Phone calls and e-mail messages to Extension offices from landowners concerned about the health of maples should soon be on the rise. That's because maples in much of Ohio, as well as Indiana and Kentucky, are producing loads of winged seeds (samaras).
The problem is two-fold. Abundant springtime samaras by themselves can draw attention to maple trees, particularly when the seeds mature and turn brown. The dense clusters of samaras are made more apparent because tiny leaves fail to cover-up the seed.
The stunted leaves result from trees shifting energy to support heavy seed production at the expense of leaf expansion which makes "seedy trees" look unhealthy. Of course, once the seeds drop, the resulting maple seedlings become a serious weed issue as they sprout throughout landscapes and in uncovered building gutters.
It was once believed that prolific maple seed production is connected to tree stress; the theory was that heavy seed production occurred on stressed or dying trees as a last hurrah in support of the species. However, research has failed to provide support for this speculative conjecture. For example, a study published in 2017 in the Canadian Journal of Forest Research found no evidence that precipitation or drought over previous seasons influenced seed production in sugar maples (Acer saccharum).
Another hypothesis emerged several years ago linking heavy seed production to the lack of spring freeze events. The thinking was that maples are by nature heavy seed producers. However, the successful persistence of the seed to maturity depends upon whether or not freezing temperatures killed the flowers or nascent seed. Observations across Ohio in past years seemed to support this perspective with the northern and southern parts of the state experiencing significant differences in seed production after northern areas saw late-spring freezes.
However, research has shown there is another important variable that must also be considered. As with oaks, sugar maples exhibit synchronous seed "masting" in which all trees in a population produce heavy seed in certain years. It is thought synchronous flowering by wind-pollinated trees enhances the success of pollen finding its way to receptive flowers. Also, heavy seed production can overwhelm seed predators which enhances successful maple stand regeneration.
This means freezing temperatures have the greatest potential impact on maple seed production during heavy masting years. Conversely, there's much less impact during years when seed production is naturally low.
Although I could find no research indicating whether or not other maples undergo cyclic seed production, synchronous masting may explain something else I've observed this spring in southern Ohio. While seed production appears to be particularly heavy on sugar maples, silver maples (A. saccharinum), and red maples (A. rubrum), as well as various cultivars and hybrids, flowering and seed production on boxelders (A. negundo) seems unusually light this season. At least, on the trees that I've observed thus far. Perhaps boxelders also have synchronous masting and this just isn't their year for superabundant samaras.
