154 Awardee Talk – Tares among the wheat: sericea lespedeza invasion of native tallgrass prairie

North-American tallgrass prairie provides an array of ecosystem services including carbon sequestration, biodiversity preservation, and forage for grazing livestock. Once covering 68 million ha, only 4% remains today. The largest remnant (~1.5 million ha) lies in the Kansas Flint Hills, home to ~1.3 million yearling cattle and ~90,000 beef cows annually. Unfortunately, the functionality of this ecosystem is threatened by an exotic invader - sericea lespedeza (Lespedeza cuneata). Known colloquially as sericea, it is a perennial forb with prodigious capacity to proliferate. Sericea selection by grazing cattle is poor; condensed-tannin concentrations in wild-type sericea approach 20% of plant DM. Total-tract N digestibility by steers consuming sericea-contaminated tallgrass-prairie hay was documented at < 0%. Sericea control has been attempted using herbicides. This has not limited proliferation and has resulted in collateral damage to non-target lifeforms. Attempts to naturalize sericea to the ecosystem via enhanced herbivory were evaluated. Supplementation of beef cow diets with tannin-binding feedstuffs resulted in ≥29% increases in sericea selection compared with non-supplemented cows. Co-grazing beef cows and goats was associated with >20% more defoliation of sericea than beef-cow grazing alone. Sequential grazing of yearling steers followed by mature ewes resulted in >92% defoliation of sericea compared with < 2% in pastures grazed by steers alone. Unfortunately, widespread adoption of these techniques by the ranching community hasn’t occurred because of costs or logistical constraints. More recently, prescribed fire as a low-cost means of control was evaluated. Prescribed fires in late summer greatly diminished sericea proliferation compared with prescribed fires in spring (i.e., traditional prescribed-fire season). No changes in peak forage biomass or C4 grass-species abundance were observed; moreover, native legumes and nectar-producing forbs increased ≥2-fold in response to summer fire. Cultural acceptability of prescribed fire in the region is high; significant adoption by the ranching community has been observed.