Analysis of Ecosystem Services in the Oaxacan Mixtec Region, (Tiltepec Watershed)

The term ecosystem services (ES) aroused as a result of an environmental movement in the 1970s, was promoted by conservation biologists when defining nature as a service provider, with the purpose of increasing public interest in conservation of biodiversity (Sullivan, 2009). With the creation of the organization "Millennium Ecosystem Assessment" in the 90's, interest in having tools to evaluate consequences of change in the ecosystems, establish bases and actions necessary to improve conservation and sustainable use of ecosystems and their contribution to human well-being (MEA, 2005). Despite advances and growing publications, however, there is still alack of consensus on elements that should be included in the ESconcept and its integration in decision-making of public policy on management of natural resources (De Groot et al., 2010). ESconsider all the benefits that society obtains from ecosystems (MEA, 2005), both directly and indirectly (De Groot et al., 2002), including conditions and processes through which natural ecosystems and species that make them up, sustain and nourish human life (Daily, 1997). In short, it is the relationship between ecosystems and human beings (supply-delivery and value), the latter in economic terms or non-tangible dimensions (Balvanera et al., 2012).

ESare classified as providing, regulating, cultural and support services (Balvanera and Cotler, 2011). Provision or tangible goods, are all those benefits provided by ecosystems that meet specific human needs, examples of these goods are those provided by plants (food, medicine, fiber), animals (meat, skin, workforce) and environment (water, air, soil). (WWF, 2015; De Groot et al., 2010). Regulating services refer to the natural or semi-natural capacity of ecosystems to regulate ecological processes and maintain life supports (De Groot et al., 2002). These services control and/or modify environmental parameters (Balvanera and Cotler 2011), so that the less disturbed ecosystem, regulation is performed optimally, but at a higher intensity of use these services decrease their effectiveness (De Groot et al., 2010). Cultural services are those benefits that man perceives from ecosystems (tangible or intangible) with a symbolic, cultural or intellectual value (Balvanera and Cotler, 2011). (De Groot et al., 2002) divides them into recreational and informational; the former is valued according to the accessibility of ecosystems and their value decreases with the intensity of use or degradation of them, while the latter are a function of information contained in the ecosystems and decrease with the degree of conversion. Support services are the processes and functions that characterize ecosystem, and are necessary for production of other services, and their benefits are indirect and long-term (Balvanera and Cotler, 2011).

The analysis of the ESshould take into account scales of time and space, include direct and indirect factors that influence their provision (Galán et al., 2012). Some proposed approaches to the study of ESare: diagnosis, identification, perception, assessment, and appropriation (Almeida et al., 2007; Quétier et al., 2007), socio-ecosystem analysis (biophysical, economic-productive and socio-political-cultural) (Balvanera et al., 2010) and use of cartographic tools to identify, characterize and value them (Bagstad et al., 2013a) integrating ecological, economic and geographical aspects (Bagstad et al., 2013b). The Oaxacan Mixtec culture Ñu'u Savior "People of the rain" has faced problems for food production (agricultural and livestock) due to its abrupt relief and lack of water. The inhabitants have transformed natural ecosystems through slash-and-burn systems to open cultivation and pasture areas. Their poor management has caused problems of erosion and loss of soil fertility (Spores, 1967; Lind, 2008). A harmonious relationship between man and nature is reflected in the welfare of society through ecosystem services (CONABIO, 2006). However, when an ecosystem service is affected at expense or to detriment of other services, and even at expense of the ecosystem service itself, the quality of life on present and future population is affected (Galán et al., 2012).

In the Oaxacan Mixtec area, the relationship between population and ecosystem has been one of overexploitation of natural resources, causing their deterioration or scarcity. Accelerated deforestation and overgrazing have caused soil erosion, reduction of water retention capacity, loss of fertility, shortage of firewood, scarcity of forage, reduction of water supply, among others. WWF (2015) mentions that loss of biodiversity and deterioration of vegetation cover is mainly due to hillside agriculture and overgrazing, activities that impact regulation of other services such assoil fertility, water quality, climate regulation, erosion; impacts that negatively affect agricultural production, livestock, and quantity and quality of water. WWF (2015) identified, evaluated and socially valued ES in the Mixtecan region, identifying some key provision services such as: production of food derived from agriculture and livestock, fodder, water for human consumption, use of firewood and wood. It also considered regulation of erosion as avery important service since it has a direct impact on provision of other services.

