Showing papers on "Vegetation (pathology) published in 1997"

Ecology of Shallow Lakes

Abstract: Preface. Introduction. The story of some shallow lakes. The abiotic environment. Phytoplankton. Trophic cascades. Vegetation. Managing the ecosystem. The limits of knowledge. References. Index. Symbols used. Legends to the figures.

Vegetation processes in the pelagic : a model for ecosystem theory

Abstract: Go Vegetation Processes in the Pelagic: A Model for Ecosystem Theory. Ecology Institute, Oldendorf/Luhe, Germany, 371p. [3] Reynolds, C.S., Huszar, V., Kruk, C., Naselli-Flores, L., Melo, S. 2002. Towards a functional classification of the freshwater phytoplankton. J. Plankton Res. 24: 417-428. [4] Heaney, S.I., Furnass, T.I. 1980. Laboratory models of diel vertical migration in the dinoflagellate Ceratium hirundinella. Freshwater Biol. 10: 163-170. C o n t a c t C o p y r i g h t a n d D i s c l a i m e r S i t e m a p S e a r c h

Contrasting physiological and structural vegetation feedbacks in climate change simulations

Abstract: Anthropogenic increases in the atmospheric concentration of carbon dioxide and other greenhouse gases are predicted to cause a warming of the global climate by modifying radiative forcing1. Carbon dioxide concentration increases may make a further contribution to warming by inducing a physiological response of the global vegetation—a reduced stomatal conductance, which suppresses transpiration2. Moreover, a CO2-enriched atmosphere and the corresponding change in climate may also alter the density of vegetation cover, thus modifying the physicalcharacteristics of the land surface to provide yet another climate feedback3,4,5,6. But such feedbacks from changes in vegetation structure have not yet been incorporated into general circulation model predictions of future climate change. Here we use a general circulation model iteratively coupled to an equilibrium vegetation model to quantify the effects of both physiological and structural vegetation feedbacks on a doubled-CO2 climate. On a global scale, changes in vegetation structure are found to partially offset physiological vegetation–climate feedbacks in the long term, but overall vegetation feedbacks provide significant regional-scale effects.

Global-Scale Assessment of Vegetation Phenology Using NOAA/AVHRR Satellite Measurements

Abstract: Phenology and associated canopy development exert a strong control over seasonal energy and mass exchanges between the earth’s surface and the atmosphere. Satellite measurements are used to assess main phenological stages of the vegetation at the global scale. The authors propose a method to derive the start, the maximum, the end, and the length of the vegetation cycle, based on the analysis of temporal series of weekly vegetation index, at a resolution of 1° lat × 1° long for year 1986. Global maps of these characteristics of the vegetation are presented, and their zonal distribution is discussed. The start of the vegetation cycle has been related to temperature sums in the case of temperate deciduous forest and to precipitation in the case of savannahs. It is concluded that satellite measurements offer interesting perspectives for global-scale quantitative phenology modeling.

Catastrophic vegetation shifts and soil degradation in terrestrial grazing systems.

Abstract: It has long been recognized that alternative vegetation states may occur in terrestrial grazing systems. This phenomenon may be of great importance as small environmental fluctuations may lead to relatively sudden and irreversible jumps between vegetation states. Early theoretical studies emphasized saturation of herbivore feeding to explain multiple stable states and catastrophic behaviour. Recent studies on semi-arid grasslands and arctic salt marshes, however, relate catastrophic events in these systems to plant-soil interactions.

Conspectus of classes of European vegetation

Abstract: This is a first approximation to a Conspectus of classes of European vegetation. European vegetation consists, according to the present scheme, of 73 classes. An attempt was made to compile all available names of classes which have ever appeared in European phytosociological literature. The names were checked for nomenclatural accuracy. Lists of synonyms and related names are given. The classes, are characterised by a brief diagnosis, a comprehensive list of diagnostic species, and a list of basic references. Several syntaxonomic problems are discussed in the form of short notes.

