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Olaf Erenstein - One of the best experts on this subject based on the ideXlab platform.
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intensification or extensification factors affecting technology use in peri urban Lowlands along an agro ecological gradient in west africa
Agricultural Systems, 2006Co-Authors: Olaf ErensteinAbstract:Abstract The paper analyses whether the increased use of Lowlands in proximity to urban centres in West Africa is associated with technological intensification or extensification. Technologies are typified in terms of their orientation – land or labour saving – and market dependence for their procurement and reviews the factors driving and modifying their use in Lowlands. The factors associated with technology use are analyzed empirically using geo-referenced lowland data around four urban centers along an ecological gradient in Cote d’Ivoire and Mali. The technologies analyzed include both external inputs (fertilizer, pesticide, herbicide, improved varieties) and crop management practices (plot level bunding, rice transplanting and rice direct seeding). Results from binomial logit models highlight the prominent positive and non-linear role of proximity to urban markets for the technological intensification of Lowlands – an issue associated with factor scarcities and the transaction costs for procurement and marketing. Technology use in Lowlands is also associated with the agro-ecological gradient, lowland development and non-native lowland users. A common thread linking these variables is that they modify resource scarcity and therefore intensification incentives. Lowlands are not always as valuable as they may seem and there may be limited incentives to intensify. Instances of significant lowland cultivation and intensification in the study sites tend to be associated with specific opportunities – driven by market opportunities and modified by seasonal, institutional or development-induced relative land scarcity. Market access is therefore a necessary but not sufficient factor for the technological intensification of lowland use. There is a need for better targeting of development efforts in terms of enabling lowland intensification or extensification as appropriate.
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Determinants of lowland use close to urban markets along an agro-ecological gradient in West Africa
Agriculture Ecosystems & Environment, 2006Co-Authors: Olaf Erenstein, Andreas Oswald, Moussa MahamanAbstract:Lowlanddevelopmentefforts inWestAfrica haveamixed record.Thepaperarguesthat thisisduetotheneglect ofmarketopportunityasa driving force for lowland use and the agro-ecological gradient as an important modifier. The gradient is linked to three modifiers of lowland use: the relative value of lowland cropping with respect to other livelihood strategies; the biophysical productivity of lowland cropping; and the access rights to Lowlands. The paper applies a regression-based decomposition framework to analyze the factors affecting lowland use in West Africa. It uses community-level data from 1014 geo-referenced lowland units around four urban centers along an agro-ecological
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Drivers and Modifiers of Lowland Use in West Africa
2006Co-Authors: Olaf ErensteinAbstract:Lowland development efforts in West Africa have a mixed record. The paper posits that this is due to the neglect of: (1) market opportunity as driving force for lowland use; and (2) the wider context within which Lowlands are used as important modifier. The paper applies a regression-based decomposition framework to analyze the factors driving and modifying lowland use in West Africa. It uses community-level data from 1014 geo-referenced lowland units around four urban centers along an agro-ecological gradient in Cote d'Ivoire and Mali. Tobit models are used to explain the extent of lowland non-use (seasonal fallow), its diversity (in terms of rice and other crop cultivation) and its land use intensity (double cropping). Results highlight that proximity to urban markets is positively associated with the extent, diversity and intensity of lowland use. Lowland use is also associated with the agro-ecological gradient, lowland development and migrants. A common thread linking these variables is that they modify resource scarcity and therefore lowland use incentives. Market access is therefore a necessary but not sufficient condition for the intensification and diversification of lowland use.
Dimila Mothe - One of the best experts on this subject based on the ideXlab platform.
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taxonomic revision of the quaternary gomphotheres mammalia proboscidea gomphotheriidae from the south american Lowlands
Quaternary International, 2012Co-Authors: Dimila Mothe, Leonardo Dos Santos Avilla, Mario Alberto Cozzuol, Gisele WinckAbstract:The South American gomphotheres were previously classified in three genera and three species. Two biogeographic corridors are recognized for the dispersion of gomphotheres in South America. Cuvieronius hyodon was found mainly in the highlands and west to the Andes, and Stegomastodon platensis and Haplomastodon chimborazi were found in Lowlands. The aim of the present study is to review the taxonomy of South American lowland gomphotheres. A large sample of specimens was analyzed, which included crania, teeth and postcrania from several localities in Brazil, Ecuador, Colombia, Venezuela, Argentina, and Uruguay. A review of the diagnostic characters proposed in previous taxonomic studies of South American lowland gomphotheres found that they are variable in both reputed species if large samples are considered. There is no support for more than one South American lowland gomphothere species, and it shows a significant morphological variation in some characteristics. The name for this taxon, after a taxonomic review, must be Notiomastodon platensis (Ameghino, 1888) new combination. This reduces the number of gomphothere species in South America to two genera and species. The lowland gomphothere is closely related to Cuvieronius and Rhynchotherium, and not closely related to Stegomastodon from North America, and Sinomastodon from Asia.
Gisele Winck - One of the best experts on this subject based on the ideXlab platform.
