Adaptations to Flooding Stress: From Plant Community to Molecule

Abstract: This review highlights four major topics in plant flooding research: the processes underlying vegetation zonation in the floodplain, the challenges of using model species to reveal adaptive responses in shoots and roots, the role of micro-organisms in flooded soils in relation to plant growth, and the molecular regulation of the hormone ethylene which is heavily involved in the adaptation reaction of flood-resistant plants. Model species and vegetation strategies are used to unravel mechanisms of vegetation zonation in the river flood-plain. In the case of woodlands, hydrological conditions determine to a large extent their zonation patterns under natural conditions. For softwood species, such as Salicaceae, the interaction between water levels and timing of seed dispersal is the dominating process determining their establishment success on river banks. Their strategy is well adapted to irregular, high and prolonged floods. Hardwood species, Quercus, Fraxinus, UImus and Acer, are flood-sensitive and inhabit the higher sites. They mainly have heavy seeds and germinate under shaded conditions. The most shade-tolerant hardwood species are the least well adapted to flooding. Anthropogenically influenced parts of the floodplain are characterized by grasslands with elevation level and management practices determining the species composition. Low-lying grasslands have flood-tolerant species; elevated zones are seldom flooded and have flooding-sensitive species. Following Grime (1998^[59]), plant species of major vegetation types within the floodplain zone can be divided into three categories–dominants, subordinates and transients–illustrating the diversity in plant species in relation to environmental properties. Model species that are indicative of the different conditions in the various zones are chosen to help in the understanding of morphological and physiological adaptations at the plant level. The formation of aerenchymatous roots and the capacity to elongate shoot parts upon submergence are among the main responses of surviving plants. The role of hormones in the adaptation reaction is emphasized. Owing to high porosities in roots of flood-tolerant plants, radial oxygen loss greatly influences nitrification and denitrification processes in the flooded soil. Nutrient cycles are restored by root-derived oxygen and the oxygenated rhizosphere is detoxified. A new development in flooding ecology is the unravelling of the molecular regulation of hormonally controlled processes. The expression of an ethylene receptor gene in Rumex palustris is highlighted. This paper ends with some suggestions for future flooding research.     

Grazing effects on the species‐area relationship: Variation along a climatic gradient in NE Spain

Questions: Does grazing have the same effect on plant species richness at different spatial scales? Does the effect of spatial scale vary under different climatic conditions and vegetation types? Does the slope of the species‐area curve change with grazing intensity similarly under different climatic conditions and vegetation types? Location: Pastures along a climatic gradient in northeastern Spain. Methods: In zones under different regimes of sheep grazing (high‐, low‐pressure, abandonment), plant species richness was measured in different plot sizes (from 0.01 to 100 m2) and the slope of the species‐area curves was calculated. The study was replicated in five different locations along a climatic gradient from lowland semi‐arid rangelands to upland moist grasslands. Results: Species richness tended to increase with grazing intensity at all spatial scales in the moist upland locations. On the contrary, in the most arid locations, richness tended to decrease, or remain unchanged, with grazing due to increased bare soil. Grazing differentially affected the slope (z) of the species‐area curve (power function S=c A^z) in different climatic conditions: z tended to increase with grazing in arid areas and decrease in moist‐upland ones. ß‐diversity followed similar pattern as z. Conclusions: Results confirm that the impact of grazing on plant species richness are spatial‐scale dependent. However, the effects on the species‐area relationship vary under different climatic conditions. This offers a novel insight on the patterns behind the different effects of grazing on diversity in moist vs. arid conditions reported in the literature. It is argued that the effect of spatial scale varies because of the different interaction between grazing and the intrinsic spatial structure of the vegetation. Variations in species‐area curves with grazing along moisture gradients suggest also a different balance of spatial components of diversity (i.e. a‐ and ß‐diversity).     

