Patterns of mast fruiting of common beech, sessile and common oak, Norway spruce and Scots pine in Central and Northern Europe

Occurrence of mast years, i.e. the synchronous production of vast amounts of fruits or seeds, has an important impact on forest ecosystems, their functioning and their services. We investigated the mast patterns of the forest tree species common beech, common and sessile oak, Norway spruce and Scots pine in Central and Northern Europe over the last two to three decades. We analysed data from the International Co-operative Programme on Assessment and Monitoring of Air Pollution Effects on Forests (ICP Forests) and additional Danish, German, Flemish and Swiss datasets.
Within-plot synchrony of fructification intensity in individual trees was high in beech and spruce and lower in oak species and pine. Mast frequency increased in most regions for beech, whereas the other species showed mixed or no trends. Beech, oak species and spruce showed strong mast year (MY) synchrony, but pine did not. MY synchrony between species was only significant in Bavaria, in
Switzerland and between beech, oak species and spruce in Denmark. The deciduous species showed bimodal normal masting, while the conifers had switching normal masting. Oak species and the conifers supported the large seed and the accessory costs hypotheses, and beech and spruce supported the economy of scale, predator satiation and resource allocation hypotheses.