Low-crop overlap was not clearly lower across species at one site than within species across sites in five MASTREE+ studies

We compared joint low-crop years for different tree species at one site with those for the same species at separated sites. We used MASTREE+ V2 records and the same four records and years for each comparison. The sample had 98 matched sets, 81 records and 16 species in five studies in the United States and Finland. Each set had 15–32 common years within 1948–2020. Site separations were 1.93–961.50 km. Low years were the bottom quarter of each crop record, with fractional weights at ties. We gave species pairs equal weight within studies and studies equal weight. Mean joint frequency was 9.53% for local species pairs and 10.57% for spatial same-species pairs. The difference was −1.03 percentage points. Its nominal 95% study t interval was −6.59 to +4.52 points. Three studies had lower local overlap and two had higher local overlap. Source and time-weight ranges also included zero. A secondary bottom-half definition gave a lower local frequency, but it includes moderate crops. The primary result does not establish which comparison has lower relative poor-year overlap. It does not show equal timing or measure seed mass, food shortage, or the effect of planting species mixtures. The package preserves source data, provenance, the plan, code, all results, figures, and independent and clean offline checks.

masting · seed production · spatial synchrony · species diversity · low crop years · matched comparison · MASTREE+ · null result