Cattle foraging habits shape vegetation patterns of alluvial year-round grazing systems

Year-round grazing with robust cattle is increasingly used as a near-natural tool for the restoration of structurally diverse grassland ecosystems in Western and Central Europe. The aim of this study was to evaluate the general success of year-round grazing and to analyze the interplay between emerging vegetation structures, grazing patterns and abiotic environmental conditions. In summer 2010 vegetation composition, aboveground biomass and soil properties were sampled at 44 quadrats of 4 × 4 m² within two year-round grazed floodplain sites in Northwestern Germany. For plot selection, we predefined structural vegetation types and later statistically determined indicative plant species for each structural type. Our results showed that year-round grazing resulted in the successful creation of eutrophic grassland communities on former agricultural land after 15 years. Soil parameters like phosphorous and potassium concentration and the flooding duration did not or only slightly differ between different structure types. In summer, cattle preferably fed at short-growing patches which were of better digestible biomass than taller patches. Hence, our data clearly demonstrate a positive feedback between grazing intensity and fodder quality leading to a patchy vegetation structure of intensively grazed swards and less frequented areas dominated by high-growing grasses and tall forbs, almost independently from primary differences in soil parameters and other site factors such as flooding duration. The remarkable structural and floristic diversity of year-round grazing systems clearly is a result of these spatially contrasting feeding patterns.     

Impact of different sheep grazing intensities on salt marsh vegetation in northern Germany

Abstract. Mainland salt marshes in Schleswig-Holstein (northern Germany) have been grazed intensively by sheep for several decades. In 1988 experimental sites were established in the lower and middle salt marsh of Sönke-Nissen-Koog and subjected to different grazing intensities. From 1989 to 1993 the impact of sheep grazing on the composition and structure of the salt marsh vegetation was studied through the yearly analysis of permanent plots, vegetation mapping and measurements of the vegetation height. The intensively grazed site (10 sheep/ha) is covered by a short monotonous Puccinellia maritima sward with Salicornia europaea and Suaeda maritima. Halimione portulacoides and Aster tripolium, especially flowering plants, are rare. On the sites with 1.5 and 3 sheep/ha Puccinellia maritima remained dominant. The population density of Salicornia europaea decreases after reduction of the grazing intensity, whereas Suaeda maritima finds optimal growing conditions. Stands of Halimione portulacoides and flowering Aster tripolium plants are rare near the sea dike but their cover and size increases further away from the dike. In the plot with 1.5 sheep/ha the height of the vegetation increases along the gradient from the dike towards the tidal flats, due to local differences in actual grazing intensity. When grazing is stopped, Puccinellia maritima is successively replaced by Festuca rubra, Halimione portulacoides and Aster tripolium. High variability of vegetation height indicates structural diversity. Patches of higher and lower vegetation correspond with the distribution pattern of different plant species. In terms of nature conservation cessation of grazing is recommended.     

放牧制度对草地产流产沙及氮磷流失的影响

研究不同放牧制度草场水土流失过程,对草原生态环境保护和治理具有重要的理论意义。以内蒙古呼伦贝尔草原不同放牧草场为研究对象,设置选取三种放牧制度草场(自由放牧、轮牧、休牧),采用人工模拟降雨的方法进行0.74mm/min和1.5mm/min雨强的降雨模拟试验,测定径流量,含沙量,径流和泥沙中总氮,总磷浓度,并探讨植被截留对径流的影响规律。结果表明:植被截留对减少降雨径流具有明显的作用,休牧草场径流系数减小最多,自由放牧草场减小最少,产沙量显示为自由放牧草场轮牧草场休牧草场。降雨强度对径流中的氮磷浓度影响显著,自由放牧草场总氮浓度和休牧草场总磷浓度受雨强影响最大,氮磷流失过程浓度变化曲线更符合幂函数分布。休牧草场泥沙氮含量和泥沙磷含量均为最高,自由放牧草场与休牧草场的总氮富集率基本相等且均大于轮牧草场,总磷富集率为自由放牧休牧轮牧,三种放牧草场氮磷和泥沙流失主要影响因素为径流量和含沙量。因此,适当的将呼伦贝尔草原自由放牧草场向休牧和轮牧草场转变,将有利于减少草场水土营养元素流失及草原生态可持续发展。     

The impact of site conditions and seed dispersal on restoration success in alluvial meadows

