Mesquite recruitment in the Chihuahuan Desert: Historic and prehistoric patterns with long-term impacts

Mesquite (Prosopis glandulosa) has increased in dominance over large areas of the Chihuahuan Desert, chiefly at the expense of once expansive desert grasslands. Excessive grazing and seed dissemination by livestock are often cited as the cause of this transition. We propose an alternate hypothesis that expansion of mesquite is not simply due to cause and effect relationships during recent history; rather, mesquite expansion is a result of a series of cause and effect relationships that transpired over a much longer timeframe (millennia). We assert that mesquite expansion may have ultimately occurred in the absence of widespread livestock grazing during the last 130 years because of removal of barriers to mesquite expansion created by indigenous peoples. We explore factors that attenuate or intensify mesquite expansion, and examine how a series of fine scale, but temporally seminal, events can propagate across multiple scales. Furthermore, we examine the relevance of this hypothesis for present day remediation of shrub-dominated grasslands and conclude that knowledge of historic and prehistoric events and processes are critical to effectively manage landscapes.