- Email: [email protected]
Ancient and modern perspectives on land degradation
Catena 65 (2006) 102 – 106 www.elsevier.com/locate/catena
Ancient and modern perspectives on land degradation Paul F. Hudson a,*, Irasema Alca´ntara-Ayala b b
a Department of Geography and the Environment, University of Texas at Austin, Austin, TX 78712-1098, USA Institute of Geography, UNAM, Department of Physical Geography, Circuito Exterior, Ciudad Universitaria, Coyoacan 04510, Mexico, D.F., Mexico
Concern over land degradation is not new, and is not solely the domain of geomorphology and soil scientists. Widespread and extensive reference to land degradation occurs throughout the world, and often has deep historical antecedents (Butzer, 1976b, 1982). There is increasing concern by a number of disciplines that land degradation has long term consequences to landscapes, and possibly society. In some cases land degradation is seen as a precursor and triggering mechanism to natural disasters, while social scientists have linked it to disruption of economic and political systems (Blaikie and Brookfield, 1987). Although the topic of land degradation is inherently interdisciplinary, because of its conceptual framework and intellectual breadth, geomorphology is an ideal discipline to address the multiple causes, management and prevention, and broader implications of land degradation. Moreover, because it strongly resonates with the general public, land degradation represents an opportunity for geomorphologists to communicate with a broad audience and make important societal contributions. Land degradation is commonly defined as a human or climatically induced process having negative consequences to the functioning of the land and related ecosystems, and suggest a long-standing perception that humans have played an unfavorable role, or had negative consequences, to landscapes. Most definitions also recognize explicit connections between distinct landscape components, such as hillslopes and floodplains (Fig. 1). Many studies on land degradation have understandably focused on hillslope processes (Clarke and Rendell, 2000; Harden and Matthews, 2000; Kirkby et al., 2002), often related to soil erosion (Cammeraat, 2004), changes in soil chemistry, or mass * Corresponding author. E-mail addresses: [email protected] (P.F. Hudson), [email protected] (I. Alca´ntara-Ayala). 0341-8162/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.catena.2005.11.003
wasting. These studies commonly relate land degradation to changes in ‘‘natural’’ vegetation, such as forest or grasslands, to urbanized or agricultural landscapes (Knox, 2001). Other directions in land degradation research examine changes related to rivers and floodplains. Such studies frequently address river channel siltation, increased flood frequency, floodplain sedimentation, or bank erosion, and commonly reference upper basin controls, such as changes in rates of soil erosion or runoff (Happ et al., 1940; Dickson et al., 1986; Trimble, 1999; Trustrum et al., 1999). Indeed, the explicit linkages between hillslopes and river channels suggest a basin scale framework is especially appropriate for examining causes and consequences of land degradation (Wolman, 1967; Coulthard et al., 2000; Conacher, 2002). Globally, land use and land cover change tends to increase and accelerate land degradation, particularly in lesser-developed countries. Many such nations suffer from soil decay, and from associated processes such as gullying, flooding, sedimentation, and landsliding. Moreover, the combination of degraded lands and global warming has increased the sensitivity of landscapes to high magnitude– low frequency events, and at a seasonal resolution to low magnitude high frequency events. In some instances these occurrences have significant social implications, which may include decreasing productivity, natural disasters, and lack of sustainable development (El-Swaify, 1997). This is particularly relevant in small indigenous communities where economies are highly dependent on subsistence agriculture. In view of the importance in applying a holistic approach to study land degradation, geomorphology is now conceptually and methodologically poised to shoulder the crucial task of understanding key linkages between ancient and modern landscapes, as well as developing frameworks for prevention, mitigation, and rehabilitation of degraded lands. Geomorphologists engaged in land degradation studies must be aware of the policy framework
P.F. Hudson, I. Alca´ntara-Ayala / Catena 65 (2006) 102 – 106
103
Fig. 1. Land degradation may be triggered by human or climatic influences, manifest in a variety of ways, and linked through geomorphic processes occurring within hillslopes or floodplains.
established by government agencies, and the geomorphic implications of each type of land use policy for specific geomorphic and climatic scenarios. Effective management of land degradation is also dependent upon comprehension of geomorphologic dimensions of global environmental change, requiring knowledge of historical, process, and applied geomorphology (Chorley, 1978; Goudie, 1991; Slaymaker, 2000). The significance of historical geomorphology is given by the reconstruction and understanding
of paleoenvironments, which are critical for discerning the possible range of landscape response to changes in controls. Process geomorphology approaches land degradation by studying landform response to mass and energy fluxes, with boundary conditions and thresholds often influenced by older paleoenvironmental controls (Fig. 2). To understand human induced land degradation an applied geomorphology perspective is appropriate because of the importance in integrating historical and process
Fig. 2. Approaches of geomorphology to land degradation.
