A Backyard Hedge and the Drying Ground

The Hedge and the Gap

Nia’s backyard has a tall hedge along one edge. A wide gap in the hedge opens onto a grassy lane. Nia notices that the ground behind the hedge sometimes feels damp when nearby ground feels dry. She wonders whether the hedge changes what happens to water in the soil. Her model will include land, water, air, and living things. Soil belongs to the land system, and the hedge belongs to the living system.

First, Nia watches two matching ribbons tied at the same height. One is behind the hedge. The other is beside the gap. During the same ten minutes, the gap ribbon streams outward much more often. The sheltered ribbon usually hangs down. Nia uses the ribbons as clues about moving air, not as tools for measuring an exact wind speed.

Next, an adult helps Nia set up two matching shallow trays. Each contains the same kind, amount, and depth of soil, with the same amount of water mixed in. Neither tray contains plants. One tray goes behind the hedge; the other goes beside the gap. Both places remain shaded throughout the two-hour test. The trays start at the same temperature.

Nia weighs each tray before and after the test. There is no rain, watering, or spilling during those two hours. The soil stays inside the trays. The decrease in mass records water that leaves the soil and enters the air as water vapor. This change is called evaporation. Nia repeats the test the next morning with fresh, equally damp soil. The graph shows her results.

The trays represent a small part of the backyard: its soil surface. Real backyard soil also contains roots. Roots take up water from soil, and water helps plants stay firm and grow. Nia has not measured how much water the hedge takes up. When she draws her model, she uses labeled arrows. Each arrow shows a movement or an effect, rather than simply joining two names.