Sources of water used by natural mesquite vegetation in a semi-arid region of northern Mexico

Abstract

Vegetation structure in semi-arid regions of northern Mexico and the southwestern USA has changed dramatically over the last century; shrubs such as mesquite (Prosopis sp.) have expanded into, and have become dominant in, ecosystems that once supported semi-arid grassland. The upper San Pedro River watershed, which extends from northern Sonora (Mexico) to southeastern Arizona (USA), highlights these changes. Between 1973 and 1992, grasslands decreased by 18% and the total area dominated by mesquite increased during the same period by 412%. In the areas where the density of mesquite shrub is medium to high, grass has completely disappeared under the shrub canopy and has been replaced by bare soil. Undoubtedly these cover changes have affected surface-atmosphere interactions by introducing a different partitioning of net available energy into sensible and latent heat flux. At the same time, different root system and root density and plant physiology have introduced a change to the surface water balance, reducing inflitration and increasing runoff. Our study addressed the sources of water used by mesquite (Prosopis velutina) along a natural gradient from an area of high mesquite cover with no herbaceous grass cover, to open savanna with high grass cover and widely spaced mesquite. The presented results from the SALSA 1997 monsoon-season campaign (July-October) show that mesquite shrubs that have access to both groundwater and surface water use surface water when available, potentially competing with grass for surface water and out-competing grass during successive periods of drought when only groundwater is available.Key words oxygen-18; mesquite; Prosopis velutina; water use; Sonora, Mexico; Arizona, USA; semi-desert grassland Sources de l'eau utilisée par une végétation naturelle de mesquite dans une région semi-aride du nord du MexiqueRésumé La structure de la végétation dans les régions semi-arides du nord-est du Mexique et du sud-ouest des Etats Unis a changé d'une façon spectaculaire au cours du dernier siècle. Une végétation de buissons de type mesquite (Prosopis sp.) s'est répandue partout pour devenir dominante dans ce qui était autrefois un écosystème de prairies semi-arides. Le haut bassin de la rivière San Pedro qui s'étend du nord-est du Sonora (Mexique) au sud-est de l'Arizona (USA) met bien en relief ces changements. Entre 1973 et 1992, les prairies ont diminué de 18% alors que pendant le même temps la superficie totale dominée par les mesquites s'accroissait de 412%. Dans les zones où la densité de mesquites est moyenne ou forte, l'herbe a complètement disparu sous les arbres et a été remplacée par du sol nu. Il ne fait aucun doute que ces changements de couverture végétale ont affecté les interactions surface-atmosphère en introduisant une répartition différente de l'énergie nette disponible en flux de chaleur sensible et latente. En même temps, l'accroissement du ruissellement, la diminution de l'infiltration mais aussi le développement de systèmes d'enracinement différents, et des densit...

Vegetation as affected by groundwater depth and microtopography in a shallow aquifer area of the Great Basin

“…or the shrubs Chrysothamnus spp. and SAVE, might depend on groundwater only when surface water is not available (Thomas and Sosebee, 1978; Nichols, 1994; Scott et al , 2000; Mounsif et al , 2002; Chimner and Cooper, 2004, Brunel, 2009). Romo and Haferkamp (1989) reported that plant water potential of SAVE responds to changes in soil surface water content even when the plant has a permanent groundwater source available.…”

“…Also, access to groundwater does not necessarily result in plant groundwater utilization (Thornburn and Ehleringer, 1995; Schulze et al , 1996; Scott et al , 2000; Chimner and Cooper, 2004; McLendon et al , 2008). It is increasingly clear that the use of precipitation‐derived soil water is often favoured over groundwater as it involves a simplified uptake pathway for plants (Thomas and Sosebee, 1978; Sorenson et al , 1991; Nichols, 1994; Schulze et al , 1996; Slavich et al , 1999; Zencich et al , 2002; McLendon et al , 2008; Pataki et al , 2008; Brunel, 2009).…”

Biodiversity assessment following a naturality gradient of riverbank protection structures in French prealps rivers

“…These three techniques were considered as three level of a naturality gradient. Naturality can be defined by the amount of living vegetation used in the construction as classification key criterion (Brunel, 2009;Werdin-Pfisterer et al, 2009). Mineral structures were considered as man-made environments with little plant coverage, different from the environment found on natural mountain riverbank.…”

Functional and taxonomic plant diversity for riverbank protection works: Bioengineering techniques close to natural banks and beyond hard engineering

“…They are plotted on the factorial map of BGA. The size of the ellipse provides information about intra-technique biological group variability as Brunel, (2009) andWerdin-Pfisterer et al, (2009). did.…”