Plant-parasitic Nematodes in Loess Toposequences Planted with Corn

Populations of plant-parasitic nematodes in an Iowa cornfield were studied along north- and west-facing toposequences. Samples were collected monthly during the growing season. The greatest biomass for Xiphinema americanum occurred at the footslope on the north face. Paratylenchus microdorus had its greatest biomass at the summit position, generally more in the west- than in the north-facing slope. Pratylenchus spp. in the roots peaked at the toeslope in the north-facing slope, but at the footslope in the west-facing slope. Helicotylenchus pseudorobustus peaked at the backslope and the toeslope along the north- and west-facing slopes, respectively. Diversity, as computed for each plot by the Shannon-Weiner diversity index, was highest at the backslope in both toposequences.     

Environmental relationships of vegetation patterns in saltmarshes of central Argentina

We describe vegetation-environment relationships in the saltmarshes of central Argentina. Gradient analysis (Detrended canonical correspondence analysis, DCCA) was performed involving 14 parameters of the groundwater that account for most of the variation in plant communities. We used a stepwise multivariate procedure to classify the vegetation data into 8 clusters, named according to the most abundant characteristic species:Chloris canterai, Cynodon dactylon, Distichlis, spicata, Spartina densiflora andPaspalum vaginatum clusters, containing relevés of tall grassland communities, andAtriplex undulata, Cyclolepis genistoides andHeterostachys ritteriana clusters, containing relevés from scrub. Our interpretation of DCCA ordinations suggests that vegetation pattern is primarily related to a salinity-moisture gradient. There is a strong relationship between vegetation type and the amount of salt in the groundwater and the pattern of its variation during the year. The depth of the groundwater and the conditions of submersion are also related to the compositional variation of the vegetation. Although flooding causes some differences between sites, the most important discriminant variable, and therefore the best predictor of floristic variation, is salinization.     

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.     

Proposed mechanism for the origin of sodic patches in Kruger National Park, South Africa

The accumulation of sodium on the footslopes of granitic catenas in semi‐arid southern Africa leads to the formation of sodic patches. Sodic patches are ecologically important for nutrient accumulation, predator evasion and wallowing, but they are often perceived as derelict lands because of vegetation denudation and low aesthetic quality. This negative perception, by both ecologists and tourists, often leads to ill‐advised management and ‘rehabilitation’ measures. In Kruger National Park, sodic patches occur at the riparian‐upland boundary and hence the processes originating in both systems may contribute to their origin. The upland‐based catena and riparian‐based evapotranspiration models were used to explore the hypothesis that these soils originate from both catena and evapotranspiration‐driven hydraulic processes. The models predict vegetation zonation dictated by a salt tolerance gradient and an increase in sodic patch area over time as a result of progressive salt accumulation. Vegetation structure and hillslope morphology across the riparian‐upland boundary and analysis of change in patch configuration over a 50‐year aerial photographic record were used to test the hypotheses. Sodic patches have unique vegetation, occur on the intermediate positions of hillslopes, have increased in area three‐fold over 50 years and are encroaching into the riparian zone. This behaviour is consistent with the assertion that these patches originate from both catena and evapotranspiration processes. Results imply a dynamic aspect of sodic patches, which have been previously viewed as static landscape features in pedogenic time scales. However, we show that they change over relatively smaller time scales meaning that their management should be commensurate with this dynamic nature. Therefore, sodic patches should be managed under a scheme that incorporates their small‐scale expansion and recognizes their ecological importance.     