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taxonomic revision of the quaternary gomphotheres mammalia proboscidea gomphotheriidae from the south american Lowlands
Quaternary International, 2012Co-Authors: Dimila Mothe, Leonardo Dos Santos Avilla, Mario Alberto Cozzuol, Gisele WinckAbstract:The South American gomphotheres were previously classified in three genera and three species. Two biogeographic corridors are recognized for the dispersion of gomphotheres in South America. Cuvieronius hyodon was found mainly in the highlands and west to the Andes, and Stegomastodon platensis and Haplomastodon chimborazi were found in Lowlands. The aim of the present study is to review the taxonomy of South American lowland gomphotheres. A large sample of specimens was analyzed, which included crania, teeth and postcrania from several localities in Brazil, Ecuador, Colombia, Venezuela, Argentina, and Uruguay. A review of the diagnostic characters proposed in previous taxonomic studies of South American lowland gomphotheres found that they are variable in both reputed species if large samples are considered. There is no support for more than one South American lowland gomphothere species, and it shows a significant morphological variation in some characteristics. The name for this taxon, after a taxonomic review, must be Notiomastodon platensis (Ameghino, 1888) new combination. This reduces the number of gomphothere species in South America to two genera and species. The lowland gomphothere is closely related to Cuvieronius and Rhynchotherium, and not closely related to Stegomastodon from North America, and Sinomastodon from Asia.
Herbert Frey - One of the best experts on this subject based on the ideXlab platform.
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Impact constraints on the age and origin of the Lowlands of Mars
Geophysical Research Letters, 2006Co-Authors: Herbert FreyAbstract:[1] Visible and buried impact basins, seen as “Quasi-Circular Depressions” (QCDs) in MOLA data, provide important new constraints on the age of the Martian Lowlands. The buried Lowlands are no younger than Early Noachian, at least as old as the oldest exposed (visible) surface units in the highlands. A model absolute age for these buried Lowlands is 4.04–4.11 GY (or earlier) but similar model ages for the largest lowland basins are older yet, 4.08–4.18 GY. The lowland crust both formed and became low no later than 500 million years after Mars formed, and likely even earlier. This constrains models for the origin of the fundamental crustal topographic dichotomy on Mars. Mechanisms which operated both early and quickly during the earliest history of Mars (e.g., large impacts) may be more likely than those requiring extended periods of time (i.e., endogenic models).
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Ancient Lowlands on Mars
Geophysical Research Letters, 2002Co-Authors: Herbert Frey, James H. Roark, Kelly M. Shockey, Erin Frey, S. E. H. SakimotoAbstract:[1] Mars Orbiter Laser Altimeter (MOLA) data provide compelling evidence that the martian Lowlands, below the smooth and sparsely cratered northern plains, are extremely old, far older than the plains which cover them. The evidence is in the form of a very large population of “Quasi-Circular Depressions” (QCDs), many of which are very evident in the MOLA elevation data but generally not visible in available imagery. We interpret these “invisible” QCDs to be buried impact basins. Cumulative number versus diameter curves for lowland QCDs suggests the buried lowland surface is older than the visible highland surface and that the lowland plains are a relatively thin (1–2 km) veneer overlying this much older surface. We conclude that the martian Lowlands have been low and stable for nearly all of martian history.
James W. Head - One of the best experts on this subject based on the ideXlab platform.
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Possible Ancient Oceans on Mars: Evidence from Mars Orbiter Laser Altimeter Data
Science (New York N.Y.), 1999Co-Authors: James W. Head, Harald Hiesinger, Mikhail A. Ivanov, Mikhail A. Kreslavsky, Stephen F. Pratt, Bradley J. ThomsonAbstract:High-resolution altimetric data define the detailed topography of the northern Lowlands of Mars, and a range of data is consistent with the hypothesis that a lowland-encircling geologic contact represents the ancient shoreline of a large standing body of water present in middle Mars history. The contact altitude is close to an equipotential line, the topography is smoother at all scales below the contact than above it, the volume enclosed by this contact is within the range of estimates of available water on Mars, and a series of extensive terraces parallel the contact in many places.
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oceans in the past history of mars tests for their presence using mars orbiter laser altimeter mola data
Geophysical Research Letters, 1998Co-Authors: James W. Head, Harald Hiesinger, Mikhail A. Ivanov, Mikhail A. Kreslavsky, Stephen F. Pratt, Nicole Seibert, David E Smith, Maria T ZuberAbstract:An ancient north polar ocean on Mars has been proposed (Parker et al., 1989) and we use MOLA data to test the hypothesis. Of the two proposed contacts/shorelines, the younger Contact 2 shows the closest approximation to an equipotential surface; vertical variations along this surface oc- cur in areas with post-contact-formation geological activity or suspected changes in the position of an equipotential surface (e.g., Tharsis) with time. The surface of Mars is smoother at all scales below Contact 2 than above. The volume of the re- gion below Contact 2 (-1.5 x 107 km 3) is between the mini- mum estimated total outflow channel discharge and the maxi- mum estimated megaregolith pore space. These results are con- sistent with the hypothesis that a large standing body of water occupied the northern Lowlands in the past history of Mars. gin. To account for the draped appearance, they interpreted the plains to represent sediment deposition in a sea, and suggested that the gradational unit contact represents the shoreline. In a subsequent more regional analysis, Parker et al. ( 1993) noted that the northern lowland plains comprise one-third of Mars' surface area, that most outflow channels/valley networks empty into the Lowlands, and that channel cutting does not ex- tend far into the plains, although the regional basinward topo- graphic gradient continues into the northern Lowlands. They raised the question of where the water went and favored the hypothesis that the channels represented streams that flooded the northern Lowlands to produce a standing body of water (see also Lucchitta et al., 1986; Gulick and Baker, 1989; Baker et
