GISdevelopment.net ---> Application ---> Natural Resource Management
Remotely sensed data have been utilized during most of the second half of this century (Rindfuss and Stern 1998), initially with the use of aerial photographs for military reconnaissance (since the 1940's), and subsequently (starting in the 1970's) with the use of satellite imagery for both civil and military objectives. Although some of this information has been put to use for certain social purposes such as forecast of crops, prediction of severe storms, and planning land development, remotely sensed information has not been a popular data source for social development research yet.
For many social scientists, deforestation and land-cover/use change, as well as road and building construction (development) are associated with variables such as government policies, land-tenure rules, distribution of wealth and power, market mechanisms, and social customs, "…none of which is directly reflected in the bands of the electromagnetic spectrum" (Rindfuss and Stern, 1998:2). However, remote sensing could play an important role in social science research by providing additional means of gathering contextual data, particularly in describing the biophysical context within which people live, work, and play. Additionally, remote sensing has the potential to supplement georeferenced social data by describing the characteristics of a certain area, including land-cover, soil moisture, and weather conditions.
In this context, remote sensing and GIS technology have proved to be valuable tools in the process of planning and management of natural resource, allowing the incorporation of multiple criteria for a better use of the environmental goods and services. This is particularly important in tropical developing countries, where environmental degradation has reached alarming proportions over the last decades because of the lack of planning of natural resources use and consumption. For instance, in the case of Mexico several authors have estimated different rates of deforestation for the country for the last 20 years (Repetto 1988, Castillo et al. 1989, Myers 1989, Toledo 1990, SARH 1990, Masera et al. 1992, WRI 1994, FAO 1995). Even though these studies describe different deforestation trends at national level, all of them coincide that there is much more deforestation in tropical areas, which are very rich in biodiversity, than in temperate zones.
Therefore, planning the use of land and natural resources to avoid environmental degradation in tropical mountainous areas in Mexico has become an important issue. The objective of this study consisted on developing a community-based plan for the sustainable management of natural resources in the ejido Zenzontla, a rural community located in the limits of the Sierra de Manantlan Biosphere Reserve (SMBR), a protected area located in western Mexico (Fig. 1). This community-based strategy was inscribed within the context of the Regional Sustainable Development Program (PRODERS) of the Mexican federal government, a program which defines policies and actions focused in the regional planning for a sustainable use and management of natural resources, incorporating local participation during the process.
In Mexico, like in many other developing countries, economic circumstances often create additional pressures to convert natural areas to alternative uses (Gerritsen 1998). Mexico's landscape has been modified as a result of several forces acting alone or in conjunction. These social, economical and political forces have affected the country's natural surroundings by modifying not only the traditional utilization of natural resources, but also changing people's perception of natural resources due to the application of policies aimed to increase or even change production systems (for example, the incorporation of commercial crops and livestock [primarily cattle]) into the environment (Barbier et al. 1994, Deininger and Minten 1999).
According to Barbier and Burgess (1996:204), "policies in Mexico's livestock and agricultural sectors affect deforestation by influencing the incentives to convert forest land for these economic activities, rather than maintain the forest for timber production, harvesting of non-timber products, tourism, watershed protection and other uses". These incentives include subsidies to agricultural products -fertilizers and pesticides--, price control for basic crops, and granting lands for new rural communities. Consequently, the comparative returns gained from converting forests to agriculture and livestock production is a major factor that influences the processes of deforestation and land-cover/use change in the country, even in protected areas such as the Sierra de Manantlán, a mountainous area located in western Mexico.
