Tree growth traits and social status affect the wood density of pioneer species in secondary subtropical forest.

Lingxiu Chen,Pifeng Lei,Wenhua Xiang,Xiangwen Deng,Xi Fang,Huili Wu,Shuai Ouyang,Shengli Zhang

doi:10.1002/ece3.3110

Abstract

Wood density (WD) is not only an important parameter to estimate aboveground biomass but also an indicator of timber quality and plant adaptation strategies to stressful conditions (i.e., windthrow, pests, and pathogens). This study had three objectives: (1) to compare WD among seven subtropical tree species; (2) to determine how tree growth traits may influence possible differences in WD between the pioneer and shade‐tolerant species; and (3) to examine whether or not WD differs by tree social status (dominant vs. suppressed trees) within species. To do this, 70 trees were destructively harvested. From each tree, disks at different stem heights were obtained and subjected to a method of stem analysis to measure whole tree level WD. The results showed that WD differed significantly among the seven species (p < .001). Their average WD was 0.537 g/cm3, ranging from 0.409 g/cm3 for Choerospondias axillaris to 0.691 g/cm3 for Cyclobalanopsis glauca. The average WD of the four pioneer species (0.497 ± 0.13 g/cm3) was significantly lower (p < .01) than that of the three shade‐tolerant species (0.589 ± 0.12 g/cm3). The WD of the pioneers had a significant positive correlation with their stem diameter at breast height (DBH), tree height (H), and tree age, but WD had a significant negative correlation with relative growth rate (RGR). In contrast, the WD of the shade‐tolerant tree species had no significant relationships with DBH, H, tree age, or RGR. The dominant trees of the pioneer species had a higher WD than the suppressed trees, whereas the shade‐tolerant species had a lower WD for dominant trees than the suppressed trees. However, the differences in WD between dominant and suppressed trees were not significant. Taken together, the results suggest that classifying species into pioneer and shade‐tolerant groups to examine the effects of tree growth traits and social status could improve our understanding of intra‐ and interspecific variation in WD among subtropical tree species.

Highlights

Woody stem is the most important component of stand biomass (Xiang et al, 2016), carbon (C) stocks (Gao, Taylor, Chen, & Wang, 2016), and net primary production in forest ecosystems (Gower et al, 2001)
Wood density (WD) is a vital woody stem functional trait that is closely related to the quantity and quality of woody products (Acuna & Murphy, 2007; Skovsgaard & Nord-Larsen, 2011), stand biomass, and C stock estimation (Chave et al, 2009; Plourde, Boukili, & Chazdon, 2015; Wiemann & Williamson, 2002; Zhang et al, 2012) in addition to paleoclimate reconstruction (O’Donnell et al, 2016)— WD is closely related to the survival and growth rates of species under strong selective pressure in their environment (Falster, 2006; King, Davies, Tan, & Nsm, 2006; Preston, Cornwell, & DeNoyer, 2006)
This study had three aims: (1) to compare WD among the subtropical tree species; (2) to determine how tree growth traits may influence possible differences in WD detected between pioneer and shade-tolerant species; and (3) to examine whether WD differs by tree social status for a given species, and whether these differences, if any, may be contrasted for the pioneer and shade-tolerant species

Summary

| INTRODUCTION

Woody stem is the most important component of stand biomass (Xiang et al, 2016), carbon (C) stocks (Gao, Taylor, Chen, & Wang, 2016), and net primary production in forest ecosystems (Gower et al, 2001). Pioneer tree species tend to grow very well in temporarily lighted conditions, wherein they produce low-density wood to maximize height growth and stem diameter in early successional habitats (Woodcock & Shier, 2002) These lower WD trees have a higher mass growth rate than their neighbors, often at the expense of greater longevity (Chave et al, 2009; Enquist et al, 1999; King et al, 2006; Plourde et al, 2015). It is necessary to examine whether the relationship between WD and growth traits may differ between pioneer and shade-tolerant species In forests, where they face strong competition for light, trees become vertically differentiated by their crown or social status, leading to both dominant and suppressed trees within species populations. This study had three aims: (1) to compare WD among the subtropical tree species; (2) to determine how tree growth traits may influence possible differences in WD detected between pioneer and shade-tolerant species; and (3) to examine whether WD differs by tree social status for a given species, and whether these differences, if any, may be contrasted for the pioneer and shade-tolerant species

| MATERIALS AND METHODS

| DISCUSSION

Findings

| CONCLUSIONS