Invasive buffel grass (Cenchrus ciliaris) increases water stress and reduces success of native perennial seedlings in southeastern Arizona

Although buffel grass (Cenchrus ciliaris) invasions on several continents have significant ecological impacts, little information is available on its stage-specific interactions with native vegetation. In areas of North America’s Sonoran Desert highly impacted by buffel grass, perennial plants are particularly vulnerable during the recruitment stage. We studied the impact of buffel grass on the emergence and early survival of native perennials that germinate during monsoon season with a field experiment. We used a pot experiment to test whether proximity to buffel grass induced water stress in the seedlings of a locally dominant native tree, the foothills palo verde (Parkinsonia microphylla). Seedlings of native perennials emerged at nearly twice the rate, and survived longer, on field plots where mature buffel grass was removed, or had never invaded, than where buffel grass remained. The stable isotope signatures of carbon in palo verde seedlings grown in pots with buffel grass indicated higher stomatal closure consistent with greater water stress than in seedlings grown alone. A stage-structured model based on palo verde population dynamics illustrates that if only recruitment rates were affected by buffel grass, palo verde would likely remain on the landscape, though at reduced densities. However, the long-lived nature of perennials implies we have yet to observe the full impacts of the invasion. The model indicates the kinds of studies needed to fully predict the impact of buffel grass.