Journal of Ecology 2003 91, 776 –784 © 2003 British Ecological Society Blackwell Publishing Ltd. Regeneration microsites and tree species coexistence in temperate rain forests of Chiloé Island, Chile DUNCAN A. CHRISTIE* and JUAN J. ARMESTO*† *Laboratorio de Sistemática y Ecología Vegetal, Facultad de Ciencias, Universidad de Chile, Casilla 653, Santiago, Chile, and † Centro de Estudios Avanzados en Ecología y Biodiversidad, P. Universidad Católica de Chile, Casilla 114-D, Santiago, Chile Summary 1 We studied the importance of fallen logs as recruitment sites for tree species, their role in species coexistence, and also the influence of canopy openness and litter depth on tree species establishment in mid-successional and old-growth temperate rain forests of Chiloé Island, southern Chile. 2 Old-growth (OG) stands showed significantly more fallen logs than mid-successional (MS) stands. Concomitantly, the proportion of seedlings and saplings established on logs was significantly greater in OG than MS stands. 3 Of 13 tree species found at our study sites, eight showed a significant bias towards establishment on logs, especially those in advanced stages of decomposition. 4 In some stands, all seedlings of Eucryphia cordifolia, Laureliopsis philippiana, Not- hofagus nitida, Tepualia stipularis and Weinmannia trichosperma occurred on decaying logs, whereas all Podocarpus nubigena seedlings were found on undisturbed soil sites. 5 Small-seeded species were more common on logs, whereas large-seeded trees occurred on soil. 6 On soil, litter depth negatively affected local abundance of log-dependent seedlings, suggesting that variation in litter accumulation influences species distributions across the forest floor mosaic. 7 The density of shade-intolerant seedlings was more enhanced by the presence of fallen logs under closed canopy than by the occurrence of canopy gaps over soil sites. 8 Seed size plays an important role in successful establishment of species across the mosaic of fallen logs and different litter depth on the forest floor. We suggest that this mosaic of microsites is an important factor for species coexistence. Key-words: fallen logs, litter, regeneration niche, seed size, temperate rain forests Journal of Ecology (2003) 91, 776 – 784 Introduction Far from being uniform, the forest floor is a mosaic of microsites, defined by either or both of the physical environment and biological effects (Whittaker & Levin 1977). Abundance, growth and survival of seedlings vary across microsites (Whittaker & Levin 1977; Christy & Mack 1984; Peterson & Picket 1990; Peterson & Campbell 1993). The most common microsites are defined by the presence or absence of fallen logs (Harmon & Franklin 1989; Lusk 1995), differences in thickness of the litter layer (Huenneke & Sharitz 1990; Molofsky & Augspurger 1992; Peterson & Facelli 1992; Peterson & Campbell 1993), and pits and mounds created by tree uprooting (Beatty 1986; Peterson & Campbell 1993). This small-scale heterogeneity may affect the estab- lishment of tree seedlings, which in turn influence the spatial distribution of tree species (Beatty 1984; Núñez-Farfán & Dirzo 1988; Harmon & Franklin 1989; Nakashizuka 1989). Thus, the presence of various kinds of microsites could allow differential fine-scale establishment of species with different safe site require- ments ( sensu Harper et al . 1965), and therefore the distinction of a regeneration niche among species having similar niches in their adult stages. This could contribute to local species coexistence (Grubb 1977), Correspondence: Duncan A. Christie, Laboratorio de Sistemática y Ecología Vegetal, Facultad de Ciencias, Univer- sidad de Chile, Casilla 653, Santiago, Chile (fax 56-2-2712983; e-mail duncan@sendadarwin.cl).