104
P.F. Hudson, I. Alca´ntara-Ayala / Catena 65 (2006) 102 – 106
perspectives into a single framework. Humans influence the complexity of interaction among processes and landforms, and consequently increase system variability. Time and space are key elements for considering land degradation, as geomorphic, climatic, and human processes vary spatially and temporally over local and regional scales. Time also represents a crucial input parameter in the development of mathematical models, where progressive human interference negatively impacts natural systems, and therefore influences system response and sustainability. The incorporation of advanced techniques and theory to land degradation research suggests the topic continues to be of great interest to geomorphologists. Radionuclide dating procedures, such as 137 Cs and 210 Pb (Li et al., 2003; Navas et al., 2005), provide excellent temporal scales for bracketing and constraining recent land degradation, while AMS (14 C) dating continues to push back the limits of human induced land degradation, providing fresh insights on prehistoric human – environment relationships (O’Hara et al., 1993). A variety of digital geographic information techniques (e.g., GIS, RS, GPS) and improvements in field instrumentation enable monitoring of land systems at increased temporal and spatial resolutions (Mendicino, 1999; Slaymaker, 2001; Gupta et al., 2002; Fan et al., 2004). The resulting data sets, when forged with concepts related to system response provide great opportunity to address questions related to geomorphic adjustment, feedbacks, and landscape recovery (Renschler and Harbor, 2002). Such approaches enable geomorphologists to address ‘‘general’’ environmental questions of public concern, such as water quality, coastal erosion, urbanization, and agriculture (Turkelboom et al., 1999; Wang et al., 2004). The papers in this issue were presented in sessions at the Regional Geomorphology Conference (RGC) of the International Association of Geomorphologists (IAG) that took place in Mexico City, Mexico in October – November, 2003. The theme of the conference was Geomorphic Hazards: Towards the Prevention of Disasters, whereas the sessions organized by Hudson and Alca´ntara-Ayala were entitled Soil erosion and Geomorphic Features of Land Degradation. The latter was jointly organized by the RGC/IAG and the Commission on Land Degradation and Desertification (COMLAND) of the International Geographical Union (IGU). The purpose of COMLAND is to develop a practical and theoretical understanding of land degradation processes that affect the world’s landscapes (http://www.ub.es/gram/ COMLAND%20website/index.htm). COMLAND has organized meetings in a diverse array of international settings and includes scholars from a number of disciplines. The papers in this special issue represent diversity in physical setting, approaches, and temporal and spatial scale. While many studies have emphasized the influence of land use change on soil erosion, the process commonly results in a decline in soil quality, which precedes soil erosion. Such changes are particularly important to understand land degradation tropical regions (Lal, 1990),
where it is estimated the majority of the world’s population resides. Such population places considerable pressure on natural resources that can drive rapid changes in land use. Cotler et al. examine changes in soil quality and land use within a tropical deciduous forest system within mountainous western Chamela, Mexico. Using a variety of chemical and physical analyses, the authors are able to demonstrate that conversion of forest to pasture influenced soil chemistry and aggregate stability, increasing landscape sensitivity. Most land degradation studies involve a human agency. In developing countries where large rural indigenous populations practice subsistence agriculture, proper land management depends upon an understanding of how humans utilize and manipulate land, particularly soils. In many cases the local indigenous knowledge base is derived from ancient culturally specific practices. The long-held belief that such practices are environmentally friendly is no longer widely held (Butzer, 1992; O’Hara et al., 1993). Ethnopedology provides a framework for linking land managers and indigenous groups (Sillitoe, 1998; BarreraBassols and Zinck, 2003). The paper by Barrera-Bassols and Zinck utilizes an ethnopedological approach to examine correlations between indigenous soil classification with FAO classification. Such analysis offers tremendous potential for characterizing soils and agriculture in regions where there has not yet been systematic mapping, and can be integrated into broader land use policy frameworks to reduce land degradation. Land use change should be designed for particular soil and geomorphic conditions, guided by an understanding of the possible range in amount and intensity of precipitation that has historically occurred, particularly for sensitive environments such as the Mediterranean region (Renschler et al., 1999). Employing trend analysis of precipitation data spanning nearly five decades for hilly Basilicata in southern Italy, Piccarreta et al. show that land reclamation initiated by the European Union’s Common Agricultural Policy has accelerated soil erosion, manifest as rills and gullying. Such studies are useful to demonstrate the effects of land use change, but more importantly are poised to contribute to regional refinement of land use policies. In addition to soil erosion, land use change can also be the precursor to more dramatic styles of land degradation, such as the occurrence of landslides. This is particularly true for steep mountainous volcanic settings, such as the Trans Mexican Volcanic Belt in Puebla, Mexico. Alcantara-Ayala et al. examines spatial relations between deforestation and landslides within this region, which were triggered by an extreme rainfall event in 1999. Using satellite imagery and field data it was possible to identify hundreds of slope failures, principally where vegetation densities were below a threshold value. Such approaches are essential for hazard prediction and modeling, while representing an excellent example of how geomorphology is important to planners and engineers at a community level.
