The pine-oak forest is an ecoregion of temperate zones in which there is codominance of pine species (Pinus) and oak (Quercus). They are characterized by presenting three strata.
The upper stratum is generally dominated by pines, while oaks are located in the second. It is common to see a greater number of oaks, but pines tend to have a larger trunk area.
Forests develop in temperate sub-humid climates. They are located between 1200-3000 meters above sea level. The average annual temperature ranges from 12 to 18 ° C and frosts are frequent. The rains can range from 600 to 1000 mm per year.
They are distributed from the southeastern United States to the north of Nicaragua and in Mexico they represent the largest extension of temperate forests. The most important are found in the mountainous areas of the Eastern and Western Sierras Madre. They also occur in the Transversal Volcanic Axis and in the Sierra de Chiapas.
Its flora is quite diverse. The presence of more than 40 species of pines and more than 150 of oaks have been reported. Strawberry trees, poplars and cypresses are also common..
The fauna is abundant. We can find pumas, lynxes, white-tailed deer, raccoons and armadillos. There are also a large number of birds and insects. Among the latter, the monarch butterfly is noteworthy, which fulfills its hibernation period in these forests.
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Pine-oak forests are considered an ecoregion, since they occupy a fairly large area and share species and ecological dynamics. The vegetation is interpreted as a mixed forest, since there is a codominance between two groups of plants.
They are generally distributed between 1200-3200 meters above sea level. However, some pine-oak forests have been observed at altitudes of up to 600 meters above sea level.
Pine and oak forests are common in many temperate and subtemperate mountainous regions of North America. Some authors consider that pine-oak forests are transitional between pine and oak forests, but others argue that they have their own identity and dynamics..
The trees present in these forests are predominantly of boreal origin. However, there are neotropical species mainly in the shrub and herbaceous groups.
In pine-oak forests, the species of both groups share the dominance of the vegetation. Due to the great diversity of environments in which this type of forest can occur, the associations can be highly variable.
The composition and proportion of the species will depend on the environmental factors present. Pines tend to predominate in conditions of higher humidity. When the environment is a little drier, the proportion changes and the oaks tend to be more abundant.
Likewise, in the structure of the forest it has been observed that both groups can dominate in some aspect. For example, there may be a higher density of oak individuals, but the basal area may be higher in pines..
Pines and oaks are considerably different in their physiognomy. Regarding phenology, pines are evergreen, while oaks have deciduous species. Therefore, the coverage proportions between both genders in a given place will define the structure of the forest..
In general, these forests are characterized by presenting three strata. The arboreal layer can reach up to 40 m in height. This stratum is generally dominated by pine trees.
Later there is a second layer that can reach up to 20 in height. In this there are mainly oak species, although species from other arboreal groups may be present.
Then we have a shrub layer that can reach up to 10 m. Juvenile individuals of pines and oaks are presented here, as well as other associated species.
In relation to the herbaceous stratum (1- 0.20 m), it may or may not be present. This is going to be related to how closed the tree stratum is. In very closed forests, it will only be present in the clearings that form. While in those forests with the most open tree stratum, there is a greater diversity of herbaceous species.
A great diversity of epiphytes and climbers can also be found that grow in association with oaks. The highest frequency of these life forms is related to humidity and temperature conditions. Thus, some groups of epiphytes such as orchids do not occur when the temperature is very low..
The relationship between these two groups of plants in the same type of vegetation can be beneficial for both. It has been found that there is an effect that can be considered almost symbiotic between pines and oaks when they grow together.
In the first successional stages of the forest, the pines are the first to establish themselves due to their light requirements. Later, oaks develop, which due to their physiognomy do not intercept large amounts of light.
In already established forests, the pines frequently regenerate under the oaks, because there are better soil fertility conditions in these areas, favoring the germination and establishment of the pines..
Also, pine seeds reach the ground more easily under oaks. The mantle of leaves that forms under the pines makes it more difficult for the seed to have favorable conditions for its germination..
They generally thrive in temperate sub-humid climates. However, some are distributed in colder climates (sub-humid semi-cold) or warmer.
The temperate subhumid climate is characterized by an average annual temperature of 12-18 ° C. The coldest months of the year can show temperatures below 0 ° C, so they tend to be subject to frost every year.
Average annual rainfall ranges from 600 to 1000 mm, although it can reach 1800 mm. The rainiest months are generally July and August. The first months of the year are the driest. Humidity ranges from 43-55% annually.
Pine-oak forests are distributed from the southwestern United States to Nicaragua. They also occur in some areas of Cuba.
In Mexico they are located in the Sierra Madre Oriental and Occidental, which are the mountain ranges to the east and west of the Mexican state. They are also found in the Transversal Volcanic Axis between both mountains, which is located in the center of the country..
These plant formations are also found in the Sierra Madre Sur that extend along the Pacific coasts in the states of Guerrero and Oaxaca. Also to the southeast in the Sierra Madre and the Chiapas Plateau.
In Mexico, the pine-oak forests occupy approximately 16 million hectares. It is considered that almost 90% of the surface can be used from the forestry point of view..
This area has the largest extension of pine-oak forests in Mexico. On the other hand, it is considered to be the largest association of pines and oaks worldwide.
It goes from the states of Sonora, Sinaloa and Durango to Jalisco. Pine-oak forests occupy approximately 30% of the surface of the Sierra Madre Occidental.
