Population structure, light preferences, and late-wet season pre-dispersal fruit predation in <i>Bonellia nervosa</i>, a tropical dry forest understory tree with reverse phenology

Introduction: Bonellia nervosa is a dry forest understory tree with reverse leafing phenology (it produces leaves during the dry season and is deciduous during the wet season). Being a phreatophytic species, it relies on substantial root biomass to access groundwater and flush leaves during the dry season. Objective: assess the population structure of B. nervosa in Santa Rosa National Park, Costa Rica; analyze the relationship between stem diameter and plant height; and examine how canopy structure and light availability influence its local abundance. We also evaluated fruit maturity and pre-dispersal fruit predation during the late wet season to understand its reproductive success. Methods: the study was conducted along the Indio Desnudo trail (6.16 ha). Hemispherical photographs were taken above or near each B. nervosa (n = 33) and at 10 random sites where the species was absent. We used principal component analysis to consolidate seven light and canopy structural variables. The Chapman-Richards model was applied to examine the relationship between stem diameter and height and to identify inflection points. We analyzed fruit weight and seed count and inspected each fruit for the presence of Tortricidae larvae. Results: Adults dominated the population (only three seedlings were found out of 33 individuals). The Chapman-Richards model identified an inflection point at 70.6 cm in height, indicating a shift from relatively rapid to progressively slower growth. Bonellia nervosa sites had higher canopy openness (14.68 %) and transmitted diffuse light (21.05 μmol/m²/s) than sites where the species was absent (12.42 % and 18.22 μmol/m²/s, respectively). Predispersal fruit predation was low (16 % of fruits, n = 39), and was effected by Tortricidae larvae. Conclusions: Seedlings are likely limited by high energy demands for reserve accumulation, vulnerability to drought-related mortality, mechanical damage, and susceptibility to herbivory and pathogens. Their scarcity creates a recruitment bottleneck. The dominance of adults, the low number of seedlings, and specific light preferences limit the plasticity and adaptive capacity of B. nervosa to environmental changes. Although pre-dispersal fruit predation was low, further monitoring is needed to assess its full impact. Future research should focus on the physiological mechanisms underlying B. nervosa’s reverse leaf phenology and its resilience to climate change.