Emergency control of Spartina alterniflora re-invasion with a chemical method in Chongming Dongtan,China

The exotic species Spartina alterniflora(S.alterniflora) seriously threatens the stability and functioning of saltmarsh ecosystems in the Yangtze Estuary.Ambitious efforts have been undertaken to control this species,but subsequent re-invasion is frequent,presenting a significant barrier to restoration.The complexity and high cost of integrated physical control programs has necessitated a shift in focus,leading to considerable attention being paid to the potential of herbicides to control S.alterniflora.To find a strategy for emergency control of small and scattered patches of re-invading S.alterniflora,an in situ field experiment using Gallant(Haloxyfop-R-methyl) herbicide was conducted.The growth parameters of plant density and height were used to evaluate the control efficiency of different treatment dosages and times and sediment samples were taken for environmental toxicity analysis.The results show the following:(1) the control efficacy of the maximum proposed application dose(2.70 g/m2) was 92% for continuous swards and 100% for small patches,while those of other dosages(0.45 g/m2,0.90 g/m2,and 1.35 g/m2) were lower than 40%;(2) the appropriate implementation time was July to August with 100% mortality resulting from a single application,while S.alterniflora was shown to be capable of recovering rapidly after treatment in May;and(3) there were no significant differences in the community structure of meiofauna among the herbicide treatments and the control,and no herbicide residues were detected in sediment samples collected from treatment areas.This chemical control method was implemented in the Shanghai Chongming Dongtan National Bird Nature Reserve(CDNR).The results of this study indicate that Gallant is an environmentally friendly herbicide with high efficiency,which can be adopted for emergency control of re-invading S.alterniflora.     

ECOSYSTEM ENGINEERS MODULATE EXOTIC INVASIONS IN RIPARIAN PLANT COMMUNITIES BY MODIFYING HYDROGEOMORPHIC CONNECTIVITY

Patterns of native and exotic plant species richness and cover were examined in relation with ecosystem engineer effects of pioneer vegetation within the Mediterranean gravel bed river Tech, South France. The floristic composition was characterized according to two distinct vegetation types corresponding to two habitats with contrasted conditions: (i) open and exposed alluvial bars dominated by herbaceous communities; and (ii) islands and river margins disconnected from annual hydrogeomorphic disturbances and covered by woody vegetation. A significant positive correlation between exotic and native plant species richness and cover was observed for both vegetation types. However, significant differences in native and exotic species richness and cover were found between these two vegetation types. Higher values of total species richness and Shannon diversity were attained within the herbaceous vegetation type than within the woody type. These differences are most likely related to changes in local exposure to hydrogeomorphic disturbances driven by woody engineer plant species and to vegetation succession. A lower exotic species cover within the woody vegetation type than within the herbaceous type suggested an increase of resistance to invasion by exotic species during the biogeomorphic succession. The engineer effects of woody vegetation through landform construction resulted in a decrease of alpha (α) diversity at the patch scale but, in parallel, caused an increase in gamma (γ) diversity at the scale of the studied river segment. Our study corroborates recent investigations that support the theory of biotic acceptance of exotic species by native species at the local scale (generally <10 m²) within heterogeneous and disturbed environments. Furthermore, we suggest that in riparian contexts such as the River Tech exotic species trapp sediment at the same time as native species and thus contribute to the increase in ecosystem resistance during the biogeomorphic succession. Copyright © 2012 John Wiley & Sons, Ltd.     

Changes in the hydrological regime and invasions by plant species along riparian systems of the Adour River,France

Changes in the hydrological regime affect the phenomenon of invasion by plant species along riparian systems. The dynamics of exotic (non-native) and native species were examined at five sites that differed in exposure to hydrological disturbance (floods) during three consecutive years (medium, wet and dry years). When considering the disturbance gradient, exotic plants were favoured by direct exposure to floods (main channel) and by high flood frequencies. The response to year to year changes in hydrology was rapid for both native and exotic communities. However, the exotic plants responded more rapidly and were favoured by a dry year. A general framework including human and natural factors involved in invasions by exotic plants along rivers is presented.     

