JOURNAL OF BIOGEOGRAPHY, Issue 6 2004
Philippe Mayaux
Abstract Aim, In the framework of the Global Land Cover 2000 (GLC 2000), a land-cover map of Africa has been produced at a spatial resolution of 1 km using data from four sensors on-board four different Earth observing satellites. Location, The map documents the location and distribution of major vegetation types and non-vegetated land surface formations for the entire African continent plus Madagascar and the other surrounding islands. Methods, The bulk of these data were acquired on a daily basis throughout the year 2000 by the VEGETATION sensor on-board the SPOT-4 satellite. The map of vegetation cover has been produced based upon the spectral response and the temporal profile of the vegetation cover. Digital image processing and geographical information systems techniques were employed, together with local knowledge, high resolution imagery and expert consultation, to compile a cartographic map product. Radar data and thermal sensors were also used for specific land-cover classes. Results, A total of 27 land cover categories are documented, which has more thematic classes than previously published land cover maps of Africa contain. Systematic comparison with existing land cover data and 30-m resolution imagery from Landsat are presented, and the map is also compared with other pan-continental land cover maps. The map and digital data base are freely available for non-commercial uses from http://www.gvm.jrc.it/tem/africa/products.htm Main conclusions, The map improves our state of knowledge of the land-cover of Africa and presents the most spatially detailed view yet published at this scale. This first version of the map should provide an important input for regional stratification and planning purposes for natural resources, biodiversity and climate studies. Résumé Objet, Dans le cadre du projet Global Land Cover 2000 (GLC 2000), une carte d'Afrique d'occupation du sol a été produite à la résolution spatiale de 1 km à partir de données satellitales de 4 capteurs différents. Localisation, La carte représente la distribution des principaux types de végétation et des surfaces non-végétales du continent africain plus Madagascar et les autres îles voisines du continent. Méthodes, La plupart des données fut acquise durant l'année 2000 par le capteur VEGETATION, embarquéà bord du satellite SPOT-4. La réponse spectrale et le profil temporel des formations végétales ont permis la production de la carte d'occupation du sol. Des techniques de traitement d'image et de systèmes d'information géographique ont été combinées à la consultation d'experts locaux et à l'utilisation de cartes nationales et de données à haute résolution spatiale. Des images radar et thermiques ont servi à cartographier des classes spécifiques. Résultats, Un total de 27 classes est cartographié, ce qui est plus que les précédentes cartes basées sur l'imagerie satellitale. Une comparaison systématique avec les cartes publiées et des images Landsat à 30 m est présentée. Les données sont libres d'accès pour un usage non-commercial à l'adresse http://www.gvm.jrc.it/tem/africa/products.htm Conclusion, Cette carte accroît notre connaissance de l'occupation du sol de l'Afrique et présente la vue la plus détaillée jamais publiée à cette échelle. La première version de la carte devrait fournir une base importante pour une stratification régionale et pour la planification d'études sur les ressources naturelles, la biodiversité et le climat. [source]

WIDTH OF STREAMS AND RIVERS IN RESPONSE TO VEGETATION, BANK MATERIAL, AND OTHER FACTORS,

JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 5 2004
Russell J. Anderson
ABSTRACT: An extensive group of datasets was analyzed to examine factors affecting widths of streams and rivers. Results indicate that vegetative controls on channel size are scale dependent. In channels with watersheds greater than 10 to 100 km2, widths are narrower in channels with thick woody bank vegetation than in grass lined or nonforested banks. The converse is true in smaller streams apparently due to interactions between woody debris, shading, understory vegetation, rooting characteristics, and channel size. A tree based statistical method (regression tree) is introduced and tested as a tool for identifying thresholds of response and interpreting interactions between variables. The implications of scale dependent controls on channel width are discussed in the context of stable channel design methods and development of regional hydraulic geometry curves. [source]

Effects of vegetation on channel morphodynamics: results and insights from laboratory experiments

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 9 2010
Michal Tal
Abstract A series of laboratory experiments demonstrates that riparian vegetation can cause a braided channel to self-organize to, and maintain, a dynamic, single-thread channel. The initial condition for the experiments was steady-state braiding in non-cohesive sand under uniform discharge. From here, an experiment consisted of repeated cycles alternating a short duration high flow with a long duration low flow, and uniform dispersal of alfalfa seeds over the bed at the end of each high flow. Plants established on freshly deposited bars and areas of braidplain that were unoccupied during low flow. The presence of the plants had the effect of progressively focusing the high flow so that a single dominant channel developed. The single-thread channel self-adjusted to carry the high flow. Vegetation also slowed the rate of bank erosion. Matching of deposition along the point bar with erosion along the outer bend enabled the channel to develop sinuosity and migrate laterally while suppressing channel splitting and the creation of new channel width. The experimental channels spontaneously reproduced many of the mechanisms by which natural meandering channels migrate and maintain a single dominant channel, in particular bend growth and channel cutoff. In contrast with the braided system, where channel switching is a nearly continuous process, vegetation maintained a coherent channel until wholesale diversion of flow via cutoff and/or avulsion occurred, by which point the previous channel tended to be highly unfavorable for flow. Thus vegetation discouraged the coexistence of multiple channels. Varying discharge was key to allowing expression of feedbacks between the plants and the flow and promoting the transition from braiding to a single-thread channel that was then dynamically maintained. Copyright © 2010 John Wiley & Sons, Ltd. [source]

Vegetation and topographic controls on sediment deposition and storage on gully beds in a degraded mountain area

