Principal types of vegetation

Due to the fact that elevations in the Valle de Bravo basin vary between 1 800 and 3 600 m.s.n.m. and that the climates are predominantly sub-humid or humid temperate, the principal type of vegetation found in this region are pine and oak forests.

Most of the plant communities are subject to different types of handling by man, and there are only a few areas where the vegetation has not been altered. However, reforestation practices implemented by members of the "ejido" and communal property settlements seem to be sufficiently good in some cases, consequently deterioration in certain zones is almost imperceptible.

"Conserved" vegetation is found in the hillocks with steep slopes, while induced pastureland and the various types of agricultural lands are distributed in areas that have no slopes or practically none. The main types of vegetation found in the Valle de Bravo basin are the following:

Located towards the upper part of the basin, at heights greater than 2 900 m.s.n.m. and with a Cb’(w₂) climate (temperate, semi-cold, with a long sub-humid fresh summer, summer rains from 5 to 10.2% annual). These conditions are found only in the Eastern portion of the basin and it is here where we find the Boreal forest. Nevertheless, it is pointed out that this community presents an ecotone with pine forest, thus it is common to find belts where the Pinus species is found mixed with the Abies species.

Boreal-Pine forest with pasture at the foot of the mountain. Road to Corral de Piedra, municipality of Temascaltepec, September 22, 2000

99° 56’ 06.5", 19° 10’28.53"

The Boreal forest in this region presents the three strata: arboreal, shrub-like and herbaceous; the first has an average height of 30 m and it is the most important. The predominant species in this community is Abies religiosa and its treetops cover generally between 80 and 100% of the surface.

At the sites where the dossal is closed, due to the high density of trees, the shaded areas are such that the lower strata are only slightly developed. Where lighting conditions so allow, there is a lower arboreal stratum constituted by Barrya ovata, Buddleia sp. and juvenile individuals of Abies religiosa. Within the herbaceous stratum, the best represented families are Asteraceae and Gramineae. Certain species of ferns are also frequent in the zone.

Boreal forest with medium disturbance, with felling of trees. There is agricultural activity at the foot of the mountain. Cerro El Faro municipality of Amanalco, State of Mexico, September 23, 2000

99° 55’ 20.75", 19° 15’38.89"

Pine trees are characteristic communities of the mountains in the region, although they are not the predominant type of vegetation. For the most part, the pine trees tend to be associated with species of oak to form pine-oak forests, consequently patches constituted exclusively of the Pinus genus are less frequent. The pine forest is located at heights over 2 400 m.s.n.m. and reach heights of up to 2 900 at which height they normally become mixed with the oyamel and form patches in which neither the Pinus nor the Abies clearly predominates. Pine forests are communities where the most important stratum is arboreal, with average heights ranging between 20 and 30m and where the predominant genus (Pinus) "allows" for the presence at times of individuals of the genus Quercus, Abies, Alnus, Buddleia and Arbutus; generally speaking the groves are poor in shrubs and the herbaceous stratum is normally abundant, containing mainly species of the Asteraceae and Gramineae families.

Pine forests disturbed to a medium degree with felling of trees and an itinerant agricultural system. Municipality Villa de Allende, State of Mexico, September 23, 2000

100° 01’ 46.30", 19° 18’08.73"

This is the predominant type of vegetation in the Valle de Bravo basin; it is located at heights above 1 800 m.s.n.m., reaching heights of up to 2 700 m, where the species of the Pinus genus begins to clearly predominate. Regarding their vertical structure, this type of vegetation presents from two to three strata: arboreal, shrub-line and herbaceous the most important stratum is the arboreal, with average heights ranging between 15 and 25m. The presence (or absence) of a well defined shrub-line stratum is related to how the forest is being handled at each site; in areas where lumber is extracted, where no reforestation practice is carried out or in disturbed sites (open to cultivation and later abandoned), the shrub-like stratum is only slightly represented or does not exist and the treetops of the arboreal stratum cover less than 60% of the surface. The predominant species in this type of vegetation pertain to the genera Pinus and Quercus and are normally accompanied by species of the genera Arbutus, Buddleia, Alnus and Cupressus.

