Showing papers in "Progress in Physical Geography in 1995"
TL;DR: Predictive vegetation mapping as discussed by the authors is defined as predicting the geographic distribution of the vegetation composition across a landscape from mapped environmental variables, which is made possible by the availability of digital maps of topography and other environmental variables such as soils, geology and climate variables.
Abstract: Predictive vegetation mapping can be defined as predicting the geographic distribution of the vegetation composition across a landscape from mapped environmental variables. Comput erized predictive vegetation mapping is made possible by the availability of digital maps of topography and other environmental variables such as soils, geology and climate variables, and geographic information system software for manipulating these data. Especially important to predictive vegetation mapping are interpolated climatic variables related to physiological tolerances, and topographic variables, derived from digital elevation grids, related to site energy and moisture balance. Predictive vegetation mapping is founded in ecological niche theory and gradient analysis, and driven by the need to map vegetation patterns over large areas for resource conservation planning, and to predict the effects of environmental change on vegetation distributions. Predictive vegetation mapping has advanced over the past two decades espe...
912 citations
TL;DR: In this article, it was shown that stream capture may be a relatively rare event in long-term drainage evolution, and uncertainties with interpretations of supposed elbows of capture, mean that it should not be routinely invoked in interpretations of long term drainage evolution.
Abstract: Drainage rearrangement, involving stream piracy (capture), drainage diversion and/or beheading, may be significant for sediment budgets (including sediment provenance) and biotic distributions, as well as for its more usually considered role in landscape evolution. The processes involved in drainage rearrangement are not as self-evident as its abundant literature indicates. This is especially the case with the commonly invoked stream capture. The key process in stream capture, namely, drainage head retreat, is difficult to envisage as a normal part of drainage net evolution, especially in the light of recent findings on drainage hollow evolution. Stream capture may therefore be a relatively rare event in drainage net evolution. This, and uncertainties with interpretations of supposed elbows of capture, mean that stream capture should not be routinely invoked in interpretations of long-term drainage evolution. Further uncertainties associated with the maintenance of drainage lines during the erosion of sig...
357 citations
TL;DR: In this paper, the authors describe the factors controlling the generation and propagation of what they term sediment slugs, which can be defined as bodies of clastic material associated with disequilibrium conditions in fluvial systems over time periods above the event scale.
Abstract: Variations in fluvial sediment transport rates and storage volumes have been described previously as sediment waves or pulses. These features have been identified over a wide range of temporal and spatial scales and have been categorized using existing bedform classifications. Here we describe the factors controlling the generation and propagation of what we term sediment slugs. These can be defined as bodies of clastic material associated with disequilibrium conditions in fluvial systems over time periods above the event scale. Slugs range in magnitude from unit bars (Smith, 1974) up to sedimentary features generated by basin-scale sediment supply disturbances (Trimble, 1981). At lower slug magnitudes, perturbations in sediment transport are generated by local riverbank and/or bed erosion. Larger-scale features result from the occurrence of rare high- magnitude geomorphic events, and the impacts on water and sediment production of tectonics, glaciation, climate change and anthropogenic influences. Simple sediment routing functions are presented which may be used to describe the propagation of sediment slugs in fluvial systems. Attention is drawn to components of the fluvial system where future research is urgently required to improve our quantitative understanding of drainage-basin sediment dynamics.
177 citations
TL;DR: Variations in glacier horizontal and vertical motion occur at a variety of intra-annual timescales: monthly, daily and even hourly as mentioned in this paper, and these variations have been identified from measurements made both made both on the ground and in the air.
Abstract: Variations in glacier horizontal and vertical motion occur at a variety of intra-annual timescales: monthly, daily and even hourly. These variations have been identified from measurements made both...
125 citations
TL;DR: In this article, it is suggested that both subglacial deposition and erosion are produced by a number of processes at the 1) icesheet/subglacial deforming layer interface; 2) within the sub-glacial layer; and 3) at the base of the deformation layer.