MORE EXOTIC AND FEWER NATIVE PLANT SPECIES: RIVERINE VEGETATION PATTERNS ASSOCIATED WITH ALTERED SEASONAL FLOW PATTERNS

Natural flow regimes are important for sustaining riverine vegetation. The regulation of river flows to provide water for agriculture often results in changes to flow timing. This study assesses the impact of altered seasonal flow patterns on riverine flora. Within temperate Australia, we surveyed the vegetation of five lowland rivers, three of which have large dams that alter their seasonal flow patterns; the other two are unregulated. From four to six sites were selected on each river, and these were classified into three levels of regulation based on the extent to which the timing of their seasonal flow patterns were altered. Sites were surveyed in winter and the following summer. Permanent quadrats were also established at a number of the surveyed sites and resurveyed every 3 months. Of the 267 plant taxa identified, 145 were exotic (non‐native). More exotic taxa and fewer native taxa were associated with increasing level of seasonal flow inversion (regulation). In particular, greater numbers of short‐lived exotic terrestrial taxa and fewer native woody taxa were associated with increasing level of regulation. Some exotic woody species (e.g. willows) were more common in the unregulated rivers and may have life‐history traits favoured by the natural seasonal flow patterns of study area. Multivariate analyses showed that level of regulation had a significant effect on the overall composition of the riverine vegetation. Our results provide support for the hypotheses that flow regulation adversely affects native species diversity and increases the vulnerability of riparian zones to invasion by exotic species; however, these effects are dependent on plant species' life‐history strategies. Our study highlights the importance of natural seasonal flow patterns for sustaining native riverine plant communities. Flow management aimed at maintaining or restoring ecological values should consider seasonal flow patterns. Winter/spring flow peaks may be particularly important for the recruitment of native riverine plants, especially trees and shrubs, and reducing the extent of exotic annuals and grasses. Copyright © 2012 John Wiley & Sons, Ltd.     

DRIVERS OF RIPARIAN TREE INVASION ON A DESERT STREAM

Understanding mechanisms of exotic species' invasions is essential to managing riparian landscapes throughout the world. In the southwestern USA, the two most dominant invaders of riparian habitats are the exotic tree species tamarisk (Tamarix ramosissima, Tamarix chinensis, and their hybrids) and Russian olive (Elaeagnus angustifolia). These plants were introduced around 1900, and their success may be facilitated by river regulation, river channel changes, and precipitation patterns. We hypothesized that riparian invasion in Canyon de Chelly, Arizona, was initiated by a change point event such as plantings, dam construction, or channel incision and that establishment near a change point was tied to flood events. We aged tamarisk, Russian olive, and native cottonwood trees from study sites in Canyon de Chelly and used tree ring analysis to determine the year of establishment and the elevation of the germination point relative to the channel. We used Bayesian Poisson regression and information theoretics to identify change points and precipitation variables driving annual tree establishment. We found that most tamarisk and Russian olive trees established in the late 1980s, and most cottonwoods established in 1930‐1950 and 1980‐2000. Regression models indicated that change points occurred in 1983 for Russian olive and 1988 for tamarisk, and precipitation was important for establishment. Although plantings and river regulation probably played a role in tree invasion, our results suggest that these species required precipitation and stream channel change for widespread establishment in Canyon de Chelly. The factors driving riparian invasions may not be those often associated with degraded rivers, such as altered hydrographs and land management changes, thus requiring analyses of the full range of ecological and physical processes. Copyright © 2012 John Wiley & Sons, Ltd.     

Environmental factors associated with the occurrence of the Ponto–Caspian gobies in a lowland river belonging to the central European invasion corridor

Ponto–Caspian goby fish belong to the most successful invaders in freshwater ecosystems of Europe and North America. So far, three alien goby species have been present in the Polish section of the Dnieper–Rhine River corridor: the monkey goby Neogobius fluviatilis, the racer goby Babka gymnotrachelus, and the western tubenose goby Proterorhinus semilunaris. Their assemblages in this region are unique because, in contrast to their native region or the Danube–Rhine corridor, they are unaffected by other gobiid species. We conducted electrofishing and habitat quality surveys to gather information on key environmental factors associated with the distribution of these fish in the lower river Vistula, which constitutes a vast middle part of the corridor used by the Ponto–Caspian species to migrate westward in Europe. We showed that the sandy bottom was beneficial for the monkey goby allowing the species to attain the highest abundance among the gobies in the river. Habitat complexity generated by artificial bank structures, as well as dense macrophyte coverage in the main channel, favoured mostly the expansion of the racer goby. Off‐channel areas with vegetation and a muddy bottom (old river beds and pools) were the most suitable habitats for the western tubenose goby. We did not find any negative spatial relationships among gobies of various species and sizes except the avoidance of the monkey goby by small western tubenose goby. Thus, our study demonstrates substantial habitat partitioning, suggesting a low level of interspecific competition among the three species in a lowland river.     

