Pressure indicators

Land use change

Population growth, with its increasing food and space demands, has fostered a growing demand for land which, in turn, has led to more intense pressures to change the natural suitability of soil for other uses. The removal of vegetation cover to devote the land to agriculture and livestock-raising is perhaps the most obvious example of this shift, although land-use changes towards urban uses, even of sites previously devoted to agriculture or livestock-raising also occur. The removal of the natural vegetation cover, along with the misuse of newly opened areas, fosters soil degradation, affecting its current and future uses. The most important effects of plant cover removal is the loss of soil organic matter, which prevents the development of the soil’s surface layers structures and makes it more susceptible to erosion and degradation (FAO, 2008). When this process persists, plants, animals and ecological processes that provide environmental services (e.g. aquifer recharge and carbon sequestration) are also affected and their permanence and future performance are jeopardized (FAO, 2008). The indicator Land-use change denotes the extent and trends in land use, as well as the potential pressures of activities that foster land-use changes. This indicator is included in the UN’s list of sustainable development indicators (UN, 2007) and the EU’s Sustainable Development Strategy (UE, 2011); it is also used by Chilean Environmental Information System (Ministerio del Medio Ambiente, Gobierno de Chile, 2012). The indicator of this pressure factor is included in the Terrestrial Ecosystems section of the Biodiversity chapter.

Agriculture

In developing countries, socioeconomic conditions and market pressures force communities to expand the agricultural frontier at the expense of modifying the natural suitability of land. This causes soil degradation and erosion and also affects, in parallel and over the long-term, the ecosystems present and the economic and social sectors involved (OECD-FAO, 2009; PNUMA, 2012). The indicator Agricultural area denotes the extent of the pressure that agricultural activities impose on soil resources. This indicator is also used by FAO (2001), and has been included in various systems of environmental indicators in Latin American countries with similar problems, e.g. Chilean Environmental Information System (Ministerio del Medio Ambiente, Gobierno de Chile, 2012),  and Indicator System of Sustainable Development for Argentina (Secretaría de Ambiente y Desarrollo Sustentable, 2012). Information on agricultural activities imposing pressures on the environment, and specifically on soils, has been used by the OECD as part of its environmental performance assessments of its member countries (OECD, 2013).

Consumption of agrochemicals

Excessive use of agrochemicals also leads to soil deterioration by altering the soil’s physicochemical characteristics and natural recovery mechanisms (Mirsal, 2008). Agro chemicals (mostly fertilizers and pesticides) have enabled farmers to obtain higher yields by controlling pests and weeds, and by increasing nutrient availability for their crops (PNUMA, 2012). However, these synthetic chemicals contain substances whose properties can cause harmful effects to the environment and human health, especially when used in excess and without the necessary precautions (FAO, 2006; PNUMA, 2012). One of the most important negative effects on soil is the damage to populations of microorganisms and invertebrates present in the plants’ rhizosphere, which are key elements in food chains and nutrient cycles (e.g. phosphorus and nitrogen). In severe cases, excessive use causes soil sterility and may have negative effects on ground and surface waters through leachates and surface runoff (Mirsal, 2008; see the chapter on Water in this publication).

In Mexico, as in most emerging economies, toxic agrochemicals are still used despite their negative effects (OCDE, 2013). The indicators Apparent pesticide consumption and Apparent fertilizer consumption denote the potential pressure that the use of these substances imposes on soil. Both indicators are discussed in the Quality section of the Water chapter of this report. These two indicators have been included in other countries and organizations indicators systems such as Argentina (Secretaría de Ambiente y Desarrollo Sustentable, 2012), Spain (Ministerio de Agricultura, Alimentación y Medio Ambiente, 2013) and the ECLAC (CEPAL, 2007).

Overgrazing

Extensive cattle-raising also causes soil degradation, mainly through overgrazing, which produces loss or degradation of the vegetation cover and, thereby, affects the ability to retain organic matter and soil particles. Overgrazed areas are more exposed to wind and water erosion. In the rainy season, an accelerated compaction of the soil’s uppermost layers may occur as a result of the continuous trampling by livestock, which creates an impervious structure that favors surface runoff and the formation of soil crusts that prevent infiltration and hence plant development (LEAD, FAO, 2006).

In Mexico, an extensive cattle-raising model was favored during decades, which accelerated vegetation removal in large areas, with the consequent negative effects on ecosystems and soil (Gerritsen and Douwe van der Ploeg, 2006). The indicator Area affected by overgrazing denotes the magnitude of the pressure that livestock imposes on soil. This indicator is included in the Initiative for Livestock, Environment and Development (LEAD), whose secretariat is based at FAO and is supported by other international agencies in order to protect and improve natural resources affected by livestock (FAO, s/a). The European Union considers the relationship between the cattle headcount per unit area relative to the agricultural area used as an indicator of the intensification of agricultural activities (UE, 2011).

Land tenure

Land tenure is another factor that may be used as an indicator of pressure on soil, as the legal uncertainty of property rights results in an irrational use and destruction of resources (FAO, 2009). In Mexico, as in Latin America, this issue dates back to colonial times, when the indiscriminate appropriation and distribution of land to favoured groups took place and continued for a long time. Unfortunately, the study and analysis of land tenure has been approached from the social and economic sciences rather than from the ecological and environmental standpoint (Edouard, 2010). The cases of uncertain land tenure have favored illegal land occupation that favoured land-use practices with negative effects on soil and the ecosystems supported by it (FAO, 2009). Nevertheless, currently there is not sufficient information available for developing this indicator.