The influence of herbivory and ecological site on the persistence of a native perennial cool-season grass. An exploration from seed and axillary bud to the community level.

Authors: Hendrickson, John; FIELD, AARON - North Dakota State University; SEDIVEC, KEVIN - North Dakota State University; BRENNAN, JAMIE - South Dakota State University; JOHNSON, PATRICIA - South Dakota State University; Liebig, Mark; IGATHINATHANE, C. - North Dakota State University; HALVORSON, G. - Sitting Bull College; GARRETT, JAMES - Sitting Bull College; XU, LAN - South Dakota State University

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 4/21/2023
Publication Date: 8/7/2023
Citation: Hendrickson, J.R., Field, A., Sedivec, K., Brennan, J., Johnson, P., Liebig, M.A., Igathinathane, C., Halvorson, G., Garrett, J., Xu, L. 2023. The influence of herbivory and ecological site on the persistence of a native perennial cool-season grass. An exploration from seed and axillary bud to the community level.. Meeting Abstract. 1.

Interpretive Summary:

Technical Abstract: Grasslands in the Great Plains of the US and Canada have evolved under a history of grazing. However, these grasslands are composed of several ecological sites which contain different soils and topographic position which complicate interpreting how perennial grasses respond to herbivory. Therefore, we evaluated how Pascopyrum smithii [(Rydb.) Á. Löve] (PS), a native perennial C3 grass present throughout our research site, responded to herbivory by either black-tailed prairie dog (Cynomys ludovicianus), a burrowing, herbivorous, keystone wildlife species, cattle (Bos taurus), a domesticated large herbivore, or both on loamy (Ly) and thin claypan (Tcp) ecological sites. By placing 30 x 30 m exclosures, on- and off- prairie dog colonies on the two ecological sites, we created four different treatment combinations that were replicated three times. Treatments were 1) no cattle or prairie dog grazing (CON); 2) prairie dog grazing but no cattle grazing (PDNC); 3) cattle grazing but no prairie dog grazing (CNPD) and 4) both cattle and prairie dog grazing (PDC). The PS response variables included 1) seed bank cores 2) axillary bud counts, 3) tiller demography, and 4) contribution to species composition. The data were collected from 2013 to 2016. There were no differences between either the different grazing treatments or ecological sites on the numbers of axillary buds per PS tiller. Examination of the seed bank suggests there were differences in ecological site on contribution of seedlings. Mean tiller lifespan was 368, 368, 375 and 354 days for PDC, PDNC, CNPD and control; respectively, and 366 and 369 day for the Tcp and Ly ecological sites; respectively. Tiller replacement ratios (TRR) or number of new tillers recruited at the plant population level were low and never rose above replacement levels (<1) for the Ly ecological sites and the PDNC grazing treatment during the study period. In 2015, TRR for all treatments and ecological sites was > 0.5. The low tiller recruitment in 2015 was reflected in the number of tillers per m2 which exhibited a sharp decline for most herbivory treatments on both ecological sites. The TRR decline may have contributed to the 3 to 5% reduction in PS as part of the relative species composition. While TRR suggests that environmental conditions impact recruitment of new PS tillers, the increased mean PS tiller lifespan under grazing indicate longer survivorship allows these tillers to persist in unfavorable conditions.