Desertification alters patterns of aboveground net primary production in Chihuahuan ecosystems

Abstract The Chihuahuan desert of New Mexico, USA, has changed in historical times from semiarid grassland to desert shrublands dominated by Larrea tridentata and Prosopis glandulosa. Similar displacement of perennial grasslands by shrubs typifies desertification in many regions. Such structural vegetation change could alter average values of net primary productivity, as well as spatial and temporal patterns of production. We investigated patterns of aboveground plant biomass and net primary production in five ecosystem types of the Jornada Basin Long‐Term Ecological Research (LTER) site. Comparisons of shrub‐dominated desertified systems and remnant grass‐dominated systems allowed us to test the prediction that shrublands are more heterogeneous spatially, but less variable over time, than grasslands. We measured aboveground plant biomass and aboveground net primary productivity (ANPP) by species, three times per year for 10 years, in 15 sites of five ecosystem types (three each in Larrea shrubland, Bouteloua eriopoda grassland, Prosopis dune systems, Flourensia cernua alluvial flats, and grass‐dominated dry lakes or playas). Spatial heterogeneity of biomass at the scale of our measurements was significantly greater in shrub‐dominated systems than in grass‐dominated vegetation. ANPP was homogeneous across space in grass‐dominated systems, and in most growing seasons was significantly more patchy in shrub vegetation. Substantial interannual variability in ANPP complicates comparison of mean values across ecosystem types, but grasslands tended to support higher ANPP values than did shrub‐dominated systems. There were significant interactions between ecosystem type and season. Grasslands demonstrated higher interannual variation than did shrub systems. Desertification has apparently altered the seasonality of productivity in these systems; grasslands were dominated by summer growth, while sites dominated by Larrea or Prosopis tended to have higher spring ANPP. Production was frequently uncorrelated across sites of an ecosystem type, suggesting that factors other than season, regional climate, or dominant vegetation may be significant determinants of actual NPP.     

基于像元三分模型的锡林郭勒草原光合植被和非光合植被覆盖度估算

定量的估算草原光合植被覆盖度(f_(PV))和非光合植被覆盖度(f_(NPV))对草原畜牧业和土地荒漠化具有重要的意义。以锡林郭勒盟西乌珠穆沁旗为研究区,以MODIS 500 m分辨率地表反射率产品MOD09GHK为数据源,采用干枯燃料指数(DFI)指数构建NDVI-DFI像元三分模型估算了锡林郭勒草原的fPV和f_(NPV),并分析了锡林郭勒草原fPV和f_(NPV)的动态变化。研究结果表明:锡林郭勒草原NDVI-DFI特征空间表现为三角形,与理论上的概念模型基本一致,符合像元三分模型的基本假设;NDVI-DFI像元三分模型适用于对草原黄枯期_(NPV)的监测,对草原生长期_(NPV)监测并不十分敏感;利用NDVI-DFI像元三分模型估算的fPV和f_(NPV)动态变化与牧草物候发育特征相吻合,可以有效的估算典型草原地区fPV和f_(NPV)值,进一步将其应用于长时间序列的典型草原fPV和f_(NPV)动态变化分析。     

Variation in Aboveground Cover Influences Soil Nitrogen Availability at Fine Spatial Scales Following Severe Fire in Subalpine Conifer Forests

Following fire, fine-scale variation in early successional vegetation and soil nutrients may influence development of ecosystem structure and function. We studied conifer forests burned by stand-replacing wildfire in Greater Yellowstone (Wyoming, USA) to address two questions: (1) How do the variability and spatial structure of aboveground cover and soil nitrogen availability change during the first 4 years following stand-replacing fire? (2) At fine scales (2–20 m), are postfire soil inorganic N pools and fluxes related to aboveground cover? Aboveground cover, soil N pools, and annual net N transformations were measured from 2001 to 2004 using a spatially explicit sampling design in four 0.25-ha plots that burned during summer 2000. Within-stand variability (coefficient of variation) in postfire live vegetative cover declined with time since fire, whereas variability in bare mineral soil, charred litter and fresh litter was greatest 2-3 years postfire. The soil nitrate pool was more variable than the soil ammonium pool, but annual net nitrification was less variable than annual net N mineralization. Spatial structure (quantified by semivariograms) was observed in some aboveground cover variables (for example, graminoids and fresh litter), but there was little spatial structure in soil N variables and no obvious congruence in spatial scales of autocorrelation for soil N and aboveground cover. Significant Spearman correlations (at the sample point) indicated that aboveground cover and soil N were coupled following severe fire, and the dominant influence was from aboveground cover to soil N, rather than from soil N to vegetation. Initial patterns of fire severity and re-vegetation contributed to fine-scale heterogeneity in soil N availability for at least 4 years after severe fire.     

