|Lenz, James - Jim|
Submitted to: Journal of Arid Environments
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/26/1998
Publication Date: N/A
Citation: Interpretive Summary: Creosotebush and tarbush are two common plants in the Chihuahuan Desert, the largest desert in North America. The Chihuahuan Desert occurs in New Mexico, Texas and Arizona, and throughout much of north central Mexico. Over the past 100 years both creosotebush and tarbush have invaded desert grasslands throughout much of this region. Many of these invaded areas are enow in poor condition. There are several causes of this general invasion and it is expected that bush invasion into grasslands will continue in some areas. This study was conducted to determine soil characteristics common to areas where creosotebush and tarbush have invaded. A purpose of this study was to learn what areas in this desert might still be susceptible to invasion by these two plant species. This study determined that both of these shrubs have roots that are well suited to coarse soils containing gravel. Even soils that contained a cement-like layer below the surface and that could be 3 feet thick in places were suited to growth of these plants. The roots of both of these bushes were able to find cracks in these cement-like layers and were able to grow further down into the soil below these hard layers. Plants grew on young and old soils, and on slopes and in flat areas. In some areas roots were found to depths of 16 feet below the soil surface. It was concluded that much of this desert is still open to invasion by these plants, and management practices need to control the movement of these shrubs into new areas suited to their growth.
Technical Abstract: Creosotebush and tarbush are 2 of the major shrub invaders of grassland in desert areas of southern New Mexico. Soils and root systems associated with these 2 shrubs were studied at 3 sites on an alluvial-fan piedmont. The soils have formed in alluvium derived from monzonite, rhyolite, and andesite, in deposits ranging in age from late Holocene to middle Pleistocene. Soil age, carbonate morphology, particle size, and landscape position were major factors associated with root variability. The stage I carbonate that occurs in youngest soils has little influence on root distribution because the carbonate consists of thin coatings on sand grains and pebbles. The increasing carbonate that occurs in stages II, III, and IV results in denser zones of carbonate that control the routes for movement of soil water and roots. Individual nodules and cemented pebbly zones grow and eventually merge, and they represent zones of restricted hydraulic conductivity, funneling soil water and roots to as yet uncemented parts of the horizon. Continued carbonate accumulation leads to a plugged horizon and an overlying stage IV laminar horizon that is a barrier to roots. Particle size controls the time and amount of carbonate required for formation of these horizons. Calciargids of late Pleistocene age that averaged 4% and 32% by volume of gravel and contained 415 and 317 kg/m**2 of pedogenic carbonate respectively had stage III horizons. In contrast, a Petrocalcid of the same age and averaging 63% by volume of gravel required 205 kg/m**2 of carbonate to form the stage IV horizon. Runoff from soils sloping 2% reduces the number of days with available soil water at various depths as compared to 1% slopes below. At the 2% slope, roots did not extend below 2 m depth whereas at the 1% slope, roots extended to 5 m.