This mountainous area, located more specifically in the central western states of Jalisco and Colima falls within the limits of the Sierra de Manantlán Biosphere Reserve (SMBR), the most important protected area in western Mexico due to its biodiversity and resource richness. Ecologically, the watershed lies within the transition between two biogeographic provinces, the Neartic and the Neotropic. This transition results in a large array of ecosystems with an associated floral and faunal high diversity. Vegetation types may include tropical deciduous forest, tropical subdeciduos forest, oak forest, pine-oak forest, pine forest, fir forest, mountain mesophytic forest, secondary vegetation and pasture lands (Jardel 1992). The Sierra de Manantlan has 2,900 species of identified vascular plants, which represent around 35 - 40% of the vascular plants of the state of Jalisco. One example of these endemic species is the perenne ''teosintle', Zea diploperenis, a wild relative of cultivated corn. The Sierra de Manantlan also encompasses 110 species of mammals, 336 birds, 85 reptiles and amphibians, 238 insect families, and 7 orders of arachnids (SEMARNAP, 2000).
The community of Zenzontla is located in southwest Jalisco (Fig. 1) and within the limits of the SMBR. The ejido (a type of communal land property) encompasses an area of 4344 ha. Most of the ejido's lands are covered by tropical deciduous forest, which is characterized by arboreal species that lose their leaves during a long period of the year that coincides with the dry season (Vázquez et al. 1995). The importance of this type of vegetation resides not only in its richness of endemic species (both plants and animals), but also in its high diversity of medicinal plants that are utilized by the local population. Other types of vegetation found in the ejido include oak forest, pine forest and oak-pine forests, which are located in the higher lands of the ejido. The ejido also encompasses tropical sub-deciduous forest and mesophytic forests, mixed with riparian vegetation along the streams.
The economy in this area is based mostly on agriculture, livestock production and fishing, which represent up to 90% of the total income of the ejido (IMECBIO 1998). Agriculture is based mostly on seasonal corn cultivation, although some inhabitants also cultivate medicinal plants and fruit trees (i.e. papaya). This income is normally complemented by raising pigs, chicken and goats, and by fishing in the Ayuquila River (Aguilar-Guerrero et al. 1995). Besides agriculture, livestock production is still one of the most important activities in the ejido (Louette et al. 1998).
This mosaic of vegetation in Zenzontla has changed over the last 50 to 60 years. In some areas of the ejido, tropical deciduous forest has been replaced by crops, natural and introduced grass, and shrubs or secondary vegetation. Deforested areas currently used for agriculture and livestock coincide with the flattest areas of the ejido, while the steepest zones are still covered by forests.
Overgrazing, inadequate management of pastures and clearing of forests in order to increase pasturelands have been changing the landscape of the ejido Zenzontla, and thus the patterns of land-cover/use in the area. Moreover, the ejido has been experiencing changes in its traditional production systems during the last 30 years as a result of the low profitability of crops such as maize, and the environmental and climatic limitations to commercial agriculture in the area. These factors have motivated the residents to reorient their efforts towards livestock and cattle ranching (IMECBIO 1998). Currently, cultivation of maize in Zenzontla is carried out mostly in the best areas of the ejido, and the crop is being destined mostly to auto consumption rather than commerce. Pasture for livestock has been replacing forestlands and areas where maize was formerly cultivated (IMECBIO 1998).
To avoid these environmental problems, it was necessary to implement a process of Landscape Management Plan based on multiple criteria analysis that included : a) Land Use Change and Land Use Capability; b) Soil Erosion Risk and; c) Land use planning. IDRISI a Raster- based GIS and SPOT images were used for developing the Management Plan.
SPOT images from 1971 and 1993 were used for land use change estimates in Zenzontla founded that in 1971 open areas was representing 784 ha compared with 708 ha found in 1993. Apparently this information do not represents any change in land use, however, in 1971, agriculture represented only 10% and pasture land 90% and for 1993, agriculture represented 50% and pasture land 50%, affecting this increase in agriculture lands principally soil erosion process due to that main agriculture crop is maize. In addition, there was changes in geographic location of open areas, where in 1971 open areas were located in land capability classes of VI and VII (Montgomery -------- ) were moved to IV, V and VI, allowing that more steep areas could cover with forest vegetation again.
