Tales from a “Lifer” in the Long-Term Ecological Research Program

As a long-time member of the Long-Term Ecological Research (LTER) network, first as a graduate student and scientist at the Shortgrass Steppe (SGS) site (1984–1997), then as a scientist at the Sevilleta (SEV) site (1996–present) and now as principal investigator at the Jornada Basin (JRN) site (2003–present), my professional career has been shaped almost entirely by my LTER experiences. My experiences in the LTER program directly contributed to my individual-based approach to ecosystem dynamics combined with the knowledge that the dominant ecological processes can change as the spatial extent increases, and that long-term data are critical to disentangle how these pattern–process relationships change across scales. The LTER program has provided me with international experience and exposure that are valuable to my career. My opportunity to travel overseas has led to bonding experiences and new insights into other ecosystems. My appreciation for the value of K–12 education and the amount of work that is involved in “doing it right” has been shaped by my experiences with the Jornada Schoolyard LTER Program. One of the key challenges that I face in working at an LTER site is the tension between continuing to collect long-term observations with the need and desire to test new ideas that often result from the long-term data but then compete for resources with the collection of those data. Another challenge is in mentoring young scientists to become principal investigators, and in cultivating new relationships with potential co–principal investigators. Currently, I am the principal investigator at the JRN LTER program at New Mexico State University (NMSU) in Las Cruces, New Mexico. I am also a collaborating scientist at the SEV LTER program at the University of New Mexico in Albuquerque, New Mexico. I received my BS in biology at Iowa State University in 1981 and my MS in biology from San Diego State University (SDSU) in 1983. My LTER experiences began as a PhD student at Colorado State University (CSU) through the SGS LTER program in 1984, and these continued while I was a postdoctoral fellow (1988–1989).

A Dryland Ecologist’s Mid-Career Retrospective on Long-Term Ecological Research and the Science–Management Interface

My association with the Long-Term Ecological Research (LTER) program has encouraged a multidisciplinary scientific approach emphasizing broad spatial scales and site-based knowledge. It also provides a solid basis from which to link science and management. In my position as a federal research scientist, I do not teach university classes. When I teach in other venues and advise graduate students, my LTER experiences facilitate my ability to draw connections among disciplines that bear on particular ecological problems. Multidisciplinary breadth alongside site-specific depth afforded by the LTER program is especially useful for communicating to the public. It is important to know a lot about one area (place-based knowledge), in addition to something broader. Collaboration is especially important for scientists working together at an LTER site and is also important for cross- site LTER efforts addressing regional to global problems. Within- group collaboration comes rather easily when there are healthy interpersonal relationships. Cross- site collaboration requires greater effort and network-level leadership. I have been a co–principal investigator of the Jornada Basin site (JRN) of the LTER program since 2006 and a research ecologist with the US Agricultural Research Service, Jornada Experimental Range (JER), since 2003. In both capacities, my research addresses land change in drylands (arid, semiarid, and dry subhumid deserts, grasslands, shrublands, woodlands). Specifically, I work on ecosystem state changes or regime shifts, including subjects such as land degradation and desertification; these may include how land managers perceive and react to state change via mental models, information, and restoration approaches (e.g., Bestelmeyer et al. 2009). My work has been centered at the JRN in the Chihuahuan Desert grasslands of southern New Mexico and also in grasslands and woodlands of Mongolia and Argentina. My activities include those generally associated with academia (research, publishing, grants, and supervising graduate students and postdoctoral fellows) in addition to work that is applied, such as outreach through workshops, trainings, field reviews, and writing to support management or government policy. The trade-off is not teaching university courses, although leading agency workshops and trainings partially fills this niche in my scientific career.

