The Role of Herbaceous Plant Communities in the Maintenance of Shrub Patches

Project Number:

09R-09

Project Duration:

24 months

Dates:

December 1, 2009 to November 30, 2011

Institution of Principle Investigator while on this project:

Ben-Gurion University of the Negev

Investigators (most current known information)

Boeken, Bertrand (PI)

Senior Lecturer, Ben-Gurion University of the Negev, Sde Boker Campus, The Jacob Blaustein Institute for Desert Research, Midreshet Ben-Gurion 84990, ISRAEL

TEL: +972-52-384-7603, FAX: +972-8-659-6757, Email: bboeken@bgu.ac.il

Herrick, Jeffrey E.

Soil Scientist, New Mexico State University, Jornada Experimental Range, MSC 3JER, NMSU, Box 30003, Las Cruces NM 88003-8003, USA

TEL: +1-575-646-5194, FAX: +1-575-646-5889, Email: jherrick@nmsu.edu

Okin, Gregory S.

Associate Professor, Department of Geography, University of California, Los Angeles, 1255 Bunche Hall, Los Angeles CA 90095

TEL: +1-310-746-6964, FAX: +1-310-206-5976, Email: okin@ucla.edu

Yizhaq, Hezi

Research Associate, Ben-Gurion University of the Negev, Jacob Blaustein Institute for Desert Research, Sde Boker Campus, Midreshet Ben-Gurion 84990, ISRAEL

TEL: +972-54-788-0762, FAX: +972-8-659-6921, Email: yiyeh@bgu.ac.il

Proposal Abstract

In semiarid shrubland in many desert regions of the world, shrubs occur in patches with a raised mound of loose soil and plant litter, and a understory of herbaceous plants. We hypothesize that this herbaceous vegetation plays an important role in expansion of the mound by capture of sediment and organic matter, and in preventing its erosion by the impact of runoff flow and wind. Until now, the small-scale hydrological and aeolian processes of mound expansion and reduction have not been studied in great detail, and have largely been attributed to the shrub canopy architecture and/or the mound soil surface, but not to the herbaceous vegetation. We hypothesize that the herbaceous understory vegetation of shrub patches is a dominant determinant of the size, surface and soil properties of the patch. We propose to test the hypothesis experimentally in the filed in the Negev in Israel and the Chihuahua Desert in New Mexico by manipulating the herbaceous vegetation of shrub mounds and exposing them to a range of runoff intensities, and by mathematical modeling of the relationships between herbaceous plant cover, runoff and wind, and changes in mound dimensions.

At larger spatial and temporal scales, shrub mound expansion and reduction may cause changes in the spatial structure of semiarid shrublands. Consequently, the hypothesized role of herbaceous vegetation of shrub patches for their maintenance and expansion is central to the spatial structure of semiarid shrubland and its ecosystem functions (resource distribution, retention and loss, and productivity and biological diversity).

Since livestock grazing targets herbaceous vegetation, the proposed study addresses its effect on system structure and function, as well prevention of system degradation, and restoration of degraded systems. If the hypothesis is found to be valid, management measures aimed at reducing loss of herbaceous understory vegetation may be very effective. This becomes even more important if expected climate change causes prolonged periods of drought and more intense rainfall, both reducing the herbaceous vegetation. The results of the proposed study should benefit private, public, and government stakeholders involved in management and utilization of semiarid rangeland.

The field experiments test how shrub patches with herbaceous understory vegetation respond to manipulations of mound cover and runoff in Park Shaked in the northern Negev of Israel and Jornada Experimental Range in southern New Mexico, USA. The responses are measured as changes in mound dimensions and texture, by in situ 3D laser scanning. At Park Shaked, understory biomass, infiltration rates, runoff flow patterns and wind profiles will also be estimated, and substrate structure will be analyzed.

We will integrate the results in a mathematical model of the relationships among the herbaceous understory vegetation, runoff and wind flows, accumulation/removal of mound material, and changes in mound dimensions. The model includes feedbacks among these interrelationships and thresholds to describe the interface dynamics between shrub mounds and the surrounding surface. The establishment of two more or less parallel experiments in the Negev and the Chihuahua Deserts and the development of a single model highlights the global importance of these processes for semiarid shrubland in general. The results will be a used to develop a plan fo a global study of the relative importance of shrub-grass-sediment interactions in controlling the spatial vegetation structure in environments dominated by aeolian and alluvial sediment redistribution processes