Soil erosion estimates and soil erosion risks maps were developed also using GIS and Revised Universal Soil Loss Equation ( Milward and Mersey, 1999). Erosion estimates were calculated for dry and wet season, found that for dry season, 6% of total land has soil loss large than 10 ton/ha/yr and for wet season 50% of land were found also in this category. The limit of 10 ton/ha/yr was took as soil loss tolerance limit was based in boundary recommended by Morgan (1995). This map allowed us to detect sensitive areas for soil erosion and to make prediction on change of soil loss after land use change for improve landscape planning.
Land use planning were based in two approach, one proposed by local communities based in a traditional use of land for agriculture and grazing and a second approach based technical criteria for a sustainable management and conservation of natural resources (Fig. 2). Technical map were obtained overlaying with a GIS layer of soil, capability classes, vegetation, soil erosion risk, slope and Biosphere Reserve limits classification (core and buffer zones limits). Final landscape map will be done when technician and local communities trough participatory approach define the limits and the use of land over the territory of Zenzontla, process who is actually running. However, it is possible to see in both maps that in general there are similarity on both approaches that would facilitate the acceptance for both instances. Three classes were obtained for these land use planning, Zone for irrigation (actual and potential), Zone for agriculture and grazing for non-irrigated areas, and Zone for conservation, that include forest and riparian zones protection (Table 1).
Discussion
These are critical issues, particularly for areas such as Zenzontla, which is located in a zone with a high biological diversity, and that has been considered as a critical area for the conservation of endemic and threatened species of birds (Contreras-Martínez 1999). The ejido also encompasses a fair amount of tropical deciduous forest, a threatened type of vegetation at global level. Therefore, it is necessary to develop an appropriate way to utilize the resources in the area, in order to decrease deforestation and changes in the use of land. This approach should integrate not only the need for protecting critical areas of Zenzontla, but also the needs of local residents, who have expressed their wish to clear more forested areas to establish pasturelands for cattle grazing. This might aggravate the situation since the ejido could loose more forests and face severe environmental damage (i.e. soils) over the next few years.
GIS and remote sensing played and important role defining the more adequate land use planning, accounting temporal and spatial analysis that would be difficult to do without this important tool. However, it is important to say that this geographic tools for natural resources management are still expensive for communities in developing countries and it is necessary to develop GIS software and strategies to increase its use for participatory decision planning process in developing countries.
Figure 1. Location of the Ejido Zenzontla and the Sierra de Manantlán Biosphere Reserve.
Figure 2. Proposals of land use by Zenzontla residents (left) and researchers (rigth).
Table 1. Actual and proposed zonification using technical approach
A GIS- based approach for participatory decision making in Mexico: a case study in the Sierra De Manantlan biosphere reserve
Oscar G. Cardenas-Hernandez and Luis M. Martinez Rivera
Instituto Manantlan de Ecología y Conservación de la Biodiversidad
Universidad de Guadalajara
Independencia Nacional # 151
Autlan, Jal. 48900, Mexico
Oscar G. Cardenas-Hernandez and Luis M. Martinez Rivera
Instituto Manantlan de Ecología y Conservación de la Biodiversidad
Universidad de Guadalajara
Independencia Nacional # 151
Autlan, Jal. 48900, Mexico
Remotely sensed data have been utilized during most of the second half of this century (Rindfuss and Stern 1998), initially with the use of aerial photographs for military reconnaissance (since the 1940's), and subsequently (starting in the 1970's) with the use of satellite imagery for both civil and military objectives. Although some of this information has been put to use for certain social purposes such as forecast of crops, prediction of severe storms, and planning land development, remotely sensed information has not been a popular data source for social development research yet.
