Endemic to western Michoacan, Mexico where it is threatened by fire
Endemic to Mexico in western Michoacan (Cerro de Chiqueritos, Cerro Ocotoso, Puerto del Pinabete, Fresno, Alberca and seven other more recently discovered localities within the municipality of Coalcomán).
The population is small and consists of 12 more or less separate localities, in each ranging from 1 to 3500 individuals, totaling 6000–6500 individuals (Delgado et al., 1999). Regeneration is quite abundant at some of the sites. From this it is inferred that the total of mature trees is probably around 1000. There is considerable genetic diversity, indicating a larger population in the (geological?) past (Delgado et al., 1999).
Habitat and Ecology
The two smaller ‘classical’ subpopulations, Cerro de Chiqueritos and Cerro Ocotoso, are on steep talus of large, eroded limestone blocks, near the summits of small mountains in the mainly volcanic Sierra Madre del Sur. Each have only from 10 to a few score trees, from old to saplings. Some subpopulations are on more level ground, also with limestone boulders, but interspaced with other rocky substrates. In the two former areas, the trees remain small, less than 15m tall; in some of the larger subpopulations trees to 30m have been found. The altitudinal range is 1714–2480 metres above sea-level. Annual precipitation is ca.1500mm, most of it occurs from July to October. The climate is warm-temperate, with a minimum of -5° C (December) and a maximum of 30° C (April). Although surrounded by extensive mixed pine forest with species like P. pseudostrobus, P. herrerae and P. oocarpa, these species do not grow on the limestone talus. There, Quercus and shrubs, e.g. Clusia salvinii, form an understorey with Agave and tall herbs. Fires occur frequently, but regeneration seemed good at least at Cerro Chiqueritos.
No uses are recorded of this species. It is a botanical rarity only present in a few botanic gardens and private collections. Its altitudinal range implies occasional light frosts, so it might prove hardy in mild regions.
Global status and rationale
Discoveries of several new localities with mostly very small subpopulations since the late 1990’s have not greatly altered the range of this species. It’s extent of occurrence and area of occupancy are very small, and had there been evidence of continuous decline it would easily have met the criteria for EN or perhaps CR. Risk of extinction by major fires is especially high in the very small subpopulations. However, the study by Delgado et al. (1999) seems to imply that there is no decline of the population. This species therefore meets the critereria under D for Vulnerable.
The greatest threat to this species would appear to be a forest fire, as it is not a fire-adapted pine. Its occurrence amidst extensive pine forests make it vulnerable to this hazard. There is evidence in several of the scattered stands of ground fires having occurred (Perry, 1991).
No logging seems to take place of this rare pine, probably because of the inaccessibility of its populations in remote locations and the poor form of most trees from a lumberman's viewpoint. A fire-lookout post is established near one of the localities of P. rzedowskii, as it is located on the upper slope of a small peak in the area. Studies in population dynamics related to environmental factors, especially fire and reproduction, are much wanted to ensure proper management of this evolutionarily interesting pine. Pinus rzedowski is listed as Endangered on the official 2010 Mexican National Redlist (the Mexican Redlist categories are similar but not equivalent to the IUCN system).