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 6 2009
Armando Molina
Abstract Active gully systems developed on highly weathered or loose parent material are an important source of runoff and sediment production in degraded areas. However, a decrease of land pressure may lead to a return of a partial vegetation cover, whereby gully beds are preferred recolonization spots. Although the current knowledge on the role of vegetation on reducing sediment production on slopes is well developed, few studies exist on the significance of restoring sediment transport pathways on the total sediment budget of degraded mountainous catchments. This study in the Ecuadorian Andes evaluates the potential of vegetation to stabilize active gully systems by trapping and retaining eroded sediment in the gully bed, and analyses the significance of vegetation restoration in the gully bed in reducing sediment export from degraded catchments. Field measurements on 138 gully segments located in 13 ephemeral steep gullies with different ground vegetation cover indicate that gully bed vegetation is the most important factor in promoting short-term (1,15 years) sediment deposition and gully stabilization. In well-vegetated gully systems ( , 30% of ground vegetation cover), 0.035 m3 m,1 of sediment is deposited yearly in the gully bed. Almost 50 per cent of the observed variance in sediment deposition volumes can be explained by the mean ground vegetation cover of the gully bed. The presence of vegetation in gully beds gives rise to the formation of vegetated buffer zones, which enhance short-term sediment trapping even in active gully systems in mountainous environments. Vegetation buffer zones are shown to modify the connectivity of sediment fluxes, as they reduce the transport efficiency of gully systems. First calculations on data on sediment deposition patterns in our study area show that gully bed deposition in response to gully bed revegetation can represent more than 25 per cent of the volume of sediment generated within the catchment. Our findings indicate that relatively small changes in landscape connectivity have the potential to create strong (positive) feedback loops between erosion and vegetation dynamics. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Response of collembolan communities to land-use change and grassland succession

ECOGRAPHY, Issue 2 2007
Matthieu Chauvat
This study focuses on the long-term changes of collembolan communities occurring after the conversion of arable land to managed grassland. We analysed collembolan communities at grassland sites of different age that had been gradually converted over a period of 50 yr. Abundance and biomass responded rapidly and very positively to the conversion of arable land to grassland, while species richness was not affected. Collembolan assemblages changed only little during grassland maturation. The impact of land-use change on community structure was more obvious at the functional level because the colonization processes observed in our study mostly relied on hemiedaphic species. Vegetation and soil parameters were good predictors of collembolan community structure during development of managed grassland. The present study demonstrated that past landscape patterns and processes like land-use conversion and subsequent succession had a considerable impact on the present day pattern of species richness and community composition of Collembola within a landscape. Our results strongly differ from those obtained for other invertebrate groups, highlighting on the one hand the very diverse reactions of invertebrates to a common factor, and on the other hand the need to survey more than one taxa in order to draw conclusions on effects of land-use change on faunistic communities. [source]

Vegetation impacts on near bank flow

ECOHYDROLOGY, Issue 4 2009
Leslie Hopkinson
Abstract Vegetation is an important component of stream restoration designs used to control streambank retreat, but vegetation effects on near bank flows need to be quantified. The goal of this research was to evaluate how three-dimensional velocity structure and turbulence characteristics vary with three vegetation treatments: tree, shrub and grass. A second order prototype stream (Tom's Creek in Blacksburg, Virginia, USA) with individual reaches dominated by each vegetation treatment was modelled in a research flume using a fixed-bed Froude-scale modelling technique. One model streambank of the prototype stream was constructed for each vegetation type and compared to a bare control (only grain roughness). Velocity profiles perpendicular to the flume model boundary were measured using a three-dimensional acoustic Doppler velocimeter. Three-dimensional velocity records, turbulent kinetic energy characteristics, and Reynolds stresses were analysed. The addition of vegetation on a sloping streambank increased the free stream streamwise velocity as compared to a bare streambank. Velocity in the downstream direction decreased in the area close to the streambank boundary for all vegetation treatments. Tree turbulence intensity and Reynolds stress distributions were similar to the bare condition due to the sparse tree placement characteristic of mature forests. The turbulence caused by the upright shrub treatment increased turbulent kinetic energy and Reynolds stresses near the streambank, particularly at the toe. The flexible grass vegetation folded and protected the streambank, reducing shear stress near the boundary. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Vegetation of the river Yamuna floodplain in the Delhi stretch, with reference to hydrological characteristics

ECOHYDROLOGY, Issue 2 2009
Tanveera Tabasum
Abstract Vegetation in the Delhi stretch of the floodplain of the river Yamuna was examined in relation to hydrological characteristics. The floodplain was delineated into four zones based on hydrological interventions. Seventy-four plant species including forty-two aquatic/semi-aquatic were identified. The decrease in water discharge from Jhangola to downstream Okhla, led to reduction in species richness. Co-structures between hydrological characteristics and vegetational composition indicated that vegetation in the four identified zones was governed essentially by hydrological factors. Zones I and III exhibited near-perfect correspondence signifying that variation in vegetational composition in these zones could be explained, to a great extent, on the basis of variations in the hydrological conditions. Zone II and IV, with relatively weaker correspondence, indicated that there were gradients other than hydrological conditions, which caused variations in vegetational characteristics. The present study highlighted the importance of allocation of water for periodic inundation to maintain floodplain characteristics including aquatic/semi-aquatic vegetation cover as critical to the management of the river ecosystem. The current policy of water use focused entirely on human uses ignoring ecological requirements, and had clear adverse implications on the health of the river ecosystem. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Increase in Riparian Vegetation along Peterson Creek, North Queensland 1938,2004

ECOLOGICAL MANAGEMENT & RESTORATION, Issue 1 2006
Amanda N. D. Freeman
First page of article [source]

Microsite-dependent changes in methanogenic populations in a boreal oligotrophic fen

ENVIRONMENTAL MICROBIOLOGY, Issue 11 2003
Pierre E. Galand
Summary Wetlands, including peatlands, are the main source of natural methane emission. Well-defined fen microsites have different methane emissions rates, but it is not known whether the methane-producing Archaea communities vary at these sites. Possible horizontal variations of communities, in a natural oligotrophic fen, were analysed by characterizing the methanogens from two well-defined microsites: Eriophorum lawn and Hummock. Community structures were studied at two different layers of the fen, showing, respectively, high and low methane production. The structure of methanogen populations was determined using molecular techniques targeting the 16SrRNA gene and combined denaturing gradient gel electrophoresis (DGGE) and restriction fragment length polymorphism (RFLP) analysis. Results subjected to non-metric multidimensional scaling (MDS), diversity indices calculation and phylogenetic analysis revealed that upper layer communities changed with site while deeper layer communities remained the same. Phylogenetic analyses revealed six different clusters of sequences grouping with only two known orders of methanogens. Upper layers of Hummock were dominated by sequences clustering with members of Methanomicrobiales and sequences dominating the upper part of the Eriophorum lawn were related to members of the order Methanosarcinales. Novel methanogenic sequences were found at both sites at both depths. Vegetation characterizing the microsites probably influences the microbial communities in the layers of the fen where methane is produced. [source]

