Linking size‐dependent growth and mortality with architectural traits across 145 co‐occurring tropical tree species

Abstract

Tree architecture, growth, and mortality change with increasing tree size and associated light conditions. To date, few studies have quantified how size-dependent changes in growth and mortality rates co-vary with architectural traits, and how such size-dependent changes differ across species and possible light capture strategies. We applied a hierarchical Bayesian model to quantify size-dependent changes in demographic rates and correlated demographic rates and architectural traits for 145 co-occurring Malaysian rain-forest tree species covering a wide range of tree sizes. Demographic rates were estimated using relative growth rate in stem diameter (RGR) and mortality rate as a function of stem diameter. Architectural traits examined were adult stature measured as the 95-percentile of the maximum stem diameter (upper diameter), wood density, and three tree architectural variables: tree height, foliage height, and crown width. Correlations between demographic rates and architectural traits were examined for stem diameters ranging from 1 to 47 cm. As a result, RGR and mortality varied significantly with increasing stem diameter across species. At smaller stem diameters, RGR was higher for tall trees with wide crowns, large upper diameter, and low wood density. Increased mortality was associated with low wood density at small diameters, and associated with small upper diameter and wide crowns over a wide range of stem diameters. Positive correlations between RGR and mortality were found over the whole range of stem diameters, but they were significant only at small stem diameters. Associations between architectural traits and demographic rates were strongest at small stem diameters. In the dark understory of tropical rain forests, the limiting amount of light is likely to make the interspecific difference in the effects of functional traits on demography more clear. Demographic performance is therefore tightly linked with architectural traits such as adult stature, wood density, and capacity for horizontal crown expansion. The enhancement of a demographic trade-off due to interspecific variation in functional traits in the understory helps to explain species coexistence in diverse rain forests.

Demographic Properties Shape Tree Size Distribution in a Malaysian Rain Forest

“…Tallstatured species showed a high growth rate, low mortality, and low fecundity, whereas low-statured species showed the opposite demographic properties (table 1). This demographic trade-off between tree vitality (in growth and survival) and fecundity supported the prediction of the foliage partitioning theory for stable species coexistence by differentiating maximum adult size (Kohyama and Takada 2009), which has also been supported empirically (Thomas 1996;Kohyama et al 2003;King et al 2006aKing et al , 2006bPoorter et al 2008;Iida et al 2014). We found that differentiations in size-distribution skewness and upper size were associated with similar demographic properties, while we also detected that the low skewness was principally explained by low mortality-to-growth ratio in small tree sizes, whereas large upper size was mainly related to high growth rate, particularly of large-sized trees (table 1).…”

“…Actually, Iida et al (2014) and this study ( fig. 5A) found a weak indication of a growth-survival trade-off for small-sized trees in the Pasoh forest.…”

“…The estimation of size dependence in growth and mortality is inevitably affected by the size distribution itself. It is therefore preferable for interspecific comparison to employ community-wide statistical procedures for estimating the demographic parameters of each species (Rüger et al 2011a(Rüger et al , 2011bIida et al 2014).…”

“…We employed the morp p 1 Ϫ exp(ϪM(x)Dt) tality function previously used by Rüger et al (2011b) and Iida et al (2014):…”

Abiotic Controls on Macroscale Variations of Humid Tropical Forest Height

“…In addition, recent or past human induced land use activities such as small and large-scale forest clearing or tree extractions may have also influenced the variations of forest structure. This heterogeneity, generally using tree height and/or diameter as a measurable quantity, is therefore a reflection of environmental impacts on the local vegetated surface in humid tropical forests [20].…”