Demography of the seedling bank of Manilkara zapota (L.) Royen, in a subtropical rain forest of Mexico Juan Antonio Cruz-Rodríguez 1 and Lauro López-Mata 2, * 1 Departamento de Agroecología, Universidad Autónoma Chapingo, Chapingo 56230, Texcoco, Estado de México. México; 2 Programa de Botánica, Colegio de Postgraduados, Montecillo 56230, Texcoco, Estado de México. México; * Author for correspondence (tel.: (+55) 580-45-947; fax: (+595) 95-20-247; e-mail: lauro@colpos.colpos.mx) Received 2 July 2002; accepted in revised form 27 June 2003 Key words: Forest floor, Seedling survival, Growth, Shade tolerant species, Neotropical trees, Mexico Abstract Selection of individuals in tropical trees, occurs mainly in the seedling phase, which in part explains the low densities of most species. The main objective of this work was to gain an insight into those factors that influence growth and survival of Manilkara zapota seedlings, one of the most abundant species in the lowland forests of Mexico and Central America. Eight 10-m 2 rectangular plots 5m2m were established, in which all  35-cm- high M. zapota seedlings were marked, measured and enumerated at bimonthly intervals. In each census seedling height, number of leaves, length of largest leaf, type of damage and seedling death were registered. Seedling survival during 2 yr was high, reaching 82% including newly emerged seedlings. A maximum likelihood regres- sion analysis showed that both number of leaves and length of largest leaf had a direct influence on seedling survival; however, neither type of damage nor seedling density and height had significant effect. Seedling height growth averaged 2.8 cm in the 2 yr of study. The combined effect of high seedling survival, reduced growth, and impact of physical damage mainly due to falling branches and leaves reveals the occurrence of a persistent seed- ling bank. Such a bank would contribute to recruitment of individuals in the juvenile and eventually in the adult stages. This seedling bank could explain the high density of individuals of M. zapota in the tropical forests of Mexico. Introduction Regeneration patterns and species composition of mature forests are closely related to processes of seedling establishment, growth, and persistence on the forest floor. On the seedling stage, however, oc- curs one of the greatest selection pressures in any particular tropical tree species. In this stage, a high rate of mortality occurs Fenner 1987; Whitmore 1996, mainly caused by density-dependent and den- sity-independent factors. Among the former are natu- ral enemies, i.e., pathogenic fungi Augspurger 1988, and herbivores Janzen 1970; Clark and Clark 1984; Clark and Clark 1985. Among the later are water stress Poorter and Hayashida-Oliver 2000, nutrient Whitmore 1996, and light limitation Malcolm et al. 1996, and mechanical damage due to falling branches and leaves Clark and Clark 1989; Clark and Clark 1991; Scariot 2000. Seedlings beneath closed canopies are limited mainly by their ability to fix C with very little light Pearcy 1983; Peters 1989; Kobe et al. 1995; Walters and Reich 1996. Shade-tolerant tree seedlings typi- cally have slow growth rates Hubbell and Foster 1992; Walters et al. 1993; Reich et al. 1998, a trait that is characteristic of plants growing in resource- poor habitats Grime 1977; Chapin 1980; Lambers and Poorter 1992. 227 © 2004 Kluwer Academic Publishers. Printed in the Netherlands. Plant Ecology 172: 227–235, 2004.