Vegetation,environment relationships along El-Salam Canal, Egypt

ENVIRONMETRICS, Issue 3 2001
Mamdouh S. Serag
Abstract The bank and open water vegetation along El-Salam Canal in north-eastern Egypt were studied in relation to the prevailing environmental factors. The hypothesis that terresterial and aquatic species would show different downstream patterns of species richness was tested by sampling species composition and environmental variables along 80,km of the canal. Species richness was highest in the first 30,km of the canal. The downstream decrease in species richness exhibits interpretable downstream patterns. Total species richness increased with increasing organic matter in the soil and decreased with both increasing soil and water salinity along the gradient. The indicator species of TWINSPAN analysis are: Azolla filiculoides, Echinochloa stagnina, Eichhornia crassipes and Saccharum spontaneum (cluster I); Ceratophyllum demersum, Ludwigia stolonifera and Typha domingensis (cluster II); Potamogeton pectinatus and Phragmites australis (cluster III); Tamarix nilotica and Suaeda vera (cluster IV). The environmental factors influencing the vegetation clusters were analysed using canonical correspondence analysis ordination (CCA). The water salinity, total nitrogen and total phosphorus appeared to be the most important factors controlling the abundance of aquatic plant distribution along the canal. The shoreline vegetation is mainly controlled by salinity, K+ and organic carbon of the soil. Water analysis indicated that the salinity of the water increases southwards and the minimum salinity of the water (0.78,mS/cm) was recorded at the intake of the canal. The maximum value (7.5,mS/cm) of water salinity was recorded near the Suez Canal. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Palaeoecology and depositional environments of the Tendaguru Beds (Late Jurassic to Early Cretaceous, Tanzania)

FOSSIL RECORD-MITTEILUNGEN AUS DEM MUSEUM FUER NATURKUNDE, Issue 1 2002
Martin Aberhan
Abstract The Late Jurassic to Early Cretaceous Tendaguru Beds (Tanzania, East Africa) have been well known for nearly a century for their diverse dinosaur assemblages. Here, we present sedimentological and palaeontological data collected by the German-Tanzanian Tendaguru Expedition 2000 in an attempt to reconstruct the palaeo-ecosystems of the Tendaguru Beds at their type locality. Our reconstructions are based on sedimentological data and on a palaeoecological analysis of macroinvertebrates, microvertebrates, plant fossils and microfossils (ostracods, foraminifera, charophytes, palynomorphs). In addition, we included data from previous expeditions, particularly those on the dinosaur assemblages. The environmental model of the Tendaguru Beds presented herein comprises three broad palaeoenvironmental units in a marginal marine setting: (1) Lagoon-like, shallow marine environments above fair weather wave base and with evidence of tides and storms. These formed behind barriers such as ooid bar and siliciclastic sand bar complexes and were generally subject to minor salinity fluctuations. (2) Extended tidal flats and low-relief coastal plains. These include low-energy, brackish coastal lakes and ponds as well as pools and small fluvial channels of coastal plains in which the large dinosaurs were buried. Since these environments apparently were, at best, poorly vegetated, the main feeding grounds of giant sauropods must have been elsewhere. Presumably, tidal flats and coastal plains were visited by dinosaurs primarily during periods of drought. (3) Vegetated hinterland. Vegetation of this environment can only be inferred indirectly from plant material transported into the other depositional environments. Vegetation was dominated by a diverse conifer flora, which apparently formed part of the food source of large herbivorous sauropods. Evidence from various sources suggests a subtropical to tropical palaeoclimate, characterised by seasonal rainfall alternating with a pronounced dry season during the Late Jurassic. In Early Cretaceous times, sedimentological and palaeontological proxies suggest a climatic shift towards more humid conditions. Die Tendaguru-Schichten von Tansania in Ostafrika (Oberjura bis Unterkreide) sind als Lagerstätte oberjurassischer Dinosaurier seit nahezu einem Jahrhundert weltweit bekannt. Anhand von sedimentologischen und paläontologischen Daten, die während der Deutsch-Tansanischen Tendaguru Expedition 2000 im Typus-Gebiet der Tendaguru-Schichten gewonnen wurden, werden Paläo-Ökosysteme rekonstruiert. Grundlage der Rekonstruktionen sind die Auswertung sedimentologischer Daten sowie die paläo-ökologische Analyse von Makroinvertebraten, Mikrovertebraten, pflanzlichen Fossilien und Mikrofossilien (Ostrakoden, Foraminiferen, Charophyten, Palynomorphen). Darüber hinaus werden Informationen über Dinosaurier berücksichtigt, die bei früheren Expeditionen gewonnen wurden. Das hier vorgestellte Ablagerungsmodell der Tendaguru-Schichten umfaßt drei Teilbereiche eines randlich marinen Sedimentationsraumes, die wie folgt gekennzeichnet werden können: (1) Lagunen-artige, marine Flachwasserbereiche, die oberhalb der Schönwetter-Wellenbasis lagen und unter deutlichem Einfluß von Gezeiten und Stürmen standen. Sie waren vom offenen Meer durch Barrieren, wie Ooidbarren und siliziklastischen Sandbarrenkomplexen, getrennt und wiesen einen leicht schwankenden Salzgehalt auf. (2) Ausgedehnte Wattgebiete und flache Küstenebenen. Dort befanden sich niedrig-energetische, brackische Strandseen und Teiche sowie Tümpel und kleinere Flußrinnen, in denen die großen Dinosaurier eingebettet wurden. Da diese Lebensräume bestenfalls dürftig bewachsen waren, müssen die Nahrungsquellen und der eigentliche Lebensraum der riesigen Sauropoden anderswo gelegen haben. Vermutlich wurden die Wattgebiete und Flachküsten von Dinosauriern vorrangig in den Trockenzeiten aufgesucht. (3 ) Bewachsenes Hinterland. Die Vegetation dieses Lebensraumes kann nur indirekt aus Pflanzenresten erschlossen werden, die in die anderen Ablagerungsraume transportiert wurden. Die Vegetation wurde von einer diversen Koniferenflora dominiert, die zumindest teilweise die Nahrungsgrundlage der großen, herbivoren Sauropoden bildete. Sedimentologische und paläontologische Indikatoren sprechen für ein subtropisches bis tropisches Klima wahrend der späten Jurazeit mit einem jahreszeitlichen Wechsel von Regenfällen und ausgeprägten Trockenzeiten. In der frühen Kreidezeit deutet sich ein Wechsel zu starker humiden Bedingungen an. [source]

