Pinus greggii Engelm. is endemic to eastern Mexico and of great ecological and economic importance. It occurs between 20°13' and 25°29' N latitude with a large gap of 360 km in the central portion of its range. The northern populations of the species are recognized as P. greggii var. greggii and the southern ones as P. greggii var. australis. The elevational range of the species is from 1,400 to 2,613 m above sea level. Populations in the southern region are located at lower elevations with higher mean temperatures and annual precipitation (± 1,720 m, ± 17.5°C and ± 1,370 mm) than populations in the northern region (± 2,450 m, ± 13°C and ± 640 mm). Twenty natural populations of the species were sampled, and huge differences were found among them in the area that they cover and the associated tree species. Southern populations are typically associated with species of temperate-subtropical tree communities, whereas in the northern region tree species from colder and semi-arid communities are more common. Juniperus flaccida and Quercus spp. are common to both regions. In general, populations at the extreme of the natural distribution were smaller and had a lower density of mature trees and seedlings. Most P. greggii populations are subjected to great human impact associated with wood extraction and farming activities, resulting in reduced regeneration. Options for in situ and ex situ conservation of this species are discussed.
