Scientific Basis for Regionalization at the JRN LTER Site
vegetation change alter the distribution of soil resources,
development of a patchy distribution of soil nutrients. Nutrient-rich areas that develop under shrub canopies are known as islands of fertility, while soil resources are lost from the adjacent inter-shrub spaces by wind and water erosion. (Schlesinger et al. l990)
Jornada LTER program can be used to infer the causes and consequences of desertification worldwide.
habitat types studied at the Jornada are most representative of the northern, Trans-Pecos subdivision of this region
Jornada LTER focuses on 5 habitat types: black grama grassland (Bouteloua eriopoda), creosotebush scrub (Larrea tridentata), mesquite duneland (Prosopis glandulosa), tarbush shrublands (Flourensia cernua) and playa
playas, dominated by a variety of grasses, are found in low- lying, periodically flooded areas that receive drainage waters from the various upslope communities.
climate of the northern Chihuahuan desert is characterized by abundant sunshine, wide diurnal ranges of temperature, low relative humidity, and extremely variable precipitation. The average maximum temperature of 36 C is usually recorded in June; during January the average maximum temperature is l3 C. Precipitation averages 23 cm annually, with 52% typically occurring in brief, local, but intense, convective thundershowers during July to September. Winter precipitation during synoptic weather patterns that derive from the Pacific Ocean is more variable than summer precipitation, but it is more effective in wetting the soil profile.
Topographic position, soil development, and human impact interact to determine vegetation dynamics in the northern Chihuahuan desert, where dramatic changes in vegetation have been observed during the last l00 years (Buffington and Herbel l965). Large areas of former black grama grassland have been replaced by shrubland communities dominated by creosotebush, mesquite and tarbush
over-grazing, climatic change, fire suppression, or rising concentrations of atmospheric CO2 have acted solely or in concert to lead to these changes in vegetation.
Rangeland Carbon Balance Study: ARS scientists have established a network of 10 sites (including the Jornada) where rates of exchange of CO2 and water vapor between the atmosphere and the soil/vegetation of grasslands are measures. ... data include NPP, leaf area, C and N of soil and vegetation, and other soil chemical and physical properties. The network includes sites in the northern cool season grasslands, the prairie grasslands as well as the desert grasslands.
Comparative watershed hydrology. Comparisons between the hydrology (especially at the hillslope or patch mosaic scale) of Jornada and Walnut Gulch, Arizona,
hydrology studies (e.g., infiltration, runoff, sediment transport
automated water level recorders and sediment samplers at both sites.
Wind erosion and dust production. This is arguably one of the most significant impacts of desertification at the global scale.
Small mammal effects on soil and vegetation heterogeneity. We are conducting a regional intersite comparative experiment to observe the influence of small mammals (kangaroo rats and rabbits) along a latitude/climatic gradient
potential for these systems to sequester additional carbon under elevated carbon dioxide concentrations (Connin et al. 1997a,b).
we are using our Jornada models in a comparative modeling study of ecosystem productivity and carrying capacity in semi-arid grassland-shrublands of the Karoo in South Africa; arid rangelands of Australia; and the Monte scrub of Argentina