Abstract
Propagule dispersal is a crucial life history stage, which affects population recruitment and regeneration as well as community structure and functions. The windborne process of samara dispersal is affected not only by samara traits and other plant traits, but also by environmental factors. Therefore, studying samara traits related to its dispersal and intraspecific variation in relation to other plant traits and environmental factors could help to understand population distribution and dynamics. Hopea hainanensis, a Dipterocarpaceae tree species dominant in lowland rainforests in Hainan (China) but endangered due to anthropogenic disturbances, is dispersed mainly by wind because of its sepal-winged samara. Here, we measured dispersal-related intraspecific samara traits of H. hainanensis, and analyzed their variation and correlation in relation to plant height, DBH (diameter at breast height), and elevation plant location. Great variations in the samara traits existed, and the variations were larger within than among individuals, which indicated a “bet-hedging” strategy of this species. Plant height, DBH, and elevation explained slight variation in the samara traits. Samara dispersal potential is mainly affected by the samara mass and morphological traits. Samara settling velocity was significantly positively correlated with fruit mass, seed mass, length and width, as well as samara wing loading, and negatively correlated with wing mass ratio, wing area, and wing aspect ratio. Substantial proportions of intraspecific variation in samara dispersal are explained by the samara mass and morphological traits. Natural regeneration with human-aided dispersal is necessary for recovering the H. hainanensis population. This finding contributes to the generalization of trait-based plant ecology, modeling of seed dispersal in tropical forests, and conservation and recovery of rare and endangered species such as H. hainanensis.
Highlights
Plant functional traits are morphological, physiological, and phenological characteristics by which plants interact with their environment during evolutionary processes
Intraspecific Samara Trait Variations (Struckman et al, 2019), species distribution models (Benito Garzón et al, 2019), community assembly (Ackerly and Cornwell, 2007), ecosystem function (Cornwell et al, 2008), global vegetation models, prediction of ecosystem responses to global changes (Diamond et al, 2012), and evaluation of ecosystem services (Díaz et al, 2007, 2011), which has been a new paradigm in ecology (Wright et al, 2004; van Bodegom et al, 2014; Díaz et al, 2016; He et al, 2019, 2020)
Identifying and measuring functional traits related to responses to environmental changes and ecosystem function of endangered species could contribute to understanding the mechanism of being endangered or threatened and its implications for conservation practice (Chown, 2012; Cochrane et al, 2015; Turner et al, 2017; Álvarez-Yépiz et al, 2019), especially under the uncertainty of climate changes in the future (Di Musciano et al, 2020)
Summary
Plant functional traits are morphological, physiological, and phenological characteristics by which plants interact with their environment during evolutionary processes. Seed dispersal traits (and their variations), such as seed size, mass, and dispersal mode affect dispersal distance and potential, seedling emergence and survival, plant colonization and growth (Janzen, 1970; Saatkamp et al, 2019; Schupp et al, 2019; Snell et al, 2019; Beckman et al, 2020) These dispersal traits impact population dynamics, interspecific interactions, population regeneration, community assembly and succession, and ecosystem service delivery (Grubb, 1977; Ribeiro et al, 2016; Saatkamp et al, 2019). Dipterocarpaceae has 16 genera and approximately 500 species widely distributed in Asian tropical forests Seeds from this family usually are bract-winged samaras possessing aerodynamic behavior of helicopters characterized by relatively stable flight, explicit dispersal direction, and long dispersal distance (Augspurger, 1986). We sampled and measured samaras of H. hainanensis from natural populations in a tropical mountain cloud forest, located in Bawangling Nature Reserve, Hainan Island, South China, to answer the following scientific questions: (1) What are intraspecific variations of samara traits? (2) Are such traits related to intrinsic or extrinsic factors? (3) Is there any tradeoff among samara traits in H. hainanensis? and (4) Which samara traits affect samara settling velocity in H. hainanensis?
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