Runoff and Soil Loss Response to Vegetation Removal in a Semiarid Environment

Abstract: The removal of vegetation is the main cause of soil degradation in semiarid areas. We hypothesized that the changes in soil properties induced by vegetation removal modified the runoff and soil erosion response in a semiarid area of Spain. To test this, two plots (15 by 5 m) were installed on a 23% slope on a Lithic Haploxeroll. Vegetation was removed by clipping from one of the plots (Plot D) and the changes in surface runoff and soil loss were compared with an undisturbed control plot (Plot N) from 1989 to 1993. Total runoff was significantly greater in Plot D (48.8 mm) than in Plot N (34.9 mm). Runoff ratios between the disturbed and natural plots increased with time from 1.4:1 in 1990 to 2.5:1 in 1993. Vegetation removal increased the soil losses in Plot D (150.2 g m -2 ) by 127% compared with those in Plot N (66.3 g m -2 ) . The annual soil loss ratio between the disturbed and natural plots increased from 1.6:1 in 1989 to 4.2:1 in 1993. The observed increase in surface runoff and soil loss was attributed to a progressive deterioration of soil physical properties in Plot D. Bulk density increased by 8.4% (from 1.55 to 1.68 Mg m -3 ) and a reduction of total organic carbon (from 4.0 to 2.6%) and the percentage of stable aggregates (from 81.6 to 56.3%) were observed. There was no evidence of vegetation recovery, suggesting that reduced vegetal cover might lead to irreversible soil degradation in semiarid areas.

The vegetation and physiography of Sumatra

Abstract: Introduction. 1: Methodology. I. Critical review of the main methods used for vegetation mapping and vegetation studies in the tropics. II. Method used for vegetation classification and analysis during the present survey. 2: Physical environment and physiographic classification of the vegetation. I. Geomorphology, geology and pedology. II. Bioclimates. III. Physiographic classification of the vegetation. 3: History of the vegetation and phytogeography. I. History of the vegetation. II. Phytogeography of Malesia. III. Phytogeography of Sumatra. 4: Vegetation and forest types. I. A short cartographical analysis of the main plant formations of Sumatra. II. Plant formations in lowland swamp areas. III. Plant formations of the plains and piedmonts (alt.

Amphibians and Reptiles of Trinidad and Tobago

Abstract: Physiographic Features and Geology Climate Vegetation Previous Herpetological Investigations Species Reported in Error Zoogeography Methods Keys Species Accounts.

Site-specific properties and irreversible vegetation changes in semi-arid grazing systems

Abstract: There is an urgent need to develop a mechanistic understanding of how site-specific properties can lead to irreversible vegetation changes. We show, by means of a bifurcation analysis of two mathematical models, how site-specific properties determine the resilience of vegetation changes in semi-arid grazing systems. The models predict that if available soil water limits plant growth, the vegetation supported by sandy soils is generally resilient to herbivore impact and rainfall fluctuations, unlike the vegetation on clayey soils. This depends on the capacity of vegetation communities to improve the structural and water-holding capacities of the soil. In contrast, if plant growth is nutrient limited, vegetation on sandy soils is generally not resilient to herbivore impact and fluctuations in external nutrient input, unlike the vegetation supported by clayey soils. This is affected by the nutrient retention capacity of vegetation communities. We stress the applicability of the general theory provided by this model to the Sahel environment. The model predictions are consistent with field observations documented in the literature.

The use of vegetation indices in forested regions: issues of linearity and saturation

Abstract: Numerous problems and difficulties have been reported with the use of vegetation indices in high biomass, forested regions. In this study the authors analyzed Landsat-5 Thematic Mapper (TM) scenes from various temperate and tropical forested biomes, representing needleleaf and broadleaf canopy structures in the Pacific Northwest (Oregon), Eastern U.S. (Harvard Forest), southern Chile, the Amazon, and Central America. The TM scenes were atmospherically corrected and reduced to MODIS surface reflectance data at 250 m pixel sizes. Various vegetation indices (VIs) were then computed including the normalized difference vegetation index (NDVI), simple ratio, soil-adjusted vegetation index (SAVI), enhanced vegetation index (EVI), and green vegetation index (GVI). The NDVI was also tested utilizing the green and middle-infrared (MIR) bands. All of the NDVIs were non-linear and were fairly saturated across the forested biomes. In contrast, the remaining indices remained sensitive to canopy structure variations over all of the forested biomes with minimal saturation problems. The high 'penetrating' capability of the near-infrared band through forested canopies was the dominant factor in vegetation index sensitivity and performance. The authors found that indices with higher weighing coefficients in the "near-infrared" to be the best approach in extending vegetation index performance over forested and dense vegetated canopies.

