Soil C and N minimum detectable changes and treatment differences in a multi-treatment forest experiment.

Abstract

Detecting changes in forest soil C and N is vital to the study of global budgets and long-term ecosystem productivity. Identifying differences among land-use practices may guide future management. Our objective was to determine the relation of minimum detectable changes (MDCs) and minimum detectable differences between treatments (MDDs) to soil C and N variability at multiple spatial scales. The three study sites were 70- to 100-year-old coniferous forests in Washington and Oregon. Area- and volumetric-based soil measurements were made before implementation of seven treatments on 2-ha experimental units, replicated in three or four blocks per site. In the absence of treatment effects, whole-site MDCs are ~10 percent for mineral soil C and N masses and concentrations and ~40 percent for O-horizon C and N masses. When treatment differences occur, MDDs are ~40 percent for mineral soil and ~150 percent for O-horizon. MDDs are reduced as much as two-thirds by evaluating change from pre- to posttreatment rather than only posttreatment values, and by pairing pre- and posttreatment measurements within small subplots. The magnitude of MDD reduction is quantitatively related to pretreatment soil variability at multiple spatial scales, with the greatest reductions associated with the largest within-block:within-plot and within-plot:within-subplot variability ratios. These quantified benefits can be weighed against costs and challenges to make informed decisions when selecting the most appropriate sampling design.

Citation

Homann, P.S.; Bormann, B.T.; Boyle, J.R.; Darbyshire, R.L.; Bigley, R. 2008. Soil C and N minimum detectable changes and treatment differences in a multi-treatment forest experiment. Forest Ecology and Management. 255: 1724-1734