Although functional traits are defined based on their impact on demographic parameters, trait-demography relationships are often reported as weak. These weak relationships might be due to disregarding trait interactions and environmental contexts, which should modulate species trait-demography relationships. We applied different models, including boosted regression tree (BRT) models, to investigate changes in the relationship between traits and demographic rates of tropical tree species in plots along an elevational gradient and among time intervals between censuses, analyzing the effect of a strong drought event. Based on a large dataset of 18,000 tree individuals from 133 common species, distributed among twelve 1-ha plots (habitats) in the Atlantic Forest (Brazil), we evaluated how trait interactions and the environmental context influence the demographic rates (growth, mortality, and recruitment). Functional traits, trait-trait, and trait-habitat interactions predicted demography with a good fit through either BRTs or linear mixed-models. Changes in growth rates were best related to size (diameter), and mortality rates to habitats, while changes in recruitment rates were best related to the specific leaf area. Moreover, the influence of traits differed among time intervals, and for demographic parameters, habitat affected growth and mortality by interacting with diameter. Here, we provide evidence that trait-demography relationships can be improved when considering the environmental context (space and time) and trait interactions to cope with the complexity of changes in the demography of tropical tree communities. Thus, to expand predictions of demography based on functional traits, we show that it is useful to fully incorporate the concept of multiple trait-fitness optima, resulting from trait interactions in different habitats and growth conditions. 

Data from forest inventories conducted in twelve 1-ha plots distributed in undisturbed areas of “Restinga” (one plot), Lowland forest (four plots), Submontane forest (four plots), and Montane forest (three plots) of the Serra do Mar. All woody stems (trees, palms, and tree ferns) with a diameter at breast height (DBH) equal to or larger than 4.8 cm were tagged, taxonomically identified, and measured for diameter and re-censused four times over 12 years (2005 – 2016). The forest inventories database represents 22,770 stems from 21,509 tree individuals belonging to 685 species from 70 botanical families. For each species, we collected data on six functional traits representing the leaf, seed, and wood economics spectra. We measured leaf area (LA, cm²), leaf dry matter content (LDMC, mg g- ¹), and specific leaf area (SLA, cm² g- ¹) from ten leaves of ten individuals per species.  As a measure of the species’ potential size, hereafter referred to as ‘DBH’, we calculated the 0.95 percentile of the distribution of stem DBH for each species using the forest inventories dataset. Seed mass (SM, mg) and wood density (WD, cm³ g- ¹) were obtained from three global repositories, Global wood density database (Zanne et al., 2009), BIEN (Maitner et al., 2018) and TRY (Kattge et al., 2011), and from the literature (Bello et al., 2017; Bufalo et al., 2016; Chave et al., 2009; Wanderley et al., 2016). When the same species was present in two or more datasets, we computed the average for its trait values.