Metazoan Parasites of Introduced Round and Tubenose Gobies in the Great Lakes: Support for the “Enemy Release Hypothesis”

Recent invasion theory has hypothesized that newly established exotic species may initially be free of their native parasites, augmenting their population success. Others have hypothesized that invaders may introduce exotic parasites to native species and/or may become hosts to native parasites in their new habitats. Our study analyzed the parasites of two exotic Eurasian gobies that were detected in the Great Lakes in 1990: the round goby Apollonia melanostoma and the tubenose goby Proterorhinus semilunaris. We compared our results from the central region of their introduced ranges in Lakes Huron, St. Clair, and Erie with other studies in the Great Lakes over the past decade, as well as Eurasian native and nonindigenous habitats. Results showed that goby-specific metazoan parasites were absent in the Great Lakes, and all but one species were represented only as larvae, suggesting that adult parasites presently are poorly-adapted to the new gobies as hosts. Seven parasitic species are known to infest the tubenose goby in the Great Lakes, including our new finding of the acanthocephalan Southwellina hispida, and all are rare. We provide the first findings of four parasite species in the round goby and clarified two others, totaling 22 in the Great Lakes—with most being rare. In contrast, 72 round goby parasites occur in the Black Sea region. Trematodes are the most common parasitic group of the round goby in the Great Lakes, as in their native Black Sea range and Baltic Sea introduction. Holarctic trematode Diplostomum spathaceum larvae, which are one of two widely distributed species shared with Eurasia, were found in round goby eyes from all Great Lakes localities except Lake Huron proper. Our study and others reveal no overall increases in parasitism of the invasive gobies over the past decade after their establishment in the Great Lakes. In conclusion, the parasite “load” on the invasive gobies appears relatively low in comparison with their native habitats, lending support to the “enemy release hypothesis.”     

三峡库区巴东黄土坡巨型古滑坡体形成机理

本文采用现场调查、裂隙统计及室内试验相结合的方法，并结合少量钻孔试验，研究了巴东县黄土坡滑坡的边界和深度。研究表明，黄土坡滑坡分为上、中、下三段，是一个巨型古滑坡体。在此基础上，结合宏观地貌特征对该巨型古滑坡体的形成机理进行了分析，认为黄土坡滑坡是分次发生的，中、下段滑坡发生时间较早，且为同时滑动；而上段滑坡则发生时间相对较晚。本文研究成果有助于对黄土坡滑坡的时空稳定性进行预测，以制定相应的防治措施。     

Spatial organization of fish diversity in a species‐rich basin

Many abiotic and biotic environmental characteristics in river basins show spatial gradients from river source to main stem. We examined the spatial organization of fish within the Duck River Basin to document patterns in diversity that could help guide conservation strategies relevant to controlling the detrimental effects of basin development. In all, over 0.33 million fishes representing 145 species and 18 families, including 9 non‐native species, were collected in 207 samples distributed throughout the basin. Main stem sites with large catchment areas supported more fish diversity than smaller sites in tributaries. Moreover, rare species were most common in the main stem and ubiquitous species in tributaries. The spatial organization of species assemblages was mostly nested, as assemblages appeared to disassemble in an upstream direction from main stem sites and confluences. These findings suggest that fish conservation efforts might emphasize main stem segments and confluences that support higher biodiversity including the rare species often most in need of protection. The main stem can support the populations needed to recolonize tributaries and rescue populations that might periodically go extinct after droughts or other major disturbances. In tributaries, conservation of species assemblages may focus on managing between‐patch connectivity via corridor maintenance or creation.     

