Herbivory has influenced the evolution of plant traits and has shaped the assembly of dryland plant communities across the globe. Plant–herbivore interactions and defoliation tolerance of mature vegetation have been extensively studied, but how herbivores affect seedlings and dryland plant communities during restoration is still poorly understood. It is thought that herbivory by insects and small mammals may be an overlooked cause of seedling mortality. Herbivory during the vulnerable seedling stage may have substantial consequences on the resulting plant community structure because of potential influences on recruitment, productivity and resulting reproductive output.
In their new study published in AoBP, Denton et al. monitored how three perennial grass species commonly used to revegetate degraded North American drylands responded to defoliation at the seedling stage. The species investigated included the two native species bluebunch wheatgrass (Pseudoroegneria spicata) and Sandberg bluegrass (Poa secunda), as well as crested wheatgrass (Agropyron cristatum), a large, introduced perennial frequently used to revegetate degraded drylands. The field study was run at the Northern Great Basin Experimental Range (NGBER) in Oregon. Seedlings were defoliated at two intensities (30 % and 70 % leaf length removal) and frequencies (one or two clippings) and compared to a non-defoliated control, with seedling survival and tillering monitored for two years.
Higher defoliation intensity and frequency were expected to limit survival and vegetative growth; however, this was only the case for the native bluegrass Poa secunda. Overall, grass seedlings were largely resilient to defoliation, with wheatgrass survival greater under some defoliation treatments than non-defoliated control plants. Individuals with more tillers had greater survival but tillering was unaffected by defoliation. Denton et al. suggest that further research may help us to understand the mechanisms perennial grass seedlings use to compensate for or benefit from defoliation. In the meantime, they propose that managers select defoliation-tolerant species if they anticipate herbivory will be problematic at dryland restoration sites.
Denton, E.M., Pyle, L.A., Sheley, R.L., 2021. Seedling defoliation may enhance survival of dominant wheatgrasses but not Poa secunda seeded for restoration in the sagebrush steppe of the Northern Great Basin. AoB PLANTS. https://doi.org/10.1093/aobpla/plab047