Abstract: There is an inter-relationship among subglacial deformation, deposition and erosion associated with a glacier moving over a deformable bed. It is suggested that both subglacial deposition and erosion are produced by a number of processes at the 1) icesheet/subglacial deforming layer interface; 2) within the subglacial deforming layer; and 3) at the base of the deforming layer. These processes may result in two styles of net subglacial deforming bed deposition: 1) constructional deformation where the deforming layer moves upwards through the sequence; or 2) excavational deformation where the deforming layer moves down through the sequence. It is suggested that the best evidence for net subglacial deforming bed erosional conditions are drumlins. Changes in subglacial hydrology are also discussed, and the relationship of eskers and tunnel valleys to deforming bed conditions. Sedimentary techniques to identify homogeneous deforming bed tills in the field are also suggested. Criteria include a wide range of fa...
124 citations
TL;DR: The clearance, cultivation and abandonment of tropical forest lands has resulted in a rapid increase in the area of tropical secondary forests as discussed by the authors. Despite their growing extent, however, these forests...
Abstract: The clearance, cultivation and abandonment of tropical forest lands has resulted in a rapid increase in the area of tropical secondary forests. Despite their growing extent, however, these forests ...
91 citations
TL;DR: In this article, the authors present a survey of field-based and plot-based methods of measuring soil erosion and their suitability for use in farmers' fields, as well as some comments on the technique most widely used to measure erosion experimental plots.
Abstract: A recently published study (Evans, 1993a) gave the extent, frequency and rates of rill erosion in farmers’ fields in 17 localities in England and Wales. The amounts eroded were assessed volumetrically (in m3) by estimating how much soil was removed from rills or was deposited in fans. Such a study raises the question: Can such field-based measures be related to other direct measures of erosion? Direct measures of erosion are those which measure the transport of soil between points either as, more commonly, the mass or weight of soil, or as a volume. Here, brief reference is made to ways of directly measuring soil erosion and their suitability for use in farmers’ fields. Some comments are made on the technique most widely used to measure erosion experimental plots. Measurements of erosion made in farmers’ fields are then described and the results from plot-based experiments are compared with them.
83 citations
TL;DR: In this paper, the authors discuss the application of landscape ecological principles to a specific and pressing issue: nature reserve design and functioning, and outline and review five landscape ecological themes with relevance to reserve design, including reserve distribution, reserve shape, landscape corridor design, boundary dynamics and reserve functioning.
Abstract: The growing recognition that spatial scale and heterogeneity affect ecological processes has focused heightened attention over the last decade on principles from the field of landscape ecology. Landscape ecologists, drawing on principles from a diverse array of disciplines and fields, including physical and human geography, focus explicitly on the interrelation between landscape structure (i.e., pattern) and landscape function (i.e., processes). In this article, I discuss the application of landscape ecological principles to a specific and pressing issue: nature reserve design and functioning. To do so, I outline and review five landscape ecological themes with relevance to reserve design and management: reserve distribution, reserve shape, landscape corridor design and functioning, boundary dynamics, and reserve functioning. I particularly stress: 1) the role that landscape ecological theories may have in integrating existing principles from applied biogeography and population biology, and 2) the unique ...
72 citations
51 citations
TL;DR: In this paper, the development of topographic relief demonstrates the principle that landscape evolution may be characterized by both self-organization and non-self-organizing (soil landscape evolution) geomorphic systems.
Abstract: Self-organization is common in earth surface systems, and related principles have been proposed as general principles applicable to geomorphic systems. Non-self-organizing behaviour is also observed in geomorphic systems, however. If a reasonable box-and-arrow diagram and associated qualitative interaction matrix can be devised for a geomorphic system, one can determine whether or not (or under what conditions) the system is self-organizing. Both self- organizing (at-a-station hydraulic geometry) and non-self-organizing (soil landscape evolution) geomorphic systems are illustrated. The development of topographic relief demonstrates the principle that landscape evolution may be characterized by both modes at different times or under different circumstances. Increasing relief, involving a mean divergence of elevations, may be self- organizing. Topographic development by decreasing relief, where elevations generally converge, is always non-self-organizing. Self-organization in geomorphology may be similar to...
48 citations
TL;DR: A review of the study and geomorphology of Australia's fluvial systems by offering comment on the development, concerns and future of the subject is provided in this article, where the authors highlight the importance of long-term landscape evolution, thresholds and riverin...