Abstract. We studied the restoration success of flood plain meadows in the northern Upper Rhine valley, where between 1988 and 1992, 35 ha of arable land was converted into grassland and subsequently managed for nature conservation. Remnant populations of typical alluvial meadow species were found in old meadows and along drainage ditches that dissect the whole area. We analysed the site conditions and phytosociological relevés in old and new meadows. Small differences in site parameters between old and new meadows contrasted with a clear floristic differentiation between the two meadow types. The vegetation of old meadows was much more differentiated along prevailing environmental gradients than the vegetation of new meadows. Despite the favourable site conditions for the re‐establishment of species‐rich meadows on the former arable land, restoration success was limited to the vicinity of remnant stands. In contrast to old meadows, indicator species of new grassland were still typical species of regularly disturbed ruderal and arable habitats, often capable of building up a persistent seed bank. The precise mapping of 23 target species revealed that even wind dispersal predominantly leads to re‐establishment in the close circumference of parent plants. We found no indication that regular flooding, hay‐making and autumnal grazing had an impact on recolonization of newly created grassland. Even under favourable conditions for the re‐establishment of target species, restoration success in alluvial meadows proved to be strongly dispersal limited. We discuss the implications of our findings for future restoration management in grasslands.     

Effects of grazing on patch structure in a semi‐arid two‐phase vegetation mosaic

Abstract. Question: What are the grazing effects in the spatial organization and the internal structure of high and low cover patches from a two‐phase vegetation mosaic? Location: Patagonian steppe, Argentina. Methods: We mapped vegetation under three different grazing conditions: ungrazed, lightly grazed and heavily grazed. We analysed the spatial patterns of the dominant life forms. Also, in each patch type, we determined density, species composition, richness, diversity, size structure and dead biomass of grasses under different grazing conditions. Results: The vegetation was spatially organized in a two‐phase mosaic. High cover patches resulted from the association of grasses and shrubs and low cover patches were represented by scattered tussock grasses on bare ground. This spatial organization was not affected by grazing, but heavy grazing changed the grass species involved in high cover patches and reduced the density and cover of grasses in both patch types. Species richness and diversity in high cover patches decreased under grazing conditions, whereas in low cover patches it remained unchanged. Also, the decrease of palatable grasses was steeper in high cover patches than in low cover patches under grazing conditions. Conclusions: We suggest that although grazing promotes or inhibits particular species, it does not modify the mosaic structure of Patagonian steppe. The fact that the mosaic remained unchanged after 100 years of grazing suggests that grazing does not compromize population processes involved in maintaining patch structure, including seed dispersal, establishment or biotic interactions among life forms.     

An Ecohydrological Cellular Automata Model Investigation of Juniper Tree Encroachment in a Western North American Landscape

Woody plant encroachment over the past 140 years has substantially changed grasslands in western North American. We studied encroachment of western juniper (Juniperus occidentalis var. occidentalis) into a previously mixed shrub–grassland site in central Oregon (USA) using a modified version of Cellular Automata Tree–Grass–Shrub Simulator (CATGraSS) ecohydrological model. We developed simple algorithms to simulate three encroachment factors (grazing, fire frequency reduction, and seed dispersal by herbivores) in CATGraSS. Local ecohydrological dynamics represented by the model were first evaluated using satellite-derived leaf area index and measured evapotranspiration data. Reconstructed pre-encroachment vegetation cover percentages and the National Land Cover Database (NLCD 2006) vegetation map were used to estimate parameters for encroachment factors to represent juniper encroachment in CATGraSS. Model sensitivity experiments examined the influence of each encroachment factor and their combinations on trajectories of modeled percent cover of each plant functional type and emergent spatial vegetation patterns in the modeled domain. Simulation results identified grazing as the key factor leading to juniper encroachment, by reducing shrub and grass cover and promoting the formation of juniper tree clusters. Reduced fire frequency and increased seed dispersal by grazers further amplified juniper encroachment into grassland patches between clusters of juniper trees. Each encroachment factor showed different consequences on modeled vegetation patterns. Time series of modeled plant cover and spatial patterns of plant functional types were found to be consistent with an existing conceptual model described in the literature. The proposed model provides a tool that can be used to improve our understanding of the drivers and processes of woody plant encroachment and vegetation response to global change.     

Coastal sand dune vegetation of Tabasco and Campeche,Mexico

Abstract. Sand dune vegetation along the coast of the Mexican states of Tabasco and Campeche was sampled by means of 1501 releves and the data were analyzed with classification and ordination programs. 36 community types were distinguished, which were grouped into 10 higher-order groups. The communities are described in a sequence reflecting the main vegetation zonation. Beach, embryo dune and foredune community groups include 12 community types, the sheltered zone includes 16 types and the fixed dunes 8 types. The ordination results reveal one main vegetation gradient corresponding to the increase in mean distance from the shoreline and elevation, and being covariant with species richness, mean vegetation cover and mean vegetation height. Additional differences are related to the geographical transition between the Gulf and Caribbean coastal vegetation and environmental conditions, mainly type of sand, occurring in the study area. Siliceous sand and a Gulf climate are characteristic for most of Tabasco, and calcareous sand and a Caribbean-type climate are characteristic for Campeche. Disturbance caused by coconut plantations, cattle grazing and tourism favours the invasion of ruderal species from waste places behind the dunes, which attain local dominance in the dunes described here. Consequently some separate community types had to be distinguished. The distribution of community types is analyzed in the context of the transitions between calcareous and siliceous substrates in the study area.     