P.F. Hudson, I. Alca´ntara-Ayala / Catena 65 (2006) 102 – 106
Southeast of Puebla, in the humid lowland tropics of the Yucatan Peninsula, the theme of soil erosion is continued by Beach et al. The authors identify three episodes of soil erosion associated with the prehistoric Maya using a variety of techniques, including chemical and physical soil properties, archaeological materials, and radiocarbon dating. Interestingly, soil erosion was highest with low populations of pioneer farmers during the Preclassic. Soil erosion was less than expected during the apex of Maya civilization during the Late Classic. These findings suggest that soil erosion and geomorphic response is not necessarily a function of population density, but instead is very dependent on the order or sequence of landscape disturbance. As above papers emphasize, most studies of floodplain land degradation examines linkages between floodplains and basin headwaters. A minority of research has also examined direct manipulation of the floodplain surface (Butzer, 1976a; Siemens, 1983) and how it influences floodplain hydrology and soils. On this theme, the paper by Doolittle considers the geomorphic consequences of prehistoric and historic agricultural manipulations to large floodplain environments located in North America’s arid Basin and Range region. The paper considers the implications of actions such as irrigation, channel straightening, leveling, and land clearing, and serves as a reminder that modern floodplain surfaces can be partially an artifact of older human manipulations. The editors are very appreciative to the Catena editorial board and staff, particularly S. Trimble and E. Cramer. A sincere thanks to all manuscript reviewers, which includes anonymous reviewers and the following: Robert Dull (University of Texas at Austin, USA), Janet Hooke (University of Portsmouth, UK), Jonathan Philips (University of Kentucky, USA), Steven Rainey (McNeese State University, USA), Dan Royall (University of North Carolina at Greensboro, USA), David Shankman (University of Alabama, USA), Michael Slattery (Texas Christian University, U.S.), Victor Toledo (UNAM, Me´xico), and William Woods (University of Kansas, U.S.). Each paper was peer reviewed in accordance with Catena guidelines.
References Barrera-Bassols, N., Zinck, J.A., 2003. Ethnopedology: a worldwide view on the soil knowledge of local people. Geoderma 111, 171 – 195. Blaikie, P., Brookfield, H., 1987. Land Degradation and Society. Methuen and Co. Ltd., London. Butzer, K.W., 1976a. Early Hydraulic Civilization in Egypt. University of Chicago Press, Chicago. Butzer, K.W., 1976b. Geomorphology from the Earth. Harper and Row, New York. 512 pp. Butzer, K.W., 1982. Archaeology as Human Ecology. Cambridge University Press, Cambridge. Butzer, K.W., 1992. The Americas before and after 1492: an introduction to current geographical research. Annals of the Association of American Geographers 82, 345 – 368.