Physiological Integration among Clonal Ramets during Invasion of Disturbance Patches in a New England Salt Marsh

Resource sharing between ramets growing across environmentalresource gradients may have important consequences for clonalplant populations and community dynamics. As the clonal saltmarsh grasses, Spartina patens and Distichlis spicata, vegetativelycolonize disturbance-generated bare patches, they span steepgradients in soil salinity and available sunlight. Examinationof water relations and carbon translocation in the field andgreenhouse revealed that connected ramets of these marsh grassesshare water and carbon in response to gradients in resourceavailability. Ramets colonizing disturbance patches rely uponphysiological integration with connected parent ramets to overcomewater stress associated with hypersaline patch environments.In addition, upon establishment inside a bare patch, daughterramets may translocate carbon back to shaded parent ramets inthe surrounding vegetation outside of patches. Physiological integration of ramets colonizing disturbance-generatedbare patches and parent ramets outside of patches may explainthe predominance of vegetative invasion over sexual recruitmentin marsh succession. Hypersaline soil conditions, which inhibitseedling recruitment into patches, have little effect on thesuccess of clonal colonizers that can import water from parentramets. This success appears to be due to the ability of clonalmarsh grasses to translocate water and carbon products betweenramets growing across opposing gradients in resource availability.Copyright1995, 1999 Academic Press Clonal integration, Distichlis spicata, halophytes, salt marsh ecology, secondary succession, Spartina patens     

Vascular plant diversity and climate change in the alpine zone of the Lefka Ori,Crete

The aim of this study is to analyse the vascular flora and the local climate along an altitudinal gradient in the Lefka Ori massif Crete and to evaluate the potential effects of climate change on the plant diversity of the sub-alpine and alpine zones. It provides a quantitative/qualitative analysis of vegetation-environment relationships for four summits along an altitude gradient on the Lefka Ori massif Crete (1664–2339 m). The GLORIA multi-summit approach was used to provide vegetation and floristic data together with temperature records for every summit. Species richness and species turnover was calculated together with floristic similarity between the summits. 70 species were recorded, 20 of which were endemic, belonging to 23 different families. Cretan endemics dominate at these high altitudes. Species richness and turnover decreased with altitude. The two highest summits showed greater floristic similarity. Only 20% of the total flora recorded reaches the highest summit while 10% is common among summits. Overall there was a 4.96°C decrease in temperature along the 675 m gradient. Given a scenario of temperature increase the ecotone between the sub-alpine and alpine zone would be likely to have the greatest species turnover. Southern exposures are likely to be invaded first by thermophilous species while northern exposures are likely to be more resistant to changes. Species distribution shifts will also depend on habitat availability. Many, already threatened, local endemic species will be affected first.     

Pattern diversity analysis of a clearing in a Quercus cerris wood

Linear transects were used to examine the spatial structure of the vegetation in a clearing in a Quercus cerris wood in Central Italy. A grassland-margin-shrubland-woodland gradient was identified.Multivariate classification and ordination methods and pattern diversity analysis were used to detect both floristic variation and spatial organization. One of the transects shows a clear gradient of variation as a function of space, crossing the floristically and structurally most heterogeneous part of the clearing. For the detailed analysis of this transect a sectorization is achieved. Each sector is characterized according to its floristic types and to the internal spatial organization.The pieces of information derived from the different analyses were concordant. In particular, the validity of the floristic types in the qualification of the different forms of spatial organization is confirmed.     

Interstitial Protozoa and Algae of Louisiana Salt Marshes

SYNOPSIS. The majority of Louisiana salt marshes consists of stagnant pools among a vegetation of Spartina spp. and Distichlis spicata. The sediments constitute a "sulphide biome,'with Eh values reaching to –350 mV. The 200 interstitial ciliate species had definite stratification. Generally, algivores and omnivores occurred in the upper, and bactivores in the lower layers of the sediments. Compaction of particles prevented the flexible and large ciliates from inhabiting the lower layers, while Eh below –200 mV limited the distribution of some species but favored certain bactivores. The pH/Eh range and the abundance of nutrients in the sulfide biome provide habitable conditions for all the major groups of microflora. These, in turn, support nutritionally diverse predatory ciliate populations.     

