祁连山鲜黄小檗灌丛穿透雨特征

鲜黄小檗是我国祁连山区长期适应高寒气候条件而发展起来的主要的亚高山灌丛类型之一,通过野外观测,对祁连山西水林区鲜黄小檗灌丛在39次降雨事件中冠下穿透雨的分区性、径向分布特征及影响因素进行了分析,结果表明:鲜黄小檗灌丛单株的平均穿透雨率为40.44%;冠层中心区和辐散区的穿透雨量与次降雨量之间均为线性关系,当降雨量小于0.7 mm时,冠层中心区没有穿透雨产生;冠层辐散区穿透雨率随降雨量的增大出现先增大后趋于稳定的幂函数关系,受冠层结构影响,冠层辐散区穿透雨具有明显的空间异质性,沿径向由距灌丛基部10 cm处的16.19%单调递增至90 cm处的69.92%,30~70 cm为主要递增区,穿透雨率径向空间变异系数随降雨量的增大而降低;此外,鲜黄小檗灌丛的穿透雨率随物候期发生变化,叶量稳定期比展叶期的穿透雨率低11.82%。研究结果可为祁连山鲜黄小檗灌丛生态水文功能的定量评价和基于生态过程的灌丛水文模型的参数化提供数据支撑。     

高寒河谷灌丛冠层降雨再分配特征及影响因素

通过植被冠层的降雨被分割成冠层截留、穿透雨和树干茎流3个部分,这个过程（冠层降雨再分配）是高寒河谷灌丛生态演变的关键驱动因子之一,对于认识高寒河谷灌丛的水文循环过程及水分收支规律也具有重要意义。选取青海湖流域最重要的河谷灌丛--具鳞水柏枝作为研究对象,通过野外定点观测,深入分析了冠层降雨再分配特征及影响因素\.结果显示:①穿透雨量、树干茎流量、冠层截留量占同期降雨量的比例平均为48.40%、4.04%和47.56%,并在不同降雨量等级之间存在显著差异;②冠层降雨再分配各组成要素（穿透雨、树干茎流、冠层截留）与降雨特征参数存在高度相关性,伴随降雨量和降雨历时的增加,穿透雨量、树干茎流量、冠层截留量占同期降雨量的比例均逐渐趋于稳定,极限稳定值分别介于60.45%～61.07%、6.45%～7.42%、33.11%～34.17%;③产生穿透雨和树干茎流的临界降雨量分别为1.10 mm和1.87 mm,表明2 mm以下的降雨对土壤水分的补给基本没有贡献。因此,高寒河谷灌丛冠层降雨再分配与其他林木类型存在明显差异,需要深入研究其内在机制及水分利用规律。     

油蒿(Artemisia ordosica)退化阶段对灌丛沙堆形态的影响

典型固沙灌木油蒿(Artemisia ordosica)退化过程中如何影响灌丛沙堆的形态特征,仍然未知。在腾格里沙漠东南缘1990年建立的人工固沙植被区,分别对油蒿生殖株、半死株和死株3个阶段灌丛沙堆形态特征进行了调查。结果表明:半死株油蒿灌丛沙堆的高度和体积显著高于死株和生殖株形成的灌丛沙堆,生殖株、半死株和死株灌丛沙堆高度分别为4.8cm、21.0cm和12.4cm,体积分别为0.031m3、0.159m3和0.109m3,坡度分别为3.5°~7.8°、32°~36°和16°~26°。植株特征的改变及所引起的气流变化影响到灌丛沙堆形态特征,不同退化阶段的油蒿显著影响到灌丛沙堆的形成和发育。因此,油蒿灌丛逐渐退化的过程,是灌丛沙堆逐渐演化的过程,也是干旱、半干旱区微地形塑造和景观逐渐变化的过程。     

荒漠灌丛降雨再分配对土壤pH值的影响

对腾格里沙漠东南缘沙坡头地区1989年建植人工植被区优势固沙灌木柠条（Caragana korshinskii）和半灌木油蒿（Artemisia ordosica）树干茎流及穿透雨的pH值,以及灌丛基部、灌丛下和灌丛外裸地0～10 cm和10～20 cm剖面深度土壤pH值分别进行测定,并与大气降雨pH值进行比较,以探讨荒漠灌丛降雨再分配对土壤pH值空间变异的影响。结果表明:大气降雨pH值最高,穿透雨pH值次之,树干茎流pH值最低,三者之间具有显著差异（p<0.05）。灌丛外裸地土壤pH值最高,灌丛下次之,树干基部最低。总体而言,0～10 cm剖面深度土壤pH值小于其下方10～20 cm剖面深度土壤pH值。柠条灌丛产生的树干茎流对土壤的酸化作用强于油蒿灌丛。树干茎流和穿透雨的酸化作用是导致土壤pH值从灌丛间裸地到灌丛基部方向上降低的一个重要原因。     

