Invasion promotes invasion: Facilitation of C(3) perennial grass dominance in mixed C(3)/C(4) grassland by an invasive C(3) woody sprouter (Prosopis glandulosa)

1. In the Southern Great Plains (SGP) of the United States, encroachment of the native invasive woody legume, honey mesquite (Prosopis glandulosa Torr.), has caused a decline in C(4) mid‐grass abundance. Prosopis glandulosa invasion has also facilitated growth of the C(3) mid‐grass species, Texas wintergrass (Nassella leucotricha [Trin & Rupr.] Pohl) initially beneath its canopy but extending to interspaces between P. glandulosa as stand density increases. Little is known about the stability of the Prosopis/Nassella association or C(4) grass recovery following P. glandulosa disturbance. 2. We quantified C(3) and C(4) grass production in interspaces, and basal cover in interspaces and P. glandulosa subcanopy microsites for 9 years following P. glandulosa suppression (top‐kill) and compared this to untreated P. glandulosa woodland (woodland). 3. The Prosopis/Nassella association limited the window of C(4) mid‐grass recovery to only a few years. Nassella leucotricha dominated grass production during the first 3 years after top‐kill. C(4) mid‐grass recovery began in year 4, but was interrupted by severe drought in years 5 through 7. Recovery resumed in year 8, due to above‐average summer rainfall, but P. glandulosa regrowth was large enough by this time to limit C(4) mid‐grass production to a third of its potential. 4. Nassella leucotricha basal cover remained dominant and stable in woodland subcanopy microsites, even during drought, and only briefly declined in top‐kill subcanopy microsites before returning to pretreatment levels by year 8 as P. glandulosa regrowth increased and provided shade. 5. Synthesis and applications. A single suppression event had little impact on disrupting the Prosopis/Nassella association and allowing C(4) mid‐grass recovery. The coupling of a deciduous, N‐fixing C(3) woody species with this C(3) perennial grass may be a vegetative “state” that is resistant to multiple woody suppression disturbances and permanently limits the transition back to C(4) grassland.