Seasonality of reproduction in an ever‐wet lowland tropical forest in Amazonian Ecuador

Abstract

Flowering and fruiting phenology have been infrequently studied in the ever‐wet hyperdiverse lowland forests of northwestern equatorial Amazonía. These Neotropical forests are typically called aseasonal with reference to climate because they are ever‐wet, and it is often assumed they are also aseasonal with respect to phenology. The physiological limits to plant reproduction imposed by water and light availability are difficult to disentangle in seasonal forests because these variables are often temporally correlated, and both are rarely studied together, challenging our understanding of their relative importance as drivers of reproduction. Here we report on the first long‐term study (18 years) of flowering and fruiting phenology in a diverse equatorial forest, Yasuní in eastern Ecuador, and the first to include a full suite of on‐site monthly climate data. Using twice monthly censuses of 200 traps and >1000 species, we determined whether reproduction at Yasuní is seasonal at the community and species levels and analyzed the relationships between environmental variables and phenology. We also tested the hypothesis that seasonality in phenology, if present, is driven primarily by irradiance. Both the community‐ and species‐level measures demonstrated strong reproductive seasonality at Yasuní. Flowering peaked in September–November and fruiting peaked in March–April, with a strong annual signal for both phenophases. Irradiance and rainfall were also highly seasonal, even though no month on average experienced drought (a month with <100 mm rainfall). Flowering was positively correlated with current or near‐current irradiance, supporting our hypothesis that the extra energy available during the period of peak irradiance drives the seasonality of flowering at Yasuní. As Yasuní is representative of lowland ever‐wet equatorial forests of northwestern Amazonía, we expect that reproductive phenology will be strongly seasonal throughout this region.

Flower production decreases with warmer and more humid atmospheric conditions in a western Amazonian forest

“…Solar irradiance (measured in Wm À2 ), rainfall (mm), and temperature (°C) were recorded hourly at ECY from May 2000 to February 2012 using two LI-COR LI-200S pyranometers (calibrated for the daylight spectrum, 400 to 1100 nm), a LI-1400-102 air temperature sensor, a LI-1400-106 tipping bucket, and a Li-1400 data logger (LI-COR Inc., Lincoln, NE, USA; Garwood et al, 2023). Relative humidity was recorded from January 2008 by a LI-COR 1400-04 sensor.…”

“…Flowering activity was monitored at the YFDP using the stationary trap methodology of Wright & Calderon (1995). Two hundred horizontal traps of 0.75 × 0.75 m (0.57 m 2 ) made of 1-mm fibreglass wire mesh were placed throughout the YFPD at 0.75 m aboveground (Garwood et al, 2023). Traps were inventoried approximately every 2 wk from February 2000 to February 2018 (435 censuses).…”

“…We combined hermaphroditic, female, or male flower fragments into a single 'flower presence' for each species. Morphospecies were assigned a unique code before further taxonomic identification, based on local reproductive adults and our permanent voucher collection (Valencia et al, 2004a;Garwood et al, 2023).…”