Population structure of Pinus nelsoni Shaw, an endemic pinyon pine in Tamaulipas, Mexico

Pinus nelsoni Shaw and Pinus cembroides Zucc. are the most important pinyon pine species in the northern region of the Sierra Madre Oriental in Mexico. A demographic study of these two species was conducted between 1996 and 1998. The two species differed in their size structure: P. cembroides had a higher proportion of large individuals and seedlings that P. nelsoni. The growth rate of the P. nelsoni population projected with the 1996 data indicated moderate positive growth ( λ=1.083), but the drought of 1997 predicted a long-run annual population decrease of 1% ( λ=0.990). The forest fires of 1998, which occurred in 30% of the distribution area of these two species, will have long-term population consequences. The importance of this particular event in the development of a management strategy for these species is discussed in light of the results obtained from the previous 2 years.