Functional differences between summer and winter season rain assessed with MODIS‐derived phenology in a semi‐arid region

Questions: We asked several linked questions about phenology and precipitation relationships at local, landscape, and regional spatial scales within individual seasons, between seasons, and between year temporal scales. (1) How do winter and summer phenological patterns vary in response to total seasonal rainfall? (2) How are phenological rates affected by the previous season rainfall? (3) How does phenological variability differ at landscape and regional spatial scales and at season and inter‐annual temporal scales? Location: Southern Arizona, USA. Methods: We compared satellite‐derived phenological variation between 38 distinct 625‐km² landscapes distributed in the northern Sonoran Desert region from 2000 to 2007. Regression analyses were used to identify relationships between landscape phenology dynamics in response to precipitation variability across multiple spatial and temporal scales. Results: While both summer and winter seasons show increases of peak greenness and peak growth with more precipitation, the timing of peak growth was advanced with more precipitation in winter, while the timing of peak greenness was advanced with more precipitation in summer. Surprisingly, summer maximum growth was negatively affected by winter precipitation. The spatial variations between summer and winter phenology were similar in magnitude and response. Larger‐scale spatial and temporal variation showed strong differences in precipitation patterns; however the magnitudes of phenological spatial variability in these two seasons were similar. Conclusions: Vegetation patterns were clearly coupled to precipitation variability, with distinct responses at alternative spatial and temporal scales. Disaggregating vegetation into phenological variation, spanning value, timing, and integrated components revealed substantial complexity in precipitation‐phenological relationships.     

宁夏东部风沙区沙化草地土壤水分和植被的空间特征

土壤水分作为土壤-植被-大气连续体的关键因子,对沙化草地的演化过程具有重要作用。为探讨宁夏东部风沙区沙化草地土壤水分、物种丰富度指数及植被盖度的空间变异及其相互关系,以哈巴湖自然保护区沙化草地为对象,采用样线法自潜在沙化草地至重度沙化草地进行植被调查和土壤取样,通过经典统计学和地统计学分析,得出以下结果：0—100 m各土层土壤水分含量、植被盖度和物种丰富度指数的分布范围分别为0.82%—28.22%、41.00%—93.00%和0.82—2.80,变异系数范围为0.20—0.48,均属于中等变异。各土层土壤水分和物种丰富度指数表现为中等的空间自相关性,植被盖度则表现为强烈的空间自相关性。Kriging插值结果表明,0—100 cm各土层土壤水分和植被盖度的空间插值图呈条带状和斑块状的梯度变化,物种丰富度呈斑块分布,自潜在沙化草地至重度沙化草地,表现为逐渐降低的趋势。相关分析表明,植被盖度与0—40 cm各土层土壤水分呈显著正相关,与40—100 cm各土层土壤水分呈极显著正相关。宁夏东部风沙区沙化草地土壤水分含量总体较低,由于结构因素和随机因素的共同作用,随草地沙化程度的加重,表现为...     