长江经济带城市生态效率时空格局及驱动因子探测

研究区域生态效率的时空格局,并探讨其形成机制,对于引导城市生态文明建设和实现区域可持续发展具有重要意义。利用DEA模型和空间自相关,系统研究了2006～2016年长江经济带108个城市生态效率的时空格局特征和演化规律,并利用地理探测器模型对其驱动因子进行探测。研究表明:①2006～2016年长江经济带城市生态效率一直处于较高水平,呈波动递增趋势,上、中、下游3个地区的城市生态效率差距在逐年缩小。②空间格局上,长江经济带的城市生态效率类型差异显著,由"东高西低"格局向"多中心"格局转变。③从空间集聚变化看,长江经济带的生态效率空间相关性很小,集聚特征不明显。④生态效率受多种因子共同作用,不同年份的主导因素存在显著差异,各因子在上、中、下游地区表现出明显的地域性和差异性。     

长江流域气象干旱演变特征及未来变化趋势预估

基于长江流域及周边范围在内的318个气象站点1956—2018年的实测资料和CMIP5全球气候模式在3种RCPs情景下的预估数据,以标准化降水蒸散发指数作为干旱等级的划分指标,对流域历史气象干旱时空演变特征进行了分析,并预估了流域未来不同排放情景下的气象干旱时空变化趋势。结果表明:①近60 a,流域干旱率年际变化较大,平均干旱率为18.21%。从年代变化来看,近20 a干旱影响范围普遍较大;干旱频发地区主要位于岷江流域,干旱次数呈从上游向下游递减的趋势;高强度的干旱多发生于金沙江中下游地区和成都平原地区,平均场次干旱强度也呈从上游向下游递减的趋势;②在RCP2.6、RCP4.5和RCP8.5情景下,2020—2050年长江流域多年平均干旱面积分别为74.1万km²、75.7万km²和126.4万km²;流域上、中、下游干旱频次多年平均值分别为1.1~1.2次/a、1.0~1.1次/a、1.0~1.1次/a。预估时段内上、中、下游干旱频次较历史时段分别增加38.4%~50.7%,33.7%~45.3%和32.6%~49.6%;预估时段内上、中、下游干旱强度多年平均值分别为-1.68,-1.64,-1.60,与历史时段差别不大。研究结果可为相关部门制订科学合理的干旱灾害防范措施和对策提供科学依据。     

Patterns of species richness and introduced species in native freshwater fish faunas of a Mediterranean‐type basin: the Guadiana River (southwest Iberian Peninsula)

In this study, we analysed the factors affecting species richness and introduced species component patterns in native fish faunas of 30 streams of the Middle Basin of the Guadiana River. From a principal component analysis and a stepwise multiple regression analysis performed on a data matrix composed of ten hydrological and biotic variables, we showed that: (1) fish species richness increased with stream length and watershed area, (2) the number of native species in a stream declined as channelizations and river regulation (constructions of dams) are higher, whereas introduced species increased in the same way, (3) the two main negative factors affecting native ichthyofaunas affected dissimilar ecological areas: channelizations, which depend on land‐use intensity of floodplain, mainly occurred in lower reaches of streams, but construction of dams mainly took place in upper sections of rivers, (4) the length of the remaining well‐preserved reaches in a stream appeared to be the only factor accurately predicting native fish species richness, and (5) native fish faunas of small isolated streams are more vulnerable to habitat alteration than those of large streams. Both isolation and fragmentation of populations were recorded, so the conservation status of native and highly endemic fish fauna of the study area is extreme. Protection of the few still extant, well‐preserved small streams and upper reaches, habitat restoration of channeled areas, and inclusion of the need for native fish fauna conservation in long‐term public planning of water use become a priority. Fish communities appear to be a sensitive indicator of biological monitoring to assess environmental degradation. Copyright © 2001 John Wiley & Sons, Ltd.     

Functional trait differences between extant exotic,native and extinct native plants in the Hunter River,NSW: a potential tool in riparian rehabilitation

Riparian and riverine systems around the world are subject to human mediated degradation. It is increasingly recognized that rehabilitation of these systems is important to retain biodiversity and important ecosystem services. Plant functional traits represent a potentially useful but underutilized tool in the restoration or rehabilitation of ecosystems such as riparian systems. This study uses a functional trait approach to provide insight into the changes in ecosystem function that have occurred with the loss of native plant species and their replacement by exotics. We examined the plant functional traits associated with extinct native, extant native and extant exotic species in the riparian margin of the Hunter River, New South Wales, Australia. Comparisons of 11 traits were conducted using univariate (analysis of variance and χ ²) and multivariate (principal component analysis and analysis of similarity) methods. Both extant native and extant exotic species had traits associated with a short lived, ruderal strategy: high specific leaf area (SLA), soft leaves, herbaceous growth forms and therophyte life form. In contrast, extinct native species had traits such as low SLA, tough leaves, tree and shrub growth form and phanerophyte life form. This shift in plant trait assemblages associated with the transition from a native to predominately exotic flora has important implications for ecosystem processes in this riverine system. We suggest that such a functional trait approach can be integrated with knowledge of other ecosystem components to provide an understanding of ecosystem function that can be used to guide rehabilitation initiatives. Copyright © 2008 John Wiley & Sons, Ltd.     

