Herbivory can reduce perennial grass seedling survival, but temperature and cumulative precipitation are more important predictors in the first growing season

Authors: Denton, Elsie; Sheley, Roger

Submitted to: Restoration Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/7/2024
Publication Date: 10/29/2024
Citation: Denton, E.M., Sheley, R.L. 2024. Herbivory can reduce perennial grass seedling survival, but temperature and cumulative precipitation are more important predictors in the first growing season. Restoration Ecology. Article e14320. https://doi.org/10.1111/rec.14320.
DOI: https://doi.org/10.1111/rec.14320

Interpretive Summary: Successful restoration of desired species is a challenging task in dryland systems. We investigated whether seedling defoliation could be a cause of restoration failure in perennial grasses on actual restorations. We found that defoliations occurred primarily from insects but impacted much less than 50% of individual seedlings. Defoliation generally didn’t result in large percentages of vegetation removal. Large perennial grass seedlings (primarily of the Triticease tribe) received more defoliation than bluegrasses, and had small reductions in survival when that defoliation was extensive. However, abiotic variables such as precipitation and temperature were far more associated with survival than defoliation. Based on the results of this study, seedling herbivory is unlikely to cause restoration failure in the Northern Great Basin.

Technical Abstract: Successful establishment of desired species during restoration is challenging in drylands. Much research has focused on the importance of the critical life stages such as germination and emergence, but factors influencing survival through the seedling stages of perennial grasses may be equally important. We asked whether seedling defoliation by insects and/or mammals could cause restoration failure. We quantified the degree of defoliation on seedlings of common perennial grass species at 46 restoration sites throughout Oregon, Idaho, and Nevada, and calculated survival probabilities during the first growing season after planting. At each site, we excluded small mammals and insects for 6'weeks and compared defoliation and survival probabilities with seedlings in controls without exclusions. Seedlings were classified as either: large perennial grasses (LPG), primarily from the Triticeae tribe, or Bluegrasses (Poa spp.). Defoliation of LPG reduced seedling survival, but the effect was small compared to the influence of meteorological variables, such as precipitation and temperature. Based on bite patterns, most defoliation resulted from insects. Only a small percentage of vegetation was removed (36% of individuals were defoliated, mean'='13.2% vegetation removal). Defoliation of bluegrasses was less common than that of LPG seedlings, with only 16% experiencing defoliation, primarily from insects (mean'='4.3% vegetation removal). Some defoliation did occur within the exclusion treatments, but the effect of defoliation on seedling survival did not appear to interact with treatment. Based on the results of this study, seedling herbivory is unlikely to be a major factor in restoration failure in the Northern Great Basin.