SURVIVAL OF SEEDLING COHORTS OF A TROPICAL LEGUME ON A SAND DUNE SYSTEM ALONG THE GULF-OF-MEXICO - INFLUENCE OF GERMINATION DATE

Abstract

Chamaecrista chamaecristoides is a legume endemic to the coastal sand dunes along the coasts of Mexico. Hard-coat dormancy of seeds is broken through naturally occurring temperature fluctuations, and seedlings can emerge and establish throughout the year. In the study site, winter storms (called Nortes) are responsible for moving large quantities of sand that bury young seedlings. The objectives of the study were (i) to elucidate the timing of seedling emergence, (ii) to investigate the effect of date of emergence on seedling survival, and (iii) to evaluate different factors of mortality. Seedling survival was monitored under natural conditions, from January 1988 to April 1991. Survivorship curves were compared using the log-rank Peto and Peto test. It was found that the probability of survival or reproduction was not strictly determined by chronological age but by size. Larger sized seedlings survived better during the Nortes. Timing of germination has a great impact on C. chamaecristoides populations, since it affects seedling growth possibilities and thus survival and reproduction. In a changing environment like the sand dunes, there seems to be a selective advantage for maintaining cohorts germinating during different seasons of the year.