A GIS- based approach for participatory decision making in Mexico: a case study in the Sierra De Manantlan biosphere reserve
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
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.