Ecological theory and practice in arid and semiarid ecosystems: a tale of two LTER sites

The chapter compares the conceptual history of two Long Term Ecological Research (LTER) programs at U.S. Department of Agriculture (USDA) research sites established following land overuse in the early 1900s. Early USDA studies were based on a Clementsian model, where vegetation following disturbance was expected to return to the climax determined by climate and soils. Management-based alternatives to the Clementsian model were developed after the dominant vegetation failed to recover and alternative states were observed. The Central Plains Experimental Range LTER (later Shortgrass Steppe LTER) program began in 1981 at a site in northern Colorado. Early studies focused on the inability of the dominant species, blue grama (Bouteloua gracilis), to recover on long-abandoned agricultural fields. These observations were in contrast to the resilience of blue grama-dominated ecosystems in response to livestock grazing and drought. The Jornada Basin LTER program began in 1982 at a Chihuahuan Desert site in southern New Mexico, where black grama-dominated (Bouteloua eriopoda) grasslands converted to shrublands following livestock overgrazing and drought. Early Jornada studies focused on the causes and consequences of this desertification. In collaboration with USDA scientists, the two LTER programs developed new research ideas and approaches which brought an improved understanding of historic dynamics and nuance to the Clementsian-based paradigm. New paradigms also reflected the importance of objective, long-term studies and the dynamic, multi-scale nature of these arid and semiarid ecosystems. Comparing two LTER programs at research sites sharing a conceptual basis, but with different ecosystem properties, can provide insights into the development of US grassland ecology over the past century.