Effects of grazing,topography, and precipitation on the structure of a semiarid grassland

Structural aspects of the shortgrass steppe plant community, functional groups, and species populations were examined in response to long-term heavy grazing and exclosure from grazing, contiguous wet or dry years, and an environmental gradient of topography. Of the three factors, relatively greater differences in community similarity were observed between catena positions, particularly on the ungrazed treatments. Grazing was intermediate between catena position and short-term weather in shaping plant community structure. Grazed treatments and ridgetops had a less variable species composition through fluctuations in weather.An increase with grazing of the dominant, heavily grazed species was observed. Basal cover and density of total species was also greater on grazed sites. The more uniform grazing lawn structure of the grazed plant communities had an influence on segregation of plant populations along topographical gradients. Segregation was less on grazed catenas, but diversity and the abundance of introduced and opportunistic-colonizer species was also less.Although the shortgrass steppe community was relatively invariant, less abundant species were dynamic and interactions occurred with respect to grazing, weather, and catena position. The effects of grazing may be mitigated by favorable growing seasons but magnified in unfavorable years in populations that are adapted to favorable sites. Grazing can be considered a disturbance at the level of the individual but it may or may not be a disturbance at the level of the population, and it is not a disturbance at the level of the community in this particular grassland.     

Can edaphic factors demonstrate landscape-scale differences in vegetation responses to grazing?

We focused on land units as landscape characteristics and selected seven typical land units on a land catena comprising two areas of southern Mongolia. Hierarchical analysis was used to test the hypothesis that a land unit’s edaphic factors could explain the differences in vegetation responses to grazing. We established the survey sites at increasing distances from a livestock camp or water point within each land unit, then analysed patterns of change in floristic and functional compositions, vegetation volume and soil properties within each land unit to reveal differences in vegetation responses to grazing. We also examined the variations in floristic and functional compositions across land units to identify the edaphic factors that may underlie these differences. Changes in vegetation and soil properties at increasing distances from a camp or water point within each land unit were into three different patterns. Ordination techniques consistently indicated that land unit groups categorised using edaphic factors corresponded to those categorised using response patterns. Our study revealed that edaphic factors were responsible for the observed landscape-scale differences in vegetation responses to grazing in the study areas. In addition, the mechanisms underlying vegetation responses to grazing may have been primarily determined by edaphic factors.     

Is there environmental differentiation in the <Emphasis Type="Italic">Quercus</Emphasis>-dominated forests of west-central Mexico?

Detailed information on 38 species and 26 environmental variables was recorded from a network of 86 permanent plots across a geographical range of 10 km, in order to determine the patterns of floristic composition in Quercus-dominated forests; to elucidate environmental differentiation in such forests; and to determine whether species are partitioning their environment. To examine likely patterns of floristic composition, a data matrix expressed as relative volume + relative density was used to run non-metric multidimensional scaling. Canonical correspondence analysis extracted the environmental variation that best correlates with the observed patterns of floristic composition. Our results indicate that congeneric Quercus individuals represent the largest proportion of the species pool in the study plots. They coexist with other species having similar ecological requirements in at least three distinct floristic groups. Examination of the two largest groups and their species compositions reveals that one floristic gradient runs across the most xeric zone of the study area, and the second major floristic gradient runs across a mesic zone. The most important environmental variable explaining the observed patterns of floristic composition is altitude, although partial canonical correspondence analysis suggests that micro-habitat heterogeneity (catena position and canopy maturity) was most significant.     

Floristic distributional patterns in a diverse ecotonal area in South America

The Paraguayan territory and region, in the centre of South America, is a huge transition area with a succession of various vegetation types. However, this area has received little attention from researchers, with few works published on its flora and its delimitations. We aimed to identify the most important environmental driving forces and delimit floristic patterns in this region, since understanding the forces that drive floristic variations in this ecotonal region could help comprehend the distribution of vegetation not only in this region but throughout South America. We obtained 1234 tree species occurrence records, 205 geographic coordinates and 23 environmental variables and altitude from the ‘NeoTropTree’ database and verified the influence and contribution of environmental factors through variance partition. We tested the floristic consistency of the different vegetation types using dendrogram, indicator species and ordination analyses. We also constructed multiple linear models to check the correlation between species distribution and environmental variables. We found eight consistent vegetation types. The spatial variables coupled with environmental variables were more important than individual environmental or spatial variables. Among the environmental variables, the aridity index was the most important. Despite the importance of spatial factors, due to environmental heterogeneity, we found a gradient related to climate and edaphic variables related to tree flora. The results confirm that the Paraguayan territory and region can be considered to be a diversified and important ecotone area in South America with respect to tree flora.     