Effect of cattle grazing on soil salinity and vegetation composition along an elevation gradient in a temperate coastal salt marsh of Samborombón Bay (Argentina)

Salt marshes of Samborombón Bay (Argentina) have been grazed sporadically at very low stocking rates, but in the last decade, grazing intensity increased due to agriculture expansion. We investigated the effect of cattle grazing on vegetation and soil salinity on the most extended Spartina densiflora community. This community develops along an elevation gradient where the frequency and duration of tidal flooding and soil salinity increased as elevation decreased. Vegetation and soil data were collected from a national park excluded to cattle grazing for 30 years and from an adjacent commercial livestock farm continuously grazed by cattle. As elevation level decreased, plant cover, richness and diversity of functional groups and species decreased. As we expected, grazing altered soil salinity and vegetation composition in different extent along the elevation gradient. Grazing changed vegetation structure more intensively in the high elevation level because it reduced the competitive exclusion exerted by S. densiflora, allowing the increase in floristic richness. Grazing increased soil salinity and the contribution of salt-tolerant species only in the medium but not in the low elevation level probably because the higher frequency and duration of tidal flooding counterbalanced the increase in evaporation promoted by biomass removal in the low respect to the medium elevation level. While grazing may cause positive impacts for plant conservation in the high elevation level, it may cause negative consequence for livestock production because of the reduction in forage quality along the entire elevation gradient.     

藏北高寒草地植被和土壤对不同放牧强度的响应

放牧压力在时间和空间的不均衡分布导致局部土地过度利用和生态退化,然而当前对放牧强度的量化多采用替代性指标或对照试验,缺乏直接监测数据,也缺乏不同草地类型对放牧强度变化的响应差异性研究。以西藏自治区那曲市为研究区,利用佩戴式GPS牛羊定位器构建高精度放牧轨迹数据集模拟放牧强度,构建栅格尺度放牧强度空间分布和划分方法,结合草地群落样方调查,通过Duncan法（Duncan''s multiple comparative analysis）进行多重比较分析,探究自由放牧模式下高寒草甸和高寒草原两类区域植被和土壤对不同放牧强度的响应方式及差异性。本研究可为放牧行为环境效应监测提供新思路,并根据不同草地状况因地制宜提出放牧优化管理策略,助力高寒传统牧区的可持续发展。主要结论有：1）随着放牧强度的增大,高寒草原地上生物量先升高后降低,高强度放牧对高寒草原植被的影响大于高寒草甸。2）高放牧强度下,高寒草原土壤水分显著高于中低强度,高寒草甸土壤容重显著低于低强度。可能原因是放牧压力多集聚于水源附近。高寒草原区土壤的砂粒含量随放牧强度的增大而增加。放牧强度的增大导致草甸上层土壤有机质增加,草甸下层、草原上层、草原下层土壤有机质先增加后减小。草甸上下层土壤全磷含量在低放牧强度下显著低于中高强度。3）植被土壤变化受到自然因子和放牧活动的共同影响。高寒草甸更加耐牧,高强度放牧对高寒草原的负面影响更大,而中度放牧有利于草地尤其是高寒草原的放牧利用。4）放牧生态系统是一个环境-植物-家畜自适应系统。在放牧管理中不能仅通过控制载畜量缓解草地超载,还需要综合考虑生态系统的弹性及各营养级的适应性,合理配置放牧强度,控制季节性超载和局部超载。     

Diversity and Above-Ground Biomass Patterns of Vascular Flora Induced by Flooding in the Drawdown Area of China's Three Gorges Reservoir