Changes in soil macrofaunal community composition under selective afforestation in shifting sand lands in Horqin of Inner Mongolia, northern China

Large-scale afforestation programs have had some beneficial effects on reducing severity of dust storms and controlling desertification in arid and semi-arid regions. However, the influences of selective afforestation on soil arthropod community are largely unknown in desertified ecosystems. Soil macrofaunal communities, soil physico-chemical properties, and herb vegetation were investigated in afforested shrublands and woodlands (both approximately 30 years old post-afforestation), which were compared to shifting sand lands in Horqin, northern China. In the shrublands, environmental parameters (soil and vegetation properties) indicated a significant improvement of soil organic carbon, total nitrogen, and herbaceous density and cover, in comparison to the woodlands and shifting sand lands. The improved shrubland habitat maintained significantly higher soil macrofaunal abundance and group richness together with higher diversity compared with the woodlands and shifting sand lands. There were no significant differences in soil macrofaunal diversity between the woodlands and shifting sand lands. The results suggest that shrubs can facilitate macrofaunal assemblies and improve soil and vegetation properties when planted in shifting sand lands. Shrub afforestation is beneficial for the restoration of shifting sand lands, and is recommended for management of artificial plantations in these sandy ecosystems.     

Soil surface complexity has a larger effect on food exploitation by ants than a change from grassland to shrubland

1. Changes in vegetation community composition, such as a transition from grassland to shrubland (woody encroachment), are associated with reductions in plant cover and increases in bare ground. Encroachment‐driven changes in surface cover at small spatial scales can alter ant community assemblages by changing their foraging behaviour and their ability to locate and monopolise resources. 2. Artificial arenas with three levels of complexity were used to examine changes in ant foraging efficiency, body size and ability to monopolise food. The three levels of complexity included a control (no substrate), low‐complexity treatment (woody debris) and high‐complexity treatment (leaf litter). 3. No difference was found in ant species composition within the complexity arenas between grassland and shrubland, but ant functional groups ‘generalised Myrmicinae’ and ‘subordinate Camponotini’ were more abundant in grassland arenas, whereas ‘opportunists’ were more abundant in shrubland arenas. Ants took twice as long to find baits in high‐complexity treatments, and 1.5 times as long in low‐complexity treatments, than in control treatments, which were bare arenas with no substrate. Ant body size declined with increasing surface complexity, suggesting that larger ants are discouraged from foraging in complex habitats. 4. There was also significantly greater monopolisation of the protein bait (tuna) in low‐ and high‐complexity treatments, but there were no differences between tuna and carbohydrate (honey) in the control treatment. Consistently, no differences were found in ant behaviour between grasslands and shrublands. 5. The present study shows that ants are more responsive to small‐scale alterations in soil surface complexity than to changes in vegetation community composition. Changes in soil surface complexity select for ants based on body size, which in turn influences their foraging success. Changes in vegetation complexity at small spatial scales are therefore likely to influence ant behaviour and abundance of some functional groups, potentially having an effect on the many ecosystem functions carried out by ants.     

2001—2010年黄河流域生态系统植被净第一性生产力变化及气候因素驱动分析

基于MODIS-NDVI遥感数据,利用CASA模型分析黄河流域2001—2010年植被净第一性生产力（NPP）的空间分布格局,并结合同期气温和降水量数据,分别从不同空间和时间尺度上分析了黄河流域6种生态系统类型区域植被NPP的变化趋势,并对其与气候因素的相关关系进行分析.结果表明： 植被NPP空间分布呈西北低、东南高的分布特征,平均NPP年总量为108.53 Tg C,植被NPP的分布与生态系统类型呈现较高的相关性;2001—2010年,植被NPP总体呈上升趋势但波动较大,55.4%的面积呈现增加趋势,不同生态系统类型区域呈现不同的变化趋势;在年际水平上,黄河流域植被NPP变化与气候因素没有显著相关性,但在月际水平上呈现了较高的相关性,降水量和气温对植被NPP变化的影响作用相当;不同生态系统类型对气候因素呈现不同的相关性质以及时滞效应,草地对降水量的响应存在一定程度的时滞效应,荒漠对气温存在时滞效应.     