Remediation Research in the Jornada Basin: Past and Future

Land degradation in most of the Chihuahuan Desert is characterized by a shift from grass- to shrub-dominated plant communities (Ballín Cortés 1987; Grover and Musick 1990; Fredrickson et al. 1998; see also chapter 10). This shift is associated with increased soil resource redistribution and spatial variability at the plant-interspace scale (Schlesinger et al. 1990; see also chapter 6). Earlier descriptions focused more specifically on the loss of plant species, such as black grama (Bouteloua eriopoda), which were palatable to livestock (Nelson 1934). In 1958, it was estimated that one section (3.2 km2) of black grama grassland could support 18 animal units yearlong, while a similar area dominated by mesquite (Prosopis glandulosa) dunes could support just three animal units (Jornada Experimental Range Staff 1958; see also chapter 13). It was recognized that overgrazing facilitated the increase of less palatable species, including shrubs. Consequently, the objectives of the first organized rangeland research in the Southwest were to identify proper techniques to restore grasslands that had been overgrazed (Jardine and Hurtt 1917; Havstad 1996). Today, we recognize the importance of multiple, interacting factors in addition to overgrazing, and research is more broadly focused on the recovery of ecosystem functions necessary to support multiple ecosystem services. This chapter details this extensive history of research to identify and develop technologies to revegetate, restore, reclaim, rehabilitate, or more generally remediate degraded rangelands. The Society for Ecological Restoration considers that “an ecosystem has recovered when it contains sufficient biotic and abiotic resources to continue its development without assistance or subsidy. It will demonstrate resilience to normal ranges of environmental stress and disturbance. It will interact with contiguous ecosystems in terms of biotic and abiotic flows and cultural interactions” (Society for Ecological Restoration Science and Policy Working Group 2002). Although restoration of perennial grasslands is often cited as the ultimate objective of management intervention in the Southwest, we recognize that in many if not most cases complete restoration of a preexisting plant and animal community is impossible, even if we had perfect knowledge of all of the elements they contained. We also recognize that many of the historic management interventions discussed herein had more limited objectives.

Plant Communities in the Jornada Basin: The Dynamic Landscape

Plant communities of the Jornada Basin are characteristic of the northern Chihuahuan Desert both in structure and dynamics. Although a number of plant communities can be differentiated, five major vegetation types are often distinguished that differ in plant species cover and composition, as well as other factors, such as animal populations, soil properties, and elevation. These five types are black grama (Bouteloua eriopoda) grasslands, playa grasslands, tarbush (Flourensia cernua) shrublands, creosotebush (Larrea tridentata) shrublands, and mesquite (Prosopis grandulosa) shrublands. Similar to many other parts of the Chihuahuan Desert, these plant communities have experienced major shifts in vegetation composition over the past 50–150 years (York and Dick-Peddie 1969). The most dramatic changes in vegetation and associated ecosystem processes have occurred as a result of a shift in life form due to woody plant encroachment into perennial grasslands (Grover and Musick 1990; Bahre and Shelton 1993). This encroachment of shrubs has occurred in many arid and semiarid regions of the world, including the Western United States, northern Mexico, southern Africa, South America, New Zealand, and Australia (McPherson 1997; Scholes and Archer 1997). A number of drivers have been implicated in these grass–shrub dynamics, including various combinations of livestock grazing, small animal activity, drought, changes in fire regime, and changes in climate (Humphrey 1958; Archer 1989; Allred 1996; Reynolds et al. 1997; Van Auken 2000). The causes of shrub invasion are quite variable and often poorly understood, although the consequences consistently lead to the process of desertification (Schlesinger et al. 1990). This chapter describes the characteristics of each vegetation type and the documented changes in each type at the Jornada Basin. We then discuss the key drivers influencing these dynamics. Vegetation in the Chihuahuan Desert region has been classified as desert-grassland transition (Shreve 1917), desert savanna (Shantz and Zon 1924), desert plains grasslands (Clements 1920), desert shrub grassland (Darrow 1944), and shrubsteppe (Kuchler 1964). Desert grassland is often used as a general descriptive name for the area (McClaran 1995), although landscapes at the Jornada and throughout the northern Chihuahuan Desert often consist of a mosaic of desert grasslands, Chihuahuan Desert shrublands, and plains-mesa sand scrub (Dick-Peddie 1993).

