|Gile, Leland - SOIL CONSERVATION SERVICE|
Submitted to: Journal of Arid Environments
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 26, 1996
Publication Date: N/A
Interpretive Summary: To achieve a better understanding of why mesquite has been such a successful invader of desert grasslands root systems of mesquite were excavated in a variety of soil environments. Mesquite roots of a single coppice dune were measured to extend laterally for 52 feet, traversing a complex pattern of four different soil types. The roots penetrated all soil horizons, even indurated caliche where roots grew downward through cracks and soil pipes to depths exceeding 10 feet. In a playa with a deep, fine-silty soil, mesquite roots descended to a depth of at least 18 feet. In both dune and playa sites, mesquite roots grew vertically upward to within two inches of the soil surface, enabling the plants to harvest water from small rainfall events. Thus, the successful establishment of mesquite is in no small part 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 descend to great depths along cracks and other openings in the soil, down which soil water also penetrates, and thus their ability to utilize available soil water at all depths.
Technical Abstract: A major invasion of grassland by shrubs began about 1850 A.D. in many desert areas of southern New Mexico. In the broad floor of the Jornada del Muerto Basin, mesquite (Prosopis glandulosa) is the most numerous of these invading shrubs. Mesquite roots in a coppice dune were excavated and traced laterally in an area with an extremely complex soil pattern (Petrocalcids, Torripsamments, Haplargids, and Calciargids). The roots readily penetrated all soil horizons except the continuously indurated petrocalcic horizon of the Petrocalcids. However, the roots grew along the top of the petrocalcic horizon 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 study site mesquite encroached into a playa dominated by Haplocalcids, in one of which mesquite roots descended to a depth of at least 5.5 m. Although the spread dof mesquite seed by cattle was a major factor in the spread of mesquite, its successful establishment over large areas was 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; 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.