This region is transitional between the Holartic floristic kingdoms (with species whose center of origin are the temperate zones) and the Neotropical (with species originating from the American tropics). In this sense, it is appreciated that the woody elements have a boreal affinity. Most of the herbaceous flora tends to be neotropical and endemisms are common..
Depending on the region, the altitude and the climate, there is a predominance of different species of Pinus Y Quercus. Thus, in the north there are mainly P. arizonica Y P. engelmanii, and the white oaks Q. rough Y Q. gambelli.
Interesting to highlight are the forests in Chihuahua and northern Durango, where there is an oak of very restricted distribution (Q. tarahumara). This species grows in shallow soils.
Likewise, in areas with high environmental humidity it is very high, the pine-oak forests are intermediate with the mesophilic forest.
They occupy a large area, being considered the third largest in the Mexican territory, representing 4.5% of the country's pine-oak forests. They extend from the center of Nuevo León and South of Coahuila and continue south to the center of Puebla. It reaches Hidalgo, Querétaro and Veracruz, where it connects with the Transversal Volcanic Axis.
There is a great diversity of species of both genera. The Sierra Madre Oriental is considered a center of diversity for both Pinus What Quercus.
In the case of Pinus, 17 species have been recorded, two of which are endemic to this region. In order to Quercus more than 30 species have been reported.
The climate tends to be slightly more humid than in other temperate zones, due to the favorable exposure to the trade winds from the Gulf of Mexico. For this reason, oak species may slightly predominate in some areas..
The Sierra de San Carlos to the north of Tamaulipas is an isolated area, where these forests predominate. The dominant species are mainly oaks (Q. rysophylla, Q sartorii Y Q sideroxyla) accompanied by Pinus oocarpa.
This forms a mountain range that marks the limit between North America and what is currently the Isthmus of Tehuantepec to Central America. 77% of its surface is made up of mountain ranges, so temperate forests predominate.
Pine-oak forests are the second largest in Mexico. They are located from Jalisco, north of Michoacán, south of Querétaro, south of Guanajuato, Mexico City to the center-west of Veracruz.
The diversity of species of pines and oaks is considered superior to those found in the Sierra Madre Oriental and Occidental. In the case of oaks, it has been found that it has a high genetic variability in these forests.
The pine-oak forests in this area are considered among the most threatened in Mexico. In this region are the largest populated centers in the country such as Mexico City, Puebla and Guadalajara. Therefore, the forested areas have been deforested for urban development and other uses..
In Central America there is a region with the presence of pine-oak forests. It occupies an approximate area of more than 110,000 km2. It extends from the central part of Chiapas, southern Guatemala, Honduras, El Salvador, to small areas of Nicaragua.
The Sierra Madre de Chiapas constitutes the limit of the Boreal floristic kingdom and has a great influence from the Neotropical kingdom. Here the pine-oak forests present their lowest altitudinal distribution (600-1800 masl).
The presence of 11 species of pine and approximately 21 species of oak have been reported. The most common species in these forests are P. strobus, P. ayacuahauite Y Q. acatenangensis.
The most important floristic elements in these plant formations are pines and oaks. The species present vary in each region where these forests occur. The groups that make up the shrub and herbaceous strata are very different depending on the region.
In Mexico there are some 47 species of the genus, with a 55% percentage of endemism. Most of these are important elements of pine-oak forests..
Some species such as the Chinese ocotes (P. leophylla Y P. oocarpa) can occur in almost all regions where forests are distributed. Others do not go as far south, as P. durangensis.
In other cases, pine-oak forests are made up of elements of very restricted distribution. Such is the case of P. maximartinezii, that only occurs in two communities, one in Durango and another in Zacatecas.
The presence of 161 oak species has been reported in Mexico, of which 109 (67.7%) are endemic to the country. Among the most common in pine-oak forests are Q. crassifolia (oak) and Q. rough (quebracho oak).
Most of the species have regional endemism, so their distribution is moderately restricted. Q. hirtifolia is located only in the Sierra Madre Oriental, while Q. coahulensis It occurs in Coahuila and Chihuahua.
Other common species in these plant formations are strawberry trees (Arbutus) and the táscate (Juniperus deppeana). Poplar trees also stand out (Populus), cypress trees (Cupressus spp.) and zapotillo (Garrya sp), among others. Likewise, various shrub genera are frequent such as Baccharis (hut) and Vaccinum (chap).
The herbaceous strata are not very diverse, ferns being frequent. Asteraceae species are also present. Epiphytes are rare and only some species of orchids and bromeliads occur in forests with higher humidity..
The fauna of the pine-oak forests is quite varied. Among the mammals, felines such as the lynx (Lynx rufus) and the puma (Puma concolor).
The white-tailed deer (Odocoileus virginianus), armadillos (Dasypus novemcinctus), raccoons (Procyon lotor) and the northern coati (Nasua narica).
Birds are among the most diverse groups. In some areas more than 100 different species have been found. Woodpeckers, such as the Greater Woodpecker (Picoides villosus), and the acorn tree (Mexican sialia). Raptors are abundant, highlighting the golden eagle (Aquila chrysaetos), the American kestrel (Falco sparverius) and the red-breasted hawk (Accipiter striatus).
Among the snakes there are several of the genus Crotalus. The transvolcanic rattlesnake stands out (Crotalus triseriatus), which is distributed in the Transversal Volcanic Axis.
There is an abundance of insects of various groups. Of special ecological and conservation interest is the monarch butterfly (Danaus plexippus). This species fulfills its hibernation period in forests of the Transversal Volcanic Axis between the states of Mexico and Michoacán.
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