Sand Dune Restoration in North Brittany, France: A 10-Year Monitoring Study

Dunes, which account for 13% of the Ille et Vilaine north Brittany coast, France, were degraded by high tourist pressure, and they were restored from 1988 onward. Ten years after commencing work an assessment of the restoration was made on three dunes: Les Chevrets, L'Anse Du Guesclin, and Le Verger. Annual monitoring of the vegetation and dune morphology provided an opportunity to study the restoration process. The dune front, which is similar to a reference pioneer dune, lies in front of the mobile dune. The highest part of the dune is an advanced stage of mobile dune. The restoration of the fixed rear dune was accomplished neither in terms of vegetation composition nor in terms of species richness. The vegetation parameter study allows differentiation between the dune front, the dune summit, and the rear dune. The variation in species richness and floristic composition from one zone to another can be explained by abiotic factors such as salinity and the accretion of sand. The restoration was satisfactory in terms of the geomorphology. Marram grass is a good tool for restoring the topography, but it will take a very long time to restore the conservation value of the dune.     

Spatially heterogeneous refugia and predation risk in intertidal salt marshes

The effect of habitat structure on interactions between predators and prey may vary spatially. In estuarine salt marshes, heterogeneity in refuge quality derives from spatial variation in vegetation structure and in tidal inundation. We investigated whether predation by blue crabs on periwinkle snails was influenced by distance from the seaward edge of the salt marsh and by characteristics of the primary habitat structure, smooth cordgrass ( Spartina alterniflora ). Spartina may provide refuge for snails and interfere with foraging by crabs. Furthermore, predation risk should decline with distance from the seaward edge because landward regions require more travel time for crabs during tidal inundation. We investigated these processes using a comparative survey of snails and habitat traits, an experiment that assessed the crab population and measured predation risk, and a size-structured model that estimated encounter rates. Taken together, these approaches indicated that predation risk for snails was lower where Spartina was present and was lower in a landward direction. Furthermore, Spartina architecture and distance from the seaward edge interacted. The strength of the predation gradient between seaward and landward regions of the marsh was greater where Spartina was tall or dense. These predation gradients emerge because vegetation and distance inland decrease encounter rates between crabs and snails. This study suggests that habitat modification, a process not uncommon in salt marshes, may have consequences for interactions among intertidal fauna.     

Relations of soil properties to topography and vegetation in a subtropical rain forest in southern Taiwan

Soil chemical properties for a subtropical rain forest in the Nanjenshan Reserve, southern Taiwan, were examined to determine soil-landscape and soil-vegetation relationships. Soil sampling sites were separated into four groups based on landscape features and exposure to the prevailing northeasterly monsoon winds. Corresponding vegetation types were delimited along the first DCA axis. The forest showed a drastic change both in structure and floristic composition along the wind-stress gradient. Redundancy analysis (RDA) showed that both topographic variables and vegetation types were needed to explain the variation in soil data. Soil properties that differed significantly among landforms were pH, available N, CEC, exchangeable Al, K, Ca and Mg. Levels of pH, exchangeable Ca and Mg increased in a downslope direction, and exchangeable Al tended to be higher in the upper slope soils. These trends pointed to the importance of slope processes in redistribution of soil minerals. The main differences in soil properties attributed to the influence of the occupying vegetation were apparently aspect dependent. The contents of available N, exchangeable K, and CEC in the 0–40 cm depth of soils under windward low-stature (mostly sclerophyllous) forest were consistently lower compared to those under the leeward forest. For a given catena, however, soil variability associated with vegetation differences seemed to be confounded by the slope processes.     

