Analysis of functional traits of woody plant seedlings in an old-growth tropical lowland rain forest on Hainan Island, China

Abstract

Aims The traits of seedlings are often directly related to the performance and function of adult plants in an ecosystem.Measurements of seedling traits are easy and accurate compared to adult traits.Many studies have been conducted on the trait-based assembly of trees in tropical forests in recent years;however,studies on functional traits of seedlings with diameter at breast height(DBH) 1 cm are scarce.Our objective was to explore the variation of functional traits of woody seedlings in the old-growth tropical lowland rain forest on Hainan Island,China.Methods We selected the 16 most abundant species of woody plant seedling with a DBH 1 cm.They represented three growth forms: trees(nine species),shrubs(three species) and lianas(four species).They were also grouped into four growth stages according to the seedling height(H) classes: I(5 ≤ H 20 cm),II(20 ≤ H 40 cm),III(40 ≤ H 80 cm) and IV(80 ≤ H 120 cm).The major functional traits of these seedlings,specific leaf area(SLA),leaf mass fraction(LMF),specific stem density(SSD) and stem mass fraction(SMF) were measured.We assessed the variation in seedling functional traits among different growth forms and height classes and examined the correlations among functional traits.Important findings There were significant differences among varied growth stages in seedling functional traits.SLA and LMF decreased gradually,but SMF increased with the growth stages of seedlings.SSD was lowest in the first growth stage,but showed no significant difference among the subsequent three growth stages.There were no significant differences between trees and shrubs for any functional traits.Seedlings adapt to the stressful rainforest understory environment(such as low light) by decreasing SLA and LMF and increasing SMF.However,lianas adapt to the environment through the opposite strategy.There were significant correlations between the different functional traits of seedlings.Our study suggests that the seedlings of different growth forms in the tropical lowland rainforest adapt to their environment by changing the value of different functional traits.