Low and high reproductive years each had 48% mean co-occurrence in 11 North American tree species

We tested whether low reproductive years occurred together across sites more often than high reproductive years in 11 North American tree species. We used MASTREE+ v2 records from 103 species-site series at 76 recorded locations. There were 493 pairs with 20 to 53 common years, within 1967-2020, and distances of 1 to 1000 km. At each site, we assigned the lowest and highest quarters of common years to events. Equal values at a boundary received equal fractional weights. We calculated conditional event co-occurrence and gave each species equal weight. Low-year co-occurrence was 47.62% and high-year co-occurrence was 47.59%. The difference was +0.03 percentage points, with a 95% interval of -8.82 to +6.89 points from shared calendar-year blocks and shared site weights. Seven species had a positive difference and four had a negative difference. Changes to event frequency, distance, zeros, coordinate quality, record length, and source study did not reveal a large common difference in the point estimates. Independent scalar calculations verified every pair score. The result is a scoped null result. It does not prove equal probabilities or exclude species-specific differences. The selected records do not represent all North American trees. Relative quartiles do not define food shortage. Our event score differs from the partial rank correlations used in earlier European studies. The package preserves source data, provenance, code, results, figures, and reproduction instructions.

masting · seed production · spatial synchrony · tail dependence · North America · MASTREE+ · reproducibility · null result