Location: Livestock and Range Research LaboratoryTitle: Soil aggregates stability was an uncertain predictor of ecosystem functioning in a temperate and semiarid grassland
Submitted to: Ecological Applications
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/18/2015
Publication Date: 11/20/2015
Citation: Reinhart, K.O., Nichols, K.A., Petersen, M.K., Vermeire, L.T. 2015. Soil aggregates stability was an uncertain predictor of ecosystem functioning in a temperate and semiarid grassland. Ecological Applications. 6(11):238. doi:10/1890/ES15-00056.1.
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 empirical evidence indicating soil stability is a robust indicator of ecosystem health and evidence to the contrary. • Accomplishment- We determined that water infiltration was a main predictor of forage production. Measures of soil stability were poor predictors of either forage production or water infiltration. • Indictor implications- A good indicator is one that provides consistent information and is easy and inexpensive to measure. Our literature review and data suggest a narrow range of contexts where soil stability is likely a valuable indicator of rangeland health. • Management implications- We interpret that direct measures of plant production and cover coupled with more direct measures of soil/site stability (e.g. soil cover, litter cover, gullies, bare ground, litter movement, rills) are likely of more value in estimating rangeland health than measures rangeland health soil stability tests. Ecosystems like the Northern Great Plains may require new indicators of ecosystem processes to improve ecological and economic sustainability of regional rangelands.
Technical Abstract: Science-based information is needed to identify indicators of ecosystem health that may then be used to monitor natural resources and guide management decisions. We conducted a local gradient study to elucidate correlative associations between vegetation and multiple soil properties for rangelands in the Northern Great Plains. This approach helped identify associations between measures of soil stability (e.g. water-stable aggregates) and two measures of ecosystem function (annual net primary productivity [ANPP] and water infiltration). We sampled a 0.3 ha area with equal sampling in a livestock exclosure (est. 1999) and two adjacent pastures. Sampling included: ANPP, elevation, soil moisture, soil stability (water stability test of two macroaggregates size classes and rangeland health soil stability tests), and soil structure (field-saturated infiltrability and sorptivity). We used multiple linear regression to determine that the greatest amount of variation in ANPP was explained by a model with field-saturated infiltrability and soil moisture (R2= 0.33). Infiltrability explained slightly more of the variation. Multiple linear regression was then used to identify the independent variables that best explained the variability in infiltrability. Moderate amounts of variation in infiltrability were explained by elevation, sorptivity (a measure of initial infiltration), and % water-stable aggregates (0.25-1 mm size class) (R2= 0.39). We determined that most of this variation was explained by sorptivity. These findings support the belief that plant growth is regulated by soil structure, though feedbacks between perennial plants and soil structure are likely. Our findings failed to indicate that measures of soil stability were useful predictors of ANPP and determined soil stability was a weak predictor of infiltrability. We interpret that the power of soil stability to predict measures of ecosystem health is context dependent and primarily useful for detecting either severe degradation of ecosystem health or initial recovery after a major disturbance. Other indicators are likely necessary for ecosystems with relatively stable natural plant communities, cases of subtle shifts in the functioning of these ecosystems, and to help discern best (not worst) management practices in rangelands.