masting

Masting, also called mast seeding, is a pattern of reproduction in which the plants of a population produce seed or fruit in large amounts in some years and little in others, and do it in step with one another. Ecologists define it as synchronous, annually variable seed production by plant populations. It is especially widespread in temperate trees, and its boom years ripple through food webs, nutrient cycles, carbon storage and human disease risk.

Plants that mast gain from economies of scale. A huge crop in one year satisfies the animals that eat seeds, so more seeds survive, and flowering together makes pollination more efficient. Four decades of records for European beech show natural selection favouring individual trees that follow this boom and bust rhythm in step with their neighbours.

Mast years can be predicted. Across 26 long-term data sets from five plant families, the temperature difference between the two previous summers predicted seed crops better than a warm summer alone. That matters for the animals that depend on the crop. In New Zealand the kākāpō, a critically endangered parrot, breeds when forest trees such as rimu fruit heavily, and the recovery team reads summer temperature differences to get about two years of warning.