Hydrological alternation can dramatically influence riparian environments and shape riparian vegetation zonation. However, it was difficult to predict the status in the drawdown area of the Three Gorges Reservoir (TGR), because the hydrological regime created by the dam involves both short periods of summer flooding and long-term winter impoundment for half a year. In order to examine the effects of hydrological alternation on plant diversity and biomass in the drawdown area of TGR, twelve sites distributed along the length of the drawdown area of TGR were chosen to explore the lateral pattern of plant diversity and above-ground biomass at the ends of growing seasons in 2009 and 2010. We recorded 175 vascular plant species in 2009 and 127 in 2010, indicating that a significant loss of vascular flora in the drawdown area of TGR resulted from the new hydrological regimes. Cynodon dactylon and Cyperus rotundus had high tolerance to short periods of summer flooding and long-term winter flooding. Almost half of the remnant species were annuals. Species richness, Shannon-Wiener Index and above-ground biomass of vegetation exhibited an increasing pattern along the elevation gradient, being greater at higher elevations subjected to lower submergence stress. Plant diversity, above-ground biomass and species distribution were significantly influenced by the duration of submergence relative to elevation in both summer and previous winter. Several million tonnes of vegetation would be accumulated on the drawdown area of TGR in every summer and some adverse environmental problems may be introduced when it was submerged in winter. We conclude that vascular flora biodiversity in the drawdown area of TGR has dramatically declined after the impoundment to full capacity. The new hydrological condition, characterized by long-term winter flooding and short periods of summer flooding, determined vegetation biodiversity and above-ground biomass patterns along the elevation gradient in the drawdown area.     

Alternative transient states and slow plant community responses after changed flooding regimes

Climate change will have large consequences for flooding frequencies in freshwater systems. In interaction with anthropogenic activities (flow regulation, channel restoration and catchment land‐use) this will both increase flooding and drought across the world. Like in many other ecosystems facing changed environmental conditions, it remains difficult to predict the rate and trajectory of vegetation responses to changed conditions. Given that critical ecosystem services (e.g. bank stabilization, carbon subsidies to aquatic communities or water purification) depend on riparian vegetation composition, it is important to understand how and how fast riparian vegetation responds to changing flooding regimes. We studied vegetation changes over 19 growing seasons in turfs that were transplanted in a full‐factorial design between three riparian elevations with different flooding frequencies. We found that (a) some transplanted communities may have developed into an alternative stable state and were still different from the target community, and (b) pathways of vegetation change were highly directional but alternative trajectories did occur, (c) changes were rather linear but faster when flooding frequencies increased than when they decreased, and (d) we observed fastest changes in turfs when proxies for mortality and colonization were highest. These results provide rare examples of alternative transient trajectories and stable states under field conditions, which is an important step towards understanding their drivers and their frequency in a changing world.     

A novel approach to assess livestock management effects on biodiversity of drylands

In drylands livestock grazing is the main production activity, but overgrazing due to mismanagement is a major cause of biodiversity loss. Continuous grazing around water sources generates a radial gradient of grazing intensity called the piosphere. The ecological sustainability of this system is questionable and alternative management needs to be evaluated. We apply simple indicators of species response to grazing gradients, and we propose a novel methodological approach to compare community response to grazing gradients (double reciprocal analysis). We assessed degradation gradients of biodiversity under different management strategies in semiarid rangelands of the Monte desert (Argentina) by analyzing changes in vegetation, ants and small mammal richness and diversity, and variation due to seasonality. At the species level, we determined the trend in abundance of each species along the gradient, and the potential cross-taxa surrogacy. At the community level, the new methodological consists of assessing the magnitude of biodiversity degradation along different piospheres by comparing the slopes of linear functions obtained by the double reciprocal analysis. We found that most species showed a decreasing trend along the gradient under continuous grazing; while under rotational grazing fewer species showed a decreasing trend, and a neutral trend (no change in the abundance along the gradient of grazing intensity) was the most common. We found that vegetation cannot be used as a surrogacy taxon of animal response. Moreover, weak cross-taxa surrogacy was found only for animal assemblages during the wet season. The double reciprocal analysis allowed for comparison of multi-taxa response under different seasons and management types. By its application, we found that constrains in precipitation interacted with disturbance by increasing the negative effect of grazing on vegetation, but not on animal assemblages. Continuous grazing causes biodiversity loss in all situations. Rotational grazing prevents the occurrence of vegetation degradation and maintains higher levels of animal diversity, acting as an opportunity for biodiversity conservation under current scenarios of land use extensification. Our approach highlights the importance of considering multi-taxa and intrinsic variability in the analysis, and should be of value to managers concerned with biodiversity conservation.     