喀斯特峰丛洼地生态系统服务空间权衡度及其分异特征

我国西南喀斯特峰丛洼地区脆弱的生态环境与剧烈的人类活动导致石漠化现象以及生态功能退化,制约了区域生态-福祉耦合效益的提升。首先从数值变化与空间变异综合的角度,构建了融合均方根偏差法与地理探测器的生态系统服务空间权衡度指标,进而围绕喀斯特水源涵养-土壤侵蚀关系以及植被固碳-土壤侵蚀关系,在不同环境因子梯度下和地貌形态类型区内开展生态系统服务空间权衡度计算及其分异特征研究。环境因子梯度分析表明,由于植被显著的保持水土能力,水源涵养与土壤侵蚀之间的空间权衡度随植被覆盖度的增大而逐渐减小;地形因子对地表水土过程与植被功能影响深刻,植被固碳和土壤侵蚀之间的空间权衡度随海拔和坡度的升高而逐渐增大,1000 m以上中海拔以及陡坡地区的空间权衡度是低海拔与缓坡地区的4-6倍。地貌形态类型区的统计结果显示,地貌特征对生态系统服务之间的空间权衡关系具有宏观控制作用,植被固碳-土壤侵蚀之间的空间权衡度随地形起伏度的升高而逐渐增大,具体为：中海拔平原 < 中海拔台地 < 中海拔丘陵 < 小起伏中山 < 中起伏中山,水源涵养与土壤侵蚀之间则成相反趋势。因此,今后在以生态系统服务协同提升为目标的喀斯特石漠化治理工作中,应强调环境因子作用程度的空间差异以及地貌形态特征的宏观控制作用。     

我国三北地区植被变化的动因分析

地表植被变化是气候变化、人类活动等多种因素共同作的结果。然而,以往的研究要么集中在与气候变化有关的气象因素,要么集中在与人类活动有关的人为因素,鲜有基于长期数据监测下对自然与社会因素之间相互作用的定量评估。因此,气候变化和人为因素对地表植被变化的相互作用并不明确,各个因素对植被变化影响的量化贡献仍然不确定。为了评价生态修复项目对荒漠化防治的效果、以及在土地荒漠化防治中自然与社会因素对我国植被变化的影响、及其复杂的相互作用机理,该研究应用卫星遥感影像资料,通过面板数据混合回归模型大数据分析方法,计算了1983年至2012年气候变化和人类活动对我国北方地区植被变化的贡献率。结果表明,气候变化和人类活动对NDVI变化均有重要作用,其中人类活动对植被覆盖度变化的影响占58.2%—90.4%、气候变化占9.6%—41.8%;不同地区表现出不同的地理分异特征,并存在时滞效应。由此可见,荒漠化防治必须充分考虑不同因素的综合作用和地域特征,才能取得事半功倍的效果。研究结果较好地体现了卫星遥感影像资料在大尺度(省域尺度)下与社会经济统计指标的融合,为进一步中尺度(县域尺度)研究提供了方法借鉴。     

Directional climate change and potential reversal of desertification in arid and semiarid ecosystems

Our objective was to determine if long‐term increases in precipitation can maintain grasslands susceptible to desertification, and initiate a reversal of historic regime shifts on desertified shrublands. Perennial grass production and species richness in a multi‐year wet period were hypothesized to be greater than expected based on precipitation in a sequence of dry years. These responses were expected to differ for grasslands and shrublands with different dominant species and topo‐edaphic properties. Long‐term trends in desertification were documented using vegetation maps beginning in 1858, 1915, 1928, and 1998). These trends were compared with herbaceous and woody species responses to a sequence of dry (1994–2003) and wet years (2004–2008) for two grassland (uplands, playas) and three desertified shrubland types (honey mesquite, creosotebush, tarbush) in the Chihuahuan Desert. Analyses showed that both types of grasslands decreased in spatial extent since 1858 whereas areas dominated by mesquite or creosotebush increased. Production of upland grasslands in the wet period was greater than expected based on responses during the dry period whereas the relationships between species richness and precipitation was the same for both periods. Precipitation was not important to responses in playa grasslands in either period. For all ecosystem types, the production response in wet years primarily was an increase in herbaceous plants, and the most pronounced responses occurred on sandy sites (upland grasslands, mesquite shrubland). Results suggest that multiple wet years are needed to initiate a sequence of grass establishment and survival processes that can maintain upland grasslands without management inputs and lead to a state change reversal in desertified shrublands. Restoration strategies need to take advantage of opportunities provided by future climates while recognizing the importance of ecosystem type.     

