Submitted to: Journal of Applied Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/10/2018
Publication Date: 9/16/2018
Citation: Reinhart, K.O., Rinella, M.J., Waterman, R.C., Petersen, M.K., Vermeire, L.T. 2018. Testing rangeland health theory in the Northern Great Plains. Journal of Applied Ecology. 56:319-329. https://doi.org/10.1111/1365-2664.13273.
DOI: https://doi.org/10.1111/1365-2664.13273

Interpretive Summary: • Background- Measures of soil stability (water stable aggregates & rangeland health soil stability test) are being widely measured and interpreted as a robust indictor of rangeland health. • Problem- A problem is that there is actually limited and confusing empirical evidence indicating soil (aggregate) stability is actually a valid indicator of rangeland health and functioning. • Accomplishment- We determined that plant properties are a better predictor of infiltration than aggregate stability (or other measured soil properties). • Indictor implications- A good indicator is one that provides consistent information and is easy and inexpensive to measure. Soil stability is likely a useful indicator under a very narrow set of contexts. There simply is not sufficient empirical support that soil stability is a universally reliable indicator of rangeland function.

Technical Abstract: • Correctly assessing whether rangeland ecosystem services are stable, improving, or degrading is of global importance. Soil aggregate stability (SAS) is widely used to infer rangeland health, partly because high SAS is thought to reduce runoff by increasing infiltration. We studied the sensitivity of SAS to grazing and other disturbances, the effects of SAS on infiltration, and the utility of alternative indicators of infiltration in the Northern Great Plains. • To test grazing effects on SAS, we compared SAS between paired areas that were lightly to moderately grazed or excluded from grazing for 6 years. Additionally, we compared SAS between grazed and not-grazed plots of a two-year controlled grazing experiment with moderate and severe grazing. Also, we applied herbicide, mowing, and fungicide treatments to test SAS responses to disturbances more generally, as well as effects of SAS and other factors on infiltration. To more generally test for a SAS-infiltration relationship, we performed a meta-analysis of our data combined with other data from the region. • Grazing often reduced stability of small macroaggregates (0.25-1 mm) in the controlled grazing experiment but not the paired grazing area experiment. Grazing had no detectible effect on SAS of larger macroaggregates (1-2 mm). Herbicide tended to reduce SAS, and mowing sometimes increased SAS. Infiltration exhibited high plot-to-plot variation and was not significantly affected by treatments. Variation in infiltration was best explained by plant community composition variables and was not explained by either SAS or other soil properties. Our meta-analysis revealed no general SAS-infiltration relationship. • Synthesis and applications. Our findings counter prevailing expectations that SAS is consistently sensitive to rangeland disturbance(s) and a leading indicator of infiltration. Plant community composition properties were better predictors of infiltration. Our findings support theory that excessive grazing increases the prevalence of a grazing tolerant species, which was associated with low levels of infiltration irrespective of SAS.