Biomass of primary and secondary vegetation in Rondônia, Western Brazilian Amazon

Abstract: Biomass estimates of primary and different ages of secondary vegetation are reported for a tropical forest region in Rondonia, Western Brazilian Amazon. The estimates are based on published allometric equations, and on vegetation composition and allometric data collected in areas of primary forest and secondary vegetation of ages 2, 3, 5, 9, 11, 16 and 18 years. Primary forest biomass estimates varied from 290 to 495 t ha–1. Secondary vegetation biomass estimates accounted for 40–60% of the primary forest biomass after 18 years of abandonment. Secondary growth rates in lightly used areas are estimated to have varied from 6.6 to 8.7 t ha–1 y–1 between the third and the eighteenth years after abandonment. CO2 sequestration by regrowing vegetation is discussed for two scenarios of land abandonment.

Carbon Dioxide and Vegetation

Abstract: The effect of carbon dioxide on Earth9s vegetation over time is both of historical interest and current importance. In his Perspective, Farquhar discusses results presented in the same issue by Street-Perrott et al. that describe how carbon dioxide levels have influenced the paleenvironmental history of high-altitude lakes and surrounding vegetation in East Africa. From the early record, it is apparent that the increasing concentration of carbon dioxide over the last 13,000 years has allowed trees to grow in places that were once almost treeless, grassy heathland.

Classification of vegetation: past, present and future

Abstract: This paper is a report on the past, status-quo and perspectives of vegetation classification, still a major occupa- tion of many vegetation scientists. The history of vegetation classification is discussed against a background of several controversial issues such as the problem of continuum vs. discontinuum, naturalness vs. arbitrariness of the nature of plant communities, universality vs. ad hoc character of syn- taxonomic schemes, as well as classical versus numerical approaches to data analysis for classification purposes. The development of the methodology of vegetation sci- ence and the present image of vegetation classification is documented by a bibliometric analysis of the publication record of four major journals: Journal of Vegetation Science, Vegetatio, Phytocoenologia and Tuexenia. This analysis revealed a per- sisting controversy between traditional and numerical ap- proaches to vegetation classification. A series of important changes in vegetation science (foundation of new journals, change of editorial policy by the established, important meet- ings) punctuate a period called the 'Innovation period'. Several trends in the development of methods of vegeta- tion systematics are summarized under the headings formal- ism, pluralism, functionalism, pragmatism and indetermin- ism. Some new features, such as the development and im- provement of numerical tools, use of large data banks and attempts to summarize the theory of vegetation classification are discussed. The new growth-form system of Barkman initiated a revival of physiognomy-based vegetation classifi- cation. Within this framework the use of the character-type concept and the development of new numerical methods for studying the hierarchical structure of character-set types seems to be a promising approach. The achievements of population biology and ecophysiology have affected vegetation science by emphasizing the functionality of species within plant communi- ties. The use of guilds and other functional groups has experi- enced an increasing interest from vegetation scientists. Applied in vegetation science, fuzzy-set theory has bridged the tech- niques of classification and ordination of plant communities.

Questing behaviour of Ixodes ricinus ticks (Acari: Ixodidae)

Abstract: The vertical distribution in the vegetation of questing Ixodes ricinus ticks was investigated in two different vegetation types (‘high’ and ‘low’ vegetation) at two localities in south-central Sweden during 1992-1993 (Toro) and 1995 (Bogesund). Significant correlations were found between the vertical distribution of immature ticks and the height of the vegetation. The greatest mean availabilities of the larvae and nymphs in low vegetation were in the intervals 0-9 and 30-39 cm, respectively. The larval numbers were greatest close to the ground (0-29 cm) in both high and low vegetation. The larval : nymphal ratio, at ground level at localities free of ground vegetation, varied between 8 : 1 and 32 : 1. In high vegetation, the greatest mean numbers of nymphal and adult ticks were at height intervals of 50-59 and 60-79 cm, respectively. These ranges are within the estimated height interval (40-100 cm) of the main part of the body surface of their ‘preferred’ host, the roe deer (Capreolus capreolus). The presence of most questing I. ricinus larvae at ground level would favour the transmission of Borrelia burgdorferi s.l., since this is where the highly reservoir-competent rodents and shrews usually occur.

