At a 25% event rate, low crop years showed no clear excess of joint events across 20 MASTREE+ studies

Do low crop years occur together more often than high crop years when both events have the same rate? We tested the lowest and highest 25% of crops in the shared years of each population pair in MASTREE+ V2. The test used 625 same-species pairs from 181 population records, 25 species, and 20 studies. Pairs were more than 1 km and no more than 1,000 km apart and had 20 to 53 shared years. We gave tied boundary values fractional event membership and gave each study equal weight. Given a low event at one population, the other had a low event in 54.1% of cases. The rate for high events was 57.4%. The low rate minus the high rate was -3.3 percentage points, with a study bootstrap 95% interval of -12.2 to +5.3 points. Checks with other event rates, longer records, seed traps, short distances, and fewer zeros also gave intervals that included zero. An independent calculation reproduced all 625 pair estimates. A split at half the observed crop range gave far more low years and a large low-event excess; a simulation showed how that excess can occur without asymmetric rank dependence. That diagnostic is not the partial Spearman statistic used in earlier work. This test does not establish equal rates, a global pattern, absolute crop failures, or effects on seed consumers. It provides an equal-frequency event test for a mainly northern temperate and boreal sample. The package contains source data, provenance, code, figures, all results, and offline reproduction checks.

mast seeding · seed production · spatial synchrony · MASTREE+ · event frequency · zero values · reproducible ecology