Abstract

VELASCO-GARCIA, Mario V. et al. Pseudotsuga menziesii seed disperson in populations of central México. Agrociencia [online]. 2007, vol.41, n.1, pp.121-131. ISSN 2521-9766.

Pseudotsuga menziesii is a valuable tree in silvicultural production around the world. In Mexico it is found at the southernmost limit of its natural distribution, but its capacity to disperse seed, which helps in its regeneration, is unknown. In this study, quantity and period of seed dispersion was studied in four contrasting natural populations of P. menziesii (Douglas fir) in the States of Hidalgo (San José Capulines and El Salto) and Tlaxcala (Zapata and La Rosa). Samples were collected from October 2003 to September 2004 using 16 traps measuring 0.5 m2 per site. Significant differences (p≤0.05) were found in quantity and type of seed dispersed among populations and sampling dates. Annual seed dispersion varied among sites from 0.3 up to 4.8 million seeds (filled, empty and damaged) per hectare, 30 to 50% of which were found in cones that fell into the traps. Of all the dispersed seed, 90.3% were empty (80 to 98.7% among sites), 5.8% were damaged by several agents (0.5 to 16.6%) and only 3.9% were filled (0.3 to 9%). The number of filled seeds that fall on the forest floor varied among sites, from 649 to a little more than 66 200 ha-1. With the exception of one site, natural dispersion of the seed is constant all year round, although 97% is concentrated between October and June. The proportion of filled seeds fluctuated over the year, with peaks during the period from November to February in most of the sites. The period of maximum dispersion and the low quantity of seeds disposed to germinate do not favor natural regeneration of the species.

Keywords : In situ conservation; reproductive efficiency; reproductive phenology; Douglas fir; natural regeneration.

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