Eolian Processes on the Jornada Basin

In arid and semiarid lands, soil erosion by wind is an important process that affects both the surface features and the biological potential of the ecosystem. The eolian flux of soil nutrients into or out of an ecosystem results in enrichment or impoverishment of its biological potential. In the Jornada Basin, wind erosion is the only significant mechanism for the net loss of soil materials because fluvial processes do not remove materials from the basin. Vigorous wind erosion leads to topographic changes, altering the growing conditions for plants and animals. Examples of such changes in topography are the formation of sand dunes or the removal of whole soil horizons. Our goal in this chapter is to describe the construction of a mathematical model for wind erosion and dust production for the Jornada Basin. The model attempts to answer the following questions: 1. Which soils are affected by wind erosion? 2. How does wind erosion occur on Jornada soils? 3. Does changing vegetation cover lead to a change in the source/sink relationship? 4. Is the Jornada a source or sink of eolian materials? If it is a source, what materials are lost? 5. How does wind erosion change the soil-forming process? We will provide provisional answers for the questions and outline work that will more clearly define these answers. Airborne dust has a significant residence time in the atmosphere and acts to modify the radiative properties of the atmosphere, mainly by back-scattering the incoming solar radiation (Andreae 1996). Changing land uses in arid and semiarid areas (e.g., overgrazing and cultivation) can drastically alter the dust emissions to the atmosphere (Tegen et al. 1996). The climatic effects of soil-derived dust were investigated in an experiment in central Asia (Golitsyn and Gillette 1993). Using measured size distributions for emitted dust (Sviridenkov et al. 1993) and various real and imaginary indices of refraction (Sokolik et al. 1993), Sokolik and Golitsyn (1993) calculated climatic effects. Atmospheric dust decreased the total radiative balance of the underlying surface and at the same time induced general warming of the underlying surface–atmosphere system due to a decrease in the system albedo over the arid zones.

Biogeochemical Fluxes across Piedmont Slopes of the Jornada Basin

This chapter is an overview of recent studies of the movement of water, sediment, and nutrients across a principle piedmont slope, or bajada, of the Jornada Basin. Bajadas are extensive, gently sloping surfaces formed by the coalescence of alluvial fans and are a major landscape component of the basin and range province. Over the past four decades a considerable body of research has elucidated the form and function of alluvial fans (Bull 1977; Blair and McPherson 1994; Harvey 1997), but less attention has been paid to bajadas. In particular, the bajadas most neglected are those where channels converge and diverge at irregular intervals downslope. This type of bajada is found at the base of Summerford Mountain, the northernmost peak of the Doña Ana Mountains on the western edge of the Jornada Basin. For convenience, this bajada is hereafter referred to as the Summerford bajada. The research has involved rainfall simulation experiments on small plots, monitoring of two small watersheds on this bajada, and computer modeling of the processes operating in these watersheds and over the bajada as a whole. A detailed understanding of the hydrology and hydraulics of overland flow on this bajada requires a numerical model of the rainfall-runoff process. The objective of this chapter is to detail the model and draw conclusions from model simulations about hydrologic transports of sediment and nutrients across this bajada. Because these piedmonts are important surfaces in this desert (chapter 2) an understanding of their hydrologic and biogeochemical dynamics is crucial to understanding landscape dynamics in the basin and throughout arid regions. Summerford Mountain is a steep-sided, rocky inselberg (i.e., isolated mountain) that rises 380 m above the surrounding bajada to an elevation of 1,780 m. The mountain is composed of monzonite porphyry of Oligocene age (Seager et al. 1976) and has a fringing bajada on its northern and eastern sides. This study focuses on the bajada to the east, which extends 2.5 km to the basin floor at an average gradient of 4%.