For many social scientists, deforestation and land-cover/use change, as well as road and building construction (development) are associated with variables such as government policies, land-tenure rules, distribution of wealth and power, market mechanisms, and social customs, "…none of which is directly reflected in the bands of the electromagnetic spectrum" (Rindfuss and Stern, 1998:2). However, remote sensing could play an important role in social science research by providing additional means of gathering contextual data, particularly in describing the biophysical context within which people live, work, and play. Additionally, remote sensing has the potential to supplement georeferenced social data by describing the characteristics of a certain area, including land-cover, soil moisture, and weather conditions.
In this context, remote sensing and GIS technology have proved to be valuable tools in the process of planning and management of natural resource, allowing the incorporation of multiple criteria for a better use of the environmental goods and services. This is particularly important in tropical developing countries, where environmental degradation has reached alarming proportions over the last decades because of the lack of planning of natural resources use and consumption. For instance, in the case of Mexico several authors have estimated different rates of deforestation for the country for the last 20 years (Repetto 1988, Castillo et al. 1989, Myers 1989, Toledo 1990, SARH 1990, Masera et al. 1992, WRI 1994, FAO 1995). Even though these studies describe different deforestation trends at national level, all of them coincide that there is much more deforestation in tropical areas, which are very rich in biodiversity, than in temperate zones.
Therefore, planning the use of land and natural resources to avoid environmental degradation in tropical mountainous areas in Mexico has become an important issue. The objective of this study consisted on developing a community-based plan for the sustainable management of natural resources in the ejido Zenzontla, a rural community located in the limits of the Sierra de Manantlan Biosphere Reserve (SMBR), a protected area located in western Mexico (Fig. 1). This community-based strategy was inscribed within the context of the Regional Sustainable Development Program (PRODERS) of the Mexican federal government, a program which defines policies and actions focused in the regional planning for a sustainable use and management of natural resources, incorporating local participation during the process.
In Mexico, like in many other developing countries, economic circumstances often create additional pressures to convert natural areas to alternative uses (Gerritsen 1998). Mexico's landscape has been modified as a result of several forces acting alone or in conjunction. These social, economical and political forces have affected the country's natural surroundings by modifying not only the traditional utilization of natural resources, but also changing people's perception of natural resources due to the application of policies aimed to increase or even change production systems (for example, the incorporation of commercial crops and livestock [primarily cattle]) into the environment (Barbier et al. 1994, Deininger and Minten 1999).
According to Barbier and Burgess (1996:204), "policies in Mexico's livestock and agricultural sectors affect deforestation by influencing the incentives to convert forest land for these economic activities, rather than maintain the forest for timber production, harvesting of non-timber products, tourism, watershed protection and other uses". These incentives include subsidies to agricultural products -fertilizers and pesticides--, price control for basic crops, and granting lands for new rural communities. Consequently, the comparative returns gained from converting forests to agriculture and livestock production is a major factor that influences the processes of deforestation and land-cover/use change in the country, even in protected areas such as the Sierra de Manantlán, a mountainous area located in western Mexico.
This mountainous area, located more specifically in the central western states of Jalisco and Colima falls within the limits of the Sierra de Manantlán Biosphere Reserve (SMBR), the most important protected area in western Mexico due to its biodiversity and resource richness. Ecologically, the watershed lies within the transition between two biogeographic provinces, the Neartic and the Neotropic. This transition results in a large array of ecosystems with an associated floral and faunal high diversity. Vegetation types may include tropical deciduous forest, tropical subdeciduos forest, oak forest, pine-oak forest, pine forest, fir forest, mountain mesophytic forest, secondary vegetation and pasture lands (Jardel 1992). The Sierra de Manantlan has 2,900 species of identified vascular plants, which represent around 35 - 40% of the vascular plants of the state of Jalisco. One example of these endemic species is the perenne ''teosintle', Zea diploperenis, a wild relative of cultivated corn. The Sierra de Manantlan also encompasses 110 species of mammals, 336 birds, 85 reptiles and amphibians, 238 insect families, and 7 orders of arachnids (SEMARNAP, 2000).
