NOTES AND COMMENTS Regeneration of deep-forest Stemmadenia donnell-smithii (Apocynaceae) at Los Tuxtlas, Mexico SONIA SHWEIKI and HENRY F. HOWE Biological Sciences (m/c 066), 845 West Taylor Street, University of Illinois, Chicago, IL 60607, USA Abstract Stemmadenia donnell-smithii is a subcanopy neotropical tree that occurs in a wide variety of forest and successional habitats. Often regarded as a species of highly disturbed habitats, we tested the hypothesis that regeneration in old-growth forest is consistent with that of a late-pioneer tree, with the number of established seedlings (stature <50 cm) near fruiting trees directly proportional to canopy openness (rs = 0.82, P < 0.01). Scarce larger juveniles (stature >50 cm in forest conditions) occurred only under broken canopies. Keywords: light gaps, Los Tuxtlas, seedling distributions, Stemmadenia, tropical rainforest. Received 18 May 2009; accepted 27 July 2009 Introduction One of the challenges of this century will be assessing the capacity for regeneration of species in habitats profoundly altered by human activity (Vitousek et al. 1997). Huevos de Toro, Stemmadenia donnell-smithii (Rose) Woodson (Apocynaceae), is a subcanopy tree found in a variety of habitats in fragmented landscapes from tropical Mexico to Panama (Woodson 1928). In seasonal dry forest of western Costa Rica, it is common in pastures and in deciduous dry forest, where its fleshy arillate seeds are dispersed by a variety of fruit-eating birds (McDiarmid et al. 1977). The tree is similarly a common pasture, forest-edge and forest species in southern Mexico (Williams-Linera et al. 1998). Although commonly considered a tree of disturbed areas, where seedlings establish following natural dispersal, S. donnell-smithii is found in old-growth rainforests at both ends of its geographical range (Janos 1980; Coates- Estrada et al. 1993). Virtually nothing is known of its regeneration in deep forest. We hypothesized that S. donnell-smithii is a late pioneer in forest succession, a species that colonizes disturbances after more rapidly growing pioneers arrive and reach maturity in 20–30 years as the early cohort of trees dies (see Martinez-Ramos 1985; Finegan 1996; Guadarrama et al. 2004). If this were a light-demanding species, the number of seedlings surrounding fruiting trees should be directly proportional to the sizes of the existing light gaps (Hubbell et al. 1999). Consistent with this hypothesis, some seedlings might survive in deep shade longer than species entirely dependent on large gaps for establish- ment and persistence (Augspurger 1984). Our objectives were to determine whether seedling and juvenile distri- butions near fruiting trees suggest recruitment within the forest consistent with the hypothesis of late-pioneer regeneration. Materials and methods We report a preliminary study of S. donnell-smithii from the Los Tuxtlas Biological Station (18°34′N, 95°4′W), which is owned and operated by the Institute of Biology of the Universidad Nacional Autónoma de México in southern Veracruz, Mexico. This station forms part of the complex of the northernmost limit of tropical rainforest in Mesoamerica. The reserve of 640 ha receives approxi- mately 4900 mm of precipitation annually. The area is part of a deeply fragmented landscape of larger old-growth remnants with 30–40 m canopies, patches of secondary forest and agricultural land. A comprehensive description of the site can be found in Gonzalez-Soriano et al. (1997). Stemmadenia donnell-smithii is a middle-story tree reach- ing 10–20 m in height. In Mexican rainforest, the tree has an extended fruiting season with none to a few fruits open Correspondence: Henry F. Howe Email: hfhowe@sbcglobal.net; hfhowe@uic.edu Plant Species Biology (2009) 24, 225–228 doi: 10.1111/j.1442-1984.2009.00259.x © 2009 The Authors Journal compilation © 2009 The Society for the Study of Species Biology