基于元胞自动机的喀斯特石漠化格局模拟研究

西南喀斯特山区的石漠化问题是目前我国西部地区最为突出的地域环境问题之一,其迅速发展已经严重影响到当地人们的生产生活。以导致石漠化发生发展的自然、人文因子为切入点,通过模拟影响喀斯特系统地表覆被变化的基本生态过程(如植物定居、植物死亡、水蚀风蚀引起的土地退化以及岩石成土过程等),利用随机元胞自动机具有的简单邻域规则产生复杂空间格局的特点,使喀斯特系统地表覆被植被-裸土-裸岩状态在一定概率下发生状态转换,并结合RS和GIS技术,构建了简单、有效的喀斯特石漠化模拟及预测模型(KarstCA)。以典型喀斯特石漠化地区关岭县为研究区,在自然、人文驱动因素共同影响以及只考虑自然驱动因素情景下,KarstCA模型模拟的研究区2007年石漠化空间分布格局的差异主要分布在中部和南部,其主要是不同空间范围上人类活动作用方式和强度差异所致。在16a中(1992—2007年)喀斯特地区地物(植被-裸土-裸岩)丰度变化成非线性关系,当植被覆达到54%以上并继续增加时,裸岩发展趋势与之呈明显的负相关(P<0.01)。在模拟期内人类活动对研究区石漠化的发展起到抑制作用,人类活动的正效应(植树造林等)与负效应(乱砍滥伐、过度放牧等)在一定程度上抵消了植被总面积的剧烈变化趋势。将地表过程耦合进元胞自动机模型,突破了以往该类研究只通过概率考虑状态转换,而对其机理认识的不足;同时本研究考虑了自然、人文驱动因素在不同空间尺度上作用于石漠化现象的复杂性,对于探索这些因素是如何作用于地表过程及其贡献率等研究具有一定的参考价值。     

Ecosystem engineering varies spatially: a test of the vegetation modification paradigm for prairie dogs

Colonial, burrowing herbivores can be engineers of grassland and shrubland ecosystems worldwide. Spatial variation in landscapes suggests caution when extrapolating single‐place studies of single species, but lack of data and the need to generalize often leads to ‘model system’ thinking and application of results beyond appropriate statistical inference. Generalizations about the engineering effects of prairie dogs (Cynomys sp.) developed largely from intensive study at a single complex of black‐tailed prairie dogs C. ludovicianus in northern mixed prairie, but have been extrapolated to other ecoregions and prairie dog species in North America, and other colonial, burrowing herbivores. We tested the paradigm that prairie dogs decrease vegetation volume and the cover of grasses and tall shrubs, and increase bare ground and forb cover. We sampled vegetation on and off 279 colonies at 13 complexes of 3 prairie dog species widely distributed across 5 ecoregions in North America. The paradigm was generally supported at 7 black‐tailed prairie dog complexes in northern mixed prairie, where vegetation volume, grass cover, and tall shrub cover were lower, and bare ground and forb cover were higher, on colonies than at paired off‐colony sites. Outside the northern mixed prairie, all 3 prairie dog species consistently reduced vegetation volume, but their effects on cover of plant functional groups varied with prairie dog species and the grazing tolerance of dominant perennial grasses. White‐tailed prairie dogs C. leucurus in sagebrush steppe did not reduce shrub cover, whereas black‐tailed prairie dogs suppressed shrub cover at all complexes with tall shrubs in the surrounding habitat matrix. Black‐tailed prairie dogs in shortgrass steppe and Gunnison's prairie dogs C. gunnisoni in Colorado Plateau grassland both had relatively minor effects on grass cover, which may reflect the dominance of grazing‐tolerant shortgrasses at both complexes. Variation in modification of vegetation structure may be understood in terms of the responses of different dominant perennial grasses to intense defoliation and differences in foraging behavior among prairie dog species. Spatial variation in the engineering role of prairie dogs suggests spatial variation in their keystone role, and spatial variation in the roles of other ecosystem engineers. Thus, ecosystem engineering can have a spatial component not evident from single‐place studies.     