毛乌素沙地南缘油蒿(Artemisia ordosica)灌丛沙堆形态特征

对毛乌素沙地南缘不同演化阶段油蒿(Artemisia ordosica)灌丛沙堆进行了调查和统计分析,探讨了演化过程中沙堆形态特征变化及其与灌丛形态间相互关系。结果显示:(1)研究区油蒿灌丛沙堆以发育阶段和稳定阶段主,衰退阶段灌丛沙堆较少。随灌丛沙堆演化,油蒿灌丛高度保持相对稳定,灌丛长轴和沙堆长轴、短轴都显著增大;(2)沙堆的形态参数间存在显著的相关性,其中发育阶段沙堆长轴、短轴和高度之间显著线性相关,且长轴和短轴相对高度增长较快,稳定阶段沙堆3个参数间协同发展到稳定,而衰退阶段沙堆形态参数间相关性下降;(3)除衰退阶段外,沙堆形态参数与灌丛形态参数间有显著的相关关系,其中沙堆长轴与灌丛长轴、沙堆短轴与灌丛短轴、沙堆底面积与灌丛投影面积,均呈显著线性关系。在环境因素作用下,油蒿灌丛沙堆间整体相互协调发展,使其呈现不同形态特征。     

乌兰布和沙漠东南缘白沙蒿(Artemisia sphaerocphala)灌丛沙堆形态特征与固沙能力

白沙蒿(Artemisia sphaerocphala)灌丛沙堆是乌兰布和沙漠最为广泛分布的典型荒漠灌丛沙堆之一。本研究对白沙蒿灌丛的灌丛形态参数、沙堆形态参数进行了野外测定,探讨沙堆形态发育及固沙能力与白沙蒿灌丛形态的关系。结果表明:白沙蒿灌丛高度随着灌丛半径的增加而呈对数曲线增加,在灌丛较小时灌丛高度增长较快,随后渐趋于稳定,其水平方向发育速度大于垂直方向;白沙蒿灌丛沙堆半径及高度随灌丛半径和高度增加而增加,二者呈显著线性关系,沙堆水平方向发育受到灌丛冠幅的影响,沙堆垂直方向的发育水平取决于灌丛高度;随白沙蒿地上部分鲜重的增加,灌丛沙堆底面积、高度、沙堆体积和固沙效率均呈极显著线性增加(p0.01);白沙蒿灌丛越大其固积沙堆也越大,固沙率越高,不同大小灌丛白沙蒿间的固沙效率差异显著(p0.05);白沙蒿灌丛背风侧的积沙宽度(y)与积沙距离(x)显著相关(R2=0.9917),其线性回归方程为y=-19.654x+122.41,在距离灌丛背风面6~7倍高度的地方,积沙接近消失。     

油蒿(Artemisia ordosica)退化阶段对生物土壤结皮拓殖和发育的影响

2013年8月,在腾格里沙漠东南缘1990年建立的人工固沙植被区,分别对油蒿(Artemisia ordosica)生殖株、半死株和死株3个退化阶段植株西北、西南、东北和东南4个方向生物土壤结皮(BSCs)类型、盖度和厚度进行了调查。结果表明:油蒿灌丛周围共出现了3类BSCs,分别为藻类结皮、地衣结皮和藓类结皮,藻类结皮分布范围最广。油蒿生殖株、半死株、死株灌丛均表现出西北方向BSCs盖度最大分别为89.75%、98.55%、80.40%;东南方向的盖度最小分别为23.10%、35.40%、25.44%;BSCs的厚度同样表现为西北方向最大分别为4.48、6.86、5.14mm,东南方向最小分别为2.14、3.26、2.80mm。油蒿生殖株、半死株和死株3个退化阶段BSCs总盖度表现为半死株生殖株死株,厚度表现为半死株死株生殖株。不同退化阶段的油蒿显著影响BSCs的拓殖和发育,尤其是处于BSCs演替后期的地衣结皮和藓类结皮;油蒿植株的生长过程的也是干旱、半干旱区地表微地貌逐渐变化的过程。     

