The pipe model theory half a century on: a review

Area of Science:

• Plant Biology
• Ecology
• Mathematical Modeling

Background:

• The pipe model theory (PMT), proposed in 1964, explains the relationship between stem tissue and supported leaves, addressing plant form and biomass allocation.
• PMT provided answers to key questions about tree form determination and foliar area estimation, becoming a milestone in understanding plant structure and function.

Purpose of the Study:

• To review the pipe model theory (PMT) by examining its initial formulation and properties.
• To assess the validity and applicability of PMT in light of current biological knowledge and experimental evidence.
• To discuss PMT's application in tree biomechanics, hydraulics, and functional-structural plant modeling.

Main Methods:

• Revisiting the original formulation of the pipe model theory (PMT).
• Analyzing explicit and implicit properties of PMT.
• Evaluating PMT against modern biological understanding and experimental data.

Main Results:

• Most PMT properties are not universally valid under modern biological scrutiny.
• The hydraulic aspect of PMT is more influential than its mechanical aspect.
• The conductive stem portion, not the entire cross-section, is proportional to foliage, but is hard to measure and varies, potentially explaining non-linear relationships.

Conclusions:

• While not universally applicable, PMT offers a valuable framework for analyzing functional-structural plant relationships.
• The theory's hydraulic implications are significant, though practical measurement challenges exist.
• PMT remains a foundational concept for integrating diverse aspects of plant form and function.