The community of Zenzontla is located in southwest Jalisco (Fig. 1) and within the limits of the SMBR. The ejido (a type of communal land property) encompasses an area of 4344 ha. Most of the ejido's lands are covered by tropical deciduous forest, which is characterized by arboreal species that lose their leaves during a long period of the year that coincides with the dry season (Vázquez et al. 1995). The importance of this type of vegetation resides not only in its richness of endemic species (both plants and animals), but also in its high diversity of medicinal plants that are utilized by the local population. Other types of vegetation found in the ejido include oak forest, pine forest and oak-pine forests, which are located in the higher lands of the ejido. The ejido also encompasses tropical sub-deciduous forest and mesophytic forests, mixed with riparian vegetation along the streams.
The economy in this area is based mostly on agriculture, livestock production and fishing, which represent up to 90% of the total income of the ejido (IMECBIO 1998). Agriculture is based mostly on seasonal corn cultivation, although some inhabitants also cultivate medicinal plants and fruit trees (i.e. papaya). This income is normally complemented by raising pigs, chicken and goats, and by fishing in the Ayuquila River (Aguilar-Guerrero et al. 1995). Besides agriculture, livestock production is still one of the most important activities in the ejido (Louette et al. 1998).
This mosaic of vegetation in Zenzontla has changed over the last 50 to 60 years. In some areas of the ejido, tropical deciduous forest has been replaced by crops, natural and introduced grass, and shrubs or secondary vegetation. Deforested areas currently used for agriculture and livestock coincide with the flattest areas of the ejido, while the steepest zones are still covered by forests.
Overgrazing, inadequate management of pastures and clearing of forests in order to increase pasturelands have been changing the landscape of the ejido Zenzontla, and thus the patterns of land-cover/use in the area. Moreover, the ejido has been experiencing changes in its traditional production systems during the last 30 years as a result of the low profitability of crops such as maize, and the environmental and climatic limitations to commercial agriculture in the area. These factors have motivated the residents to reorient their efforts towards livestock and cattle ranching (IMECBIO 1998). Currently, cultivation of maize in Zenzontla is carried out mostly in the best areas of the ejido, and the crop is being destined mostly to auto consumption rather than commerce. Pasture for livestock has been replacing forestlands and areas where maize was formerly cultivated (IMECBIO 1998).
To avoid these environmental problems, it was necessary to implement a process of Landscape Management Plan based on multiple criteria analysis that included : a) Land Use Change and Land Use Capability; b) Soil Erosion Risk and; c) Land use planning. IDRISI a Raster- based GIS and SPOT images were used for developing the Management Plan.
SPOT images from 1971 and 1993 were used for land use change estimates in Zenzontla founded that in 1971 open areas was representing 784 ha compared with 708 ha found in 1993. Apparently this information do not represents any change in land use, however, in 1971, agriculture represented only 10% and pasture land 90% and for 1993, agriculture represented 50% and pasture land 50%, affecting this increase in agriculture lands principally soil erosion process due to that main agriculture crop is maize. In addition, there was changes in geographic location of open areas, where in 1971 open areas were located in land capability classes of VI and VII (Montgomery -------- ) were moved to IV, V and VI, allowing that more steep areas could cover with forest vegetation again.
Soil erosion estimates and soil erosion risks maps were developed also using GIS and Revised Universal Soil Loss Equation ( Milward and Mersey, 1999). Erosion estimates were calculated for dry and wet season, found that for dry season, 6% of total land has soil loss large than 10 ton/ha/yr and for wet season 50% of land were found also in this category. The limit of 10 ton/ha/yr was took as soil loss tolerance limit was based in boundary recommended by Morgan (1995). This map allowed us to detect sensitive areas for soil erosion and to make prediction on change of soil loss after land use change for improve landscape planning.