Are interactions among Ponto-Caspian invaders driving amphipod species replacement in the St. Lawrence River?

In Lake Erie and Lake Ontario, the Ponto-Caspian amphipod Echinogammarus ischnus has replaced the native amphipod Gammarus fasciatus on rocky substrates colonized by dreissenid mussels, which provide interstitial refugia for small invertebrates. Based on the premise that an invader's vulnerability to predation is influenced by its evolutionary experience with the predator and its ability to compete for refugia, we hypothesized that amphipod species replacement is facilitated through selective predation by the round goby Neogobius melanostomus, a Ponto-Caspian fish that invaded the Great Lakes in the early 1990s and is now colonizing the St. Lawrence River. In laboratory experiments, we determined if E. ischnus excludes G. fasciatus from mussel patches, and if the vulnerability of G. fasciatus to predation by gobies is increased in the presence of the invasive amphipod. E. ischnus and G. fasciatus did not differ in their use of mussel patches, either when alone or in each other's presence. Both species were equally vulnerable to predation by the round goby. In field experiments, we determined if the round goby exerts a stronger impact than native predators on the relative abundance of amphipod species. Our results suggest that E. ischnus is more vulnerable to native predators, but the round goby does not have a differential impact on the native amphipod. We conclude that competition with E. ischnus does not increase the vulnerability of G. fasciatus to goby predation, and that the round goby does not promote the replacement of G. fasciatus by E. ischnus in the St. Lawrence River. The outcome of antagonistic interactions between exotic and native amphipods is mediated more by abiotic factors than by shared evolutionary history with other co-occurring exotic species.     

Legacies of flood reduction on a Dryland river

The Bill Williams (Arizona) is a regulated dryland river that is being managed, in part, for biodiversity via flow management. To inform management, we contrasted riparian plant communities between the Bill Williams and an upstream free‐flowing tributary (Santa Maria). Goals of a first study (1996–1997) were to identify environmental controls on herbaceous species richness and compare richness among forest types. Analyses revealed that herbaceous species richness was negatively related to woody stem density, basal area and litter cover and positively related to light levels. Introduced Tamarix spp. was more frequent at the Bill Williams, but all three main forest types (Tamarix, Salix/Populus, Prosopis) had low understory richness, as well as high stem density and low light, on the Bill Williams as compared to the Santa Maria. The few edaphic differences between rivers (higher salinity at Bill Williams) had only weak connections with richness. A second study (2006–2007) focused on floristic richness at larger spatial scales. It revealed that during spring, and for the study cumulatively (spring and fall samplings combined), the riparian zone of the unregulated river had considerably more plant species. Annuals (vs. herbaceous perennials and woody species) showed the largest between‐river difference. Relative richness of exotic (vs. native) species did not differ. We conclude that: (1) The legacy of reduced scouring frequency and extent at the Bill Williams has reduced the open space available for colonization by annuals; and (2) Change in forest biomass structure, more so than change in forest composition, is the major driver of changes in plant species richness along this flow‐altered river. Our study informs dryland river management options by revealing trade‐offs that exist between forest biomass structure and plant species richness. Copyright © 2010 John Wiley & Sons, Ltd.     

Restoration and colonization of freshwater mussels and fish in a southeastern United States tailwater

