Showing papers on "Vegetation (pathology) published in 2002"

Climatic control of the high-latitude vegetation greening trend and Pinatubo effect

Abstract: A biogeochemical model of vegetation using observed climate data predicts the high northern latitude greening trend over the past two decades observed by satellites and a marked setback in this trend after the Mount Pinatubo volcano eruption in 1991. The observed trend toward earlier spring budburst and increased maximum leaf area is produced by the model as a consequence of biogeochemical vegetation responses mainly to changes in temperature. The post-Pinatubo decline in vegetation in 1992-1993 is apparent as the effect of temporary cooling caused by the eruption. High-latitude CO(2) uptake during these years is predicted as a consequence of the differential response of heterotrophic respiration and net primary production.

Drought Monitoring with NDVI-Based Standardized Vegetation Index

Abstract: Drought is one of the major natural hazards affecting the environment and economy of countries worldwide. Reliance on weather data alone is not sufficient to monitor areas of drought, particularly when these data can be untimely, sparse, and incomplete. Augmenting weather data with satellite images to identify the location and severity of droughts is a must for complete, up-to-date, and comprehensive coverage of current drought conditions. The objective of this research was to standardize, by time of year, the Normalized Difference Vegetation Index (NDVT) to augment drought-monitoring techniques. The Standardized Vegetation Index (SVI) describes the probability of vegetation condition deviation from "normal," based on calculations from weekly NDvI values. The study was conducted with 12 years (1989-2000) of Advanced Very High-Resolution Radiometer (AVHRR) satellite images. Z-scores of the NDVI distribution are used to estimate the probability of occurrence of the present vegetation condition at a given location relative to the possible range of vegetative vigor, historically. The ~VI can be interpreted as vegetation condition based on the fact that vegetation is an efficient integrator of climatic and anthropogenic impacts in the boundary layer of the atmosphere. It thereby provides a spatially and temporally continuous short-term indicator of climatic conditions. Findings indicate that the svr, along with other drought monitoring tools, is useful for assessing the extent and severity of drought at a spatial resolution of 1 km. The SVI is capable of providing a near-real-time indicator of vegetation condition within drought regions, and more specifically areas of varying drought conditions.

Ecological restoration of land with particular reference to the mining of metals and industrial minerals: A review of theory and practice

Abstract: Mining causes the destruction of natural ecosystems through removal of soil and vegetation and burial beneath waste disposal sites. The restoration of mined land in practice can largely be consider...

Modeling vegetation as a dynamic component in soil‐vegetation‐atmosphere transfer schemes and hydrological models

Abstract: [1] Vegetation affects the climate by modifying the energy, momentum, and hydrologic balance of the land surface. Soil-vegetation-atmosphere transfer (SVAT) schemes explicitly consider the role of vegetation in affecting water and energy balance by taking into account its physiological properties, in particular, leaf area index (LAI) and stomatal conductance. These two physiological properties are also the basis of evapotranspiration parameterizations in physically based hydrological models. However, most current SVAT schemes and hydrological models do not parameterize vegetation as a dynamic component. The seasonal evolution of LAI is prescribed, and monthly LAI values are kept constant year after year. The effect of CO2 on the structure and physiological properties of vegetation is also neglected, which is likely to be important in transient climate simulations with increasing CO2 concentration and for hydrological models that are used to study climate change impact. The net carbon uptake by vegetation, which is the difference between photosynthesis and respiration, is allocated to leaves, stems, and roots. Carbon allocation to leaves determines their biomass and LAI. The timing of bud burst, leaf senescence, and leaf abscission (i.e., the phenology) determines the length of the growing season. Together, photosynthesis, respiration, allocation, and phenology, which are all strongly dependent on environmental conditions, make vegetation a dynamic component. This paper (1) familiarizes the reader with the basic physical processes associated with the functioning of the terrestrial biosphere using simple nonbiogeochemical terminology, (2) summarizes the range of parameterizations used to model these processes in the current generation of process-based vegetation and plant growth models and discusses their suitability for inclusion in SVAT schemes and hydrological models, and (3) illustrates the manner in which the coupling of vegetation models and SVAT schemes/hydrological models may be accomplished.

Localized vegetation patches: A self-organized response to resource scarcity

Abstract: We show that spatial self-organization allows vegetation to survive greater resource limitation. Isolated vegetation patches observed in nutrient-poor territories of South America and West Africa are interpreted as localized structures arising from the bistability between the bare state and the patchy vegetation state.

