VARIATION AMONG Abies religiosa (HBK) Schl. et Cham POPULATIONS ALONG AN ALTITUDINAL GRADIENT. I. SEED GERMINATION CAPACITY

Abies religiosa (HBK) Schl. & Cham. (oyamel fir) is a conifer native to Mexico. The oyamel forest located on the border of the State of Mexico and Michoacan serves as a refuge for Monarch butterfly populations Danaus plexippus L., but there is concern about the future of Abies religiosa in the region due to the change in land use and the climate change; thus, a reduction of its ecological niche is expected. In order to generate information that allows plannning the amount of seed necessary to be collected to carry out large-scale reforestation programs in the region of the Monarch Butterfly Biosphere Reserve, the viability and germination of oyamel fir seeds collected from 15 populations along an altitudinal gradient (2850 to 3550 m, one every 50 m), on the San Andres hill, Michoacan, were evaluated. There were statistically significant differences among populations in seed viability (P = 0.0007) and germination (P = 0.0001). A significant quadratic relationship of seed viability (R-2 = 0.510, P = 0.0138) and germination (R-2 = 0.768, P = 0.0002) with the altitude of seed source was found. Seeds from populations between 3000 and 3350 msnm (middle of the altitudinal distribution) had the highest viability (48.7 %) and germination (19.6 %), higher than those of the upper and lower altitudinal limits. If collecting is made at the intermediate altitude zone (zone II from 3000 to 3350 msnm), approximately 2.0 kg of seed will be required to produce 10,000 seedlings in the nursery; in contrast, the same goal would require five times more seed from the lower altitude zone (11.1 kg, Zone I, 2650 to 3000 msnm). This indicates the practical difficulties for supplying seed that a large-scale reforestation program would face, especially if germplasm originating from low-altitude populations is required, to implement assisted migration to higher altitudes to lessen the effects of climate change.