Seedling defoliation may enhance survival of dominant wheatgrasses but not Poa secunda seeded for restoration in the sagebrush steppe of the Northern Great Basin

Authors: Denton, Elsie; PYLE, LYSANDRA - University Of California Agriculture And Natural Resources (UCANR); Sheley, Roger

Submitted to: AoB Plants
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/30/2021
Publication Date: 8/9/2021
Citation: 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. 13:(4). Article plab047. https://doi.org/10.1093/aobpla/plab047.
DOI: https://doi.org/10.1093/aobpla/plab047

Interpretive Summary: Defoliation caused by insects and small mammals could be an overlooked cause of restoration failure in the Northern Great Basin, we defoliated seedlings of common restoration grasses to see if this was true. Crested wheatgrass seedlings were defoliation tolerant. Seedlings that received repeated defoliations actually had greater survival when compared to non-defoliated individuals. Similar patterns were observed for bluebunch wheatgrass, but not Sandberg bluegrass. Seedlings with a greater number of tillers had a higher probability of survival, but tiller number was not affected by defoliation treatments in this study. Some grasses seeded for dryland restoration can tolerate or even benefit from defoliation as seedlings. If seedling herbivory is a concern on a restoration site, defoliation tolerant species should be selected.

Technical Abstract: Restoration of dryland ecosystems is often limited by low seedling establishment and survival. Defoliation caused by insects and small mammals could be an overlooked cause of seedling mortality. In the sagebrush steppe, we examined the effect of seedling defoliation on the survival of perennial grasses commonly used as restoration materials. Under field conditions, seedlings of three perennial bunchgrass species [non-native Agropyron cristatum (L.) Gaertn., and native grasses Poa secunda J. Presl, Pseudoroegneria spicata (Pursh) Á. Löve] were defoliated at two intensities (30% and 70% leaf length removal) and frequencies (1 or 2 clippings) and compared to a non-defoliated control. Following emergence the first year, clippings occurred at the 2-leaf stage; a second clipping occurred one month later for repeated defoliation treatments. We monitored seedling survival and tillering for 2 years. We expected higher defoliation intensity and frequency to reduce survival for all species, but only a few treatments reduced P. secunda survival. Conversely, larger-statured Triticeae (wheatgrasses) benefited from some defoliation treatments. In both years, A. cristatum survival increased with repeated defoliation at both intensities. Defoliation did not affect P. spicata survival in the first year, but a single defoliation in the second year resulted in increased survival. In both A. cristatum and P. spicata, higher intensity defoliation reduced the boost to survival resulting from defoliation frequency. Seedlings with more tillers had greater survival probabilities, but tiller number was unaffected by defoliation. Further research may elucidate mechanisms seedlings use to compensate for or benefit from defoliation. In the meantime, managers should aim to select defoliation-tolerant species if they anticipate herbivory will be problematic for restoration sites.