The near-ubiquitous pedogenic world of mesquite roots in an arid basin floor

A major invasion of grassland by shrubs began about 1850 A.D. in many desert areas of southern New Mexico. Mesquite (Prosopis glandulosa) is the most numerous of these invading shrubs in a studied basin floor. Mesquite roots readily penetrated all soil horizons except for continuously indurated petrocalcic horizons. However, roots grew along the top of petrocalcic horizons and in places found locations for penetration, such as cracks and pipes, with numerous, often upward-growing roots enroute to utilize the sparse precipitation. At another site, mesquite roots descended to a depth of at least 5•5 m. Although the spread of mesquite seed by cattle was a major factor in the spread of mesquite, its successful establishment over large areas is apparently due to the ability of mesquite roots to adapt to a wide variety of soils and soil conditions to take advantage of the sparse precipitation; to their ability to greatly proliferate while spreading laterally over long distances; to grow upward and take advantage of small precipitation events that only wet the soil to depths of a few centimeters; and to descend to great depths along cracks and other openings in the soil, down which soil water also penetrates, and thus to their ability to utilize available water at all depths.