Why Trees Don't Grow Indefinitely Tall: Hydraulic and Genetic Limits

Maximum tree height is governed by **multiple interacting factors**:

1. Hydraulic Limitation (Physics)

• Water moves up via **cohesion-tension** (transpiration pull).
• Gravity + path length resistance + cavitation risk increase with height.
• Beyond ~100–130 m (330–425 ft), water column breaks—**hydraulic failure**.
• Explains global max height (coastal redwoods ~380 ft).

2. Genetic Programming (Species Potential)

• Each species has a **genetically determined height range**.
• Breeding programs select for height/straightness (e.g., timber pines).

3. Site Index (Soil + Climate)

• Foresters use **Site Index** = height at 50 years on a given soil.
• Moist, deep, fertile soils → taller trees.
• Dry, shallow, poor soils → shorter trees.

4. Age-Related Decline

• Old trees **reduce height growth**; crown becomes flat/rounded.
• Hydraulic efficiency declines; carbon allocation shifts to maintenance/defense.

Key Reference

Ryan, M.G. et al. "Hydraulic Limits to Tree Height and Plant Growth" – Colorado State

**Trees grow tall until physics, genetics, or site says stop.**