不同郁闭度天山云杉林林冠截留量及穿透雨量特征研究

天山云杉(Picea schrenkiana var.tianschanica(Rupr.)Chen et Fu)是构成天山山地森林生态系统的主体。选取天山森林生态系统定位研究站不同郁闭度天山云杉林作为研究对象,研究了不同郁闭度条件下天山云杉林冠截留量及穿透雨量的月变化特征、林冠截留量及穿透雨量与总降雨量间的数量关系,通过研究得出结论:林冠截留率与郁闭度表现出显著正相关关系,而穿透雨比率与郁闭度表现出显著负相关关系;穿透雨量、穿透雨比率及林冠截留量的月变化与总降雨量基本一致,林冠截留率则相反;郁闭度为0.8和0.6、0.4和0.2之间的穿透雨量无显著性差异,0.8和0.6与0.4和0.2之间差异明显,林冠截留量相邻郁闭度间均无显著性差异,而不相邻郁闭度之间均差异显著;建立了穿透雨量及林冠截留量与总降雨量间的数学关系,用以定量评价该地区天山云杉林水文生态效益。     

半干旱沙地樟子松林降雨再分配特征

森林植被的降雨再分配过程是影响区域水资源利用效率以及生态系统生产力的重要因素。于2018年5-8月观测27 a生樟子松人工林降雨再分配特征,探究降雨再分配的比例变化对林地水分平衡的影响机制,分析、量化林内穿透雨、林冠截留、树干径流、枯落物层入渗部分产生的阈值。结果表明:樟子松林内穿透雨量占同期降雨量的86.45%,穿透雨量随着降雨量的增加呈线性增加趋势,降雨量>0.63 mm时产生穿透雨;林冠截留量和树干径流量分别占降雨量的10.44%和2.54%,树干径流量与降雨量之间呈正线性关系,降雨量>1.19 mm时,产生树干径流;枯落物层截留量占降雨量的12.37%,枯落物层截留量随着降雨量的增加而增加;枯落物在0~24 h内平均吸水速率为1.83 mm·h^-1,其最大持水量为3.23 mm,并且枯落物层截留量占其最大持水量的42.37%。从林冠到枯落物各层截留总量为25.35%,其中有74.65%的雨水最后从枯落物层入渗进入地表,用于补充土壤水分、下渗或补充地下水。半干旱沙地樟子松林可以有效地发挥截留降雨、贮存雨水的功能,继而改善沙地土壤含水量和地下水的有效补给量,提高森林生态系统生产力。     

毛乌素沙地南缘固沙灌丛下地表凝结水特征

尽管凝结水在干旱生态系统中所发挥的重要作用已被广泛关注,但对其在固沙灌丛下时空变化特征的研究仍然比较薄弱。为探明固沙灌丛对地表凝结水的影响,在毛乌素沙地南缘沙区选择3种典型固沙灌丛（沙柳Salix psammophila、柠条Caragana korshinskii和油蒿Artemisia ordosica）,以无固沙灌丛影响的裸沙作为对照,用微型蒸渗仪测定了固沙灌丛下不同位置（根部、1/2冠幅和外缘）和不同方向（东、南、西、北）上地表凝结水的形成和蒸发特征。结果表明：（1）与对照相比,固沙灌丛的存在显著降低了地表凝结水量,沙柳、油蒿和柠条灌丛下凝结水量分别降低了29%、32%和33%;(2)不同类型固沙灌丛下地表凝结水量由里向外均呈显著增加的趋势,但不同方向上地表凝结水量差异不显著;（3）固沙灌丛的存在减缓了凝结水的形成和蒸发过程,即凝结水自19:00开始形成,到次日08:00基本结束,至13:00—15:00蒸发殆尽,其形成过程整体上表现出增加—平缓—增加的趋势,柠条和油蒿灌丛下地表凝结水在03:00—05:00甚至有少量蒸发,而蒸发过程呈稳定下降趋势;（4）凝结水的形成过程与空气...     