Firewood is an ES of provision and mainly source of fuel for rural communities. Some studies on their availability start from a forest inventory to know available volume, according to species susceptible for exploitation (Contreras et al., 2003a), and complementing them with interviews to know socioeconomic and cultural characteristics for use, extraction and preference (Quiroz and Orellana, 2010; Santos et al., 2012). According to (Ghilardi et al., 2007) the ecosystems that contributed the most fuelwood are mangroves, tropical forests, broadleaf and coniferous forests with 5.1, 3.1, 2.6 and 2.4 t ha-1 year-1 aboveground in dry weight. The consumption of firewood per ecological zone for Mexico is 3 kg DMhab-1 day-1 for humid tropical regions, 2 kg DMhab-1 day-1 intemperate zones and 1.5 kg DMhab-1 day-1 in semi-arid zones (Masera et al., 2010). (GIRA, 2014) reported a supply of firewood of 273 thousand tMS for the Mixtecan region of Oaxaca and a consumption of 311 thousand tMS year-1 for the municipality of Yanhuitlán and availability of firewood of 2,793 m3 and 203 m3 was estimated for coverage of 60-100% and 20-60% with an average consumption of 1.8 kg person-1 day-1 (Contreras et al., 2003a). Tiltepec reports a consumption of 1.21 loads of firewood (30 kg family-1 week-1) (Cruz and Aguirre, 1992). Livestock and agricultural transformation are the main factors associated to land use change in Mexico, losing between 189 thousand to 501 thousand hectares of tropical forests and 127 thousand to 167 thousand hectares on temperate forests (Balvanera et al., 2009). Grazing lands are defined as lands of natural or introduced vegetation where grasses, herbaceous and shrubs predominate (Pellant et al., 2005), for livestock grazing (INIFAP, 2011) and wildlife and soil and water conservation (CONAZA, 1994). These grazing areas are characterized as areas with physical limitations for agricultural production, generally have low rainfall, rugged topography, poor drainage, dry or sandy soils (Cruz and Aguirre, 1992). The four principles for the management of the grazing land are: time, distribution, type/class of livestock and animal load. Being the carrying capacity, the maximum animal load that allows maintaining and improving vegetation and even other resources involved (Walker, 1995).

The Technical Advisory Committee for Grazing Loads (COTECOCA) established for the state of Oaxaca a minimum of 0.80 ha AU-1 year-1 and a maximum of 33.40 ha AU-1 year-1 and an average of 4.12 ha AU-1 year-1 (SAGARPA, 2009). (Contreras et al., 2003b) noted that 3.1 ha per grazing animal is required considering only sheep and goats, that is, 24.8 ha AU-1 for the municipality of Yanhuitlán. (Cruz and Aguirre, 1992) reported for Tiltepec areal animal load of 0.36 AU ha-1 (2.81 ha AU-1) from March to October and 0.26 AU ha-1 (3.84 ha AU-1) from November to February, including cultivated areas after harvesting.

Water is an ESsupply regulated by infiltration, retention and storage processes (De Groot et al., 2002), as well as vegetation cover, precipitation, topography, soil properties and subsoil characteristics (Balvanera et al., 2009; Galán et al., 2012). The land resource is an ES of sustenance, provision and regulation that functions as a reserve of goods that generate a flow of other services. Forming processes are carried out (nutrient cycle, hydrological cycle and biological activity) and degradation (physical, chemical and biological) (Dominati et al., 2010). Water erosion as a degradation process is a function of soil properties, topography, soil cover and human activities. Erosion and sediment production is estimated with models such as: Universal Soil Loss Equation (USLE), Modified Universal Soil Loss Equation (MUSLE), Water Erosion Prediction Project (WEPP), Limburg Soil Erosion Model (LISEM), MIKE-11 software developed by Danish Hydrologic Institute (DHI), Simulator for Water Resources in Rural Basins (SWRRB), Chemical Runoff and Erosion from Agricultural Management Systems model (CREAMS), Areal Nonpoint Source Watershed Environment Response Simulation (ANSWERS), among others (Merritt et al., 2003).

This research identified and quantified some ecosystem services of provision (production of water, firewood and fodder) and regulation (sediment retention and runoff production) with the MUSLE model for the Tiltepec basin, Oaxaca.