Most trees and other plants have root systems that grow less than three feet deep and pull water from soil. A small number of species called phreatophytes have root systems capable of reaching deep into groundwater supplies. That helps them survive in arid and semiarid climates where soil moisture is scarce.
Phreatophytes often grow in riparian zones along rivers where the water table is shallow. Most phreatophyte roots stop when they reach the water table and likely don't grow down more than 30 feet (10 m). However, one salt cedar root system found during excavation of the Suez canal in the 1950s went more than 100 feet (30 m), or about eight stories, deep.
Cottonwood, willow, and mulberry trees are common phreatophytes native to Kansas. In some places, they are being pushed out by non-native phreatophytes such as salt cedar (Tamarix) and Russian olive trees. These invaders, native to central Asia, were brought into the area as early as the late 1800s to be used as ornamental plants or to protect river and creek banks from erosion. Producing prodigious amounts of seeds that carry long distances in the wind, they have spread and easily adapted to the environment in western and south-central Kansas.
Researchers at the Kansas Geological Survey studied the effect that this spread of non-native species had on the native cottonwood, willow, and mulberry trees. Survey study sites included one along the Arkansas River near Larned in Pawnee County and another on the Cimarron River near Ashland in Clark County.