Introduction

Terrestrial areas cover approximately 30% of the Earth's surface (about 150 million square kilometers). In these areas, the complex interactions between climate, solar radiation, geology and soils, among other factors, have made possible the development of a variety of ecosystems with different species assemblages. Although terrestrial ecosystems harbor a lower number of phyla than oceans, they are considerably more diverse in terms of the total number of species in them (Groombridge and Jenkins, 2002). The diversity of terrestrial ecosystems in Mexico is comparable to that of Brazil (Dinerstein et al., 1995), India and Peru (Rzedowski, 1998). The country still includes low and high tropical forests, temperate conifer and hardwood forests, mountain cloud forests, xeric shrublands, wetlands and natural grasslands, among many other types of vegetation, which are home to a wealth of species and make of Mexico one of the five most diverse countries worldwide.

Terrestrial ecosystems are major suppliers of products for the subsistence and development of mankind, and also offer a wide range of environmental services from which society has been directly or indirectly benefitted. Terrestrial ecosystems are sources of many types of food (both plant and animal), wood and timber, fiber, fuel, construction materials and active ingredients with medicinal properties, among others (Conabio, 2006, Groombridge and Jenkins, 2002; Chivian, 2008). Some basic environmental services provided by terrestrial ecosystems include the following: conservation of biodiversity, carbon sequestration, soil formation and stabilization, erosion control, watershed protection and degradation of organic waste (CBD, 2001, Groombridge and Jenkins, 2002; Pagiola et al., 2003; Ranganathan, 2008). This adds to their aesthetic, scientific and cultural value, as well as to their recreational use.

The development of human societies and their intrinsic need to produce goods and services has exerted considerable pressure on terrestrial ecosystems worldwide. During the past 50 years the planet has lost 50% of forest cover and 35% of mangrove area, in parallel with the expansion of crop areas which reached about 30% of the world’s area (Sánchez-Colón et al., 2009). Currently, the major threats to terrestrial ecosystems are changes in land use (mainly driven by the expansion of the agricultural and urban frontier), population growth and infrastructure (e. g. roads, power networks and dams) , forest fires, overexploitation of natural resources, introduction of alien species and global climate change (Vitousek et al., 1997; Walker and Steffen, 1997; Manson, 2009; FAO, 2006; CBD, 2007, Groombridge and Jenkins, 2002; PNUMA, 2003; Nellemann et al., 2009). As a result of the loss or degradation of these ecosystems, their functioning is impaired as well as their interactions with the atmosphere and aquatic ecosystems (marine and freshwater), biogeochemical cycles are disrupted and populations of vulnerable species either decline or become extinct (Vitousek et al., 1997; Groombridge and Jenkins, 2002; Baena et al., 2008).

In view of the alarming loss and degradation of the natural vegetation cover, Mexico and the world have implemented various strategies aimed at eliminating or reducing pressures that threaten it, mitigate its effects and even reverse its decline. These strategies have followed different lines: one focuses on preserving ecosystem integrity and ecosystem services, the clearest example being the creation of protected natural areas at national and state levels. There are other programs the core objectives of which do not contemplate but promote the preservation of terrestrial biodiversity, such as the Payment for Hydrological Environmental Services Program (PSAH¹), described in chapter of Water in this publication. Other initiatives implemented include programs the main objective of which is the sustainable use of biodiversity in terrestrial ecosystems; the System of Management Units for Wildlife Conservation (SUMA¹), referred to in the section Species of this chapter, is an outstanding example: it indirectly preserves ecosystems inhabited by target species. This same line includes programs in other sectors (forestry, mainly) that promote the rational use of the country’s forest biodiversity, such as the Forestry Development Program (Prodefor¹) and the Project on Conservation and Sustainable Management of Forest Resources (Procymaf¹) described in the chapter of Forest Resources. Finally, the last line addresses the recovery of the national vegetation cover, particularly through reforestation, through the Program for Conservation and Restoration of Forest Ecosystems (Procoref¹). This program is also included within the set of indicators in the chapter on Forest Resources.

¹ For its acronym in Spanish

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