Rainfall interception by sand-stabilizing shrubs related to crown structure

On the edge of the Tengger Desert in northern China,revegetation has changed the landscape from moving dunes to stabilized dunes covered by shrubs,which further modifies the pattern of rainfall redistribution.To study rainfall interception loss by shrubs and its relationship to rainfall properties and crown structure,throughfalls passing through crowns of Artemisia ordosica Krash.and Caragana korshinskii Kom.were measured using nine PVC cups under the canopy of each of the two shrubs during 73 rain events over a three-year period,with total rainfall of 260.9 mm.Interception losses of gross rainfall by A.ordosica and C.korshinskii account for 15% and 27% of the total on a crown area basis,and 6% and 11% on a ground area basis,respectively.Individual throughfall(T) and interception(I) were significantly related to rainfall amount(Pg),duration(D),and intensity(R).Ratios of throughfall to rainfall(T/Pg) and interception to rainfall(I/Pg) were not only significantly related to Pg,D,and R,but also to shrub species,and interactions of species with crown volume(CV) and leaf area index(LAI).Under most rain events,interceptions by C.korshinskii with greater CV and LAI were significantly higher than those by A.ordosica,and more rainfall interception occurred at locations closer to the stems of the two shrubs.For C.korshinskii,I/Pg had a significant positive linear relation with CV and LAI,while T/Pg had a significant negative linear relation with them.CV has a greater influence on T/Pg and I/Pg than does LAI.Using a regression method,canopy water storage capacities are estimated to be 0.52 and 0.68 mm,and free throughfall coefficient to be 0.62 and 0.47 for A.ordosica and C.korshinskii,respectively.     

Effects of soil nitrogen:phosphorus ratio on growth rate of Artemisia ordosica seedlings

To address how the ratios of nitrogen and phosphorus (N:P ratios) in soil affect plant growth, we performed a two-factor (soil available N:P ratios and plant density) randomized block pot experiment to examine the relationships between soil N:P ratios, and the N:P ratios and growth rate of Artemisia ordosica seedlings. Under moderate water stress and adequate nutrient status, both soil N:P and plant density influenced the N:P ratios and growth rates of A. ordosica. With the increase of soil N:P ratios, the growth rates of A. ordosica seedlings decreased significantly. With the increase of soil N:P ratios, N:P ratios in A. ordosica seedlings increased significantly. While the nitrogen concentrations in the plant increased slightly, the phosphorus concentrations significantly decreased. With the increase of plant density, the shoot N:P ratios and growth rates significantly decreased, which resulted from soil N:P ratios. Thus, soil N:P ratios influenced the N:P ratios in A. ordosica seedlings, and hence, influenced its growth. Our results suggest that, under adequate nutrient environment, soil N:P ratios can be a limiting factor for plant growth.     

Rainfall partitioning by desert shrubs in arid regions

We measured the rainfall partitioning among throughfall, stemflow, and interception by desert shrubs in an arid region of China, and analyzed the influence of rainfall and canopy characteristics on this partitioning and its ecohydrological effects. The percent-ages of total rainfall accounted for by throughfall, stemflow, and interception ranged from 78.85±2.78 percent to 86.29±5.07 per-cent, from 5.50±3.73 percent to 8.47±4.19 percent, and from 7.54±2.36 percent to 15.95±4.70 percent, respectively, for the four shrubs in our study (Haloxylon ammodendron, Elaeagnus angustifolia, Tamarix ramosissima, and Nitraria sphaerocarpa). Rain-fall was significantly linearly correlated with throughfall, stemflow, and interception (P < 0.0001). The throughfall, stemflow, and interception percentages were logarithmically related to total rainfall (P < 0.01), but were quadratically related to the maximum 1-hour rainfall intensity (P < 0.01). The throughfall and stemflow percentages increased significantly with increasing values of the rainfall characteristics, whereas the interception percentage generally decreased (except for average wind speed, air temperature, and canopy evaporation). Regression analysis suggested that the stemflow percentage increased significantly with increasing crown length, number of branches, and branch angle (R2 = 0.92, P < 0.001). The interception percentage increased significantly with increasing LAI (leaf area index) and crown length, but decreased with increasing branch angle (R2 = 0.96, P < 0.001). The mean funnelling percentages for the four shrubs ranged from 30.27±4.86 percent to 164.37±6.41 percent of the bulk precipitation. Much of the precipitation was funnelled toward the basal area of the stem, confirming that shrub stemflow conserved in deep soil layers may be an available moisture source to support plant survival and growth under arid conditions.     