2008—2018年伊犁河流域植被净初级生产力时空分异特征

基于MODIS数据和改进的光能利用率模型(CASA模型)对2008—2018年伊犁河流域植被净初级生产力(NPP)进行估算,通过一元线性回归趋势分析、变异系数、Hurst指数等方法对其时空分异特征进行分析。结论如下：(1)时间特征上,伊犁河流域植被NPP呈现波动上升趋势,年内植被NPP呈现出“单峰型”特点,该流域四季植被NPP大小关系为：夏季>春季>秋季>冬季;(2)空间特征上,伊犁河流域植被NPP呈现东北低西南高,沿天山山脉呈环状分布,各植被类型NPP的大小为：林地(624.13 g C m^-2 a^-1)>耕地(575.04 g C m^-2 a^-1)>草地(270.57 g C m^-2 a^-1)>裸地(114.26 g C m^-2 a^-1)。该流域植被NPP在海拔、经纬度方面均呈现不同的变化特征。(3)空间稳定性上,伊犁河流域植被NPP存在明显的空间差异性,各变异程度...     

Spatial heterogeneity of tundra vegetation response to recent temperature changes

The spatial heterogeneity of recent decadal dynamics in vegetation greenness and biomass in response to changes in summer warmth index (SWI) was investigated along spatial gradients on the Arctic Slope of Alaska. Image spatial analysis was used to examine the spatial pattern of greenness dynamics from 1991 to 2000 as indicated by variations of the maximum normalized difference vegetation index (Peak NDVI) and time‐integrated NDVI (TI‐NDVI) along latitudinal gradients. Spatial gradients for both the means and temporal variances of the NDVI indices for 0.1° latitude intervals crossing three bioclimate subzones were analyzed along two north–south Arctic transects. NDVI indices were generally highly variable over the decade, with great heterogeneity across the transects. The greatest variance in TI‐NDVI was found in low shrub vegetation to the south (68.7–68.8°N) and corresponded to high fractional cover of shrub tundra and moist acidic tundra (MAT), while the greatest variance in Peak‐NDVI predominately occurred in areas dominated by wet tundra (WT) and moist nonacidic tundra (MNT). Relatively high NDVI temporal variances were also related to specific transitional areas between dominant vegetation types. The regional temporal variances of NDVI from 1991 to 2000 were largely driven by meso‐scale climate dynamics. The spatial heterogeneity of the NDVI variance was mostly explained by the fractional land cover composition, different responses of each vegetation type to climate change, and patterned ground features. Aboveground plant biomass exhibited similar spatial heterogeneity as TI‐NDVI; however, spatial patterns are slightly different from NDVI because of their nonlinear relationship.     

沙地油蒿群落覆盖度的遥感定量化研究

鄂尔多斯地区荒漠化与沙地植被覆盖度有紧密的关系。用 NOAA卫星数据对沙地植被覆盖度进行动态监测可以为认识该地区的荒漠化动态变化及过程提供丰富的信息。通过分析沙地反射机理 ,建立了沙地油蒿(Artemisia ordosica)群落盖度与修正后的土壤调节植被指数 (MSAVI)之间的关系模型。然而 ,卫星数据用于该关系模型之前 ,必须进行处理。本文首先用裸沙土壤线法校正大气影响 ,然后 ,用 MSAVI消除土壤背景影响     

