BIOTROPICA 37(4): 620–630 2005 10.1111/j.1744-7429.2005.00079.x Tree Phenology in Adjacent Amazonian Flooded and Unflooded Forests 1 Torbjørn Haugaasen 2 and Carlos A. Peres Centre for Ecology, Evolution and Conservation, School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, UK ABSTRACT Most phenological studies to date have taken place in upland forest above the maximum flood level of nearby streams and rivers. In this paper, we examine the phenological patterns of tree assemblages in a large Amazonian forest landscape, including both upland (terra firme) and seasonally flooded (v´ arzea and igap´ o) forest. The abundance of vegetative and reproductive phenophases was very seasonal in all forests types. Both types of flooded forest were more deciduous than terra firme, shedding most of their leaves during the inundation period. Pulses of new leaves occurred mainly during the dry season in terra firme, whereas those in the two floodplain forests were largely restricted to the end of the inundation period. Flowering was concentrated in the dry season in all forest types and was strongly correlated with the decrease in rainfall. The two floodplain forests concentrated their fruiting peaks during the inundation period, whereas trees in terra firme tended to bear fruits at the onset of the wet season. The results suggest that the phenological patterns of all forest types are largely predictable and that the regular and prolonged seasonal flood pulse is a major determinant of phenological patterns in v´ arzea and igap´ o, whereas rainfall and solar irradiance appear to be important in terra firme. The three forest types provide a mosaic of food resources that has important implications for the conservation and maintenance of wide-ranging frugivore populations in Amazonian forests. RESUMO A maioria dos estudos fenol´ ogicos em florestas tropicais foi feito em ´ areas acima do n´ ıvel m´ aximo da inundac ¸˜ ao dos rios. Neste trabalho n´ os examinamos os padr˜ oes de produc ¸˜ ao de folhas, flores e frutos numa paisagem amazˆ onica, incluindo florestas de terra firme, v´ arzea, e igap´ o. A abundˆ ancia de fenofases vegetativas e reprodutivas mostrou-se bastante sazonal tanto nas florestas de terra firme quanto as sazonalmente inundadas. As florestas inund´ aveis eram mais dec´ ıduas do que as terra firme, deixando cair mais folhas durante o per´ ıodo de inundac ¸˜ ao. A emergˆ encia de folhas novas ocorreu principalmente durante o per´ ıodo de seca na terra firme, enquanto que nas florestas inund´ aveis isto foi mais restrito ao final do per´ ıodo de inundac ¸˜ ao. As florac ¸˜ oes foram concentradas durante o per´ ıodo de seca em todos os tipos de floresta e inversamente correlacionadas ` a pluviosidade. Florestas de v´ arzea e de igap´ o concentraram sua produc ¸˜ ao de frutos durante o per´ ıodo de inundac ¸˜ ao, ao passo que a disponibilidade de frutos na terra firme coincidiu principalmente com o in´ ıcio do per´ ıodo de chuvas. Os resultados sugerem que os padr˜ oes fenol´ ogicos em todos os tipos florestais s˜ ao em grande parte previs´ ıveis e que o regime de inundac ¸˜ ao sazonal ´ e o principal determinante dos padr˜ oes de fenologia na v´ arzea e no igap´ o, ao passo que a precipitac ¸˜ ao e a radiac ¸˜ ao solar parecem ser importantes na terra firme. Na paisagem heterogˆ enea do baixo Rio Pur´ us, os trˆ es tipos de floresta fornecem um mosaico espac ¸o-temporal de recursos para a fauna local, o que gera implicac ¸˜ oes importantes para a manutenc ¸˜ ao de populac ¸˜ oes de vertebrados frug´ ıvoros que requerem grandes ´ areas de vida na floresta amazˆ onica. Key words: Amazonia; Brazil; inundation forest; leaf phenology; reproductive phenology; supra-annual; tree mortality. PLANT PHENOLOGY IS THE STUDY OF PERIODICITY IN THE PRO- DUCTION OF VEGETATIVE and reproductive plant structures, most notably the leafing, flowering, and fruiting schedules. In tropical forests, individual trees vary from nearly continuous to repeated, brief bursts of activity, to erratic, supra-annual phenological pat- terns. Species may also display patterns ranging from complete in- trapopulation synchrony to complete asynchrony. However, only a small proportion of individuals generally exhibit continuous leafing, flowering, or fruiting; most phenological observations in tropical plants show that flowering and fruiting is episodic and that the availability of flowers and fruits varies seasonally. This trend has been demonstrated for all major blocks of tropical for- est: South-East Asia (e.g., Medway 1972, Hilty 1980, Leighton & Leighton 1983, van Schaik 1986), South and Central Amer- ica (Frankie et al. 1974, Opler et al. 1980, Foster 1982, Terborgh 1983), and Africa (Lieberman 1982, Gautier-Hion et al. 1985, White 1994, Chapman et al. 1999). Likewise, long-term stud- ies have demonstrated significant differences in flower and fruit 1 Received 1 November 2004; revision accepted 15 March 2005. 2 Corresponding author; e-mail: T.Haugaasen@uea.ac.uk availability among years (Foster 1982, Leighton & Leighton 1983, Corlett 1990). The common denominator of all the above studies is that they were carried out in a diverse range of upland forests, i.e., forests that are situated above the maximum flood level of nearby rivers and streams. However, in a region such as lowland Amazonia, a mosaic of different forest types can be found embedded in an otherwise homogenous-looking landscape. In addition to the upland forest known as terra firme, several types of floodplain forests are recog- nized in the Amazon region based on hydrochemical (Sioli 1968) and floristic differences (Prance 1979). These floodplain forests have received comparatively little attention. For most species in flood- plain forests, we do not even know whether they are deciduous or evergreen or how their seeds are dispersed (Parolin et al. 2002). With the exception of a recent 6-yr phenological study of Ceiba pentandra L. (Bombacaceae; Gribel et al. 1999), long-term studies are almost completely lacking, as are publications summarizing and describing the phenological traits of Amazonian floodplain tree communities. Work has instead largely been carried out on a restricted number of species and focused on reproduction, physiology, morphology, or anatomy (e.g., Worbes 1988; Schl¨ uter 1993; Waldhoff et al. 1998; Parolin 2000, 2001, 2002). 620