Spatial connectivity and boundary patterns in coastal dune vegetation in the Circeo National Park,Central Italy

Abstract. Distribution patterns of coastal sand dune plant communities in the Circeo National Park (Central Italy) are quantified and compared by measuring spatial connectivity and richness of community boundaries along the dune profile. The purpose of this study is: (1) to evaluate patchiness and frequency of spatial links between communities; (2) to identify the communities most sensitive to disturbance; and (3) to predict probable changes due to modification of spatial zonation. Data were obtained using belt transects across the Holocene coastal dune zone. Vegetation zonation from the seashore to the foredune slacks is analysed in relation to chorological, phytosociological and life‐form types. We found that under relatively undisturbed environmental conditions communities formed a sequence (communities 1 to 7), with the exception of a replacement community, which occupied gaps in the perennial vegetation. The spatial distribution of some communities was reduced as a consequence of disturbance; others became fragmented in small patches or even disappeared. In coastal environments with strong, complex gradients, the existence of certain communities depends on specific links (neighbourhood effects) and high connectivity values do not indicate better conservation conditions.     

放牧管理模式对高寒草甸鼢鼠鼠丘群落演替的影响

高寒草甸放牧利用下高原鼢鼠(Eospalax baileyi)等危害的发生是草地管理的关键难题,分析放牧管理模式对鼢鼠鼠丘植被群落演替的影响能为草地管理提供重要依据。研究选择划区轮牧(RG)、生长季休牧(GSG)、连续放牧(CG)和禁牧(PG)4种放牧管理模式,以及各模式下不同年限鼠丘(一年(ZM1)、两年(ZM2)、三年(ZM3)和多年鼠丘(ZMM))与对照(CM)草地。分析不同放牧管理模式对鼠丘植被群落特征和生物量等的影响,结果发现:PG和GSG下所有年限鼠丘的植被高度、地上生物量均高于RG和CG;RG和GSG下ZM1和ZM2物种Shannon-wiener指数均高于对照样地物种Shannon-wiener指数。主成分分析表明:RG下地上生物量和物种丰富度指数是影响鼠丘植被群落演替的重要因子,PG下地上生物量、盖度、Shannon-wiener指数和均匀度指数是鼠丘植被群落演替的重要因子,CG下物种丰富度和重要值是影响鼠丘植被群落演替的重要指标,GSG下Shannon-wiener指数、盖度和高度是影响鼠丘植被群落演替的重要指标。可见,不同放牧制度对鼠丘植被群落演替的影响不同,禁牧和生长季休牧管理模式能够较好地恢复鼠丘植被群落演替。     

Use of GIS and high resolution LiDAR in salt marsh restoration site suitability assessments in the upper Bay of Fundy, Canada

Salt marshes exhibit striking vegetation zonation corresponding to spatially variable elevation gradients which dictate their frequency of inundation by the tides. The salt marshes in the upper Bay of Fundy, a dynamic hypertidal system, are of considerable interest due to increasing recognition of salt marsh ecosystem values and the extent of prior conversion of salt marshes to agricultural lands, much of which are no longer in use. To determine the suitability of two potential restoration sites at Beausejour Marsh in New Brunswick, Canada, geomatics technologies and techniques were used to assess vegetation and elevation patterns in an adjacent reference salt marsh and the proposed restoration sites. Light detection and ranging digital elevation models (DEMs) were created for the reference marsh and the restoration sites in both the spring (leaf-off) and late summer (leaf-on, maximum biomass) periods. Aerial photographs and Quickbird multispectral imagery were used to visually interpret vegetation zones on the reference marsh and were field validated using vegetation characteristics from quadrats referenced with differential GPS. Elevation limits of the salt marsh vegetation zones were extracted from the DEM of the reference marsh and applied to the DEM of the restoration sites to determine the percentage area of each site that would be immediately suitable for new salt marsh growth. Of the two restoration sites assessed, one had experienced significant subsidence since dyking; only about 40 % of the site area was determined to be of sufficient elevation for immediate vegetation colonization. The second site, while more than 88 % suitable, would require the installation of a large dyke on the landward side of the restoration site to prevent flooding of adjacent lands. This study provides essential high resolution elevation and vegetation zonation data for use in restoration site assessments, and highlights the usefulness of applied geomatics in the salt marsh restoration planning process.     

