Pressure indicators

Land-use change

One of the major pressures on forest resources both in Mexico and around the world is the conversion of forested land to other land uses (Matthews et al., 2000; SCBD, 2001a; Groombridge and Jenkins, 2002; UNEP, 2003; WCU , 2008; FAO, 2009). The loss of forest cover is the result of the expansion of agricultural, livestock raising and urban areas; the construction of transport networks and other infrastructure (e. g., power grids or dams); and mining. The conversion of forested land to a treeless one causes two major impacts on the state of forest resources: reduces the area of ​​forest (along with the stock of its forest products) and lowers the quality of the remaining areas through the effects of fragmentation. The reduction and fragmentation of forest areas may lead to drastic reductions in the population sizes of commercial species, foster their geographical isolation, reduce their genetic variability and gene flow, and affect their reproductive success, thus compromising their long-term viability and commercial exploitation (Templeton et al., 1990; Young et al., 1996; Groombridge and Jenkins, 2002; White et al., 2002). The indicator Land use change in forested areas denotes the pressure imposed on forest resources by the expansion of agricultural and livestock-raising activities and the growth of urban areas. This indicator describes the changes occurred between the two most-recent inventories of land use and vegetation: series III and IV of the land use and vegetation maps published by INEGI, in 2002 and 2007, respectively. This indicator is also used by the US Environmental Protection Agency (EPA, 2008).

Extraction of timber and non timber forest products

Products extracted from temperate and tropical forests are commonly classified into two main groups: timber products, including lumber, paper, veneer, plywood and firewood; and non-timber products, a wide set including forest soil, resins, fibers, waxes, fruits and plants, among others (SCBD, 2001b; FAO, 2009; Semarnat, 2009). The uncontrolled exploitation of these products may have significant effects on their long-term sustainability. The removal of commercial tree species may affect the populations’ regeneration, by removing reproductive individuals and the damages that extraction operations cause to plants in the early stages of natural regeneration. It also leads to habitat alteration, affecting microclimatic conditions, and facilitating the invasion by exotic species (Groombridge and Jenkins, 2002; Brown and Gurevitch, 2004). Examples of timber and non-timber products where uncontrolled extraction is threatening commercial exploitation are mahogany (Swietenia spp.), Red cedar (Cedrela odorata), colonial pine (Araucaria cunninghamii), the Brazilian pine (Araucaria angustifolia), cascara buckthorn (Rhamnus purshianus) and Pacific yew (Taxus brevifolia), among many others (Turner, 2001; TRAFFIC, 2002; CITES, 2006). The indicator Production of timber and non-timber forest products denotes the pressure that the extraction of forest products imposes on Mexico's forest resources. This indicator is also used in the Agenda 21 for the Baltic Sea Region (Baltic 21, 2000) as well as in the OECD’s (OECD, 2008) and European Union’s (2007) Key Environmental Indicators.

Forest fires

Forest fires occur for natural causes and constitute an important factor in the natural dynamics of many forest ecosystems in the world, especially in temperate forests. Forest fires increase the availability of soil nutrients and trigger ecological succession processes that help maintaining biodiversity (Matthews et al., 2000; Edward and Miyanishi, 2001; FAO, 2007b). However, largely due to human activities and control, today’s natural patterns of fire occurrence have been modified. Nowadays, forest fires often occur in areas that had not previously experienced fires, while fires have been suppressed in zones that had been historically exposed to regular fire regimes (FAO, 2007b). The two major factors that foster forest fires in many countries are continuous logging and the use of fire to clear the land for agricultural purposes; however, previous fires, campfires and trash burning also favour their occurrence (Cochrane, 2002; WWF, 2002; FAO, 2007b). The impacts of forest fires on forest resources are evident at two levels: first, in the deterioration and loss of forest resources and, secondly, in the quality impairment of the environment where they occur. As for the former, fire heat induces tissue death and deformities in trees, thereby reducing wood quality (Castillo et al., 2003). Fire also can eliminate completely the seedlings of populations of commercial species and facilitate the invasion of forest pests and diseases (Matthews et al., 2000; FAO, 2007b). The economic costs of the forest resources lost can be enormous. For example, between 1997 and 1998, about 4.7 million hectares of tropical forest were burnt in Indonesia, causing a loss of timber products estimated at about 2 billion USD and about 586 million USD in non-timber products (SCBD, 2001c). The indicator Number and surface area affected by forest fires is used to denote the pressure that forest fires impose on the country's forest resources. This indicator has also been used in the Greece’s Report on Sustainable Development Indicators (NCESD, 2003) and the Criteria and Indicators of Sustainable Management in Canada (2005).

Forest pests

Forest pests are any species, strain or biotype of plant, animal or pathogenic agent injurious to plants or plant products (FAO, 2006). Damage produced can be mechanical or physiological injuries, such as deformations, growth reductions, weakening or even death of individuals. Pests can directly or indirectly cause economic and environmental losses (Conafor, 2003, 2004; FAO, 2006). Pests are considered one of the main disturbances in Mexico’s temperate forests; nearly 250 insect and pathogen species have been identified that can affect the country’s tree lands (Semarnat, 2009). Natural factors that facilitate pest infestations include weather events such as droughts, hurricanes and snowstorms as well as other natural events, such as wildfires (Matthews et al., 2000; Castillo et al., 2003; UNEP, 2003). Human activities also facilitate the entry of forest pests (FAO, 2006). Unregulated exploitation and grazing, poor forest management, the introduction of pests and pathogens from other geographic regions, and induced fires, all make forest masses susceptible to the attack by insects or pathogens. The Surface area affected by forest pests denotes the pressure that this factor imposes on the state of the country’s forest resources. The surface area affected by forest pests and diseases is also included in the Criteria and Indicators of Sustainable Management in Canada (2005).

Illegal logging

One of the major factors affecting the state of forest resources in Mexico and all over the world is illegal logging in tropical and temperate forests. Illegal logging occurs when timber is harvested, transported, bought or sold in violation or circumvention of national laws (MEA, 2005; Brack, 2007). The harvesting process itself may be illegal as it may include illicit means to gain access to the forest, extract timber without the license required, harvest of protected species, or harvest more timber than the quota licensed. Illegal activities may also occur during transport, processing, export, false manifesto at customs, and tax evasion. Losses caused by illegal activities for timber-producing countries have been estimated by the World Bank between 10 and 15 billion Euros per year (Comisión Europea, 2004). Illegal logging affects forest resources both by reducing their volume and by its effects on fostering deforestation, as well as by facilitating the occurrence of forest fires and the entry of forest pests (Comisión Europea, 2004; Brack, 2007; WWF, 2009). The Volume of illegally harvested timber forest products is an indicator of the pressure imposed by this activity on the country’s forest resources. However, reliable data on the amount of illegally harvested forest products in Mexico are not currently available; because of this, the Volume of timber seized by forest inspections is hereby presented as an alternate indicator. This is, most likely, an underestimate of the actual amount of products that are illegally harvested from the country’s temperate and tropical forests.