Land use planning were based in two approach, one proposed by local communities based in a traditional use of land for agriculture and grazing and a second approach based technical criteria for a sustainable management and conservation of natural resources (Fig. 2). Technical map were obtained overlaying with a GIS layer of soil, capability classes, vegetation, soil erosion risk, slope and Biosphere Reserve limits classification (core and buffer zones limits). Final landscape map will be done when technician and local communities trough participatory approach define the limits and the use of land over the territory of Zenzontla, process who is actually running. However, it is possible to see in both maps that in general there are similarity on both approaches that would facilitate the acceptance for both instances. Three classes were obtained for these land use planning, Zone for irrigation (actual and potential), Zone for agriculture and grazing for non-irrigated areas, and Zone for conservation, that include forest and riparian zones protection (Table 1).
Discussion
These are critical issues, particularly for areas such as Zenzontla, which is located in a zone with a high biological diversity, and that has been considered as a critical area for the conservation of endemic and threatened species of birds (Contreras-Martínez 1999). The ejido also encompasses a fair amount of tropical deciduous forest, a threatened type of vegetation at global level. Therefore, it is necessary to develop an appropriate way to utilize the resources in the area, in order to decrease deforestation and changes in the use of land. This approach should integrate not only the need for protecting critical areas of Zenzontla, but also the needs of local residents, who have expressed their wish to clear more forested areas to establish pasturelands for cattle grazing. This might aggravate the situation since the ejido could loose more forests and face severe environmental damage (i.e. soils) over the next few years.
GIS and remote sensing played and important role defining the more adequate land use planning, accounting temporal and spatial analysis that would be difficult to do without this important tool. However, it is important to say that this geographic tools for natural resources management are still expensive for communities in developing countries and it is necessary to develop GIS software and strategies to increase its use for participatory decision planning process in developing countries.
Figure 1. Location of the Ejido Zenzontla and the Sierra de Manantlán Biosphere Reserve.
Figure 2. Proposals of land use by Zenzontla residents (left) and researchers (rigth).
Table 1. Actual and proposed zonification using technical approach
| Zones | Actual | Proposal | ||
| Area (ha) | Percentage of total study area | Area (ha) | Percentage of total study area | |
| Irrigation zone | 15 | 0.3 % | 110 | 3 % |
| Agriculture and grazing zone | 900 | 21 % | 2,450 | 56 % |
| Conservation zone. | 3,430 | 79 % | 1,780 | 41 % |
References
- Aguilar-Guerrero, C. C., P. Gerritsen, J. J. Rosales-Adame and E. J. Jardel P. 1995. Caracterización del Ejido Zenzontla. Reporte Interno. Instituto Manantlán de Ecología y Conservación de la Biodiversidad. Universidad de Guadalajara, 9 p.
- Barbier, E. B., J. C. Burgess and C. Folke. 1994. Paradise Lost? The Ecological Economics of Biodiversity. Earthscan Publications Ltd., London. 255 p.
- Barbier, E. B. and J. C. Burgess. 1996. Economic Analysis of Deforestation in Mexico. Environment and Development Economics 1:203-239.
- Bassols .,A. 1979. Recursos Naturales de Mexico. Ed. Nuestro Tiempo. 10a. Ed..Pp.59 - 63. Mexico.
- Castillo, P. E., P. Lehtonen, M. Simula, V. Sosa and R. Escobar. 1989. Proyecciones de los Principales Indicadores Forestales de Mexico a Largo Plazo (1988-2012). SARH, Subsecretaría Forestal, Proyecto de Cooperación México-Finlandia.
- Contreras-Martínez, S. 1999. Preliminary Analysis of Endemic and Threatened Avifauna Distribution in Southern Jalisco, Mexico. Thesis. Master of Science, Conservation Biology and Sustainable Development Program, Institute for Environmental Studies, University of Wisconsin-Madison.
- Deininger, K. W. and B. Minten. 1999. Poverty, Policies, and Deforestation: The Case of Mexico. Economic Development and Cultural Change 47(2):313-344.