Clonal Growth Strategies Along Flooding and Grazing Gradients in Atlantic Coastal Meadows

Specific composition and species clonal traits were characterized along combined flooding and grazing gradients to answer two questions. i) To what extent does the interaction of flooding and grazing influence the clonal characteristics of the vegetation? ii) Are the effects of both environmental factors independent or interactive? This study was carried out in a wet meadow along the Atlantic coast (France). Three plant communities (hygrophilous, meso-hygrophilous and mesophilous) were distinguished along a flooding gradient and five levels of grazing pressure were controlled through an experimental design (from no grazing to heavy grazing). We monitored species composition and retrieved, for each species, the type of clonal growth organs (CGOs) and clonal traits from the CLO-PLA3 database. We identified two syndromes of clonal traits: ??above-ground splitters?? and ??below-ground integrators??. Clonal traits played a key role in plant assembly in the studied meadows. The interaction of both environmental factors selected for particular syndromes of clonal traits; however, flooding had a stronger filtering effect than grazing. The hygrophilous community was dominated by above-ground splitters, whereas the meso-hygrophilous vegetation was dominated by below-ground integrators. In the mesophilous community, clonal composition was the most diverse and shared clonal traits with the vegetation of both the hygrophilous and meso-hygrophilous communities. Grazing impact on CGOs and clonal traits differed between plant communities, i.e., the effect of grazing was modulated by the flooding regime. This study confirmed that vegetation responses to grazing might depend on the pool of traits, primarily filtered by environmental factors such as flooding.     

Broad‐scale vegetation‐environment relationships in Eurasian high‐latitude areas

Question: How is tundra vegetation related to climatic, soil chemical, geological variables and grazing across a very large section of the Eurasian arctic area? We were particularly interested in broad‐scale vegetation‐environment relationships and how well do the patterns conform to climate‐vegetation schemes. Material and Methods: We sampled vegetation in 1132 plots from 16 sites from different parts of the Eurasian tundra. Clustering and ordination techniques were used for analysing compositional patterns. Vegetation‐environment relationships were analysed by fitting of environmental vectors and smooth surfaces onto non‐metric multidimensional scaling scattergrams. Results: Dominant vegetation differentiation was associated with a complex set of environmental variables. A general trend differentiated cold and continental areas from relatively warm and weakly continental areas, and several soil chemical and physical variables were associated with this broad‐scaled differentiation. Especially soil chemical variables related to soil acidity (pH, Ca) showed linear relationships with the dominant vegetation gradient. This was closely related to increasing cryoperturbation, decreasing precipitation and cooler conditions. Remarkable differences among relatively adjacent sites suggest that local factors such as geological properties and lemming grazing may strongly drive vegetation differentiation. Conclusions: Vegetation differentiation in tundra areas conforms to a major ecocline underlain by a complex set of environmental gradients, where precipitation, thermal conditions and soil chemical and physical processes are coupled. However, local factors such as bedrock conditions and lemming grazing may cause marked deviations from the general climate‐vegetation models. Overall, soil chemical factors (pH, Ca) turned out to have linear relationship with the broad‐scale differentiation of arctic vegetation.     

基于贝叶斯二项式模型分析棕头鸥种群多度与环境因子间的关系

传统的种群多度调查方法由于默认观察率 p 等于 1,因此极有可能低估种群大小,进而误判种群多度与环境因子间的关系。为了了解禽流感爆发后青海湖棕头鸥种群与环境因子间的关系,为棕头鸥管理提供有效依据,于 2010 年和 2011 年的 4 ～6 月调查了青海湖保护区 23 个观测点的棕头鸥种群数量及环境因子。通过包含观察率的贝叶斯二项式混合模型分析棕头鸥种群多度与环境因子间的关系,采用 DIC 准则进行因子筛选。结果表明: 种群数量亚模型包含取样面积、放牧强度、距公路距离和植被盖度 4 个参数,种群数量随取样面积、距公路距离和植被盖度的增加而增加,随放牧强度的增加而减少; 观察率亚模型包含观察经验和棕头鸥的行为月节律 2 个参数,观察率随观察月的递增而降低,随观察经验的增加而升高,高经验观察者平均每千米观察到 18. 1 只棕头鸥,低经验观察者可以平均观察到 13. 7 只。天气状况不影响观察率,这可能与棕头鸥的觅食栖息地距岸边较近,不影响观察者的观察有关。