did not observe significant differences in soil respiration rates associated with ground-cover i.e., the temporal variation was much larger than the spatial variation. At both sites, soil moisture was the controlling driver of soil respiration for most of the year, when temperatures were above 20 °C and constrained the response to temperature for the few months when the temperature was below 20 °C. An empirical model based on soil temperature and soil moisture explained 90% and 72% of the seasonal variability of soil respiration on the natural and degraded sites, respectively. For the first time, this study suggests that land degradation may alter the carbon balance of these ecosystems through changes in the temporal dynamics of soil respiration and plant productivity, which have important negative consequences for ecosystem functioning and sustainability.     

祁连山东段天然草地植物群落稳定性分析

利用法国生态学专家M .Godron提出的方法 ,对祁连山东段天然草地植物群落做了稳定性测定 ,其结果表明 :在测定的 5个草地型中 ,种的百分数与累积相对频度两线相交点分别为 41 5 9、39 61、44 5 6、43 5 7和 43 5 7,与稳定点 2 0 80均不趋于接近。证明祁连山东段天然草地由于放牧过重而导致放牧演替 ,造成植物群落极不稳定。今后应加强保护措施 ,使其逐步向进展演替方向发展     

Stratified vegetation cover index: A new way to assess vegetation impact on soil erosion

Vegetation cover is an important parameter used in assessing the relationship between vegetation and soil erosion. However, the intensity of soil erosion actually changes not only with vegetation cover but also with differences in vegetation type and structure. How to integrate the cumulative effect of the different growth forms making up a vegetation community into one index for inclusion in soil loss predictive equations is an open research question. This paper proposes a method to separately measure the cover of different vegetation strata, estimate their contribution to reducing soil loss, and then to integrate this into a single vegetation index called the stratified vegetation cover index (C_s). The results show that C_s is more effective than projected vegetation cover for the assessment of soil erosion and also can overcome the disadvantages of vegetation indices such as NDVI. This means that C_s is a good substitute for vegetation cover or cover-related vegetation indices in studies on the relationship between vegetation and soil erosion. The concept of Cs may help the local governors or forest department understand the importance of vegetation structure and make right management decisions.     

Spatio-temporal modelling of broad scale heterogeneity in soil moisture content: a basis for an ecologically meaningful classification of soil landscapes

We describe the classification of landscapes characterised bymineral soil using a model that calculates soil moisture availability on amonthly basis. Scotland is used as a case study area. The model uses potentialsoil moisture deficit, estimated using broad scale (40 × 40 km)climate patterns, in conjunction with meteorological station measurements toobtain finer scale values of climatic soil moisture deficit. Point estimates ofsoil available water are obtained for soil characteristics using appropriatepedotransfer functions, and geostatistical techniques are used to upscale theresults and interpolate to a 1-km grid. Known heterogeneityin soil physical characteristics is used to provide local corrections to thepotential soil moisture deficit, estimated using the climatic variables above.Temporal profiles of monthly water content are modelled for each1-km location and classified into six classes usingunsupervised cluster analysis. The spatial distribution of these classesreflects regional variations in the availability of moisture and energy, onwhich finer-grained topographic patterns are superimposed. In the case study,the broad scale spatial heterogeneity of heathlands and grasslands on mineralsoils in Scotland is shown to be strongly related to the soil moistureclassification. The results can be used in studies investigating the patternsofdistribution of communities at the landscape and regional scale.This revised version was published online in May 2005 with corrections to the Cover Date.     

1998～2008年内蒙古植被周期变化分析

利用1998～2008年SPOT VEGETATION分离出的内蒙古地区20个气象站的归一化植被指数（NDVI）数据,对内蒙古植被NDVI的变化周期进行分析.结果表明,小波变换能够很好地揭示NDVI指数的多尺度特性.NDVI的变化周期,在20个选定的气象站都是接近290 d,这表示植被生长周期将近10个月.而在不同的植被类型之间,这种变化周期没有明显的差异.