The study looked at soil water levels in forests in a dry area called the Loess Plateau. The researchers found that the soil in the forests had low moisture levels, almost at the point where plants start to wilt. The soil was driest between 1.8 to 4.0 meters deep. This dryness was not caused by the trees, but by the region's climate. Dry soil layers were common in both forests and wastelands in the area.