Location and General Description
The region is located in two important mountain ranges in the state of Baja California, Mexico: the Sierra de Juarez and the Sierra de San Pedro Martir. Both mountain ranges belong to the physiographical province of Baja California, and constitute the northernmost elevated peaks of the state. The mountainous range that descends into a large portion of Baja California becomes more abrupt at Juarez and San Pedro Martir; the eastern slope is steeper than the western. Altitudes range between 1100-2800 m. The granitic mountains of Juarez and San Pedro Martir have young rocky soils and are poorly developed, shallow, and low in organic matter.
The climate is temperate subhumid with winter rains; its precipitation levels (400-700 mm/year) are the second highest in the entire peninsula (Nieto-Garibay 1999). The climatic conditions have led some researchers to consider the region among the few within Mexico with a Mediterranean climate (Ferrusquía-Villafranca 1993). There are many rivers in this region which drain the mountain slopes (e.g. Las Palmas, Guadalupe, San Antonio, San Telmo and El Rosario).
The dominant species are Pinus quadrifolia, P. jeffreyi, P. contorta, P. lambertiana, Abies concolor, and Libocedrus decurren. The herbaceous stratum is formed by Bromus sp. and Artemisia tridentata. Epiphytes and fungi are abundant throughout the forests.
The region consists of islands of coniferous forests in an enormous desert of arid terrains; it thus contains a unique biota composed of many endemic and endangered species. Conifer forests in the Sierra de Juárez are among the most important of Mexico because of the diversity of pine trees they contain (Vargas-Márquez 1997). At least ten species of Pinus inhabit the steep slopes of the mountains of Baja California. The conifer forests are unique to Mexico because they are the only multi-species mediterranean-climate forests in the country. Not only are pine trees diverse in this region, but the forests of north Baja California constitute the only habitat in Mexico for the species Pinus contorta murrayana, which at the Sierra de San Pedro Martir reaches its most meridional limit of distribution (Styles 1993). San Pedro Martir is also home to some of the largest pine trees in Mexico: the 70 m. tall Pinus lambertiana, with cones of 70 cm in length. Pinus lagunae, which is also a member of these communities, is restricted to the peninsula of Baja California. Pine-oak forests in general contain high numbers of restricted distribution vertebrate species (Flores-Villela & Gerez 1994). This ecotone between temperate forests and the desert represents an ideal habitat for many species of birds; some birds eat the pinyons from pine trees and store them for the winter in underground places, where misplaces or forgotten pine seeds find an ideal habitat to grow (Attenborough, 1995).
Characteristic mammals include: Ornate shrew (Sorex ornatus), puma (Puma concolor), fringed Myotis bat (Myotis thysanodes), California chipmunk (Tamias obscurus), bobcat (Lynx rufus), coyote (Canis latrans), and bighorn sheep (Ovis canadensis)
Birds include the rare, bald eagle (Haliaeetus leucocephalus), California condor (Gymnogyps californianus), pinyon jay (Gymnohinus cyanocephalus), and white-breasted nuthatch (Sitta carolinensis).
A great portion of Sierra de Juarez and San Pedro Martir coniferous forests are still intact, mostly due to the inaccessibility to the mountains. However, diverse threats such as cattle farming and intense fires have seriously deteriorated some patches of land. Fires in 1989 and 1996 consumed 70 km2 and 60 km2 of forest, respectively. The common mistletoe (Phoradendron flavescens) has widely invaded many of the trees in the forest. Many of the trees are very old (80-250 years), which contributes to their susceptibility to infection by various parasites. Some species of insects also build galleries or excavate holes in the trees’ cortex, which weakens the trees but also promotes invasion by other bark-eating insects. Cattle-grazing contributes to low rates of regeneration, and this aggravates the already serious threat that fires and parasites place on coniferous forests. The California condor (Gymngyps californianus) once soared above the mountains of north Baja California, but disappeared around 1940 due to disturbance of the habitat. Many species that inhabit these forests are endemic.
Types and Severity of Threats
The location of the temperate forests in the tall peaks of the mountains makes isolation from other similar ecosystems inevitable. The only patches of temperate forests close to this region are the pine-oak forests of Sierra de la Laguna, in the southernmost part of Baja California, and the pine-oak forests of the Sierra Madre Occidental Mountains. However, vast extensions of the Sonora and California desert stretch between these forests; thereby creating the only refuge for temperate species in a desert of arid lands. This increases the value of conserving of pine-oak forests and coniferous forests in west Mexico, because the forests represent a natural reservoir of unique animal and plant species. Toledo et al. (1989) specify that 60% of the temperate forests in Mexico remain intact. According to them, 37% of the pine-oak forests in Mexico have succumbed to agricultural pressure and logging.
Justification of Ecoregion Delineation
These temperate montane pine and oak forests of the Sierra Juarez and San Pedro Martin region occur along ridge tops, valleys and slopes in two patches, and are host to a number of endemic species. Linework for this ecoregion follows the INEGI (1996) current landcover maps, encompassing all "pine-oak forests", "oak with pine forests", and "pine forest" classifications within this region, as well as portions of "chaparral" at lower elevations and agricultural activities which fall within these parameters. Classification and justification follow Rzedowski (1979). Linework was reviewed by experts during ecoregional priority setting workshops (CONABIO 1996 and 1997) in Mexico.
Attenborough, D. 1995. The private life of plants. BBC, London.
CONABIO Workshop, 17-16 September, 1996. Informe de Resultados del Taller de Ecoregionalización para la Conservación de México.
CONABIO Workshop, Mexico, D.F., November 1997. Ecological and Biogeographical Regionalization of Mexico.
Ferrusquía-Villafranca, I. 1993. Geología de México: una sinopsis. In: Ramamoorthy, T.P., Bye, R., Lot, A. & Fa, J. (Eds). Diversidad Biológica de México. Orígenes y Distribución. Instituto de Biología, UNAM. pp. 3-108.
Flores-Villela, O. & Gerez, P. 1994. Biodiversidad y conservación en México: Vertebrados, vegetación y uso de suelo. Conabio and UNAM, México.
INEGI Map (1996) Comision Nacional Para el Conocimiento y Uso de la Biodiversidad (CONABIO) habitat and land use classification database derived from ground truthed remote sensing data Insitituto Nacional de Estastica, Geografia, e Informática (INEGI). Map at a scale of 1:1,000,000.
Nieto-Garibay, A. 1999. Características generales del Noroeste de México. Pages 13-28 in S. T. Alvarez-Castañeda, and J. L. Patton, (Eds). Mamíferos del Noroeste de México. CIBNOR, S. C. México. Pp. 13-28
Rzedowski, J. 1978. Vegetación de Mexico. Editorial Limusa. Mexico, D.F., Mexico.
Rzedowski, J. pers.comm. at CONABIO Workshop, 17-16 September, 1996. Informe de Resultados del Taller de Ecoregionalización para la Conservación de México.
Styles, B.T. 1993. El género Pinus: su panorama en México. Pages 385-408 in T. P. Ramamoorthy, R. Bye, A. Lot, y J.Fa, (Editors). Diversidad Biológica de México. Mexico: Orígenes y Distribución. Instituto de Biología, UNAM.
Toledo, V. M., J. Carabias, C. Toledo, y C. González-Pacheco. 1989. La Producción rural en México: alternativas ecológicas. Colección Medio Ambiente 6. Fundación Universo XXI, México.
Vargas-Márquez, F. 1997. Parques Nacionales de México. Vol. II.
Prepared by: Alejandra Valero, Jan Schipper, and Tom Allnutt
Reviewed by: In progress