Power and limitation of soil properties as predictors of variation in peak plant biomass in a northern mixed-grass prairie

Authors: Reinhart, Kurt; Vermeire, Lance

Submitted to: Ecological Indicators
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/15/2017
Publication Date: 9/1/2017
Citation: Reinhart, K.O., Vermeire, L.T. 2017. Power and limitation of soil properties as predictors of variation in peak plant biomass in a northern mixed-grass prairie. Ecological Indicators. 80:268-274.

Interpretive Summary: Background- Any soil property that consistently corresponds with plant biomass may be a general indicator of whether a rangeland's health is stable, improving, or degrading. Soil and rangeland health are popular concepts in contemporary rangeland management. Problem- Soil properties used to describe healthy rangelands are often justified by expert opinion and decisions on what soil properties have the potential to affect agronomic (i.e. row crop) production. Here we sought to compare and contrast the predictive power (i.e. accuracy) of many soil properties and identify which explained actual (and appreciable) variation in peak biomass production in a grassland in the northern Great Plains. Accomplishment- We determined that most of the focal soil properties did not explain appreciable variation in peak biomass. One of the best predictors, subsurface inorganic carbon (carbonates), is not typically measured but is likely an indicator of soil depth and the availability of key soil nutrients. Implications- Soil erosion is a main threat to the capacity of rangelands to produce plant (and animal) biomass year-after-year. Determining whether rangeland health is stable, improving, or degrading is a challenge, except after dramatic change. We ideally need early (i.e. leading) indicators of future change. More work is needed to determine the best indicators of rangeland health.

Technical Abstract: Soil properties are thought to affect annual plant productivity in rangelands, and thus soil variables that are consistently correlated with variation in plant biomass may be general indicators of rangeland health. Here we measured several soil properties (e.g. aggregate stability, organic carbon, total nitrogen) and tested each as a would-be predictor of local variation in peak aboveground grassland biomass and plant community composition. Individual properties explained a small (=7%) amount of variation in plant biomass. Variation in plant biomass was partly explained by surface soil carbonates, ratio of carbon to nitrogen, and root biomass. Variation in plant community composition was associated with subtle shifts in elevation and subsurface carbonate and organic carbon concentrations, which are possible indicators of soil depth. Plot-to-plot variation in plant biomass is seemingly difficult to predict based on soil properties, including popular indicators of soil and rangeland health and even root biomass. While protection of soil is critical to overall rangeland ecosystem functioning, our findings suggest that the relationship between soil properties and plant biomass in natural grasslands is complex. Thus, there may not be one or even several soil properties that consistently predict appreciable variation in peak grassland biomass, especially variation within an ecosystem independent of precipitation.