Flow Velocity Measurements in Vegetated Channels

Abstract: Understanding of the hydraulics of flow over vegetation is very important to support the management of fluvial processes. In this paper the flow over flexible bottom vegetation is experimentally studied. A two-dimensional-acoustic doppler velocimeter is used to measure the local flow velocities for different vegetation concentrations, discharges, and flume slopes. The influence of vegetation concentration and the depth/vegetation height ratio on the measured velocity profiles is analyzed. All measured velocity distributions are S-shaped and exhibit a three-zone profile. The relationship between the velocity distribution and the turbulence intensity distribution is also analyzed. The characteristics ~inflection point, maximum value, asymptotes ! of the measured velocity distributions and the results of the previous investigators are used to select an analytical expression for the shape of the velocity profile. A theoretical velocity profile is deduced using the classical Prandtl's mixing length approach with a new expression for the mixing length. The deduced four-coefficient profile allows description of the flow both inside and above the vegetation. The physical and geometrical meaning of the four coefficients are also shown. DOI: 10.1061/~ASCE!0733-9429~2002!128:7~664! CE Database keywords: Velocity profile; Vegetation; Channel flow.

World droughts in the new millennium from AVHRR-based vegetation health indices

Abstract: The new millennium has started with a series of large-area droughts which have had grim consequences for the affected countries and regions. The enormous impacts of the 2000 and 2001 droughts were experienced on both physical and psychological levels, in part because no large-scale drought occurred in 1999. In some regions, severe drought continued for two years in a row.

Vegetation and soil lines in visible spectral space: a concept and technique for remote estimation of vegetation fraction

Abstract: The goal of this study is to investigate the information content of reflectance spectra of crops in the visible and near infrared range of the spectrum and develop a technique for remote estimation of vegetation fraction ( VF ). For four wheat species with VF =100% in a wide range of pigment contents and compositions, a high degree of covariance was found for paired reflectances ( R ) at 550 nm versus 700 nm ( R 550 versus R 700) and 500 nm versus 670 nm ( R 500 versus R 670). Both relationships, defined as 'vegetation lines', were linear with determination coefficients r 2 >0.9 and the plotted points were tightly clustered. Using the same coordinates to plot reflectances for a variety of soils, a high degree of covariance ( r 2 >0.94) and a distinct 'soil line' were found. The vegetation and soil lines define a two-dimensional spectral construct within which canopy reflectances, regardless of VF, may be located. Based on these optical properties of vegetation and soils, an attempt was made to estimate VF...

The Circumpolar Arctic Vegetation Map: AVHRR-derived base maps, environmental controls, and integrated mapping procedures

Abstract: A new false-colour-infrared image derived from biweekly 1993 and 1995 Advanced Very High Resolution Radiometer (AVHRR) data provides a snow-free and cloud-free base image for the interpretation of vegetation as part of a 1:7.5 M-scale Circumpolar Arctic Vegetation Map (CAVM). A maximumNDVI (Normalized Difference Vegetation Index) image prepared from the same data provides a circumpolar view of vegetation green-biomass density across the Arctic. This paper describes the remote sensing products, the environmental factors that control the principal vegetation patterns at this small scale, and the integrated geographic information-system (GIS) methods used in making the CAVM.

Vegetation growth in rivers: influences upon sediment and nutrient dynamics:

Abstract: Hydrological and geomorphological research in river environments has largely ignored the influence of instream vegetation growth; focusing rather on the role of riparian vegetation as a control on

Methods for evaluating wetland condition: Using Vegetation To Assess Environmental Conditions in Wetlands

Abstract: Notice The material in this document has been subjected to U.S. Environmental Protection Agency (EPA) technical review and has been approved for publication as an EPA document. The information contained herein is offered to the reader as a review of the " state of the science " concerning wetland bioassessment and nutrient enrichment and is not intended to be prescriptive guidance or firm advice. Mention of trade names, products or services does not convey, and should not be interpreted as conveying official EPA approval, endorsement, or recommendation.

Foraging geese, vegetation loss and soil degradation in an Arctic salt marsh

Abstract: The North American mid‐continent population of Lesser snow geese (Chen caerulescens caerulescens L.) has increased by ca. 7% per year, largely as a result of geese feeding on agricultural crops in winter and on migration. We describe the long‐term effects of increasing numbers of geese at an arctic breeding ground (La Perouse Bay, Manitoba) on intertidal salt‐marsh vegetation. Between 1985 and 1999 goose grubbing caused considerable loss of graminoid vegetation along transects in intertidal marshes. Loss of vegetation led to bare sediment with a plant cover of less than 2%. Changes in vegetation could not be described by simple linear, geometric or exponential functions; most losses occurred between 1988 and 1990 and losses were staggered in time between individual transects, some of which had all vegetation removed. Between 1979 and 1999 the standing crop in July in remaining intact heavily‐grazed swards of Puccinellia phryganodes and Carex subspathacea fell from 40–60 g m−2 to 20–30 g m−2. Inte...