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Cammeraat, E.L.H., 2004. Scale dependent thresholds in hydrological and erosion response of a semi-arid catchment in southeast Spain Agriculture. Ecosystems & Environment 104, 317 – 332. Chorley, R.J., 1978. Bases for theory in geomorphology. In: Embleton, C., Brunsden, D., Jones, D.C.K. (Eds.), Geomorphology: Present Problems and Future Prospects. Oxford University Press, Oxford, pp. 1 – 13. Clarke, M.L., Rendell, H.M., 2000. The impact of the farming practice of remodelling hillslope topography on badland morphology and soil erosion processes. Catena 40, 229 – 250. Conacher, A., 2002. A role for geomorphology in integrated catchment management. Australian Geographical Studies 40, 179 – 195. Coulthard, T.J., Kirkby, M.J., Macklin, M.G., 2000. Modeling geomorphic response to environmental change in an upland catchment. Hydrological Processes 14, 2031 – 2045. Dickson, W.T., Rudra, P.P., Wall, G.J., 1986. Identification of soil erosion and fluvial sediment problems. Hydrological Processes 1, 111 – 124. El-Swaify, S.A., 1997. Factors affecting soil erosion hazards and conservation needs for tropical steeplands. Soil Technology 11, 3 – 16. Fan, J.R., Tao, H.P., Zhang, J.H., Zhong, X.H., Liu, S.Z., 2004. Monitoring of soil erosion and assessment for contribution of sediments to rivers in a typical watershed of the Upper Yangtze River Basin. Land Degradation & Development 15, 411 – 421. Goudie, A.S., 1991. Environmental Change. Clarendon Press, Oxford. Gupta, A., Ping, C., Hock, L., Xiaojing, H., 2002. Evaluation of part of the Mekong river using satellite imagery. Geomorphology 44, 221 – 239. Happ, S.C., Rittenhouse, G., Dobson, G.C., 1940. Some Principles of Accelerated Stream and Valley Sedimentation. United States Department of Agriculture, Washington D.C. Technical Bulletin No. 965. 134 pp. Harden, C.P., Matthews, L., 2000. Rainfall response of degraded soil following reforestation in the Copper Basin, Tennessee, USA. Environmental Management 26, 163 – 174. Kirkby, M., Bracken, L., Reaney, S., 2002. The influence of land use, soils and topography on the delivery of hillslope runoff to channels in SE Spain. Earth Surface Processes and Landforms 27, 1459 – 1473. Knox, J.C., 2001. Agricultural influence on landscape sensitivity in the Upper Mississippi River Valley. Catena 42, 193 – 224. Lal, R., 1990. Soil Erosion in the Tropics: Principle and Management. McGraw-Hill, New York. Li, Y., Zhang, J.H., Poesen, J., Yang, J.C., Fu, B., 2003. Evaluating gully erosion using 137Cs and 210Pb / 137Cs ratio in a reservoir catchment. Soil & Tillage Research 69, 107 – 115. Mendicino, G., 1999. Sensitivity analysis on GIS procedures for the estimate of soil erosion risk. Natural Hazards 20, 231 – 253. Navas, A., Machı´n, J., Soto, J., 2005. Assessing soil erosion in a Pyrenean mountain catchment using GIS and fallout 137Cs. Agriculture, Ecosystems & Environment 105, 493 – 506. O’Hara, S.L., Street-Perrott, F.A., Burt, T.P., 1993. Accelerated soil erosion around a Mexican lake caused by preHispanic agriculture. Nature 362, 48 – 51. Renschler, C.S., Harbor, J., 2002. Soil erosion assessment tools from point to regional scales—the role of geomorphologists in land management research and implementation. Geomorphology 47, 189 – 209. Renschler, C.S., Mannaerts, C.M., Diekkru¨ger, B., 1999. Evaluating spatial and temporal variability in soil erosion risk—rainfall erosivity and soil loss ratios in Andalusia, Spain. Catena 40, 403 – 420. Siemens, A.H., 1983. Oriented raised fields in Central Veracruz. American Antiquity 48, 85 – 102. Sillitoe, P., 1998. Knowing the land: soil and land resource evaluation and indigenous knowledge. Soil Use and Management 14, 188 – 193. Slaymaker, O., 2000. Global environmental change: the global agenda. In: Slaymaker, O. (Ed.), Geomorphology, Human Activity and Global Environmental Change. Wiley and Sons, Chichester, pp. 3 – 20. Slaymaker, O., 2001. The role of remote sensing in geomorphology and terrain analysis in the Canadian Cordillera. ITC Journal 2001, 11 – 17.
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Trimble, S.W., 1999. Decreased rates of alluvial sediment storage in the Coon Creek basin. Science 285, 1244 – 1246. Trustrum, N.A., Hicks, D.M., Gomez, B., Page, M.J., Reid, L.M., 1999. Sediment production, storage and output: the relative role of large magnitude events in steepland catchments. Zeitschrift fur Geomorphologie, Supplementband 115, 71 – 86. Turkelboom, F., Ongprasert, S., Poesen, J., Ohler, I., 1999. Reassessment of tillage erosion rates by manual tillage on steep slopes in northern Thailand. Soil & Tillage Research 51, 245 – 259.