Abstract: This article provides a review of the study and geomorphology of Australia's fluvial systems by offering comment on the development, concerns and future of the subject. Trends in the history of fluvial landform studies in Australia are traced from the observations and comments of the early explorers and visiting scientists through to the emergence and growth of fluvial geomorphology as a study discipline. Subsequent development of the idea of a distinctive geomorphology of Australian fluvial systems that often contrast with Anglo-American observations is outlined and illustrated with particular reference to fluvial studies in south-east Australia. Key features of the Australian setting include low long-term denudation rates, the absence of extensive Quaternary glaciation and the predominance of low gradient fluvial systems over much of the continent. Some of the most important themes in contemporary Australian fluvial research are discussed and include long-term landscape evolution, thresholds and riverin...
TL;DR: In this paper, a spatially coherent pattern of high-latitude temperature trends could be an early indicator of climatic change in the polar regions of the United States, and the sensitivity of sea ice to the overlying air implies that observed trends in Arctic ice conditions may also indicate general climatic changes.
Abstract: Climatologists have been concerned for some time about the possible climatic ramifications of increased atmospheric concentrations o f anthropogenically produced greenhouse gases. Many general circulation model experiments show amplified warming in the polar regions as t h e strongest response to enhanced atmospheric greenhouse g as concentrations. In light of this, there has been speculation that a spatially coherent pattern of high-latitude temperature trends could be an early indicator of climatic change. The sensitivity of sea ice to the t em perature of the overlying air implies that observed trends in Arctic ice conditions may also indicate general climatic changes. For example, changes in t h e global average temperature might be detectable by observing variations i n sea ice extent. Extent, then, is one common climatic indicator obtainable from sea ice. Other indicators include ice type, concentration, thickness, and dynamics. These are shown to have distinct regional and spatial distributions within the Arctic. The advent of satellite remote sensing has offered intriguing opportunities to investigate, in good spatial and temporal detail, even the most r e m o t e or rarely visited areas of the earth's surface. The large extent of sea ice i n polar regions, the difficulty and expense of access, and the normally adverse weather conditions make satellite data almost indispensable f or studies requiring global or large-scale ice cover characteristics in these regions. Remote sensing in the microwave portion of the electromagnetic spectrum is particularly relevant for polar applications because
TL;DR: In this article, the use of passive microwave-derived estimates of snow cover extent and water equivalent for continental and regional-scale mapping is illustrated. And the question of the most suitable indices of changes in snow cover conditions, in terms of their use for change detection and for monitoring applications is discussed.
Abstract: The extent, and variability of seasonal snow cover are important parameters in the climate system. Changes in snow cover may provide an indicator of global climatic trends and are of considerable practical significance. The question of the most suitable indices of changes in snow cover conditions, in terms of their use for change detection and for monitoring applications, is discussed. The use of passive microwave-derived estimates of snow cover extent and water equivalent for continental and regional-scale mapping is illustrated. Problems in interpreting the microwave signatures, as well as difficulties in comparing such data to ground observations, are also noted.Up to now analyses have focused primarily on trends in Northern Hemisphere snow extent based on monthly averages using the NOAA weekly snow charts 1972-present, or on station data spanning 50-100 years. However, the latter are generally less readily available, or accessible. An overview is provided of current information on recent hemispheric t...
TL;DR: In this paper, the authors evaluated the ability of the models used to simulate current climate system and concluded that the models were not suitable for the current state of the art in climate system modeling.
Abstract: Climate system modelling has been used extensively to investigate the role of human activities in causing global change. Model evaluation assesses the ability of the models used to simulate current...
TL;DR: The environmental impact of biotechnology involves their influences on the fundamental processes of energy flows and bio- geochemical cycles, which are emanating from such diverse activities as agriculture, resource recovery, pollution abatement and the production of renewable energy resources.
Abstract: Many factors influence environmental quality and contribute to environmental change, not least of which are science and technology. Biotechnology, involving the harnessing of living organisms or components of organisms, is a case in point. Although it has been in use for many thousands of years in a limited context, e.g., fermenting and brewing, the developments in biotechnology which have occurred in the last 20 years are beginning to have a substantial impact on the environment. At present this impact concerns the manipulation of nontransgenic organisms but in the near future it will increasingly be related to the impact of transgenic organisms produced via genetic engineering. This article examines these impacts, both real and potential, which are emanating from such diverse activities as agriculture, resource recovery, pollution abatement and the production of renewable energy resources. The environmental impact of nearly all these applications involves their influences on the fundamental processes of...
TL;DR: In this paper, the authors examined the alternative impact of atmospheric acrosols on global climate in terms of the so-called dust-veil effect, which is associated with global cooling.