Effects of waterfowl and fish on submerged vegetation and macroinvertebrates

Abstract: 1. With the aim to assess the combined and separate effects of waterfowl and fish on submerged vegetation and macroinvertebrates, we performed a replicated selective exclosure study in a shallow, eutrophic lake in southern Sweden. Our results are presented together with a literature review of the effects of fish and waterfowl on macroinvertebrates and submerged vegetation. 2. Based on our experiment and on published data, we conclude that waterfowl normally will reduce submerged vegetation only at high waterfowl densities, at very low vegetation densities, or in the colonisation phase of the vegetation. 3. Further, we conclude that in shallow temperate eutrophic lakes, a naturally occurring mixed fish assemblage rarely reduces submerged vegetation. Unless the vegetation is very sparse, the risk of severe reduction of submerged vegetation as a result of waterfowl or fish grazing, should thereby be low. 4. Even relatively low densities of fish seem to reduce macroinvertebrate biomass, while a mixed waterfowl assemblage rarely has a significant effect on macroinvertebrate biomass.

Creation of digital terrain models using an adaptive lidar vegetation point removal process

Abstract: Commercial small-footprint lidar remote sensing has become an established tool for the creation of digital terrain models (DTMs). Unfortunately, even after the application of lidar vegetation point removal algorithms, vertical DTM error is not uniform and varies according to land cover. This paper presents the results of the application of an adaptive lidar vegetation removal process to a raw lidar dataset of a small area in North Carolina. This process utilized an existing lidar vegetation point removal algorithm in which the parameters were adaptively adjusted based on a vegetation map. The vegetation map was derived through the exclusive use of the lidar dataset, making the process independent of ancillary data. The vertical error and surface form of the resulting DTM were then compared to DTMs created using traditional techniques. The results indicate that the adaptive method produces a superior DTM.

Aerial photography for assessing vegetation change: a review of applications and the relevance of findings for Australian vegetation history

Abstract: Studies attempting to calibrate vegetation attributes from aerial photography with field data are reviewed in detail. It is concluded that aerial photography has considerable advantages over satellite-based data because of its capacity to assess the vertical dimension of vegetation and the longer time period the record spans. Limitations of using the aerial photo record as digital data include standardising image contrast and rectification. Some of these problems can be circumvented by manual techniques, but problems of crown exaggeration that varies with photo scale and variation in contrast between the textures of tree crowns and the ground remain. Applications of aerial photography for assessing vegetation change are also reviewed and include deforestation, reforestation, changes in vegetation boundaries, tree density, community composition and crown dieback. These changes have been assessed at scales ranging from individual tree crowns to regional landscapes. In Australia, aerial photography has provided a clear demonstration of deforestation rates and the expansion and contraction of forest and woodland, which is generally attributed to changes in grazing and fire regimes. It is suggested that manual techniques with point-based sampling, digital processing of data for complete spatial coverages and the application of photogrammetric measurements with stereo-plotters are all techniques with great promise for utilising this underrated medium for assessment of vegetation dynamics.

Predicting vegetation-related failure rates for overhead distribution feeders

Abstract: Faults on the electric power distribution system are responsible for a large portion of the interruptions that a customer will experience. To maintain a high level of system reliability, vegetation maintenance is often required. Analytical prediction of the effects of vegetation maintenance on distribution system reliability requires a model of the expected failure rate of line sections that includes the effects of vegetation. Vegetation-related failures are more likely to occur as the vegetation near the overhead power lines grows, increasing the line-section failure rate. Due to difficulties in using existing growth models, this paper proposes to use a direct model for failure-rate prediction based on factors that affect vegetation growth. Four models are considered: linear regression, exponential regression, linear multivariable regression, and an artificial neural network (ANN). The models are tested with historical vegetation growth parameter data and feeder failure rates. Results are compared and the features of each model are discussed.

Vegetation and ecological characteristics of mixed-conifer and red fir forests at the Teakettle Experimental Forest

Abstract: References Anonymous. 1970. Recommendations for an international standard for a mapping method in bird census work.