A Geostatistical Analysis of Soil, Vegetation, and Image Data Characterizing Land Surface Variation

GEOGRAPHICAL ANALYSIS, Issue 2 2007
Sarah E. Rodgers
The elucidation of spatial variation in the landscape can indicate potential wildlife habitats or breeding sites for vectors, such as ticks or mosquitoes, which cause a range of diseases. Information from remotely sensed data could aid the delineation of vegetation distribution on the ground in areas where local knowledge is limited. The data from digital images are often difficult to interpret because of pixel-to-pixel variation, that is, noise, and complex variation at more than one spatial scale. Landsat Thematic Mapper Plus (ETM+) and Satellite Pour l'Observation de La Terre (SPOT) image data were analyzed for an area close to Douna in Mali, West Africa. The variograms of the normalized difference vegetation index (NDVI) from both types of image data were nested. The parameters of the nested variogram function from the Landsat ETM+ data were used to design the sampling for a ground survey of soil and vegetation data. Variograms of the soil and vegetation data showed that their variation was anisotropic and their scales of variation were similar to those of NDVI from the SPOT data. The short- and long-range components of variation in the SPOT data were filtered out separately by factorial kriging. The map of the short-range component appears to represent the patterns of vegetation and associated shallow slopes and drainage channels of the tiger bush system. The map of the long-range component also appeared to relate to broader patterns in the tiger bush and to gentle undulations in the topography. The results suggest that the types of image data analyzed in this study could be used to identify areas with more moisture in semiarid regions that could support wildlife and also be potential vector breeding sites. [source]

Hyperspectral Remote Sensing of Vegetation

GEOGRAPHY COMPASS (ELECTRONIC), Issue 6 2008
Jungho Im
Hyperspectral analysis of vegetation involves obtaining spectral reflectance measurements in hundreds of bands in the electromagnetic spectrum. These measurements may be obtained using hand-held spectroradiometers or hyperspectral remote sensing instruments placed onboard aircraft or satellites. Hyperspectral remote sensing provides valuable information about vegetation type, leaf area index, biomass, chlorophyll, and leaf nutrient concentration which are used to understand ecosystem functions, vegetation growth, and nutrient cycling. This article first reviews hyperspectral remote sensing and then describes current modeling and classification techniques used to estimate and predict vegetation type and biophysical characteristics. [source]

Endemic species and ecosystem sensitivity to climate change in Namibia

GLOBAL CHANGE BIOLOGY, Issue 5 2006
WILFRIED THUILLER
Abstract We present a first assessment of the potential impacts of anthropogenic climate change on the endemic flora of Namibia, and on its vegetation structure and function, for a projected climate in ,2050 and ,2080. We used both niche-based models (NBM) to evaluate the sensitivity of 159 endemic species to climate change (of an original 1020 plant species modeled) and a dynamic global vegetation model (DGVM) to assess the impacts of climate change on vegetation structure and ecosystem functioning. Endemic species modeled by NBM are moderately sensitive to projected climate change. Fewer than 5% are predicted to experience complete range loss by 2080, although more than 47% of the species are expected to be vulnerable (range reduction >30%) by 2080 if they are assumed unable to migrate. Disaggregation of results by life-form showed distinct patterns. Endemic species of perennial herb, geophyte and tree life-formsare predicted to be negatively impacted in Namibia, whereas annual herb and succulent endemic species remain relatively stable by 2050 and 2080. Endemic annual herb species are even predicted to extend their range north-eastward into the tree and shrub savanna with migration, and tolerance of novel substrates. The current protected area network is predicted to meet its mandate by protecting most of the current endemicity in Namibia into the future. Vegetation simulated by DGVM is projected to experience a reduction in cover, net primary productivity and leaf area index throughout much of the country by 2050, with important implications for the faunal component of Namibia's ecosystems, and the agricultural sector. The plant functional type (PFT) composition of the major biomes may be substantially affected by climate change and rising atmospheric CO2, currently widespread deciduous broad leaved trees and C4 PFTs decline, with the C4 PFT particularly negatively affected by rising atmospheric CO2 impacts by ,2080 and deciduous broad leaved trees more likely directly impacted by drying and warming. The C3 PFT may increase in prominence in the northwestern quadrant of the country by ,2080 as CO2 concentrations increase. These results suggest that substantial changes in species diversity, vegetation structure and ecosystem functioning can be expected in Namibia with anticipated climate change, although endemic plant richness may persist in the topographically diverse central escarpment region. [source]

Dynamical effects of the statistical structure of annual rainfall on dryland vegetation