Wang, S.-J., Liu, Q.-M., Zhang, D.-F., 2004. Karst rocky desertification in southwestern China: geomorphology, landuse, impact and rehabilitation. Land Degradation & Development 15, 115 – 121. Wolman, M.G., 1967. A cycle of sedimentation and erosion in urban river channels. Geografiska Annaler. Series A. Physical Geography 49, 385 – 395.
Ancient and modern perspectives on land degradation Paul F. Hudson a,*, Irasema Alca´ntara-Ayala b b
a Department of Geography and the Environment, University of Texas at Austin, Austin, TX 78712-1098, USA Institute of Geography, UNAM, Department of Physical Geography, Circuito Exterior, Ciudad Universitaria, Coyoacan 04510, Mexico, D.F., Mexico
Concern over land degradation is not new, and is not solely the domain of geomorphology and soil scientists. Widespread and extensive reference to land degradation occurs throughout the world, and often has deep historical antecedents (Butzer, 1976b, 1982). There is increasing concern by a number of disciplines that land degradation has long term consequences to landscapes, and possibly society. In some cases land degradation is seen as a precursor and triggering mechanism to natural disasters, while social scientists have linked it to disruption of economic and political systems (Blaikie and Brookfield, 1987). Although the topic of land degradation is inherently interdisciplinary, because of its conceptual framework and intellectual breadth, geomorphology is an ideal discipline to address the multiple causes, management and prevention, and broader implications of land degradation. Moreover, because it strongly resonates with the general public, land degradation represents an opportunity for geomorphologists to communicate with a broad audience and make important societal contributions. Land degradation is commonly defined as a human or climatically induced process having negative consequences to the functioning of the land and related ecosystems, and suggest a long-standing perception that humans have played an unfavorable role, or had negative consequences, to landscapes. Most definitions also recognize explicit connections between distinct landscape components, such as hillslopes and floodplains (Fig. 1). Many studies on land degradation have understandably focused on hillslope processes (Clarke and Rendell, 2000; Harden and Matthews, 2000; Kirkby et al., 2002), often related to soil erosion (Cammeraat, 2004), changes in soil chemistry, or mass * Corresponding author. E-mail addresses: [email protected] (P.F. Hudson), [email protected] (I. Alca´ntara-Ayala). 0341-8162/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.catena.2005.11.003
wasting. These studies commonly relate land degradation to changes in ‘‘natural’’ vegetation, such as forest or grasslands, to urbanized or agricultural landscapes (Knox, 2001). Other directions in land degradation research examine changes related to rivers and floodplains. Such studies frequently address river channel siltation, increased flood frequency, floodplain sedimentation, or bank erosion, and commonly reference upper basin controls, such as changes in rates of soil erosion or runoff (Happ et al., 1940; Dickson et al., 1986; Trimble, 1999; Trustrum et al., 1999). Indeed, the explicit linkages between hillslopes and river channels suggest a basin scale framework is especially appropriate for examining causes and consequences of land degradation (Wolman, 1967; Coulthard et al., 2000; Conacher, 2002). Globally, land use and land cover change tends to increase and accelerate land degradation, particularly in lesser-developed countries. Many such nations suffer from soil decay, and from associated processes such as gullying, flooding, sedimentation, and landsliding. Moreover, the combination of degraded lands and global warming has increased the sensitivity of landscapes to high magnitude– low frequency events, and at a seasonal resolution to low magnitude high frequency events. In some instances these occurrences have significant social implications, which may include decreasing productivity, natural disasters, and lack of sustainable development (El-Swaify, 1997). This is particularly relevant in small indigenous communities where economies are highly dependent on subsistence agriculture. In view of the importance in applying a holistic approach to study land degradation, geomorphology is now conceptually and methodologically poised to shoulder the crucial task of understanding key linkages between ancient and modern landscapes, as well as developing frameworks for prevention, mitigation, and rehabilitation of degraded lands. Geomorphologists engaged in land degradation studies must be aware of the policy framework
P.F. Hudson, I. Alca´ntara-Ayala / Catena 65 (2006) 102 – 106
103
Fig. 1. Land degradation may be triggered by human or climatic influences, manifest in a variety of ways, and linked through geomorphic processes occurring within hillslopes or floodplains.
