Cues for Masting in Sugar Maple and American Beech

Many tree species exhibit the phenomenon of seed (or fruit) “masting” in which all the trees in a population produce large seed crops in a particular year. For some species this synchronous behavior is thought to favor successful regeneration by saturating seed predators, like squirrels, that also serve as seed dispersal agents – so many seeds are produced in a mast year that the squirrels don’t eat them all. But what cues all the trees in a population to mast synchronously?

Both sugar maple and American beech exhibit masting behavior at Hubbard Brook, based on twenty-five years of seed collection. In general, both species often mast in the same year with small seed crops in the intervening years, and eight mast years have been recorded since 1994 (see graph). We analyzed climatic data and determined that masting in maple and beech can be predicted by a “delta T” model: when summer temperatures in two consecutive years are very different, then high seed production occurs in the following year. One clear advantage of synchronous flowering in wind-pollinated trees is that waste of pollen is reduced, and this explanation may contribute to the selective value of masting, particularly for species that are not primarily dispersed by seed predators (e.g., sugar maple is wind dispersed). The same “delta T” cue has been observed in wind-pollinated Australian forest trees.

This research was recently published in the Canadian Journal of Forest Research.

Cleavitt, Natalie L. and Fahey, Timothy J. 2017. Seed production of sugar maple and American beech in northern hardwood forests, New Hampshire, USA. Canadian Journal of Forest Research. v. 47. p. 985-990.

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Seed production by A. sugar maple (ACSA) and B. American beech (FAGR) at Hubbard Brook from 1994-2016. Horizontal lines indicate long-term mean seed production. In C. and D. standard deviation of seed production of the two species, based on 66 seed traps, is indicated.