GLOBAL CHANGE BIOLOGY, Issue 5 2006
CHRISTOPHER A. WILLIAMS
Abstract In this study, we extend a model of daily dryland dynamics by parameterizing a modified version of a minimalistic annual model to examine how the statistical structure of annual rainfall and grazing intensity interact to influence dryland vegetation. With a Monte Carlo approach, an ensemble outcome provides a statistical description of likely dryland vegetation dynamics responding to variations in rainfall structure and grazing intensity. Results suggest that increased rainfall variability decreases the average and increases the variability of grass cover leading to more frequent degradation of the grass resource. Vegetation of drier regions is found to be more sensitive to interannual variability in rainfall. Concentrating this variability into an organized periodic mode further decreases the mean and increases the variability of grass cover. Hence, a shift toward lower, more variable, or more inter-annually correlated annual rainfall will likely lead to a general decrease in the grass resource and increased dryland vulnerability to degradation. Higher grazing intensity or lower annual rainfall both lead to more frequent and longer duration degradation of the grass condition. We note an interesting interaction in the response of grass biomass to grazing intensity and rainfall variability, where increased rainfall variability leads to longer duration degradation for low grazing, but shorter periods of degradation for high grazing. Once grass reaches a degraded condition, we find that woody vegetation strongly suppresses recovery even if successive rainfall is high. Overall, these findings suggest that the projected increase in interannual rainfall variability will likely decrease grass cover and potentially lead to more frequent, longer lasting degradation of dryland vegetation, particularly if enhanced rainfall variability is concentrated in long period (e.g. decadal) modes. [source]

Detection of vegetation change using reconnaissance imagery

GLOBAL CHANGE BIOLOGY, Issue 3 2001
Herman H. Shugart
Summary Vegetation occurs at its highest elevations on equatorial mountains. Inspection of archival and recent high-resolution reconnaissance imagery of tropical mountains shows, in all cases, features indicating an increase in the elevation of mountain vegetation zones and an increase in vigour in the high-elevation vegetation. These changes are consistent with an increased plant performance from increased levels of carbon dioxide in the atmosphere as well as with a warmer or more favourable climate. [source]

Plant species richness in continental southern Siberia: effects of pH and climate in the context of the species pool hypothesis

GLOBAL ECOLOGY, Issue 5 2007
Milan Chytrý
ABSTRACT Aim, Many high-latitude floras contain more calcicole than calcifuge vascular plant species. The species pool hypothesis explains this pattern through an historical abundance of high-pH soils in the Pleistocene and an associated opportunity for the evolutionary accumulation of calcicoles. To obtain insights into the history of calcicole/calcifuge patterns, we studied species richness,pH,climate relationships across a climatic gradient, which included cool and dry landscapes resembling the Pleistocene environments of northern Eurasia. Location, Western Sayan Mountains, southern Siberia. Methods, Vegetation and environmental variables were sampled at steppe, forest and tundra sites varying in climate and soil pH, which ranged from 3.7 to 8.6. Species richness was related to pH and other variables using linear models and regression trees. Results, Species richness is higher in areas with warmer winters and at medium altitudes that are warmer than the mountains and wetter than the lowlands. In treeless vegetation, the species richness,pH relationship is unimodal. In tundra vegetation, which occurs on low-pH soils, richness increases with pH, but it decreases in steppes, which have high-pH soils. In forests, where soils are more acidic than in the open landscape, the species richness,pH relationship is monotonic positive. Most species occur on soils with a pH of 6,7. Main conclusions, Soil pH in continental southern Siberia is strongly negatively correlated with precipitation, and species richness is determined by the opposite effects of these two variables. Species richness increases with pH until the soil is very dry. In dry soils, pH is high but species richness decreases due to drought stress. Thus, the species richness,pH relationship is unimodal in treeless vegetation. Trees do not grow on the driest soils, which results in a positive species richness,pH relationship in forests. If modern species richness resulted mainly from the species pool effects, it would suggest that historically common habitats had moderate precipitation and slightly acidic to neutral soils. [source]

Vegetation of the Stipa loess steppe in Ningxia (northern China) in relation to grazing intensity

GRASSLAND SCIENCE, Issue 3 2007
Yingzhong Xie
Abstract Large areas of northern and western China are covered with steppe vegetation which is grazed with different intensities. Areas which are not or only slightly grazed are rare and mostly exist in nature reserves. We investigated floristic composition and species diversity of the steppe vegetation of the autonomous region Ningxia Hui with emphasis on the Yunwushan dry steppe nature reserve in relation to grazing intensity; all 77 plots were analyzed using ordination techniques, and the relationship between the variation in species composition and environmental conditions was analyzed. In Ningxia, two types of loess grass steppes prevail: in areas with lower altitudes from approximately 1650,1950 m a.s.l., the Stipa bungeana steppe occurs whereas the Stipa grandis steppe is typical for higher altitudes between 1900 and 2100 m a.s.l. For both vegetation types, three subtypes can be distinguished according to different levels of grazing intensity. With increasing grazing intensity, the number of plant species per plot strongly declines and the typical steppe vegetation types are dominated by Artemisia species (A. frigida in the Stipa grandis community and A. sacrorum in the Stipa bungeana community). In contrast to studies carried out in neighboring areas, in our study area the Artemisia steppes do not represent the final state of degradation. Instead, Convolvulus ammanii dominates in heavily grazed areas of both Stipa steppe types. Detrended correspondence analysis confirms the classification and shows that the heavily grazed subtypes of the Stipa grandis and the Stipa bungeana steppe with Convolvulus ammanii are more similar to each other than the other vegetation types. The first axis of the detrended correspondence analysis is strongly related to the grazing intensity (r = 0.93). Our results show that grazing intensity is an important factor for the differentiation of the steppe grasslands and a severe threat to species diversity. [source]

Europe's 2003 heat wave: a satellite view of impacts and land,atmosphere feedbacks

INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 6 2006
Benjamin F. Zaitchik
Abstract A combination of satellite imagery, meteorological station data, and the NCEP/NCAR reanalysis has been used to explore the spatial and temporal evolution of the 2003 heat wave in France, with focus on understanding the impacts and feedbacks at the land surface. Vegetation was severely affected across the study area, especially in a swath across central France that corresponds to the Western European Broadleaf (WEB) Forests ecological zone. The remotely sensed surface temperature anomaly was also greatest in this zone, peaking at +15.4 °C in August. On a finer spatial scale, both the vegetation and surface temperature anomalies were greater for crops and pastures than for forested lands. The heat wave was also associated with an anomalous surface forcing of air temperature. Relative to other years in record, satellite-derived estimates of surface-sensible heat flux indicate an enhancement of 48,61% (24.0,30.5 W m,2) in WEB during the August heat wave maximum. Longwave radiative heating of the planetary boundary layer (PBL) was enhanced by 10.5 W m,2 in WEB for the same period. The magnitude and spatial structure of this local heating is consistent with models of the late twenty-first century climate in France, which predict a transitional climate zone that will become increasingly affected by summertime drought. Models of future climate also suggest that a soil-moisture feedback on the surface energy balance might exacerbate summertime drought, and these proposed feedback mechanisms were tested using satellite-derived heat budgets. Copyright © 2006 Royal Meteorological Society. [source]