established by government agencies, and the geomorphic implications of each type of land use policy for specific geomorphic and climatic scenarios. Effective management of land degradation is also dependent upon comprehension of geomorphologic dimensions of global environmental change, requiring knowledge of historical, process, and applied geomorphology (Chorley, 1978; Goudie, 1991; Slaymaker, 2000). The significance of historical geomorphology is given by the reconstruction and understanding
of paleoenvironments, which are critical for discerning the possible range of landscape response to changes in controls. Process geomorphology approaches land degradation by studying landform response to mass and energy fluxes, with boundary conditions and thresholds often influenced by older paleoenvironmental controls (Fig. 2). To understand human induced land degradation an applied geomorphology perspective is appropriate because of the importance in integrating historical and process
Fig. 2. Approaches of geomorphology to land degradation.
104
P.F. Hudson, I. Alca´ntara-Ayala / Catena 65 (2006) 102 – 106
perspectives into a single framework. Humans influence the complexity of interaction among processes and landforms, and consequently increase system variability. Time and space are key elements for considering land degradation, as geomorphic, climatic, and human processes vary spatially and temporally over local and regional scales. Time also represents a crucial input parameter in the development of mathematical models, where progressive human interference negatively impacts natural systems, and therefore influences system response and sustainability. The incorporation of advanced techniques and theory to land degradation research suggests the topic continues to be of great interest to geomorphologists. Radionuclide dating procedures, such as 137 Cs and 210 Pb (Li et al., 2003; Navas et al., 2005), provide excellent temporal scales for bracketing and constraining recent land degradation, while AMS (14 C) dating continues to push back the limits of human induced land degradation, providing fresh insights on prehistoric human – environment relationships (O’Hara et al., 1993). A variety of digital geographic information techniques (e.g., GIS, RS, GPS) and improvements in field instrumentation enable monitoring of land systems at increased temporal and spatial resolutions (Mendicino, 1999; Slaymaker, 2001; Gupta et al., 2002; Fan et al., 2004). The resulting data sets, when forged with concepts related to system response provide great opportunity to address questions related to geomorphic adjustment, feedbacks, and landscape recovery (Renschler and Harbor, 2002). Such approaches enable geomorphologists to address ‘‘general’’ environmental questions of public concern, such as water quality, coastal erosion, urbanization, and agriculture (Turkelboom et al., 1999; Wang et al., 2004). The papers in this issue were presented in sessions at the Regional Geomorphology Conference (RGC) of the International Association of Geomorphologists (IAG) that took place in Mexico City, Mexico in October – November, 2003. The theme of the conference was Geomorphic Hazards: Towards the Prevention of Disasters, whereas the sessions organized by Hudson and Alca´ntara-Ayala were entitled Soil erosion and Geomorphic Features of Land Degradation. The latter was jointly organized by the RGC/IAG and the Commission on Land Degradation and Desertification (COMLAND) of the International Geographical Union (IGU). The purpose of COMLAND is to develop a practical and theoretical understanding of land degradation processes that affect the world’s landscapes (http://www.ub.es/gram/ COMLAND%20website/index.htm). COMLAND has organized meetings in a diverse array of international settings and includes scholars from a number of disciplines. The papers in this special issue represent diversity in physical setting, approaches, and temporal and spatial scale. While many studies have emphasized the influence of land use change on soil erosion, the process commonly results in a decline in soil quality, which precedes soil erosion. Such changes are particularly important to understand land degradation tropical regions (Lal, 1990),
where it is estimated the majority of the world’s population resides. Such population places considerable pressure on natural resources that can drive rapid changes in land use. Cotler et al. examine changes in soil quality and land use within a tropical deciduous forest system within mountainous western Chamela, Mexico. Using a variety of chemical and physical analyses, the authors are able to demonstrate that conversion of forest to pasture influenced soil chemistry and aggregate stability, increasing landscape sensitivity. Most land degradation studies involve a human agency. In developing countries where large rural indigenous populations practice subsistence agriculture, proper land management depends upon an understanding of how humans utilize and manipulate land, particularly soils. In many cases the local indigenous knowledge base is derived from ancient culturally specific practices. The long-held belief that such