|Monger, H. Curtis|
Submitted to: Ecosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/7/2012
Publication Date: 3/5/2012
Citation: Weems, S.L., Monger, H. 2012. Banded vegetation-dune development during the Medieval Warm Period and 20th century, Chihuahuan Desert, New Mexico, USA. Ecosphere. 3(3):Article 21. Interpretive Summary: Banded vegetation visible from aerial photography, but not apparent from the ground, are a striking example of how vegetation interacts with soils and geomorphology to self-organize into geometric shapes. On the east side of the Jornada Experimental Range, Stacey Weems, then a graduate student with Curtis Monger (co-PI with the Jornada Basin LTER), used radiocarbon dating of buried land surfaces beneath banded vegetation-dune complexes to determine when these features formed. Based on the carbon-14 dates, plus evidence from carbon-13 isotopes, historic surveys of vegetation, and landscape photography (1858, 1918), there were two periods of formation. The first began during the Medieval Warm Period (ca. 900-1300 AD) after which the landscape stabilized during the Little Ice Age (ca. 1500-1850 AD) and faint soil horizons developed. The second and more intense period of banded vegetation formation was reactivated in the late-1800s during a period of widespread desertification in the American Southwest that continues today. The study shows how soil stratigraphy can record information about when and how ecosystems responded to prehistoric climate changes, which in turn can be used as baseline data against which current rates of ecosystem change can be compared.
Technical Abstract: With the advent of systematic high-resolution satellite photography, striking geometric shapes of banded vegetation several km2 in size, but not apparent from the ground, have been documented for many areas of the arid and semiarid world. Banded vegetation, in which dense perennial vegetation alternates with bands of bare soil may originate from geomorphic processes, ecological self-organization, or human land use. In the Chihuahuan Desert of New Mexico prominent arc-shaped bands of vegetation and dunes occur along the contact of a piedmont slope (bajada) and basin floor. The origin and chronology of this banded vegetation-dune complex was investigated using early aerial photography (1936–1942), landscape photography (1918), vegetation and soil surveys (1858, 1918), soil stratigraphy, 13C/12C ratios, and 14C dating. These methods reveal two periods of eolian deposition. The first began in the Medieval Warm Period (ca. AD 900–1300) and was followed by a period of landscape stability during the Little Ice Age (ca. AD 1500 to 1850). The second began in the late-1800s when widespread desertification occurred throughout the American Southwest. Banded vegetation was initiated after formation of erosional scarplets that functioned as obstacles upon which eolian sand accumulated, thus becoming a dam to overland flow and causing strips of vegetation to form. Banded vegetation in this study is an emergent pattern produced by a coupled ecologic-geomorphic-climatic system. The stratigraphic record produced by this system enables us to compare current ecological responses to climate change with baseline prehistorical responses to climate change.