Climate as a proximate factor affecting the phenology of Atlantic rain forest trees

Changes on reproductive phenology of tropical forest trees have been related to seasonal variation on climatic factors, specially rainfall patterns and temperature. Recently, light has been pointed out as another important environmental factor affecting tree phenology. Few studies have analyzed tropical rain forest trees under low climate seasonality, without a dry season. Some studies report no seasonal patterns and irregular flowering and fruiting strategies while others describe more seasonal patterns, mainly for flowering, related to small variations on light and temperature. However, few long term data are available for tropical rain forest tree phenology, especially for Neotropical forests. The present study analyses a six year phenology data for Atlantic rain forest trees from Southeastern Brazil aiming to detect the relationship among and provide additional evidence for the influence of climate, mainly light, on tropical rain forest tree phenology. The study was conducted in an Atlantic tropical rain forest, located at the Intervales Stat Park, Southeastern Brazil, under a rather non seasonal climate. Climate is tropical wet, with substantial rain occurring every month. Monthly total rainfall average is above 200 mm from October to April (wetter period) and from 100 to 160 mm from May to September (less wet or drier period). During six non-consecutive years, trees were marked along trails inside the forest and observed monthly for changes on reproductive phenology (flower buds, flowers, unripe fruits, ripe fruits). Seasonal patterns were determined using circular statistic analyses. Flowering patterns were significantly seasonal, the peak occurring during the wettest season of the year, from November to February, (mean dates ranged from 02/Nov to 01/Dec), and presented a significant correlation to day length for all six years studied. Seasonal flower patterns did not differ among years. Fruiting patterns were less seasonal, significant seasonal patterns were detected for three out of the six years analyzed (mean dates ranged from 07/Nov to 09/Dec). Temperature and rainfall were significantly correlated to fruit phenology during the seasonal years. The study corroborates the seasonal flowering patterns and the influence of day length (light) on phenology of Atlantic rain forest trees. Temperature appears as another important factor related to flower phenology. Fruiting of animal dispersed species was significantly reduced during two years, when unexpected dry months (less than 80 mm rain/month during the less wet season) occurred. In spite of the low seasonal climate, abiotic factors as light, temperature and rainfall are determining the timing of reproduction of tropical rain forest trees, although biotic factors are probably shaping their time of occurrence within seasons. Financial support: FAPESP and CNPq