practices are environmentally friendly is no longer widely held (Butzer, 1992; O’Hara et al., 1993). Ethnopedology provides a framework for linking land managers and indigenous groups (Sillitoe, 1998; BarreraBassols and Zinck, 2003). The paper by Barrera-Bassols and Zinck utilizes an ethnopedological approach to examine correlations between indigenous soil classification with FAO classification. Such analysis offers tremendous potential for characterizing soils and agriculture in regions where there has not yet been systematic mapping, and can be integrated into broader land use policy frameworks to reduce land degradation. Land use change should be designed for particular soil and geomorphic conditions, guided by an understanding of the possible range in amount and intensity of precipitation that has historically occurred, particularly for sensitive environments such as the Mediterranean region (Renschler et al., 1999). Employing trend analysis of precipitation data spanning nearly five decades for hilly Basilicata in southern Italy, Piccarreta et al. show that land reclamation initiated by the European Union’s Common Agricultural Policy has accelerated soil erosion, manifest as rills and gullying. Such studies are useful to demonstrate the effects of land use change, but more importantly are poised to contribute to regional refinement of land use policies. In addition to soil erosion, land use change can also be the precursor to more dramatic styles of land degradation, such as the occurrence of landslides. This is particularly true for steep mountainous volcanic settings, such as the Trans Mexican Volcanic Belt in Puebla, Mexico. Alcantara-Ayala et al. examines spatial relations between deforestation and landslides within this region, which were triggered by an extreme rainfall event in 1999. Using satellite imagery and field data it was possible to identify hundreds of slope failures, principally where vegetation densities were below a threshold value. Such approaches are essential for hazard prediction and modeling, while representing an excellent example of how geomorphology is important to planners and engineers at a community level.
P.F. Hudson, I. Alca´ntara-Ayala / Catena 65 (2006) 102 – 106
Southeast of Puebla, in the humid lowland tropics of the Yucatan Peninsula, the theme of soil erosion is continued by Beach et al. The authors identify three episodes of soil erosion associated with the prehistoric Maya using a variety of techniques, including chemical and physical soil properties, archaeological materials, and radiocarbon dating. Interestingly, soil erosion was highest with low populations of pioneer farmers during the Preclassic. Soil erosion was less than expected during the apex of Maya civilization during the Late Classic. These findings suggest that soil erosion and geomorphic response is not necessarily a function of population density, but instead is very dependent on the order or sequence of landscape disturbance. As above papers emphasize, most studies of floodplain land degradation examines linkages between floodplains and basin headwaters. A minority of research has also examined direct manipulation of the floodplain surface (Butzer, 1976a; Siemens, 1983) and how it influences floodplain hydrology and soils. On this theme, the paper by Doolittle considers the geomorphic consequences of prehistoric and historic agricultural manipulations to large floodplain environments located in North America’s arid Basin and Range region. The paper considers the implications of actions such as irrigation, channel straightening, leveling, and land clearing, and serves as a reminder that modern floodplain surfaces can be partially an artifact of older human manipulations. The editors are very appreciative to the Catena editorial board and staff, particularly S. Trimble and E. Cramer. A sincere thanks to all manuscript reviewers, which includes anonymous reviewers and the following: Robert Dull (University of Texas at Austin, USA), Janet Hooke (University of Portsmouth, UK), Jonathan Philips (University of Kentucky, USA), Steven Rainey (McNeese State University, USA), Dan Royall (University of North Carolina at Greensboro, USA), David Shankman (University of Alabama, USA), Michael Slattery (Texas Christian University, U.S.), Victor Toledo (UNAM, Me´xico), and William Woods (University of Kansas, U.S.). Each paper was peer reviewed in accordance with Catena guidelines.
References Barrera-Bassols, N., Zinck, J.A., 2003. Ethnopedology: a worldwide view on the soil knowledge of local people. Geoderma 111, 171 – 195. Blaikie, P., Brookfield, H., 1987. Land Degradation and Society. Methuen and Co. Ltd., London. Butzer, K.W., 1976a. Early Hydraulic Civilization in Egypt. University of Chicago Press, Chicago. Butzer, K.W., 1976b. Geomorphology from the Earth. Harper and Row, New York. 512 pp. Butzer, K.W., 1982. Archaeology as Human Ecology. Cambridge University Press, Cambridge. Butzer, K.W., 1992. The Americas before and after 1492: an introduction to current geographical research. Annals of the Association of American Geographers 82, 345 – 368.
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