Our recent Ecology paper on system-specific roles of weather and pollination dynamics in driving seed production in European trees is now available online!
In wind-pollinated trees, weather and seed production can mechanistically link through flowering and pollination dynamics in different ways. According to pollen coupling hypothesis, flowering effort of trees is driven by weather and plant resources, which directly translates into the size of seed crop through efficient pollination. In contrast, weather can affect pollination efficiency, leading to occasional high seed crops – this is so-called pollination Moran effect hypothesis. Furthermore, Moran effects can arise because of weather effects on flowering synchrony, which, in turn, drives pollination efficiency (phenology synchrony hypothesis).
Using a 19-year data set from three sites in Poland, we investigated the relationship between weather, airborn pollen, and seed production in two oak species (Quercus petraea and Q. robur) and beech (Fagus sylvatica). We found that for oaks and beech, the warm summers preceding flowering correlated with high pollen abundance and warm springs resulted in high flowering synchrony (short pollen seasons). However, in beech the best predictor of seed crops was pollen abundance, supporting the pollen coupling hypothesis. In contrast, large seed crops in oaks correlated with short pollen seasons, thus supporting the pollination Moran effect and phenology synchrony hypotheses. These findings suggest that fundamentally different proximate mechanisms may drive masting in oaks and beech.