Seventeen local MASTREE+ studies showed no clear excess of shared low crop years between species

We tested whether different plant species at the same site share low crop years more often than high crop years. We used MASTREE+ V2 quantitative records of seeds, fruits and cones. The sample has 6,174 species pairs from 190 species at 45 source-defined sites in 17 source studies. Each pair has 20 to 41 common consecutive years within 1936–2020. We split ties at the quartile boundary so that each tail has the same total weight. We averaged pairs within sites, sites within studies, and studies equally. The shared low crop score was 10.58%, and the shared high crop score was 12.13%. The low-minus-high difference was -1.54 percentage points (95% study-bootstrap interval -3.15 to +0.08). Both scores were above the 6.25% value under independent alignment. The mean Spearman correlation was 0.375 (0.255 to 0.502). All planned sensitivity checks gave negative mean differences. Most intervals included zero. Seed-only records gave -0.54 percentage points (-2.23 to +1.07). Tests that account for known source overlap did not produce a positive mean difference. Thus, this sample gives no clear evidence of greater low crop alignment between species. The result does not establish equal tail scores. It also does not measure total seed supply, consumer food shortages, or future risk. Inference assumes that source studies are independent and conditions on the observed time periods. The package preserves unchanged source data, all pair scores, code, checks, figures, and source records.

masting · seed production · species synchrony · MASTREE+ · tied values · crop scarcity · reproducible ecology