Macroinvertebrate communities in relation to submerged vegetation in two Chara-dominated lakes

Abstract: Relationships between macroinvertebrates and the presence ofsubmerged vegetation were studied in two shallow eutrophiclakes inThe Netherlands, Lake Veluwemeer and Lake Wolderwijd. A shiftfromturbid water with sparse macrophyte cover (Potamogetonperfoliatus, Potamogeton pectinatus) towards clearwaterwith a dense cover of submerged vegetation (Chara spp.)hasbeen observed in the lakes over the past 10 years. RelativelylargeChara meadows (300–500 ha) have recently developed inbothlakes. The composition of macroinvertebrate fauna wasdetermined atsites varying in cover and dominant vegetation type bysamplingsediment and water during 1992 and 1994. Macrophyte biomass,sampling year and vegetation type were the major determinantsofmacroinvertebrate community composition. Valvatapiscinalis,Bithynia tentaculata, Gammarus tigrinus and Chironomussp.characterized the sites with high charophyte biomass, whereasPotamopyrgus antipodarum, Cladotanytarsus sp., Stictochironomus sp. dominated the samples with lowcharophytebiomass. Chara vegetation was different from Potamogeton sp. by showing lower densities of the midgelarvaeEinfeldia dissidens and Cricotopus gr. sylvestris.Seasonal variations in densities of the dominant molluscspecies(V. piscinalis, P. antipodarum) were closelyrelated tothe development of Chara biomass as well as toperiphytoncover on charophytes. Thus, changes of the light climate inbothlakes, which have led to an increase in colonization bysubmergedvegetation (particular Chara meadows), indirectly had alargeimpact on macroinvertebrate communities.

Comparison of Landsat Thematic Mapper and High Resolution Photography to Identify Change in Complex Coastal Wetlands

Abstract: Landsat Thematic Mapper (TM) images were used to generate pre- and post-hurricane classifications of a complex wetland environment in southern Louisiana. Accuracies were estimated as 77% and 81.5% for the pre- and post-classifications that included water, emergent vegetation, floating vegetation, and mud flats. From the two classifications, areas of emergent vegetation loss were identified. The classifications and change map were compared to similar output generated from high resolution color infrared photography. The comparison showed spatial scale of the sensor was the most important factor in separation of classes in this type of wetland environment. Classifications derived by using the TM images provided good class separation when one class dominated more extensive areas (>30 m), but not when mixtures of wetland types were on the same order as the TM sensor spatial resolution. Boundary pixel mixtures were problematic, however problems also occurred in areas of fairly continuous canopies containing small pockets of water and floating vegetation, and in areas of degrading marsh. Both areas were predominately misclassified as emergent vegetation. In the case of change detection, loss of emergent vegetation occurring as small pockets was not identified, whereas loss of degraded marsh was identified but the spatial continuity and extent overemphasized. In combination, these misclassifications resulted in the TM change analysis overpredicting emergent vegetation loss by about 40%.

The dynamics of vegetation change: health warnings for equilibrium 'dodo' models

Abstract: Vegetation plays a part in controlling climate and in turn responds to climatic change. Therefore, projections of future climates must include the responses of vegetation, both in terms of function and distribution. Unfortunately, assessments of future climatic impacts on vegetation are still considered with equilibrium vegetation models-models which exclude processes involved in vegetation dynamics, such as succession and disturbance. The commonly held view that future spatial changes in temperature will outstrip the potential for species to migrate has no theoretical

Detection of vegetation changes associated with extensive flooding in a forested ecosystem.

