Maples in central and southwest Ohio, particularly red maple (Acer rubrum), are producing heavy seed (samara) loads. Excessive seed production can temporarily cause maples to have stunted leaves or no leaves, particularly towards the top of seedy trees. Consequently, the thin canopies coupled with brown samaras can cause homeowners to ask, “What’s wrong with my maple trees?”
A thinning maple tree canopy can signal serious tree health issues from vascular wilt diseases to stem-girdling roots, or it could be a matter of “wrong tree, wrong place.” Sugar maple (A. saccharum) does poorly in poorly drained soils, but it usually takes years for root drowning and root rot to produce noticeable canopy symptoms. Red maple, with an alternate common name of “swamp maple,” can thrive in wet-soil conditions; however, they do not thrive in highly alkaline soils.
However, it’s unlikely one or more of these tree health issues have become so common throughout central and southern Ohio they are producing a widespread maple malaise. It’s more likely the common condition of thin maple canopies is a condition common to maples. It’s common for maples to shift energy to support heavy seed production at the expense of leaf development and expansion.
The leaves take time to fully expand and mask the winged seeds after the samaras mature. Thus, abundant springtime samaras by themselves can draw attention to maple trees before they are concealed by fully expanded leaves.
Exactly when expanding leaves take precedence over seeds depends on the maple species. The timing for seed production varies widely between the dominant maple species in Ohio. Red maples are the first to bloom closely followed by silver maples (A. saccharinum). Sugar maples are the last to bloom. Thus, red, and silver maples are the first to appear sickly during the transition from samaras to leaves. Of course, the chronology can become mixed owing to the mixed genes found in hybrids.
The bottom line is that heavy maple seed production is a natural event securing the survival of the species as demonstrated by hordes of maple seedlings eventually appearing in landscapes, vegetable gardens, and gutters. However, the exact reason(s) some maples produce huge numbers of seeds has been the subject of much speculation.
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. A study published in 2017 in the Canadian Journal of Forest Research found no evidence that stress associated with drought over previous seasons influenced seed production in sugar maples.
Another hypothesis emerged several years ago that maples are a bit like rabbits. They are by nature heavy seed producers, but their effusive reproductive efforts are occasionally thwarted by freezing temperatures killing the flowers or nascent seed.
This explanation carries some common sensical weight. In previous years, light maple seed production has been observed in Ohio after flowers or emerging samaras were severely damaged by a spring freeze. Indeed, deep freezes were generally absent this spring in southwest Ohio during red maple bloom and early samara development.
While the occurrence or absence of spring freezes is likely linked to the abundance or scarcity of samaras, research has also shown that another important variable should 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 may overwhelm seed predators which enhances successful maple stand regeneration.
Thus, heavy seed production may occur with the convergence of two events: a heavy “masting” year for the maple trees coupled with the lack of a killer freeze. It appears that maples in the southwest part of the state dodged a frozen bullet.
The good news is that “temporary” is the operative word relative to the impact that heavy maple seed production can have on tree aesthetics. As shown in the image below, seedy maples will eventually recover.