In a mature pine forest, dry air changed how water moved through the soil

The result appeared even when plots received the same amount of water, pointing to a feedback between trees and soil.

Editorial illustration — not from the study.

Researchers used fine mist to lower atmospheric dryness around forest stands, while separate plots received extra irrigation or had half their rainfall excluded. The design allowed them to study atmospheric drought and soil drought independently rather than treating them as one condition.

During periods when atmospheric dryness was especially high, the mist lowered it by an average of 21%. Soil drying followed sustained high-dryness periods, starting in the topsoil and appearing later at greater depths. With the same water inputs, plots with lower atmospheric dryness showed different patterns of water loss deeper in the soil.

How dry air changed soil water

The experiment was carried out in a roughly 130-year-old Pinus sylvestris, or Scots pine, forest over two growing seasons. Fine mist reduced atmospheric dryness by an average of 21% when conditions exceeded the 90th percentile for atmospheric dryness. Soil drying after sustained periods of high atmospheric dryness began in the topsoil and progressed later at deeper layers. When water inputs were the same, reducing atmospheric dryness particularly changed deeper-soil water patterns, suggesting that plant activity helped link atmospheric conditions to soil moisture.

Why the soil connection matters

Atmospheric drought is often studied together with declining soil moisture, making it difficult to tell which stress is affecting trees and forests. These results indicate that dry air can also influence soil water dynamics through the soil–plant system, not only stress vegetation aboveground. Including atmospheric dryness in forest experiments and ecosystem models could therefore improve predictions of forest responses to increasing atmospheric drought.

Evidence and open questions

The findings come from a controlled, factorial field manipulation in one mature Scots pine forest, with continuous measurements across soil depths over two growing seasons. The study directly tested atmospheric dryness and soil water supply as separate factors, but the abstract does not establish how broadly the results apply to other forest types, climates or longer time periods. It also reports changes in soil water trajectories rather than a complete measure of long-term forest resilience.

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