This is the predominant type of vegetation in the Valle de Bravo basin; it is located at heights above 1 800 m.s.n.m., reaching heights of up to 2 700 m, where the species of the Pinus genus begins to clearly predominate. Regarding their vertical structure, this type of vegetation presents from two to three strata: arboreal, shrub-line and herbaceous the most important stratum is the arboreal, with average heights ranging between 15 and 25m. The presence (or absence) of a well defined shrub-line stratum is related to how the forest is being handled at each site; in areas where lumber is extracted, where no reforestation practice is carried out or in disturbed sites (open to cultivation and later abandoned), the shrub-like stratum is only slightly represented or does not exist and the treetops of the arboreal stratum cover less than 60% of the surface. The predominant species in this type of vegetation pertain to the genera Pinus and Quercus and are normally accompanied by species of the genera Arbutus, Buddleia, Alnus and Cupressus.

Pine-oak forest with medium disturbance, felling of trees and reforestation practices. Cerro Lodo Prieto, municipality of Amanalco, State of Mexico, September 23, 2000

99° 57’ 15.24", 19° 15’ 59.02"

This community is the one most widely localized within the basin. It is located in the central part, where certain formations of igneous rocks are found and the surface is rocky, with scarse and shallow soil.

The oak forest presents individual types of the arboreal stratum distributed horizontally and dispersed throughout the forest; the treetops cover between 50 and 60% of the surface. The average height of this stratum is 9 m, composed primarily by Quercus sp. This species is accompanied by certain individual specimens of Buddleia sp. The shrub-like stratum is formed by certain species of the Asteraceae family, as well as by individual specimens of the Comarostaphylis genus, which is the most important species in this stratum. Although not predominant, the herbaceous stratum covers approximately 85% of the surface and it is formed by several species of the families Asteraceae, Labiatae and Poaceae.

Oak forest on basalt rock, Mesa del Pedregal, Municipality of Amanalco,
State of Mexico, September 23, 2000

100° 02’ 31.64", 19° 15’ 24.89"

Of the cloud forest, the only specimens remaining are small remains or spots confined to isolated hillocks where the humidity is slightly higher and the vegetation has not been altered by human activities. Physionomically it is a dense forest with trees that range between 15 and 20 m high; it presents a low arboreal stratum, a well defined shrub-like stratum. The herbaceous stratum is exuberant, with a large number of different species. The quantity of Briophytes and Pteridophytes is high and there is a great abundance of creeping vines (among them Rhus sp.) and epiphytes (of the Orchidacea, Piperaceae and Bromeliaceae families). Within the arboreal stratum, the important species pertain to the Quercus genus. Notwithstanding that there was no indication of trees pertaining to the Clethraceae (Clethra genus), Hamamelidaceae (Liquidambar genus), Magnoliaceae (Magnolia genus) or Rosaceae (Prunus genus) families, characteristic of this type of vegetation due to the large quantity of orchids, moss and ferns present as well as the structure, it was determined that the verification point indeed corresponds to this type of vegetation.

Cloud forest, only slightly disturbed, with felling of trees. La Laguna community, municipality of Amanalco, State of Mexico, September 22, 2000

100° 02’ 28.22", 19° 07’ 22.38"

This community results from the disturbance produced by man when opening areas where the pristine vegetation was the pine-oak forest, to substitute them for this other type of community and thus sustain herds of sheep in an extensive livestock regime. The principal areas of induced grassland are located toward the eastern part of the Basin at heights lower than 3 000 m.s.n.m. and higher than 2 400 m. Generally, there are no significant shrub-like or arboreal areas and it covers practically the entire substratum, with a height of 10 to 15 cm, and a closed horizontal formation. The predominant species pertain to the Poaceae, Cyperaceae and Asteraceae families.

Induced grassland in the flat zones. Road to Corral de Piedra, municipality of Temascaltepec,
State of Mexico, September 22, 2000

99° 56’ 41.56", 19° 09’45.49"

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