Drought-modulated allometric patterns of trees in semi-arid forests

Area of Science:

• Ecology
• Forest Science
• Biometry

Background:

• Semi-arid forests exhibit distinct tree allometry: short stature with large canopies.
• This unique growth pattern is hypothesized to optimize water-use efficiency and carbon sequestration.
• Quantification of this allometry and its drivers remains a research gap.

Purpose of the Study:

• To quantify the allometric variations of Quercus mongolica in semi-arid forest ecosystems.
• To investigate the relationship between tree height, canopy area, and environmental factors, particularly water availability.
• To evaluate the accuracy of existing Dynamic Global Vegetation Models (DGVMs) in representing semi-arid forest allometry.

Main Methods:

• Terrestrial laser scanning (TLS) was employed to collect detailed 3D structural data of Quercus mongolica trees.
• Allometric relationships between tree height (Height) and canopy area (CA) were analyzed.
• Statistical analyses, including partial correlation, were used to determine the influence of water supply on Height and CA variations.

Main Results:

• Tree height (Height) exhibited significant variation influenced by water supply (P=0.000).
• Canopy area (CA) showed substantial variation but was not significantly correlated with water supply (P=0.2).
• Existing DGVMs significantly underestimate canopy area and overestimate height compared to TLS data, matching only the 5th percentile of observed CA-Height relationships.

Conclusions:

• The decoupled regulation of stem and canopy allometry, potentially driven by stem, hydraulic conductance, and leaf arrangement, ensures hydraulic safety and carbon assimilation.
• This mechanism may prevent forest dieback in water-limited environments.
• Accurate quantification of tree allometry is essential for improving drought tolerance studies and enhancing the performance of DGVMs.