Effects of Submerged Aquatic Vegetation on Macrozoobenthos in a Coastal Lagoon of the Southwestern Atlantic

INTERNATIONAL REVIEW OF HYDROBIOLOGY, Issue 1 2007
Rafael Arocena
Abstract The freshwater-dominated part of Rocha coastal lagoon recently experienced sudden colonization by submerged aquatic vegetation (SAV). Macrophytes may be beneficial or detrimental for the zoobenthos, and both assemblages may in turn affect the food availability for birds and fishes. With the aim of evaluating the effect of SAV on water conditions and on the composition, abundance and diversity of macrozoobenthos, vegetated areas (V, up to 500 g DW m,2) were compared with vegetation-free areas (N). The benthic abundance was higher in V (up to 5000 ind m,2) than in N (up to 2200 ind m,2). Species richness and abundance of amphipods, gastropods and chironomids were also higher at V compared with N. Conversely, the abundance of Tanais stanfordi (Crustacea), Erodona mactroides (Bivalvia) and Laeonereis culveri (Polychaeta), and the Shannon diversity were higher at N. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

The resilience of calcareous and mesotrophic grasslands following disturbance

JOURNAL OF APPLIED ECOLOGY, Issue 3 2005
RACHEL A. HIRST
Summary 1Understanding habitat disturbance and recovery is vital for successful conservation management and restoration, particularly of subseral communities with high nature conservation interest and sites subject to unavoidable disturbance pressures, such as that arising from access and recreational activities. 2Grassland resilience was investigated on the Salisbury Plain Training Area (SPTA) in southern England, the largest of the UK military training areas. SPTA contains the greatest expanse of unimproved chalk grassland in north-west Europe, a habitat of particular nature conservation interest. 3Historical aerial photographs were used to identify 82 calcareous and mesotrophic grassland sites disturbed over a 50-year time period. Vegetation, soils and seed bank data were collected from each old disturbance site. Revegetation time periods following disturbance were compared, and habitat resilience following disturbance investigated using the succession of surface vegetation along the chronosequence, the combined changes of vegetation and soil chemistry, and finally vegetation and seed bank composition. 4The sampled calcareous grasslands were less resilient following disturbance than the mesotrophic grasslands, with slower colonization of bare ground and target species re-assembly. The mesotrophic grasslands typically took between 30 and 40 years to re-establish following disturbance, whereas calcareous grasslands took at least 50 years. 5Even after such long time periods, there remained subtle but significant differences between the vegetation composition of the disturbed and undisturbed swards. Perennial forb species, particularly hemicryptophytes, persisted at higher frequencies in swards disturbed 50 years ago than in undisturbed swards. 6Synthesis and applications. Prediction of habitat resilience following disturbance is dependent on which components of the system are investigated. However, data such as that presented here can help land managers understand how palimpsests of current habitat characteristics may have evolved, and how disturbance regimes may be managed in the future. It is likely that the resilience of grasslands such as those on SPTA may have been overestimated, and perceptions of habitat carrying capacity for disturbance events may require re-evaluation. [source]

Vegetation and disturbance history of a rare dwarf pitch pine community in western New England, USA

JOURNAL OF BIOGEOGRAPHY, Issue 10-11 2002
Glenn Motzkin
Abstract Aim, This study documents the vegetation history and age-structure of a rare, ridgetop dwarf pine,oak community and compares the dynamics of this unusual vegetation with similar dwarf pine communities found elsewhere in the north-eastern United States (US). Location, The study area is located on the summit of Mt Everett in the Taconic Mountains of south-western Berkshire County, Massachusetts, USA (42°06,N 73°26,W). Methods, Vegetation composition, tree age-structure, physical site characteristics, and evidence of fire and other disturbances were determined for twelve 15 × 15 m plots in dwarf pine,oak vegetation and two plots in oak forests on the summit. Age-structure analyses, tree-ring patterns, and historical records of human and natural disturbance were used to investigate the long-term history and dynamics of the summit vegetation. Results, The summit of Mt Everett has been dominated by dwarf pines (1,3 m tall) and ericaceous shrubs similar to the modern vegetation throughout the historical period; there is no evidence that tall-stature forests occurred on the site at any point in the past few centuries. The summit supports uneven-aged stands; pitch pine (Pinus rigida) recruitment began in the 1830s and occurred in every decade since the 1860s. Average pitch pine age is seventy-eight with a range of 12,170 years. Red oak (Quercus rubra) and red maple (Acer rubrum) increased in importance in the twentieth century, with most stems establishing from 1940 to 1980. Pitch pine radial growth rates averaged <0.5 mm year,1 while red oak and red maple averaged 1.0 and 0.8 mm year,1, respectively. In some areas, hardwoods have overtopped pitch pines, apparently resulting in pitch pine mortality. Whereas most dwarf pitch pine communities occur on sites that burn frequently and have a high degree of cone serotiny, we found no evidence of recent fires or cone serotiny. Small amounts of macroscopic charcoal that we documented may have resulted from fires in the pre-European or early historical periods. Conclusions, Harsh edaphic conditions and chronic low-level disturbances on the summit, including frequent winter storms, have apparently contributed to the establishment, long-term persistence, and slow radial growth of dwarf pitch pines on Mt Everett. The ability of dwarf pines to persist on a site in the absence of frequent fire is highly unusual among North-eastern barrens and has not been well-incorporated into previous conceptual ecological models of these communities. Our results suggest that even among North-eastern barrens, the summit of Mt Everett is characterized by highly unusual vegetation and dynamics. The site has long been recognized as regionally significant and should be afforded the strictest conservation protection. With no evident history of human disturbance or recent fire, there is no apparent need for immediate active management of the site. [source]

