|DE SOYZA, AMRITA|
Submitted to: Journal of Arid Environments
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/4/2000
Publication Date: 1/1/2001
Citation: WHITFORD,W.G., NIELSON,R., DE SOYZA,A. ESTABLISHMENT AND EFFECTS OF ESTABLISHMENT OF CREOSOTEBUSH, LARREA TRIDENTATA, ON A CHIHUAHUAN DESERT WATERSHED. JOURNAL OF ARID ENVIRONMENTS. 2001. V. 47(1). P. 1-10.
Interpretive Summary: The spread of creosotebush, Larrea tridentata, into the grassland of Chihuahuan Desert rangelands has been documented in a number of publications. One of the key questions focusing on the loss of productivity in rangelands is "what is the relationship between grazing impacts by domestic livestock and establishment of 'woody weeds' such as creosotebush and mesquite?" The only habitat in which creosotebush seedlings survived and grew was grassland in which grass cover was greatly reduced as a consequence of grazing. Creosotebush seedlings survived for less than 2 years in creosotebush-dominated shrubland and in ungrazed black grama grassland. Fifteen years after the initial planting, the established creosotebushes reduced the aggregate stability of soils under the shrub canopies, effectively eliminated annual and perennial herbaceous plants from sub-canopy areas and reduced soil fertility in the vicinity of the shrubs. All of these effects of creosotebush establishment serve to reduce the potential for restoring production of grasses and forage plants in creosotebush-dominated areas.
Technical Abstract: Creosotebush (Larrea tridentata) seedlings were planted in plots that were irrigated, plots that were irrigated and fertilized with ammonium nitrate, and plots that were not amended in three plant communities on a Chihuahuan Desert watershed: ungrazed black grama (Bouteloua eriopoda) grassland, creosotebush shrubland, and overgrazed grassland. No seedlings were planted in one-half of the area of each plot. No seedlings survived in the black grama grassland or the creosotebush shrubland 2 years after planting. Growth of established creosotebush shrubs was highest in plots with the lowest grass cover. Fifteen years after the seedlings were planted in the overgrazed grassland, the area under the shrubs was nearly devoid of perennial grasses and forbs. The aggregate stability of the soils under the established creosotebush shrubs was significantly lower than the soils in the unplanted split-half of the plots. Electrical conductivity, calcium, and nitrate were significantly lower in soils under shrubs than soils in the unplanted split-half of the plots. There were also significant reductions in densities of annual plants growing under the shrubs than in the unplanted split-half of the plots. Successful establishment of creosotebush in desert grasslands is dependent upon the presence of large patches of soil with no perennial plant cover. Intense grazing by domestic livestock creates microsites and landscape characteristics favorable for seed dispersal, germination and establishment of creosotebush. Soil changes resulting from shrub establishment reduce the probability of reestablishing perennial grasses in creosotebush-dominated shrubland.