Height Matters: Predicting Woody Plant Growth Across Climates

The researchers studied shoot growth rates in 44 species of angiosperm woody trees and shrubs from tropical, warm temperate, and cool temperate forests in different parts of Australia. They hypothesized that plant height, leaf size, and branch diameter are linked to growth, suggesting taller species may have traits that help them better compete for resources like light and water. This study aims to clarify how adaptations and inherited traits enhance plant growth and resource use, helping ecologists and environmentalists predict growth patterns for reforestation, conservation, and mitigating global warming.

Figure 1 presents a structural equation model (SEM) analyzing various woody plant traits and their effects on shoot length and diameter. The independent variables include maximum height and traits like KS, LS, LX, TD, MOE, WD, LMA, SWC, and LN. The researchers controlled for factors like light, soil, and moisture, focusing on three key growth traits: Hydraulics (Hyd) for water transport, Biomechanics (Bio) for structural strength, and the Leaf Economics Spectrum (LES) for resource use. Their findings show that height is the main predictor of shoot growth, with a strong positive relationship of 0.80-0.91, indicating taller plants are better at capturing light and resources. Hydraulic traits positively influence growth, while biomechanical and LES traits have little to no effect, suggesting they are less important for height and support. Overall, maximum height explained 50%–67% of growth variation and 23%–32% when other traits were held constant.

Figure 2 shows the maximum height of plants located in different temperatures in length and diameter. The graph represents two sections - A and B - denoted by the symbols Tropical Temperature (+), Warm Temperature (Δ), and Cool Temperature (○). Section A represents the maximum height the plant grows (X) and the increase in length of the plant (Y). The figure also depicts that tropical weather has a substantial increase in length as opposed to the cool and warm temperatures. Section B represents the maximum height the plant grows (X) and its increase in diameter (Y). Similarly, the graph in section B shows that the tropical temperature also leads to an increase in the diameter of the plant. Overall, when the plant is placed in a tropical climate, the plant tends to grow faster and at an increase in length and diameter.

Figure 3 displays the increase in length and diameter of the plants in relation to irradiance (measure of sunlight per unit area overtime). The irradiance was measured by using a Gap Light Analyzer to estimate the mean short-wave radiation transmitted through the canopy directly hitting the plant species. The irradiance levels were highest in tropical and warm climates while being the lowest in cold climates. The tropical climate had the highest length increase in relation to irradiance, while the lowest being in warm climates. This goes against the idea that more sunlight means an increased rate of plant growth. This could be the result of natural selection and the adaptation to the conditions of the environment around the plant. Cold temperatures had yielded better results in both diameter and length in relation to its irradiance.

Height had seemed to be the largest indicator for plant growth, as when measured for most relevance to diameter and length growth it had the most significant effect. Then it showed how the maximum height correlated to increase in length and diameter, both increasing. Tropical climate had the most increase in diameter and length in accordance with irradiance. Results show how plants in tropical climates yielded the highest plant growth rate and how height was most useful in determining that.

Gleason, S.M., Stephens, A.E.A., Tozer, W., Blackman, C., Butler, D., 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., 32, 247–259. 10.1111/1365-2435.12972