Secondary production of the central rangeland region of the United States

Authors: RAYNOR, EDWARD - Colorado State University; Derner, Justin; HARTMAN, MELANNIE - Colorado State University; DORICH, CHRISTOPHER - Colorado State University; PARTON, WILLIAM - Colorado State University; Hendrickson, John; HARMONEY, KEITH - Kansas State University; BRENNAN, JAMESON - South Dakota State University; OWENSBY, CLENTON - Kansas State University; Kaplan, Nicole; LUTZ, SUSAN - Colorado State University; CONANT, RICHARD - Colorad0 State University; Hoover, David; Augustine, David

Submitted to: Ecological Applications
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/8/2024
Publication Date: 5/10/2024
Citation: Raynor, E., Derner, J.D., Hartman, M., Dorich, C., Parton, W.R., Hendrickson, J.R., Harmoney, K., Brennan, J., Owensby, C., Kaplan, N.E., Lutz, S., Conant, R.T., Hoover, D.L., Augustine, D.J. 2024. Secondary production of the central rangeland region of the United States. Ecological Applications. Article e2978. https://doi.org/10.1002/eap.2978.
DOI: https://doi.org/10.1002/eap.2978

Interpretive Summary: Rangelands in the central Great Plains region occur across a west-east annual precipitation gradient from near 12 inches in the shadow of the Rocky Mountains to over 35 inches near the boundary with the Corn Belt. While substantial efforts have examined time (temporal) and spatial variation in aboveground production to precipitation across this gradient, efforts are lacking related to net secondary productivity or livestock production in this case. Here, we used long-term (mean length = 19 years) aboveground and livestock production from six research sites across this region, each with relatively consistent across time stocking rates at the individual site level, to evaluated precipitation-productivity relationships and resource efficiencies across trophic levels (primary production to secondary production). While precipitation-productivity relationships were linear for aboveground production at individual sites and across sites, the across site precipitation-livestock production relationship saturated at wetter sites suggesting that forage quality (i.e., increasing amounts of lignin in plant stems) reduced the potential to convert aboveground production to livestock production. Trophic efficiency (ratio of aboveground production to livestock production) was highest at the sites with lower annual precipitation due to these sites being dominated by short C4 (warm-season) grasses with high forage quality as they have minimal investment in aboveground stems.

Technical Abstract: Rangelands are the dominant land use across a broad swath of central North America where they span a wide gradient, from <350 to >900 mm, in mean annual precipitation Substantial efforts have examined temporal and spatial variation in aboveground net primary production (ANPP) to precipitation (PPT) across this gradient. In contrast, net secondary productivity (NSP, e.g., primary consumer production) has not been evaluated analogously. However, livestock production, which is a form of NSP or primary consumer production supported by primary production, is the dominant non-cultivated land use and an integral economic driver in these regions. Here, we used long-term (mean length = 19 years) ANPP and NSP data from six research sites across the central Great Plains with a history of a conservative stocking to determine resource (i.e., PPT)–productivity relationships, NSP sensitivities to dry-year precipitation, and regional trophic efficiencies (e.g., NSP: ANPP ratio). PPT-ANPP relationships were linear for both temporal (site-based) and spatial (among site) gradients. The spatial PPT-NSP model revealed that PPT mediated a saturating relationship for NSP as sites became more mesic, a finding that contrasts with many plant-based PPT-ANPP relationships. A saturating response to high growing season precipitation suggests biogeochemical rather than vegetation growth constraints may govern NSP. Differential sensitivity in NSP to dry years demonstrated that the primary consumer production response heightened as sites became more xeric. Although sensitivity generally decreased with increasing precipitation as predicted from known PPT-ANPP relationships, evidence suggests that the dominant species' identity and traits influenced secondary production efficiency. Non-native northern mixed-grass prairie was outperformed by native central Great Plains rangeland in sensitivity to dry years and efficiency in converting ANPP to NSP. A more comprehensive understanding of the mechanisms leading to differences in producer and consumer responses will require multi-site experiments to assess biotic and abiotic determinants of multi-trophic level efficiency and sensitivity.