Catastrophic drought-induced die-off of perennial chenopod shrubs in arid Australia following intensive cattle browsing

Cover and survivorship of perennial chenopods, Atriplex vesicaria and Maireana astrotricha, declined markedly during a prolonged dry period at Roxby Downs in arid South Australia. Despite their resilience to browsing in favourable seasons, only 2% of the A. vesicaria shrubs browsed heavily by cattle survived the drought. M. astrotricha exhibited greater drought survivorship, although the post-drought cover retention in browsed shrubs was only half that of unbrowsed controls. Survivorship was highest for unbrowsed chenopods growing in moisture-enhanced run-on or dune-base environments. Maintenance of these patchy areas with reduced water-stress is hence important for the persistence of browsed chenopod shrublands. Light browsing by either European Rabbits (Oryctolagus cuniculus) or Greater Stick-nest Rats (Leporillus conditor) had no measurable impact upon chenopod survivorship.     

Fire in Chihuahuan Desert grassland: Short-term effects on vegetation, small mammal populations, and faunal pedoturbation

A prescribed burn resulted in significant decreases in canopy cover of the grasses: Bouteloua eriopoda, Sporobolus flexuosus, and Aristida purpurea. One year post-burn, basal cover of B. eriopoda remained significantly lower in burned patches than in unburned areas but there were no differences in basal cover of the other perennial grasses. Only one species of the 14 summer annual species occurred in both burned and unburned plots. There were six species of spring annuals in burned patches but no spring annuals in the unburned grassland ten months post-burn. Fire killed 100% of the snakeweed shrubs (Gutierrezia sarothrae), 77% of the Ephedra torreyana shrubs, and 36% of the Yucca elata. All mesquite shrubs that were top-killed by fire, resprouted one month post-burn. Fire had no effect on abundance and species richness of rodents. There were fewer wolf spider, Geolycosa spp. burrows in burned areas than in unburned grassland. The area and volume of soil in termite galleries and sheeting were significantly larger in the unburned grassland than in the burned areas.     

Influence of shrubs on soil characteristics and their function in Sahelian agro-ecosystems in semi-arid Niger

Soil beneath shrubs form ‘fertile islands’ in fallow sites and millet fields in semi-arid Niger. To gain more information about this phenomena different shrub species in fallow sites following a gradient from 350–650 mm precipitation were examined. For each shrub two different areas were distinguished: an area under the canopy of the shrubs and an area in the nearby open land. Soil samples were taken from a depth of 0–10 cm and analysed for C_org, N_total, P_Bray, pH(H₂O), exchangeable cations, effective cation exchange capacity (ECEC) and soil texture. Significantly higher concentrations between 38–51% for C, N, P and 22% on ECEC for K⁺were found in the soil under the shrubs. The pH showed only slight but significant differences, whereas Al³⁺and H⁺rates on ECEC under the shrubs were increased by 44–55%. For Guiera senegalensis, the most common shrub of the studied area, enrichment ratios of most soil properties increased relatively more with increasing aridity. In general, enrichment ratios decreased with the age of the fallows, whereas concentrations showed no clear evolution. The chemical composition of the shrub litter seems to influence the degree of soil enrichment. The main step of fertile island formation takes place during the cultivation period by trapping wind-blown sediment. This work shows that shrubs are of vital importance for the accumulation of nutrients and maintenance of soil fertility within agro-ecosystems of Niger.     

Livestock responses to droughts and severe winter weather in the Gobi Three Beauty National Park, Mongolia

We investigated how both droughts and dzuds (severe winter weather) control livestock mortality in a non-equilibrium steppe ecosystem of Mongolia, Gobi Three Beauty National Park. These steppe ecosystems have developed under high interannual variability of rainfall and nomadic grazing systems. Interannual precipitation variation was 39%, with 128 mm mean annual precipitation. The effect of climate variability and extreme events on livestock mortality is a critical aspect for the Mongolian economy. Analysis of drought and precipitation variability on livestock mortality rate was not significantly influenced by the index of mean annual precipitation and annual winter temperature. Overall, unlike hot dry regions, pastoral livestock mortality in the cold dry regions was affected more by dzuds and annual growing seasonal rain than by droughts. Dzuds can be frequent events, occurring as often as once every 2 and 3 years within a decade. The average annual livestock mortality for the combined drought and dzuds years (18%) was 4.8% greater than the years with dzuds alone, and 7% greater than in years with only drought. Thus livestock mortality appears to be more sensitive to dzuds than to droughts, and that dzuds contributes more to livestock mortality even years where combined drought and winter storms occur.     