- Enriquez R., E. 1993. El Programa de Conservación del Suelo y Agua de la Secretaria de Agricultura y Recursos Hidráulicos. In: J.F. Ruiz F. (Editor). Manejo y Conservación del suelo y agua. Primera Reunión anual Nacional. 12 - 15 Agosto, 1992. Montecillo, Estado de México.
- FAO (Food and Agriculture Organization). 1995.. Forest Resource Assessment 1990. Global Synthesis. FAO Forestry Paper 124, Rome.
- Gerritsen, Peter. 1998. Community development, natural resource management and biodiversity conservation in the Sierra de Manantlan Biosphere, Mexico. Community Development Journal, 33 (4):314-324.
- IMECBIO. 1998. Diagnóstico Integral y Plan Comunitario de los Recursos Naturales: Ejido Zenzontla, Municipio de Tuxcacuesco, Jalisco. IMECBIO, Universidad de Guadalajara, Autlán, Jalisco, 132 p.
- SEMARNAP (2000). Programa de Manejo de la Reserva de la Biosfera Sierra de Manantlan- Mexico. Instituto Nacional de Ecología. Secretaria de Medio Ambiente, Recursos Naturales y Pesca. First edition. México. 201 p.
- Jardel P., E. 1992. Estrategia para la conservación de la Reserva de la Biosfera Sierra de Manantlán. Editorial de la Universidad de Guadalajara. Guadalajara, Jal. 315 p.
- Louette, D., L. M. Martínez R., R. D. Guevara G., J. A. Carranza M., R. G. Jiménez G., E. Casillas G., J. P. Esparza C. y P. Gerritsen. 1998. Cambio de Uso del Suelo y Actividad Ganadera en 4 Regiones de la Reserva de la Biosfera Sierra de Manantlán (1971-1998). Reporte Preliminar. Instituto Manantlán de Ecología y Conservación de la Biodiversidad, Universidad de Guadalajara. Reporte Interno, 16 p.
- Masera, O., R.M. J. Ordóñez and R. Dirzo. 1992. Carbon Emissions from Deforestation in Mexico: Current Situation and Long-term Scenarios. In Makundi, W. and J. Sathaye (eds.), Carbon emission and Sequestration in Forests: Case Studies from Seven Developing Countries: Summary. Lawrence Berkeley Laboratory Report # LBL-32665, University of California-Berkeley.
- Millward, Andrew A. and Janet E. Mersey. 1999. Adapting the RUSLE to model soil erosion potential in a mountain tropical watershed. Catena 38(2):109-129.
- Myers, N. 1989. Deforestation Rates in Tropical Forest and their Climatic Implications. Friends of the Earth, London.
- Orduño,V. 1991. Programa de Manejo de Cuencas Hidrográficas (Un enfoque forestal). In: Simposio sobre Manejo de Cuencas Hidrológicas. XXIV Congreso Nacional de la Ciencia del
Suelo. Pachuca,Hgo. 12 - 16 Noviembre.
- Repetto, R. 1988. The Forests for the Trees? Government Policies and the Misuse of Forest Resources. World Resources Institute, Washington, D. C.
- Rindfuss, R. R. and P. C. Stern. 1998. "Linking Remote Sensing and Social Science: The Need and the Challenges". In
Livermand, D., E. F. Moran, R. R. Rindfuss and P. C. Stern (Eds) People and Pixels. Linking Remote Sensing and Social Sciences. National Academy Press, pp. 1-27.
- Toledo, V. M. 1990. El Proceso de la Ganaderización y la Destrucción Biológica y Ecológica de México. In
Leff, E. (ed.), Medio Ambiente y Desarrollo en México, Vol. I, Editorial Porrúa, México.
- Vázquez G., J.A., R. Cuevas G., T. S. Cochrane, H. H. Iltis, F.J. Santana M. and L. Guzmán H. 1995. Flora de Manantlán. Universidad de Guadalajara/University of Wisconsin-Madison.
- WRI (World Resources Institute). 1994. World Resources 1994-1995. Oxford University Press, New York.