Bat species diversity and distribution in three vegetation communities of Meru National Park, Kenya

AFRICAN JOURNAL OF ECOLOGY, Issue 3 2004
Paul W. Webala
Abstract Diversity and distribution of bats was determined in four vegetation types in and around Meru National Park, Kenya between September 2000 and February 2001. Bat-habitat studies were based on plant species dominance, cover and farming activities. Bats were captured using standard mist nets (18 m long × 2 m high) erected on poles averaging 3 m. Vegetation was broadly grouped as Acacia or Combretum wooded grassland, or Acacia,Commiphora bushland and studied using the Braun-Blanquet method. Analysis of floristic similarity showed five vegetation species assemblages in the three broad categories. Four hundred and ninety-five bats representing eleven genera in seven families were recorded. These were Epomophorus labiatus, E. wahlbergi, Cardioderma cor, Lavia frons, Myotis welwitschii, Scotoecus hirundo, S. leucogaster, Pipistrellus kuhlii, Mops condylurus, Chaerephon bemmeleni, Mormopterus sp., Hipposideros caffer, H. commersoni, Nycteris arge and Rhinolophus landeri. This was the first record of N. arge, M. welwitschii, C. bemmeleni and a Mormopterus species in eastern Kenya. The Combretum community was most equitable (E = 0.51) with nine bat species records, while farming areas had only four. The low species richness and increased dominance of a few generalist species on farms may be indicative of different levels of disturbance. Résumé On a déterminé la diversité et la distribution des chauves-souris dans quatre types de végétation dans et autour du Parc National de Meru, au Kenya, entre septembre 2000 et février 2001. Les études de l'habitat des chauves-souris se basaient sur la dominance et le couvert de certaines espèces végétales et sur les activités agricoles. On a capturé les chauves-souris en utilisant les filets standards (18m de long sur 2 m de haut) fixés sur des piquets d'environ 3 m de haut. La végétation fut grossièrement regroupée en prairie arborée à Acacia ou à Combretum, ou en brousse à Acacia-Commiphora, et étudiée suivant la méthode Braun-Blanquet. L'analyse des similarités floristiques a montré cinq assemblages d'espèces végétales dans ces trois grandes catégories. On a relevé 495 chauves-souris représentant onze genres appartenant à sept familles. Ce sont: Epomophorus labiatus, E. wahlberghi, Cardioderma cor, Lavia frons, Myotis welwitschii, Scotoecus hirundo, Scotophilus leucogaster, Pipistrellus kuhlii, Mops condylurus, Chaerephon bemmeleni, Mormopterus sp., Hipposideros caffer, H. commersoni, Nycteris arge et Rhinolophus landeri. Ce sont les premiers cas rapportés pour N. arge, M. welwitschii, C. bemmemeni et pour une espèce de Mormopterus dans l'est du Kenya. La communautéà Combretum était la plus équitable (E = 0,51), avec neuf espèces de chauves-souris rapportées, alors que les aires cultivées n'en comptaient que quatre. La faible richesse en espèces et la dominance croissante de quelques espèces généralistes dans les fermes pourraient indiquer divers degrés de perturbation. [source]

Measuring Change in British Vegetation.

JOURNAL OF ECOLOGY, Issue 2 2000
ECOFACT Volume 2.
No abstract is available for this article. [source]

Quantifying uncertainty in the biospheric carbon flux for England and Wales

JOURNAL OF THE ROYAL STATISTICAL SOCIETY: SERIES A (STATISTICS IN SOCIETY), Issue 1 2008
Marc Kennedy
Summary., A crucial issue in the current global warming debate is the effect of vegetation and soils on carbon dioxide (CO2) concentrations in the atmosphere. Vegetation can extract CO2 through photosynthesis, but respiration, decay of soil organic matter and disturbance effects such as fire return it to the atmosphere. The balance of these processes is the net carbon flux. To estimate the biospheric carbon flux for England and Wales, we address the statistical problem of inference for the sum of multiple outputs from a complex deterministic computer code whose input parameters are uncertain. The code is a process model which simulates the carbon dynamics of vegetation and soils, including the amount of carbon that is stored as a result of photosynthesis and the amount that is returned to the atmosphere through respiration. The aggregation of outputs corresponding to multiple sites and types of vegetation in a region gives an estimate of the total carbon flux for that region over a period of time. Expert prior opinions are elicited for marginal uncertainty about the relevant input parameters and for correlations of inputs between sites. A Gaussian process model is used to build emulators of the multiple code outputs and Bayesian uncertainty analysis is then used to propagate uncertainty in the input parameters through to uncertainty on the aggregated output. Numerical results are presented for England and Wales in the year 2000. It is estimated that vegetation and soils in England and Wales constituted a net sink of 7.55 Mt C (1 Mt C = 1012 g of carbon) in 2000, with standard deviation 0.56 Mt C resulting from the sources of uncertainty that are considered. [source]

Strong shifts in plant diversity and vegetation composition in grassland shortly after climatic change

JOURNAL OF VEGETATION SCIENCE, Issue 3 2008
Maria-Teresa Sebastià
Abstract Questions: Is plant diversity in mesic grassland ecosystems vulnerable in the short-term to extreme climate change events? How rapidly can responses in vegetation composition occur in perennial grasslands? Are the expected compositional changes related to rare species losses or to shifts in the relative abundance of the dominants? Location: Subalpine mesic grasslands on limestone in the Pyrenees. Methods: Transplanting turves from the upland, with cold-temperate climate, to a lowland location, with continental Mediterranean climate. Results: Transplanting led to decreased biodiversity and strong shifts in vegetation composition. Results from both permutation tests and traditional multivariate analysis suggested different trajectories of vegetation depending on the initial species pool. Vegetation showed a tendency to converge in composition in the lowland over time, independently of initial differences. Estimated changes in relative biomass of the five most abundant species between the upland and the lowland ranged from -89 to +96 %. The ensemble of all other species was reduced by 80%. The most dominant species in the upland, Festuca nigrescens, reduced its abundance in the lowland, shifting from having mainly positive to mainly negative associations with other species. Conclusions: Mesic grassland ecosystems in the Pyrenees showed strong shifts in plant diversity and composition after a short period of warming and drought, as a consequence of acute vulnerability of some dominant grasses, losses of rare species, and aggregate and trigger effects of originally uncommon forb species. [source]