The French Broad River originates in North Carolina, flows west into Tennessee and at its confluence with the Holston River forms the Tennessee River. Douglas Dam, located on the French Broad River 52 km above its mouth, is operated primarily for peaking hydroelectric power and flood control. Prior to completion of the dam in 1943, the lower French Broad River contained about 53 species of freshwater mussels and 100 species of fish. By 1977, the fauna in the 52‐km‐long tailwater was reduced to 12 species of mussels and 42 native species of fish. Improvements in tailwater conditions occurred following initiation of minimum flows in 1987, and consistent reaeration of discharge in 1993. From 1988 to 2002, we sampled three sites (4, 28, and 39 km downstream of the dam) to monitor the fish assemblage. Each year since 1988, we have collected one or more additional species, indicating continued immigration. We collected 82 native and 9 exotic species of fish overall, but the maximum of 67 species in 1 year suggests that some species reside in the tailwater at low densities or all immigrants may not successfully colonize the tailwater. There is limited potential for most extirpated species of mussels to naturally recolonize the tailwater because source populations are isolated. Consequently, 19 754 adult mussels of 19 species were introduced between 1997 and 2000. Survival of translocated mussels has been high, and successful reproduction of at least one translocated species has occurred. Additionally, four mussel species are naturally colonizing the tailwater. Colonization and recruitment of additional mussel species is expected as populations of their host fishes increase. We believe that the improved conditions of the tailwater may allow for the re‐establishment of sustaining populations of 30 mussel species of historic occurrence, but the continued operation of Douglas Dam as a peaking hydroelectric project will reduce the probability of successfully reintroducing some species. Published in 2006 by John Wiley & Sons, Ltd.     

漓江大型底栖无脊椎动物及其与水环境的关系

为研究漓江上游水库为下游河道枯季航运补水所造成的水生态影响,对漓江大型底栖无脊椎动物空间分布特性与相应的水环境因子进行调查,并采用Shannon-Wiener指数、Simpson指数、均匀度、丰富度指数分析物种多样性。结果表明:纹石蚕、黑龙江短沟蜷为上、中游优势种;纹石蚕、黑龙江短沟蜷、河蚬为下游优势种;纹石蚕、黑龙江短沟蜷为整个漓江水系的优势种。Shannon-Wiener指数、Simpson指数、均匀度、大型底栖无脊椎动物的平均密度和平均动物量均呈现出下游大于中游、中游大于上游的趋势;而物种丰富度指数呈现出下游小于中游、中游小于上游的趋势。大型底栖无脊椎动物和环境因子的典范对应分析表明:温度、电导率、盐度、浊度、水深、总磷、化学需氧量为影响大型底栖无脊椎动物群落结构和分布的主要环境因子。     

DECLINE AND RECOVERY OF SMALL MAMMALS AFTER FLOODING: IMPLICATIONS FOR PEST MANAGEMENT AND FLOODPLAIN COMMUNITY DYNAMICS

Floodplains often are managed both for agriculture and as habitat for native species. On the Sacramento River, farmers have expressed concern that natural areas may harbour small mammals in greater abundance than occurs on farms, which could make them sources of pests to adjoining farmlands. Concern over this has generated some opposition to riparian restoration. To better understand the issue, we studied small mammals at agricultural sites, young and older riparian restoration sites and remnant natural areas through live trapping and visual surveys over three successive years. Significant flooding occurred during the second winter of the study. We found that young riparian restoration sites (3–4 years since planting) did not harbour agricultural pests (e.g. California ground squirrel, Botta's pocket gopher) in greater abundance than agricultural sites, with the exception of California voles. Although voles were common at young sites, they declined dramatically as the sites matured, and neither 12‐ to 15‐year‐old sites nor remnant riparian habitats had higher abundances of any small mammal pest species than agricultural sites. All species except the arboreal western gray squirrel experienced significant population declines following the flood and remained at depressed levels for at least a full year thereafter. Native species were not less susceptible to flooding than exotic species. California vole was the first species to recover. Our study suggests that frequent winter flooding may be desirable from an agricultural pest management perspective. It illustrates a valuable ecosystem service, small mammal pest control, which is provided by flooding, an important natural disturbance process. Copyright © 2011 John Wiley & Sons, Ltd.     

典型滩涂环境因子对植物群落空间分布的影响

长江口滩涂生境具有较高的环境异质性,导致不同滩涂植物群落的分布特征存在显著差异。为分析长江口典型滩涂植物群与环境因子的关系,在崇明东滩和奉贤金汇港两个典型滩涂对其环境因子及植物群落特征进行了采样分析。分析结果表明,滩涂随着高程的增加,受潮汐的影响逐渐减少,环境因子呈现一定的规律性变化,滩涂植物对环境因子具有不同的适应力是导致长江口盐沼植被带状分布的重要因素。崇明东滩作为植物群落较为成熟的滩涂,芦苇和互花米草的生长表现沿高程呈"V"型。奉贤金汇港作为植物建群较短的新生带滩涂,互花米草的生长表现沿高程呈梯度分布。两区域植物群落表现不同的主要原因有可能是建群时间、演替阶段、滩涂受潮汐作用和立地条件等造成的。