Wesołowski T., Rowiński P., Maziarz M. 2015. Interannual variation in tree seed production in a primeval temperate forest: does masting prevail? European Journal of Forest Research 134: 99-112.

We assessed seed production by mature individuals of five dominant tree species in the strictly protected reserve of Białowieża National Park (Poland) from 2002 to 2013. Interannual variation in seed production was extreme, generally asynchronous among species. All species exhibited high variability in seed production, ranging from bumper crops in some years to no seeds in others. All species exhibited a typical ‘‘normal masting’’ pattern, which was most pronounced in Picea abies and Quercus robur, moderate in Carpinus betulus and least expressed in Acer platanoides and Tilia cordata. Within species, crop sizes were well synchronised among areas and individuals; seed production was most synchronised in P. abies and Q. robur and least synchronised in T. cordata and A. platanoides within a season. Among species, interannual variability was negatively correlated with seasonal synchrony among individuals. Besides a negative correlation between rainfall during the flowering period and seed crop in three deciduous species, variation in temperature and rainfall in periods critical to seed formation was uncorrelated with the variation in seed crops. Heavy defoliation by caterpillars coincided with a poor seed crop of deciduous trees in 2003. Generally, the variation in seed crops was much higher than the variability of environmental factors. Deciduous species could produce bumper crops in consecutive years and were not necessarily forced to ‘‘switch’’ to nonreproduction by resource depletion. It appears that trees could apparently assess when and how intensively to reproduce. We discuss adaptive benefits of masting reproduction that include pollination efficiency, predator satiation and seed dispersal.