Use of the ecological information system SynBioSys for the analysis of large datasets

JOURNAL OF VEGETATION SCIENCE, Issue 4 2007
Joop H.J. Schaminée
Abstract The rapid developments in computer techniques and the availability of large datasets open new perspectives for vegetation analysis aiming at better understanding of the ecology and functioning of ecosystems and underlying mechanisms. Information systems prove to be helpful tools in this new field. Such information systems may integrate different biological levels, viz. species, community and landscape. They incorporate a GIS platform for the visualization of the various layers of information, enabling the analysis of patterns and processes which relate the individual levels. An example of a newly developed information system is SynBioSys Europe, an initiative of the European Vegetation Survey (EVS). For the individual levels of the system, specific sources are available, notably national and regional Turboveg databases for the community level and data from the recently published European Map of Natural Vegetation for the landscape level. The structure of the system and its underlying databases allow user-defined queries. With regard to its application, such information systems may play a vital role in European nature planning, such as the implementation the EU-program Natura 2000. To illustrate the scope and perspectives of the program, some examples from The Netherlands are presented. They are dealing with long-term changes in grassland ecosystems, including shifts in distribution, floristic composition, and ecological indicator values. [source]

Vegetation, environment, and time: The origination and termination of ecosystems

JOURNAL OF VEGETATION SCIENCE, Issue 5 2006
Stephen T. Jackson
Abstract Terrestrial ecosystems originate when particular plant species attain dominance at specific locations under specific environmental regimes. Ecosystems terminate, gradually or abruptly, when the dominant species or functional types are replaced by others, usually owing to environmental change or severe and irreversible disturbance. Assessing whether current ecosystems are sustainable in the face of future environmental change can be aided by examining the range of environmental variation those ecosystems have experienced in the past, and by determining the environmental conditions under which those ecosystems arose. The range of environmental variation depends on the time scale at which it is assessed. A narrow time span (e.g. 200,300 years) may underestimate the range of variation within which an ecosystem is sustainable, and it may also underestimate the risk of major transformation or disruption of that ecosystem by environmental change. Longer time spans (e.g. 1000,2000 years) increase the range of variation, by encompassing a larger sample of natural variability as well as non-stationary variability in the earth system. Most modern ecosystems disappear when the time span is expanded to 10000,15 000 years owing to secular changes in earth's climate system. Paleo-ecological records can pinpoint the time of origination of specific ecosystems, and paleo-environmental records can reveal the specific environmental changes that led to development of those ecosystems and the range of environmental variation under which those ecosystems have maintained themselves in the past. This information can help identify critical environmental thresholds beyond which specific modern ecosystems can no longer be sustained. [source]

Groundwater input affecting plant distribution by controlling ammonium and iron availability

JOURNAL OF VEGETATION SCIENCE, Issue 4 2006
Esther C.H.E.T. Lucassen
Abstract Question: How does groundwater input affect plant distribution in Alnus glutinosa (black alder) carrs? Location: Alder carrs along the river Meuse, SE Netherlands. Methods: Three types of site, characterized by groundwater flow, were sampled in 17 A. glutinosa carrs. Vegetation and abiotic data (soil and water chemistry) were collected and analysed using a Canonical Correspondence Analysis. Based on the results, a laboratory experiment tested the effect of groundwater input (Ca2+) on pore water chemistry (NH4+ availability). Results: Environmental factors indicating groundwater input (Ca2+ and Fe2+), correlating with the NH+4 concentration in the pore water, best explained the variation in plant distribution. NH4+ availability was determined by Ca2+ input via the groundwater and subsequent competition for exchange sites in the sediment. As a result, nutrient-poor seepage locations fully fed by groundwater were dominated by small iron resistant plants such as Caltha palustris and Equisetum fluviatile. More nutrient-rich locations, fed by a combination of groundwater and surface water, allowed the growth of taller iron resistant plant species such as Carex paniculata. Nutrient-rich locations with stagnating surface water were hardly fed by groundwater, allowing the occurrence of fast growing and less iron tolerant wetland grasses such as Glyceria fluitans and G. maxima. Conclusion: Groundwater input affects plant composition in A. glutinosa carrs along the river Meuse by determining nutrient availability (ammonium) and concentrations of toxic iron. [source]

Community-level changes in Australian subalpine vegetation following invasion by the non-native shrub Cytisus scoparius

JOURNAL OF VEGETATION SCIENCE, Issue 5 2004
Lynise J. Wearne
Abstract: Question: What are the changes associated with the recent invasion by the non-native legume, Cytisus scoparius? Location: Subalpine vegetation (1500 m a.s.l.) in Australia. Methods: We used multivariate techniques and regression analyses to assess vegetation and environmental changes across six study sites. Vegetation and environmental variables were investigated at three different stages of invasion: (1) recent invasion (8,10 yr), (2) mature invasion (15,16 yr) and (3) long-term invasion (25 yr). Results: Substantial changes in floristic composition and species richness were evident after 15 yr and these changes became more pronounced after 25 yr. Changes due to invasion were associated with a dramatic loss of native species or a reduction in their abundance. No ,new species' were evident under invaded stands. Forbs were most affected by the establishment of C. scoparius, although all growth forms responded negatively. Dense canopy shading and an increasingly dense, homogeneous litter layer in the understorey as a result of C. scoparius were strong environmental drivers of vegetation change. Greenhouse studies confirmed the importance of these processes on the germination and growth of two native species. Conclusions: This study highlights the potential for C. scoparius to alter both vegetation and environmental processes in the subalpine region. [source]