Synchrony between weather cycles and dynamics of seed harvests of broadleaved tree species in the Czech Republic

This study provides a comprehensive analysis of the effects of temperature, precipitation, and the North Atlantic Oscillation (NAO) index on seed harvest dynamics in 12 major broadleaved tree species in the Czech Republic, specifically, European beech, English oak, sessile oak, northern red oak, sycamore maple, Norway maple, European cherry, littleleaf linden, largeleaf linden, European hornbeam, European white birch, and eastern black walnut. National seed-harvest data from the Czech Forestry Institute (ERMA2) for 2004–2023 were related to monthly climate variables in the year of harvest (Lag 0), the year before harvest (Lag −1), and two years before harvest (Lag −2). Based on Spearman correlation analysis of monthly NAO, precipitation, temperature, and harvested seed material, the highest number of significant correlations was observed for the NAO index (28 cases), followed by precipitation (22) and temperature (21), with the year before harvest identified as the key period. The dominant seed-harvest cycles are 2–2.5 years and occur in nearly all evaluated species. Longer cycles (3.5–6.6 years) are typical for less harvested species such as eastern black walnut, northern red oak, largeleaf linden, and European white birch. All species showed strong synchrony, except largeleaf linden and eastern black walnut. Results suggest that 2–2.5 cycles in precipitation and temperature are closely related to the NAO, reflected in seed harvest frequency. This study supports the Moran effect, where shared climatic triggers drive interspecific synchronization in seed harvest.