Author
|
Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 7/16/2016 Publication Date: 7/2/2016 Citation: Reinhart, K.O., Vermeire, L.T. 2016. Soil aggregate stability and grassland productivity associations in a northern mixed-grass prairie. PLoS One. 11(7):e0160262. doi:10.1371/journal.pone.0160262. 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. • Accomplishment- We determined that dominant plant species may confound predicted relationships between soil stability and plant productivity. Measures of soil stability were negatively (not positively) correlated with grass (and root) biomass. • 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 functioning. • Management implications- We interpret that direct measures of plant biomass 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. Technical Abstract: Soil (aggregate) stability is widely used as an indicator of soil and rangeland health. The empirical evidence justifying soil aggregate stability as an indicator of rangeland health, however, is thin and confusing. Here we revisit the hypothesis that soil aggregate stability is positively correlated with plant productivity. We measured local gradients in grassland community composition, plant (aboveground) productivity, root biomasses, soil aggregate stabilities, and topography. The % water-stable soil aggregates of three size classes of macroaggregates were mainly negatively correlated with dominant graminoid biomass and root biomass. The predicted positive association between factors was apparently confounded by spatial variation in plant species composition. Specifically, sampling spanned a local gradient in plant community composition which was likely driven by niche partitioning along a subtle gradient in elevation. Our results indicate an apparent trade-off between plant biomass production and soil aggregate stability, both known to affect soil (or site) stability. Empirical evidence of this trade-off and the fact that dominant plant species may affect plant biomass-soil stability associations diminish the value of soil aggregate stability as an indicator of rangeland health. Since vegetation moderates ecosystem flux and soil (or site) stability, we interpret that perennial plant attributes are likely more suitable as indicators of rangeland ecosystem functions than measures of soil aggregate stability. More empirical evidence is needed to better understand the context(s) where soil aggregate stability is a useful indicator of ecosystem functioning. |
