3 Ecological Monographs, 74(1), 2004, pp. 3–23  2004 by the Ecological Society of America LEAF DEMOGRAPHY AND PHENOLOGY IN AMAZONIAN RAIN FOREST: A CENSUS OF 40 000 LEAVES OF 23 TREE SPECIES PETER B. REICH, 1,6 CHRISTOPHER UHL, 2 MICHAEL B. WALTERS, 3 LAURA PRUGH, 4 AND DAVID S. ELLSWORTH 5 1 Department of Forest Resources, University of Minnesota, St. Paul, Minnesota 55108 USA 2 Department of Biology, Pennsylvania State University, University Park, Pennsylvania 16802 USA 3 Department of Forestry, Michigan State University, East Lansing, Michigan 48824 USA 4 Department of Zoology, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z4 5 School of Natural Resources and Environment, University of Michigan, Ann Arbor, Michigan 48109 USA Abstract. The periodicity, synchrony, and causes of variability in the demography of tree leaves in ecosystems with relatively aseasonal climates, such as tropical rain forests, is still poorly understood. To address this issue, we surveyed the timing of birth and death of 40 000 leaves of 1445 individuals of 23 evergreen rain forest species in several late primary and early secondary successional plant communities at San Carlos de Rio Negro, Venezuela, in the northern Amazon basin. In all species, the mortality rate generally in- creased with leaf age. However, in many species, deceleration of death rates with extreme leaf age was noted. In general, for each species, the age structure of leaf populations and the frequency distribution of leaf life span were broad. Species differed substantially in their leaf demography. Measured in their native habitats, seven species common to disturbed open sites had shorter median life spans (0.7 yr) than five species common to open but infertile Bana primary communities (1.9 yr average) or six species common to two tall primary forest communities (Tierra Firme and Caatinga), when measured in high-light conditions in the canopy (2.0 yr average). Variation in light availability had consistent effects on leaf life span in all species. Species native to Tierra Firme forest had average leaf life spans of 3.2, 1.9, and 1.6 yr, respectively, in deeply shaded understory microsites, in small gaps, and in sunlit mature tree canopies. Species native to Caatinga forest had average leaf life spans of 4.2, 3.4, and 2.5 yr, respectively, in these same microsite types. Two species common in gaps and in disturbed sites had much longer leaf life span in shaded understory than in open, disturbed microsites. For all species, responses were similar when trees were planted in sites differing in light availability, as when trees naturally established across light gradients. The rate of leaf production, the risk of leaf mortality, and the leaf life span were not periodic or related consistently to seasonality of climate. Negligible relationships existed between the mild annual dry season and either leaf production or leaf mortality in all species. Thus, leaf phenology and demography were essentially aseasonal in this tropical forest environment. Key words: Amazonian rain forest; leaf life span; leaf longevity; light; nutrients. INTRODUCTION Leaf longevity and phenology are important char- acteristics of species that reflect the influence of evo- lution and the environment on plant traits and that, in turn, have substantial implications for plant functioning at leaf, whole-plant, and ecosystem scales (Chabot and Hicks 1982, Coley 1988, Reich et al. 1992, 1997). This is true in tropical forests as elsewhere (Frankie et al. 1974, Borchert 1980, Reich and Borchert 1984, Coley 1988, Reich et al. 1991, Mulkey et al. 1995), although much uncertainty remains for such systems. In the markedly seasonal temperate and boreal forest biomes, trees of most species have leaf phenologies, life spans (if deciduous), and demographies that are usually syn- Manuscript received 17 June 2002; revised 20 November 2002; accepted 30 December 2002; final version received 18 Feb- ruary 2003. Corresponding Editor: S. D. Smith. 6 E-mail: preich@umn.edu chronized with seasonal patterns. A similar linkage of tree species phenology with seasonality occurs in many, but not all, species in markedly seasonal tropical forests and woodlands (Frankie et al. 1974, Reich and Borchert 1984, Shukla and Ramakrishnan 1984, Reich 1995, Williams et al. 1997). In contrast, in relatively aseasonal environments, phenology, longevity, and de- mography may be relatively asynchronous within and among different species (Borchert 1980), but the degree of asynchrony and details about leaf survivorship and mortality patterns are not well known. Data regarding the leaf life span of tropical rain for- est plants have only become available during the past quarter century. A pioneering study by Bentley (1979) reported two-year survivorship of 135 leaves (five leaves from each of 27 woody species). Since that time, only a relatively small number (15–25) of detailed leaf demography studies have been made that are rel- evant to the ecology of tropical evergreen moist forests.