Distribution

Native to México and the USA. In México this spruce is found only on the two tallest peaks of the Sierra Madre Oriental in the states of Coahuila and Nuevo León and on the tallest peak of the Sierra Madre Occidental in the state of Chihuahua, 676km distant (Ledig, 2010). In the USA it is found in Arizona in the Chiricahua Mountains.

The subpopulations are small. The largest one, from La Carmen in the Sierra de la Marta, was reported to have been virtually destroyed in a fire in 1975 (“reduced to a population of a mere 6 mature trees”, Rushforth, 1986) although later surveys revealed that an estimated 1000–2000 trees remained on the upper slopes (Ledig et al,. 2002). Regeneration is hampered by grazing.

Habitat and Ecology

This subspecies is restricted to high altitude, north-facing slopes and ravines on limestone mountains.

Conservation Status

Global status

Endangered A4acd; B2ab(ii,iii,v)

Global rationale

This subspecies has undergone an estimated recent decline (post 1950) of up to 50%. A further decline is likely so that the overall decline is estimated to be greater than 50% by 2025. This time period is within the three generation period required by the IUCN to qualify for Endangered unde the A4 criteria. In addition, the area of occupancy is much less than 100 km2, there are only three known locations, subpopulations are severely fragmented and there is a continuing decline due to grazing, fire and logging.

Global threats

The main population in the Sierra de la Marta (the type locality) was nearly exterminated in a forest fire in 1975. Other populations, e.g. on Cerro Mohinora in Chihuahua, are much smaller and declining, and even more susceptible to destructive fires. In addition, trees have been felled while regeneration is poor and slow due to grazing, especially on Cerro del Mohinora. Global warming presents a further threat as each subpopulation is growing close or on the summit of their respective mountains and there is little scope for further migration.

Conservation Actions

This subspecies is present in one protected area (Chiricahua Mountains, Arizona). Despite this the subpopulation is vulnerable to human set-fires that are likely associated with illegal immigration and drug trafficing into the USA from adjoining areas of Mexico are increasingly common. The most recent fire (Horshoe 2) burnt over 200,000ha of pine-oak and mixed conifer woodland in 2011 (US Forest Service, 2011).
The Mexican subpopulations are outside recognised reserves. The remaining stands should come under such protection, where logging, grazing and burning can be policed and controlled. Ex-situ conservation involving the collection of seed from all stands and the establishment of breeding populations in suitable areas should be a priority. According to the Secretaría de Medio Ambiente y Recursos Naturales (Mexico) (2010) this species is in danger of extinction.