Abstract: Monitoring broad-scale ecological responses to disturbance can be facilitated by automated change-detection approaches using remotely sensed data. This study evaluated the effectiveness of five unsupem'sed change-detection techniques using multispectral, multitemporal SPOT High Resolution Visible (HRV) data for identifying vegetation responses to extensive flooding of a forested ecosystem associated with Tropical Storm Alberto in July 1994. Standard statistical techniques, logistic multiple regression, and a probability vector model were used to quantitatively and visually assess classification accuracy. The change-detection techniques were (I) spectral-temporal change classification, (2) temporal change classification based on the Normalized Difference Vegetation Index (NDVI), (3) principal components analysis (PCA) of spectral data, (4) PCA of NDVI data, and (5) NDVI image differencing. Spectral-temporal change classification was the least effective of the techniques evaluated. Classification accuracy improved when temporal change classification was based on NDVI data. Both PCA methods were more sensitive to flood-affected vegetation than the temporal change classifications based on spectral and NDVI data. Vegetation changes were most accurately identified by image differencing of NDVI data. Logistic multiple regression and a probability vector model were especially useful for relating spectral responses to vegetation changes observed during field surveys and identifying areas of agreement and disagreement among the different classification methods. to utilize satellite data to assess vegetation responses to flooding in a forested ecosystem and to compare analytical approaches for vegetation change detection. Minimal wind and storm surge damage accompanied Alberto as it made landfall on the Florida panhandle near Fort Walton Beach on 3 July 1994 and traveled inland. However, due to weak steer

A decade of recovery of understory vegetation buried by volcanic tephra from mount st. helens

Abstract: We examined changes in understory vegetation under an intact forest canopy during the first decade following the deposition of tephra (aerially transported volcanic ejecta) during the 1980 eruption of Mount St. Helens, Washington State, USA. Objectives were (1) to document vegetation response to a major disturbance that has received little attention but is widespread and relatively frequent in the northwestern United States, and (2) to analyze vegetation responses in terms of characteristics of the disturbance, responses of growth forms as well as those of species, components of vegetation change, and species autecology. We used permanent plots at four study sites, representing two tephra depths (≈4.5 and 15 cm), to examine understory vegetation change in old-growth, subalpine conifer forests. The two sites at each tephra depth differed in understory vegetation and amount of snowpack at the time of disturbance. At each site, plant cover and density were measured in 100 1-m2 plots with undisturbed tephra c...

Open-Channel Flow Through Simulated Vegetation: Turbulence Modeling and Sediment Transport.

Abstract: : The two equation turbulence model based on the k-epsilon closure scheme was developed to simulate the flow and turbulence characteristics of open-channel flows through nonemergent vegetation. Once the performance of the model was verified, the flow structure of vegetated open channels was numerically simulated. Simulated rigid and flexible plants were used to validate the model. Finally, dimensional analysis allowed identification of the dimensionless parameters that govern suspended sediment transport processes in the presence of vegetation, and thus helped in the design of numerical experiments to investigate the role of different flow properties, sediment characteristics, and vegetation parameters upon the transport capacity.

Linking riparian vegetation types and fluvial geomorphology along the Sabie River within the Kruger National Park, South Africa.

Abstract: Vegetation types were studied in relation to the fluvial geomorphology along the mixed bedrock-alluvial Sabie River within the Kruger National Park, Mpumalanga, South Africa. Six vegetation types were identified using TWINSPAN analysis, namely: Phragmites mauritianus, Phyllanthus reticulatus, Breonadia salicina, Combretum erythrophyllum, Diospyros mespiliformis and Spirostachys africana vegetation types. Spirostachys africana and Diospyros mespiliformis vegetation types were found to occur predominantly on the stable, infrequently flooded macro-channel banks, while the remaining four vegetation types were found almost exclusively along the more geomorphically and hydrologically dynamic macro-channel floor. The degree of bedrock or alluvial influence was identified as being an integral factor in the distribution of the four macro-channel floor vegetation types at both the morphological unit and the channel type scale. The geomorphological continuum from the bedrock influenced bedrock anastomosing channel types, to mixed anastomosing and pool-rapid channel types, to the fully alluvial braided channel types, is reflected in the change in species composition from Breonadia salicina vegetation type, to Phyllanthus reticulatus and Phragmites mauritianus vegetation types, to Combretum erythrophyllum vegetation types, respectively. Given the vegetation/fluvial geomorphology links established, changes in vegetation composition are proposed in response to scenarios of geomorphological change as a result of progressive sedimentation.