How Coast Redwoods Drink Water from Fog
Why the world’s tallest trees rely on atmospheric moisture.
The Coast Redwood (Sequoia sempervirens) can grow to heights exceeding three hundred and fifty feet, making it the tallest tree species on Earth. Moving water from the underground roots all the way to the top of such a massive canopy requires hydraulic force. During dry summer months, gravity and friction make it nearly impossible for the tree to pull enough groundwater to sustain the highest branches. To survive, redwoods pull water directly from the air using their leaves.
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This survival strategy relies on the thick blankets of fog that roll in from the Pacific Ocean along the California coast. The fog provides a consistent source of atmospheric moisture when summer rainfall levels decrease.
Redwood needles have an anatomical structure that allows for foliar uptake, which is the direct absorption of water through the leaf surface. The outer cuticle of the needle features tiny pathways that allow liquid water from the fog to pass directly into the internal leaf tissue, bypassing the root system.
During a heavy fog event, the upper canopy leaves absorb this moisture and use it to maintain cellular hydration. If the fog persists, the process can reverse the standard direction of water flow within the tree’s vascular system. Water absorbed by the highest leaves moves downward through the xylem tubes, which hydrates the lower branches and leaks out into the soil around the base of the trunk.
This atmospheric watering system provides up to one-third of the redwood forest’s total annual water supply. By using foliar uptake, redwoods maintain active growth rates throughout the dry season, overcoming the physical height limits that restrict other tree species.