Abstract: Climate change has received considerable media attention in recent years, particularly in terms of the enhanced greenhouse effect and predicted global warming. This paper examines the alternative impact of atmospheric acrosols on global climate in terms of the so-called dust-veil effect, which is associated with global cooling. This volcanic signal is assessed through the application of dust-rating and explosivity indices, and their limitations are emphasized since both schemes ignore the more important sulphur-gas emissions. The paper discusses the causes and evidence of the volcanic signal and emphasizes its moderation by El Nino events. It concludes with a brief analysis of the contributions made by particulate matter released into the lower troposphere from human activities.
TL;DR: For almost half a century it was widely believed that the photochemistry of the stratosphere and hence ozone distribution were well understoood as discussed by the authors, but as observations revealed a gap between observed and observed and...
Abstract: For almost half a century it was widely believed that the photochemistry of the stratosphere and hence ozone distribution were well understoood. As observations revealed a gap between observed and ...
TL;DR: The Value of the Weather was first published by Maunder and Maunder as mentioned in this paper, who pointed out that it was rare for meteorologists to meet up with and talk to economists, sociologists and planners, and noted that the non-scientific aspects of the weather are still neglected by many climatologists.
Abstract: When the Value of the weather was published (Maunder, 1970), the author commented that it was rare for meteorologists to meet up with and talk to economists, sociologists and planners. By the time of the 1986 successor volume (Maunder, 1986) it was noted in the preface that the ’... non-scientific aspects [of the weather] are still neglected by many climatologists ... and the economic, social, political, planning and legal aspects still need to be very much emphasised’. (p. xxiii) Since then there have been signs of a major change. The socioeconomic impacts of greenhouse warming are regularly considered in texts on environmental issues in international relations (e.g., Thomas, 1992). Cynics might even observe that climatology seems to have become too important to leave to the climatologist
TL;DR: In this article, a review of the role of methane in the climate system is presented, with a brief discussion of biological, chemical, and physical processes responsible for the spatial and temporal distribution of atmospheric methane.
Abstract: Methane is a greenhouse gas of largely biological origin. Micro-organisms responsible for production of much of the atmospheric methane are directly affected by climate resulting in potential feedbacks between the atmosphere and the biosphere. Our current understanding of the role of methane in the climate system is reviewed in this article, with a brief discussion of biological, chemical, and physical processes responsible for the spatial and temporal distribution of atmospheric methane. The magnitude of most methane sources is highly speculative, and their distributions are qualitatively understood. Most terrestrial source regions have been surveyed, but few have been studied in much detail. The strength of enteric sources is based on laboratory measurements of emissions from a few animals and estimates of global populations. Accuracy of the resulting flux size and distribution is highly suspect. Data available on either magnitude or distribution of non-biogenic methane sources are scarce. Models of the influence of climate on biological methane sources are primarily regressions dependent on measures of heat and water in the environment. Process-based models derived from biological and physical principles are called for in order to address environmental conditions unlike the present.
Journal Article•
TL;DR: In this paper, E.C. Martin and J.M. Landim Dominguez focus on the geological history and evolution of lagoons and the barrier islands enclosing them.
Abstract: to neglect the cold region lagoons such as, for example, those of the lles-de-la-Madeleine or New Brunswick, on the east coast of Canada. After an introduction where coastal lagoons are defined, E.C.F. Bird describes their physical setting and their geomorphology, in relation to geological, hydrological, climatological and ecological factors. L. Martin and J.M. Landim Dominguez focus on the geological history and evolution of lagoons and the barrier islands enclosing lagoons. N.P. Smith presents a water,
TL;DR: In this paper, the authors discuss the human driving forces of population and income, technology, politicaleconomic institutions and culture, while the consequences of these changes in terms of atmospheric chemistry, soils and hydrology are reviewed.
Abstract: and human settlements are discussed, while the consequences of these changes in terms of atmospheric chemistry, soils and hydrology are reviewed in Part IV. The ’human driving forces’ of population and income, technology, politicaleconomic institutions and culture are considered in Part V. Part VI has three chapters on ’issues in data and modelling’. In the last of these, the problems encountered in data acquisition and modelling are encapsulated in an example focusing on deforestation in Rond6nia, Brazil. An appendix provides a review and listing of datasets useful for the analysis of change in land use and land cover.