Contents:
Quantifying Hydrological Dynamics in the Jornada Basin
In 1995, Dale Gillette, a new collaborator in the Jornada research program, established a station to provide a long-term record of wind erosion and dust transport for the LTER program. It was just in time! On January 17, 1996, with winds gusting to 60 miles per hour, a major dust storm swept the Jornada Basin. Total particle transport recorded by Gillette's instruments was nearly 25,000 g/cm during the dust storm, compared to rates of only 100 g/cm in more normal conditions (see figure).
The transport of wind-borne material from arid regions is the subject of several recent papers that attempt to incorporate the effects of suspended dust in general circulation models of global warming. Dust over barren land surfaces typically has a warming effect on the atmosphere, while over oceans the reverse is true. Recent studies by Robert Swap (U. Va.) in the western Sahara desert show that much of the dust transport over the Atlantic ocean occurs in episodic events. Similarly, the January 17 event at the Jornada was associated with an unusual southward-dipping cold front over most the western U.S. Episodes of dust transport, such as that seen at the Jornada, will be challenging to incorporate into long-term models of global climate.
These episodes of soil transport are also important for understanding the dynamics of shrub ecosystems in the Jornada basin. The invasion of mesquite is associated with the development of large dunes around the base of these shrubs. Much of the material captured in the dunes may arrive during short periods of high wind velocity, particularly during periods of drought.
Gillette, who is a member of the NOAA's Fluid Modeling Facility in Research Triangle Park, North Carolina, brings his career-long expertise in wind-erosion studies to the Jornada LTER program. His station for monitoring wind erosion is located in a central position in the Jornada basin. It includes several meteorological towers, with instruments to record wind speeds, wind direction, and particle saltation. Collections of captured dusts will be analyzed for mineralogy as a means of tracing the origin of wind-borne materials and their contributions to soils in the region. His efforts will provide a valuable long-term dataset for wind erosion at the Jornada LTER site.
A variety of papers by LTER researchers highlighted the program at the annual meeting of the Ecological Society of America in Providence, Rhode Island, August 9-12, 1996. Especially significant results were reported in a poster presented by Jim Reynolds and his colleagues, who used rainout shelters to prevent either summer or winter rain from entering the soil profile around shrubs and then monitored shrub growth for several years. They found that despite the large proportion of total annual rain that falls during large summer thundershowers, it is the recharge of the soil profile by the smaller winter rains that is most significant to shrub growth.
Greater shrub growth during multi-year periods of unusually high winter rainfall is also seen in southeastern Arizona, where Jim Brown and his colleagues have examined changes in vegetation cover for the last several decades. In a mirror image to these recent findings, about a decade ago Ron Neilsen, then a postdoctoral associate with the Jornada LTER, found that the recruitment of black grama grass declined significantly when summer rains failed to materialize for several years. Based on the results of these various studies, it will be important to examine the historical monthly records of rainfall at the Jornada to calculate the annual growth of grasses and shrubs in computer simulation models of vegetation changes in the basin.
Scientists from ten locations, including five USDA/ARS research units and the Staring Centre in Wageningen, The Netherlands, are working together to quantify the dynamics of land surface hydrology and energy balance in the desert rangeland in the Jornada Basin. These studies are integrating different types of remote sensing data and detailed micrometeorological and vegetation data to quantify moisture and energy fluxes over a 4000-ha area where desert grasslands degrade into mesquite dunelands.
Five intensive campaigns were conducted during the summer growing seasons and dormant winter periods in 1995 and 1996. Airborne data included three-camera multi-spectral (visible yellow-green, red and near-infrared) video images recorded digitally from a fixed wing aircraft at 300, 750 and 1500 m altitude. A thermal infrared radiometer and a 4-band (corresponding to the first 4 bands of the Landsat Thematic Mapper) radiometer were used to make radiance measurements at 125 and 300 m, and a laser altimeter collected imagery at 125 and 300 m. Ground data included vegetation cover, spectral reflectance, composition and height; leaf-area indices; and surface energy fluxes (using Bowen ratio and eddy correlation techniques). The intensive airborne and ground campaigns were coordinated with Landsat overpasses in February, May, and September.
These data are providing spatially-distributed information on important variables such as surface soil moisture, albedo, absorbed photosynthetically active radiation, and evaporation. The aim is to develop simulation models that capture the essential physical processes of energy and carbon balances for this heterogeneous landscape. Preliminary data were reported in June at the Second International Airborne Remote Sensing Conference and Exposition in San Francisco.
This project has been funded by the USDA/ARS Global Change research program. Additional funds have been received for 1997-98 to expand the project to a cross-site comparison with campaigns planned for the Sevilleta and Central Plains LTER sites.
--Contributed by Kris Havstad, USDA/ARS, Jornada Experimental Range
Increasing public interest in the decline of biological diversity in New Mexico led the New Mexico Academy of Sciences to devote its 1996 volume of The New Mexico Journal of Science to a general assessment of biodiversity in the state.
The special issue, entitled New Mexico's Natural Heritage, was edited by Jornada LTER investigator Laura Huenneke, and it contains chapters discussing the diversity of important taxonomic groups and environmental change in New Mexico’s important ecosystems.
There are also detailed case histories of conservation efforts for several rare plant and animal species and chapters describing the activities of governmental and nonprofit conservation agencies to promote species persistence.
The Journal will be released at the Academy's annual symposium in Albuquerque in November, and it will be distributed to educational institutions throughout the state.
Individuals who wish to purchase a copy should send $10.00 to the Department of Biology, New Mexico State University, Las Cruces, NM 88003.
--Contributed by Laura F. Huenneke, Department of Biology, New Mexico State University
This issue of Jornada Trails recognizes the contributions of Dr. Curtis Monger to the Jornada LTER program. Curtis is an associate professor of pedology in the Department of Agronomy at New Mexico State University. Over the past ten years he has maintained an active program of research to understand the origin and development of arid land soils in southern New Mexico. Recently, working with a graduate student, Arnulfo Rojas, Curtis provided a detailed soil map for the alluvial slopes of Mt. Summerford, encompassing the area of the original LTER transects.
Curtis's work shows an enormous diversity of soils and landscapes in the Jornada Basin. Alluvial soils at the foot of Mt. Summerford are Holocene, with radiocarbon ages of about 3000 years before present. In contrast, in the central basin, ancient floodplain deposits left by the Rio Grande date to 1.6 million years ago, based on argon isotope analysis. Working with Greg Mack and others, Curtis recently produced a short classroom video --aimed at an advanced high school or early college audience--describing the varied geologic history of the entire Rio Grande Valley near Las Cruces.
Curtis has just received $79,865 from the USDA Competitive Grants program to supplement his efforts in the LTER program. Specifically, he will examine the dynamics of grassland ecosystems during the Holocene by examining the d13C signature left in soil carbonates of the Jornada basin. The Jornada LTER team is certainly pleased to have the expertise and productive collegiality of Curtis Monger as part of its program.
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King, D. W., R. E. Estell, E. L. Fredrickson, K. M. Havstad, J. D. Wallace, and L. W. Murray. 1996. Effects of Flourensia cernua ingestion on intake, digesta kinetics, and ruminal fermentation of sheep consuming tobosa. Journal of Range Management 44: 325-330.
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