水热波动和土地覆盖变化对东北地区植被NPP的相对影响

研究水热波动和土地覆盖变化对植被净初级生产力（Net Primary Productivity,NPP）的影响对于估算陆地碳循环及其驱动机制具有重要意义。利用MODIS遥感影像获得的时间序列NPP和土地覆盖产品,结合气象观测数据（气温和降水）,采用相关分析、回归分析和空间分析相结合的方法,研究2000-2015年东北地区植被NPP的时空变化特征,并定量评估水热波动和土地覆盖变化对该地区植被NPP的相对影响。研究结果表明,2000-2015年东北地区植被NPP呈波动上升趋势,从2000年的369.24 g C m^-2 a^-1增加到2015年的453.84 g C m^-2 a^-1,平均值是412.10 g C m^-2 a^-1,年际增加速率为4.54 g C m^-2 a^-1。近16年来东北地区年均植被NPP空间上呈现南高北低、东高西低的分布格局,整体变化趋势以增加为主,其中轻微增加面积占该地区总面积的45.9%。不同土地覆盖类型的年均NPP差异明显,其中灌木最高为400.34 g C m^-2 a^-1,草地最低为300.49 g C m^-2 a^-1。东北地区植被NPP与气温的相关性不明显,而与降水量主要表现为正效应。水热波动对该地区不同土地覆盖类型NPP总量变化的贡献大于土地覆盖变化的贡献,其中对森林和农田的贡献最大,均达到70%以上。     

2000—2011年广西植被净初级生产力时空分布特征及其驱动因素

受人类活动及自然环境影响,广西土壤酸化、水土流失及石漠化等问题比较严重,生态环境面临巨大压力。NPP能有效反映植物群落在自然环境中的生产能力,是评价生态服务功能的重要指标。利用2000—2011年MODIS归一化植被指数(NDVI)数据,基于光能利用率模型对广西植被净初级生产力(NPP)进行估算,分析其时空变化规律,探讨气象因子、植被类型、土壤类型、海拔高度及人类活动的影响。研究表明:近12年广西全区NPP总体呈增加趋势,在西南部地区上升较为明显,而在桂林、柳州等地区呈缓慢下降趋势。广西NPP与降水呈显著正相关关系,与温度相关性不显著;NPP值随海拔高度升高而增加;NPP时空变化特征随植被类型和土壤类型的不同而不同,其中栽培植被NPP不断上升,显示人类活动逐渐成为影响NPP变化的主要因素。     

石羊河中游沙漠化逆转过程土壤种子库的动态变化

在石羊河中游,应用空间代替时间的方法,选择流动沙丘以及封育恢复5a、15a和25a的沙漠化逆转过程序列,研究了沙漠化逆转过程土壤种子库的变化特征。结果表明:石羊河中游沙漠化土地土壤种子库由4科12种植物组成,种子库主要分布于表层0-5cm。在沙漠化逆转过程中,土壤种子库物种数趋于增加,物种组成以1年生草本植物占优势逐渐向多年生草本植物和半灌木植物转变;种子库密度、表层土壤种子比例、物种多样性指数、与地上植被的相似性呈现先增大后降低趋势;沙漠化土地生态恢复间隔的时间越长,土壤种子库间的相似性程度越低;沙漠化土地与地带性植被区种子库的相似性逐渐增大,但是恢复25a沙漠化土地也仅达到0.36。研究认为,沙漠化逆转过程也是沙漠化土地土壤种子库向地带性植被土壤种子库演变的过程,而且是一个十分缓慢的过程,该研究有助于丰富干旱区土壤种子库的理论和指导干旱内陆河流域沙漠化土地的生态恢复实践。     

2000—2015年秦巴山区植被净初级生产力时空变化及其趋动因子

基于2000—2015年MOD17A3数据及各驱动因素数据,辅以地统计学理论,利用趋势分析、Hurst指数及相关分析等方法,剖析秦巴山区近16年植被净初级生产力(NPP)时空变化特征,研究气候变化、土壤类型、地形因子、植被类型及人类活动等对植被NPP的影响.结果表明: 秦巴山区植被NPP空间上呈西南高、东北低的分布格局;时间上,近16年呈西北增、东北减的变化特征,在未来呈北部持续性、南部反持续性的发展态势.秦巴山区植被NPP与降雨量和气温呈正相关;暗棕壤、黄壤、紫色土和水稻土4种土壤类型的NPP均值明显高于其他土壤类型;不同植被类型的NPP存在空间分布和变化趋势的差异;NPP的高值主要分布在坡度25°～50°、海拔500～1000 m 以及大于2500 m的区域内;人类活动对NPP具有双重扰动性,表现为正向促进,反向抑制.