Heavy Maple Seed Production = Slow Leaf Development

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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, especially silver (Acer saccharinum) and red maples (A. rubrum), in many regions of Ohio as well as Indiana and Kentucky are producing loads of winged seeds (samaras).


Maple Seed


maple seed


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.  Afterward, when the massive numbers of seeds drop from the trees, the trees will look bare because the stunted leaves need time to expand further to fill out the canopy.


maple seed


The stunted leaves result from trees shifting energy to support heavy seed production at the expense of leaf expansion which makes "heavily seeded trees" look unhealthy. 


An additional problem that follows is the resulting maple seedlings become a serious weed issue as they sprout throughout landscapes and in uncovered building gutters.


maple seed


It was once believed that prolific tree seed/fruit 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 consistent 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 (A. 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 reductions in seed loads occurring after spring freezes damaged vulnerable flowers or seeds.


maple seed


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.


maple seed


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.


The bottom line is that while heavy maple seed production is not consistent throughout Ohio, Indiana, and Kentucky, it's substantial enough in many areas to noticeably affect leaf expansion.  The good news is that canopies will eventually fill-in; it will just take a little longer on trees that have produced a lot of seed.