Technical Abstract: The Jornada Basin of southern New Mexico has long been an important location for the study of productivity in semidesert ecosystems. Researchers have studied the magnitude and sustainability of plant production since the founding of the USDA Jornada Experimental Range (JER) in 1912. The consistent administration and research focus of the Jornada Experimental Range and of the Chihuahuan Desert Rangeland Research Center (CDRRC) have facilitated a number of long-term studies of vegetation dynamics and productivity. These long-term datasets are especially critical for understanding semiarid ecosystems, where interannual and decadal scale variation in climate is so great and where plant performance is so strongly constrained by the physical environment. Long-term data, including the net primary productivity data that are the focus of this chapter, are also essential for understanding the progression or, rather, degradation of ecosystem structure that has been called desertification.