Desertification

Mainguet, Monique

doi:10.1007/978-3-642-86184-0

Cited by 63 publications

(1 citation statement)

References 33 publications

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“…But domical hills are by no means restricted to such lithological settings, for they are well developed also in arenaceous, rudaceous and carbonate sediments. as well as ancient volcanic rocks (Mainguet, 1972;Sweeting, 1973;Twidale and Bourne, 1978 ;Jennings, 1985;Campbell and Twidale, 1991). Epigene forms at least as old as Cretaceous have been identified (e.g .…”

Section: Characteristicsmentioning

confidence: 99%

Granitic bornhardts: their morphology, characteristics and origins

Twidale¹

1998

BGSM

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Bornhardts are bald domical hills either standing in isolation as inselbergs ("island mountains"), or forming components of massifs. Though especially well represented in granitic terrains, they are also developed in other lithologies. Their plan form is determined by systems of steeply inclined fractures, while their profiles are associated with convex upward fractures. They meet the adjacent plains or valleys in a piedmont angle or nick. They are climatically azonal. They occur in various topographic settings and consistently in multi cyclic landscapes. Epigene forms as old as Cretaceous are known, and exhumed forms ranging from Late Pleistocene to late Archaean in age have been recognised.Bornhardts have been explained in various ways: as literal and littoral inselbergs, as climatic (savannah) forms, as minor horsts, and so on. Some are upstanding because they are shaped in rock that is compositionally different from, and implicitly more resistant to, weathering and erosion than that which underlies the adjacent plains and valleys. Some are exposed stocks. Such explanations have local validity, but two hypotheses have been suggested as general explanations.First, bornhardt inselbergs can be construed as remnants of circumdenudation following scarp retreat but much field evidence is not accounted for and some is incompatible with several of the deducible consequences ofthe hypothesis. Second, bornhardts have been interpreted as two-stage forms, which originated at the weathering front as resistant masses due either to low fracture density or to rock type, and which became landforms as a result of the stripping of the regolith and exposure of weathering front topography. This two-stage model satisfies much of the field evidence and the isolated residuals of shield inselberg landscapes are the last remnants of resistant compartments which have survived long-continued subsurface weathering. According to this hypothesis, topography is consequent upon, and subsequent to, the formation of sheet fractures which are associated with compressional stress. Nubbins (blockand boulder-strewn domes) and castle koppies (small blocky hills) are derived from the weathering of bornhardts.

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Section: Characteristicsmentioning

confidence: 99%

Granitic bornhardts: their morphology, characteristics and origins

Twidale¹

1998

BGSM

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Land degradation processes in Portugal: farmers' perceptions of the application of European agroforestry programmes

et al. 2002

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This paper examines the effectiveness of European Union (EU) agroforestry programmes in reversing land degradation processes in the Mação region of central Portugal. Since the 1980s, the region has experienced severe forest fires, which have had serious consequences for the local ecosystem in terms of land degradation processes and changes in the hydrological cycle.In an attempt to reverse this situation, agroforestry programmes and aid schemes have been introduced to improve land management practices and increase the forest area and stabilize soil. However, evaluations of the environmental, economic and social impacts of these schemes have been limited. This paper considers the effectiveness of agroforestry programmes from the perspectives of farmers in the area, as revealed by a detailed survey of land users' perceptions of these measures. The paper also reflects on the implications for current and future policy. The results suggest that present assistance regimes may be insufficient to ensure adequate forest management in the future. A new approach to forest management is proposed involving greater cooperation among local farmers, diversification of species in new afforestation and the establishment of demonstration projects.

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Effects of soil degradation and management practices on the surface water dynamics in the Talgua River Watershed in Honduras

et al. 2004

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When tropical forests are felled, subsequent land uses affect surface runoff, soil erosion, and soil compaction. In some cases, they can markedly change the hydrology of a region with disastrous effects on human life. The objective of this paper is to investigate the effect of rainfall on stream hydrology due to conversion of primary forests to agriculture. Near surface water dynamics were compared for three land uses on the steep hillsides in the Talgua River Watershed in Honduras: degraded grasscovered field; traditional coffee plantation; and primary forest. Infiltration and surface runoff rates were measured using several methods. A clear difference was observed in hydraulic conductivity between the degraded and non-degraded lands. The degraded grass-covered hillslopes developed a surface restrictive layer with a low saturated hydraulic conductivity of 8 to 11 mm/hr, resulting in more frequent overland flow than traditional coffee plantation and primary forest. Soils under the latter two land-use types maintained high infiltration capacities and readily conducted water vertically at rates of 109 and 840 mm/hr, respectively. Dye tests confirmed that the coffee plantation and primary forest both maintained well-connected macropores through which water flowed readily. In contrast, macropores in the degraded soil profile were filled by fine soil particles. Soils in the degraded grass-covered field also showed more compaction than soils in the coffee plantation.

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Desertification

Cited by 63 publications

References 33 publications

Granitic bornhardts: their morphology, characteristics and origins

Granitic bornhardts: their morphology, characteristics and origins

Land degradation processes in Portugal: farmers' perceptions of the application of European agroforestry programmes

Effects of soil degradation and management practices on the surface water dynamics in the Talgua River Watershed in Honduras

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