The vegetation of our country is very heterogeneous. The National Institute of Statistics and Geography (INEGI, in Spanish) uses a system of hierarchical classification that considers, at its highest level, the vegetal formations, which are categories characterized by physiognomic and ecological features (i. e. forest, tropical rainforest, shrubland, etc.), among which the community types defined by their physiognomic, ecological and floristic features are included (i. e. chaparral, rosette scrub, succulent, cloudy mountain, etc.) and the types of vegetation that combine the name of the formation and the type of community (i. e. mountain cloud forest, succulent shrubland, etc.) In this publication, following physiognomic criteria of the vegetation, the widest distributed types have been added in the following categories (Map a):

Mountain cloud forest:  Vegetation characterized by a dense tree cover with the coexistence of several genera, including Liquidambar, Magnolia, Juglans, Ostrya, Clethra, Podocarpus, Turpinia, Oreopanax and many more. Pines and oaks are a frequently present as well. One of the key features is the temperate and tropical affinity of species present in the canopy and understory, respectively. This vegetation type grows at altitudes where fog banks are formed. This forest type is exuberant, with a large amount of ferns and lianas, as well as plants growing on trees (epiphytes). An important portion of the flora growing in cloudy mountain forests in Mexico is endemic of the country. Broad areas originally covered by this forest have been cleared for use in agriculture, and in several regions coffee is grown under the canopy of trees.

Temperate forest: this category includes three principal types of vegetation: in the first place, the forests of coniferous dominated by the evergreen trees where the coniferous stand out: pines (Pinus) and oyamel (Abies); although there are also firs (Pseudotsuga), juniper (Juniperus) and cedars (Cupressus). They are generally present in the temperate and cold climates of the high parts of the mountain ranges. In second place the forests of oaks stand out, dominated by broad-leaf trees, mainly oaks (Quercus), most of them deciduous. They are especially found in temperate climates in the mountains, frequently under the altitudinal level of the coniferous, although, sometimes they may develop in really warm climates. They are mainly used to produce coal and cattle. Since the soils of the oak groves are frequently very fertile, the agricultural activities are common in them. Finally, the conifer and broad-leave forests have also been included here, where the two types of trees coexist making mixed forests. Frequently, this coexistence is favored by the human activities. The exploitation of these forests is similar to the exploitation of the pine or oak forests.

Tropical rainforest: it includes the evergreen and semi evergreen tropical forests, dominated by many types of trees, in rainy and warm climates. The top of the trees may go beyond 40 meters high and it maintains an important part of its foliage over the year. According to the height of the canopy, they are divided in high tropical forests (tree vegetation of over 30 meters high), middle (between 20 and 30 meters) and low (frequently between 4 and 15 meters high). Below the tallest trees there are several vegetation strata of different heights. It is one of the most diverse biological communities in the world. The exploitation of some species of high commercial value, such as the mahogany (Swietenia) or the red cedar (Cedrella) and several forestry non-timber products, are common within these forests.

Sub humid tropical forest: it groups the deciduous and semi-decidiuous, it is a vegetation dominated by trees of different species of deciduous, which develop in warm environments with very remarkable differences between the rainy and dry seasons. In the same way as the evergreen tropical forests, they are divided in middle and low depending on the height of the dominating tree vegetation. The canopy rarely surpasses 15 meters high, although in some cases it may reach 30 meters high. The condition of the semi- deciduous or deciduous depends on the proportion of the tress that lose the foliage in the dry season. Many of the trees store water in the stem, as it is the case of the copal (Bursera), pochote (Ceiba) and several columnarcacti This vegetation is frequently subject to the bum agriculture, slash and burn and to the extensive cattle rising, which strongly degrade it, which is why it is one of the most threatened tropical ecosystems of the world.

Xerophilous shrubland:  This category includes a diverse and extensive set of vegetation types (rosette-shaped, succulent, shrublands, etc.). This is dominated by shrubs and characterizes arid and semi-arid zones. The number of endemisms in these areas is extremely high. Due to the scarcity of water and given that soils are poor and thin, agriculture is practiced at small scale, except when irrigation is available. By contrast, cattle raising is practiced extensively, and broad areas originally covered by xerofilous shrubland are heavily overgrazed.

Natural grassland: vegetation dominated by herbaceous plants, mainly gramineous (grasses, fodder or graminoids) which are found in any type of climate, but mainly in the semi arid regions of the north and the highest parts of the mountains (over the four thousand meters). Almost all of the grasslands of our country are used for the cattle raising, almost always with an excessive intensity. Other grasslands were forests or shrublands and the action of the cattle and the fire keep them in this altered shape. These ones are known as induced grassland.

Halophylous and gypsophylous vegetation: These types of vegetation, low height, are developed in soils of closed basins with high content of salts and gypsum, respectively. The rhizome grasses are dominant (dominating the species of the families Poaceae and Chenopodiaceae) and its bush cover is generally scarce. This vegetation is used, in many regions of the country, as food for the cattle, and in some cases, after being drained, it may be used in irrigation farming.

Mangrove: this community is dominated by tree such as the red mangrove (Rhizophora mangle), black mangrove (Avicennia germinans) white mangrove (Laguncularia racemosa) and green buttonwood (Conocarpus erectus). Its adaptation to the brackish water, without necessarily being a halophyte plant, allows them to be at the mouth of rivers and coastal lagoons. In addition to being a source of tannins for the leather industry, this type of vegetation is important as an area of reproduction and growth of many species of fishery importance.

Other types of vegetation such as the mangroves, reed beds, tular, palmar, hillock vegetation and chaparrals are found occupying much smaller areas and they are related to climate, soil and water conditions very particular (Figure a).

References:

Adapted from:
Semarnat. Informe de la Situación del Medio Ambiente en México. Compendio de Estadísticas Ambientales 2005. México. 2005.