The link between rain and the biomass advantage of plant richness was uncertain at Cedar Creek in 1997–2021

We tested whether plots with more planted species had a larger biomass advantage in dry periods at Cedar Creek, Minnesota. We used 154 fixed plots and 25 harvest years from 1997 to 2021. For each year, we estimated the slope of log live biomass against log2 assigned richness. We then related that slope to rain in the 90 days before the median recorded harvest. The model also included maximum temperature and a linear time term. Each 100 mm more rain was linked to a +0.00957 change in the richness slope. The nominal 95% interval was −0.01096 to +0.02700 when we sampled both plots and three-year blocks. A negative rain coefficient would support a larger richness advantage in dry periods. The result does not establish that pattern. A plot-only interval excluded zero, but intervals that included year uncertainty did not. All 14 planned model forms had year-level HC3 rain intervals that included zero. Rain was clearly linked to yearly mean log biomass in a descriptive check. This study refines an earlier same-release rain comparison with harvest alignment, weather quality checks, and uncertainty across shared years. It does not test event resistance, recovery, nonlinear water stress, or a general absence of diversity effects. The package contains unchanged source data, provenance, code, all results, figures, and independent checks.

biodiversity · grassland · rainfall · biomass · Cedar Creek · drought · shared weather · reproducibility