Gender-related differences of shrubs in stands of Atriplex canescens with different histories of grazing by cattle

Atriplex canescens is a relatively common dioecious shrub in western North America. It is considered a valuable forage resource for both wild and domestic herbivores. Sex ratios and shrub dimensions were recorded in stands of tetraploid A. canescens that had been either protected from cattle grazing or summer- or winter-grazed by cattle for at least 20 years. Stem diameter and crown shape were used as surrogates for shrub age which could not be estimated by counting growth rings. Shrub sex ratios in exclosures were significantly more female biased than the empirically derived ratio for tetraploid A. canescens (55 female:35 male: 10 monecious). Conversely, shrub sex ratios in grazed pastures were not significantly different from the empirical ratio. Proportion of female shrubs in exclosures was significantly higher than in grazed pastures. Proportion of male shrubs, on the other hand, was similar in exclosures and grazed pastures. Winter-grazed shrub stands were apparently younger than both summer-grazed and protected shrubs. Protected shrubs appeared to be the oldest. Grazed female shrubs were apparently younger than grazed males, however, shrub ages of protected male and female shrubs were apparently not different. Cattle-grazing may have affected female shrubs more negatively at this site, causing gender-based differential mortality, and/or sex-shifting. Such processes could account for the differences in sex ratios, and for the apparent gender-related differences in shrub age that were observed.     

The influence of elevation, shrub species, and biological soil crust on fertile islands in the Mojave Desert, USA

We quantified soil nutrients and biological crust cover (bryophytes and lichens) under the canopies of three species of Mojave Desert shrubs and in interspaces between shrubs at three elevations to determine the effects of shrub species, soil crust, and elevation on islands of soil fertility. Means of pH, organic matter, total Kjeldahl nitrogen, nitrogen mineralization, and gravimetric soil moisture are significantly greater in soils under Ambrosia dumosa (Gray) Payne, Larrea tridentata Cov., and Coleogyne ramosissima Torr. than soils from adjacent interspace microhabitats. Although soil moisture and soil organic matter increase by a factor of 1.5 from the low elevation to the high elevation site, the ratio of shrub to interspace concentrations, or the difference in mean soil variables between shrubs and interspaces, is effectively constant and independent of elevation. Total bryophyte and lichen cover is relatively low (24.5%), however, there are 11 species of bryophytes and two species of lichens distributed across three elevations with the highest species richness and cover at the low-elevation site. Bryophyte and lichen cover is correlated with silt but is not related, consistently, to soil nutrients. Overall, the balance of processes controlling spatial aggregation of soil nutrients under shrubs is remarkably insensitive to potential differences in organic inputs among elevations, shrub species, and soil crust surfaces.     

High-resolution images reveal rate and pattern of shrub encroachment over six decades in New Mexico, U.S.A.

Encroachment of the shrub Prosopis glandulosa Torr. (honey mesquite) into semi-arid grasslands is a serious concern in the south-western United States, yet little is known about the long-term dynamics of the invasion process. We used ten high-resolution aerial and satellite images taken from 1936 to 1996 to track the population dynamics and spatial pattern of all P. glandulosa greater than 2 m in diameter on a 75 ha area in southern New Mexico.Shrub cover and patch numbers increased from 1936 to the 1970s, then stabilized at 43% cover and 83 patches ha⁻¹. Individual patches were extremely persistent: 95% of the area occupied by shrub patches in 1936 was still occupied in 1996. Recruitment into the 2 m size class was more variable: 0·6–5·2% year⁻¹ (mean 0·8% year⁻¹). Patch-shape complexity increased from 1936 to 1983 as adjacent shrubs merged, and then declined as those clusters filled in and became rounder. Spatial pattern of shrubs showed a distinct trend over time: strongly clustered in 1936 at lag distances up to 250 m, then random arrangement at all scales, and by 1983 pattern was regular at lag distances greater than 100 m. There was no clear relationship with precipitation.The use of remote sensing imagery allowed us to examine one site over time, and revealed patterns in population dynamics and spatial pattern that would not have been visible otherwise. Comparison of field estimates collected in 2001 with 1996 image data suggest that the canopy cover estimates were accurate, but shrub densities were seriously underestimated in the satellite photographs, which do not show shrubs smaller than 2 m diameter. As long as limitations of the imagery are understood, these methods can be applied over a larger and more heterogeneous area to examine environmental correlates of invasion success.