Maple trees this year just do not look right. Why? What is going on?
Maples are in the Latin genus Acer. The genus Acer, commonly known as the maples, is an extremely diverse group of trees containing over 120 species of various size and habit. Maples are found throughout the northern hemisphere but exhibit a significant native presence in eastern North America and Eastern Asia. Maples are easily identified by oppositely arranged leaves and opposite arranged twigs and branches.
The helicopters that fall from the tree in June are actually winged fruit that develop into seeds known botanically as Samaras.
These popular ornamentals have a large variety of growth habits, cultural adaptability, cold hardiness and colorful foliage. Their widespread representation in both residential and commercial landscapes ranges from the most delicate varieties of Acer palmatum (Japanese Maple) to tough, utilitarian species well-suited to street plantings in urban environments.
This year the Acer saccharinum (Silver Maple), and Acer rubrum (Red Maple) in Northwest Ohio are producing loads of Samaras (winged seeds). The trees appear stunted and 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 the Maples 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 of the tree.
The reason why the leaves are so tiny is the tree is 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. It was once believed that prolific tree Samara 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 Acer saccharum (Sugar Maple).
Another theory 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 freezing temperatures killed the flowers on the Maple trees. Observations across Ohio in past years seemed to support this perspective with reductions in seed loads occurring after spring freezes damaged vulnerable flowers or seed.
This means freezing temperatures have the greatest potential impact on maple seed production during heavy samara or seed producing years. Conversely, there is much less impact during years when samara production is naturally low.
The freezing temperatures we experienced Mother’s Day, will that effect this year’s seed production? Though possible, it is not likely as our aples were not flowering during that time. The seed or samaras were already set, and the temperatures were not low enough to freeze the seed.
The bottom line is that while heavy maple seed production is not consistent throughout, it is 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.