Low and high crop years have positive mean synchrony across taxa at 38 MASTREE+ sites, with no clear difference

We tested whether low crop years occur together more strongly than high crop years across taxa at the same site. We used MASTREE+ V2 seed, fruit, and cone records from 38 sites in 18 source studies. Each site had 3 to 25 taxa and 15 to 41 common consecutive years. The panel has 3,536 annual values from 1948 to 2022. We compared the lowest and highest quarters of each taxon record. Tied values received equal fractional rank weights. We calculated excess joint frequency above independent timing and gave each study equal weight. Mean excess was 3.34 percentage points for low crop years (95% study bootstrap interval 2.05 to 4.79) and 2.90 points for high crop years (1.66 to 4.30). The low-minus-high difference was +0.44 points, with an interval of -0.31 to +1.21. The difference changed sign with strict quantile cuts and with a 20-year minimum record. Every tested difference interval included zero. Thus, both groups of crop years show positive mean local synchrony, but these data do not establish a stronger effect in low crop years. The intervals hold recorded years fixed. The sample has 32 US sites and only two tropical sites. Crop ranks do not measure absolute seed supply or starvation risk. We preserve unchanged source data, provenance, the plan, code, all results, three figures, and independent numerical checks. This is a test in a different dataset with a different measure from earlier studies, not a first test of local crop synchrony.

masting · seed production · local synchrony · MASTREE+ · crop failure · tied ranks · reproducible ecology