Shoot growth of woody trees and shrubs is predicted by maximum plant height and associated traits

Authors: Gleason, Sean; STEPHENS, ANDREA E.A. - Macquarie University; TOZER, WADE - Macquarie University; BLACKMAN, CHRIS - Macquarie University; BUTLER, DON - Macquarie University; CHANG, YVONNE - Macquarie University; COOK, ALICIA - Macquarie University; COOKE, JULIA - Macquarie University; LAWS, CLAIRE - Macquarie University; ROSELL, JULIETA - Macquarie University; STUART, STEPHANIE - Macquarie University; WESTOBY, MARK - Macquarie University

Submitted to: Functional Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/18/2017
Publication Date: 8/15/2017
Citation: Gleason, S.M., Stephens, A., Tozer, W.C., Blackman, C.J., Butler, D.W., Chang, Y., Cook, A.M., Cooke, J., Laws, C.A., Rosell, J.A., Stuart, S.A., Westoby, M. 2017. Shoot growth of woody trees and shrubs is predicted by maximum plant height and associated traits. Functional Ecology. 10.1111/1365-2435.12972.
DOI: https://doi.org/10.1111/1365-2435.12972

Interpretive Summary: 1. The rate of elongation and thickening of individual branches (shoots) varies across plant species. This variation is important for the outcome of competition. Here we compared rates of shoot growth across 44 species from tropical, warm temperate, and cool temperate forests of eastern Australia. 2. Shoot growth rate was found to be correlated with other plant characteristics, including leaf size, the ability of stem tissue to transport water, the potential height of the species, as well as the density and stiffness of wood. 3. Maximum plant height was the best predictor of growth rate, whereas the other traits tended to be associated with plant height, rather than growth. 4. Correlations between growth and maximum height were evident across different sites, as well as between species occurring in the same site. A particularly important driver of growth was the amount of light received, which also varied significantly from plant to plant and from site to site. 5. We interpret this bundle of associated plant traits (growth, maximum height and the other plant traits) as being “coordinated” by the process of natural selection.

Technical Abstract: 1. The rate of elongation and thickening of individual branches (shoots) varies across plant species. This variation is important for the outcome of competition and other plant-plant interactions. Here we compared rates of shoot growth across 44 species from tropical, warm temperate, and cool temperate forests of eastern Australia. 2. Shoot growth rate was found to be correlated with a suite of traits including leaf size, leaf area per xylem cross-section, twig size, potential height of the species, wood density, modulus of elasticity and xylem-specific conductivity. 3. Within this suite of traits, maximum plant height was the clearest correlate of growth rates, explaining 67% of the variation in growth overall (p < 0.0001), and 22% of the variation (p = 0.012) in growth after accounting for the influence of the other traits. One possible interpretation is that the other traits were related to growth rates only indirectly via their correlation with maximum height. Growth rates were not correlated with leaf nitrogen or leaf mass per unit leaf area. 4. Correlations between growth and maximum height arose both across latitude (47%, p < 0.0001) and from within-site differences between species (30%, p < 0.0001). Covariation between growth and maximum height was driven in part by variation in irradiance across sites as well as among canopy positions within sites (23%, p < 0.0001). A significant fraction of this shared variation was independent of irradiance (45%, p < 0.0001), reflecting intrinsic differences across species and sites. 5. We interpret growth, maximum height and the suite of associated traits as coordinated by natural selection primarily on life-histories rather than as arising from proximate physiological causation.