崇明东滩南部盐沼植被空间分布及影响因素分析

崇明东滩南部滩面高程、土壤盐度在空间上呈明显的梯度变化规律。高程整体西高东低、北高南低, 盐度东北高、西南低, 两者共同限制着盐沼植物在空间上的分布。该文围绕崇明东滩南部主要植被类群及其空间分布, 探讨了土壤盐度、潮滩高程两大环境因子与植物种群分布的对应关系。基于2013年夏、秋季植被空间网格采样和空间插值, 分析了东滩南部植物的空间分布现状, 发现不同植物类群在高程和土壤盐度上存在极显著的差异(p < 0.01)。高程差异: 莎草科类群主要分布于高程区间2.93-4.07 m的低潮滩, 禾本科主要集中分布在高程3.13-4.31 m的中、高潮滩; 盐度差异: 海三棱藨草(Scirpus mariqueter)和互花米草(Spartina alterniflora)优势种群植被覆盖区表层30 cm的平均土壤盐度为(3.2 ± 0.6) g·kg^-1, 显著高于其他类群植物分布区的平均土壤盐度(2.0 ± 0.3) g·kg^-1 (p < 0.01)。崇明东滩湿地生态系统的关键种兼先锋种——海三棱藨草, 分布高程介于2.53-3.97 m, 而互花米草能适应海三棱藨草80%的高程区间, 两者在高程上存在竞争关系。统计数据显示, 研究区域中近90%的海三棱藨草分布在研究区东北部, 土壤盐度范围为1.6-4.5 g·kg^-1, 海三棱藨草、互花米草能较好地适应该空间内的盐度胁迫, 两种植物在此交替出现。但是在高程和土壤盐度的综合作用下, 互花米草的生长状况更好, 因此该区的海三棱藨草很可能会被互花米草逐步取代。对各类群植被分布和优势面积的研究发现, 海三棱藨草总分布面积为294 hm², 优势群落面积120 hm², 海三棱藨草仅占莎草科植物总优势面积的15.7%, 占研究区总面积的6.9%, 在6种主要植物(芦苇(Phragmites australis)、白茅(Imperata cylindrica)、互花米草、糙叶薹草(Carex scabrifolia)、藨草(Scirpus triqueter)、海三棱藨草)中比重最小, 这给保护区内海三棱藨草种群的恢复和保护带来极大的挑战。     

The role of landscape structure in determining palynological and floristic richness

The associations between floristic and palynological richness and landscape structure were studied based on modern pollen?Cvegetation data from a patchy cultural landscape in southern Estonia (northern temperate vegetation zone). Nine study sites (small lakes and their surrounding vegetation) represent land cover gradient from closed forest to semi-open vegetation. Floristic richness (number of species) and floristic richness of pollen types (number of pollen-equivalent taxa) were used to describe the vegetation within the radius of 250?m from the pollen sampling sites. Palynological richness was calculated to describe the modern pollen samples diversity. Landscape structure was estimated on the basis of landscape openness and three landscape diversity measures: richness of community patches, Simpson evenness of community patches and Simpson diversity of community patches. To study the effect of the spatial scale of landscapes on the vegetation?Clandscape and pollen?Clandscape associations, landscape structure was estimated within eight radii (250?C2,000?m) around each lake. The results showed that landscape openness was the most important determinant of both floristic richness and palynological richness in southern Estonia and that landscape diversity estimated by Simpson diversity index was also significantly associated with the richness estimates. Floristic and palynological richness were significantly positively correlated with landscape structure within the radii greater than 1,000?m from the pollen sampling sites, which is similar to the estimated Relevant Source Area of Pollen in southern Estonia. We conclude that within one floristic or climatic region, palynological richness gives reliable estimates about the variation in floristic richness and landscape structure; however, caution must be taken when comparing pollen-inferred vegetation diversities from different regions or when interpreting fossil pollen records from times with highly different vegetation associations.     

Does scale‐dependent feedback explain spatial complexity in salt‐marsh ecosystems?

Complexity theory highlights scale-dependent feedback mechanisms as an explanation for regular spatial patterning in ecosystems. To what extent scale-dependent feedback clarifies spatial structure in more complex, non-regular systems remains unexplored so far. We report on a scale-dependent feedback process generating patchy landscapes at the interface of intertidal flats and salt marshes. Here, vegetation was characterized by Spartina anglica tussocks, surrounded by erosion gullies. To demonstrate the presence of a scale-dependent feedback, we determined if vegetation induced habitat modification resulted in local facilitation and large scale-inhibition of plant growth. Field surveys revealed that larger tussocks have deeper gullies, suggesting that gully erosion is caused by increased water flow around tussocks. This was confirmed by flume experiments, showing that feedback effects vary with current velocity and water depth. Transplantation of small Spartina units inside and just outside present tussocks revealed that the growth of Spartina transplants compared to transplant growth on bare sediment was higher within the raised Spartina tussocks, but lower in the gully just outside Spartina tussocks, providing clear evidence of scale-dependent feedback. Our results emphasize that scale-dependent feedback is a more general explanation for spatial complexity in ecosystems than previously considered.     

Mountain summer farms in Røldal,western Norway –; vegetation classification and patterns in species turnover and richness

This paper discusses vegetation types and diversity patterns in relation to environment and land-use at summer farms, a characteristic cultural landscape in the Norwegian mountains. Floristic data (189 taxa) were collected in 130 4-m² sample plots within 12 summer farms in Røldal, western Norway. The study was designed to sample as fully as possible the range of floristic, environmental, and land-use conditions. Vegetation types delimited by two-way indicator species analysis were consistent with results from earlier phytosociological studies. Detrended correspondence analysis and canonical correspondence analysis show that rather than being distinct vegetation types, the major floristic variation is structured along a spatial gradient from summer farm to the surrounding heathland vegetation. Species richness (alpha diversity) was modelled against environmental variables by generalized linear modelling and compositional turnover (beta diversity) by canonical correspondence analysis. Most environmental factors made significant contributions, but the spatial distance-to-farm gradient was the best predictor of both species richness and turnover. While summer farms reduce mean species richness at the plot scale, the compositional heterogeneity of the upland landscapes is increased, thereby creating ‘ecological room’ for additional vegetation types and species. Within an overall similarity across scales, soil variables (pH, base saturation, LOI, phosphate and nitrogen) differed considerably in their explanatory power for richness and turnover. A difference between ‘productivity limiting’ factors and ‘environmental sieves’ is proposed as an explanation. Species turnover with altitude is relatively low in grasslands as compared to heaths.     

Pattern of species richness and floristic spectrum along the elevation gradient: A case study from western Himalaya,India

The floristic life-form spectrum of any area unveils the prevailing phytoclimatic conditions, helps in understanding the species-environment relationship and can be applied to compare the vegetation pattern of one eco-zone to another. We scrutinized the pattern of species richness (SR) and floristic spectrum along the elevation gradient in a biodiversity-rich eco-zone of western Himalaya (western Ramganga valley, Uttarakhand, India) between 1200 m (river bank) to 3100 m a.s.l. (summit). The elevation range was classified into six elevation bands (i.e. <1500 m, 1500–1800 m, 1801–2100 m, 2101–2400 m, 2401–2700 m, >2700 m), to prepare the presence (1)/ absence (0) species data matrix using local distribution (elevation range) of each species to estimate the SR of various growth-forms and life-forms for the particular elevational band. The findings suggest that the correlation of SR with elevation is not linear as the species richness peaks at the middle elevation (humped-back shape relationship). The forest cover is large and continues up to the summit; thus, the correlation of tree and shrub SR with elevation is not clear; though, a partly positive correlation was observed between elevation and herb SR while negative correlation between climber SR and elevation. The percentage of phanerophytes and therophytes in total life-forms decreased significantly with increase in elevation while inverse trend was shown by hemicryptophytes and cryptophytes. The pattern of phytoclimate in the area varied from phanero-therophytic at the lower elevation to phanero-hemicryptophytic at the middle and hemicrypto-phanerophytic at the upper elevation. The present contribution is an attempt to fill the knowledge gap in pattern of growth-form, life-form and phytoclimate within the forest-covered montane zone of western Himalaya. It will be helpful in understanding the vegetation dynamics in mountain ecosystems and serve as a ready reference to planners in any future conservation strategy for the area.