What kid doesn’t love those maple ‘helicopters’? I grew up with two large silver maples (Acer saccharinum) in our yard and can always remember the late spring ritual of playing with one of the best toys ever produced by nature, the maple samara. These winged seeds rapidly go from tiny flowers to mature seeds over the course of a just few months each spring. I can remember playing with the odd looking seeds in so many ways as a kid, with their awesome helicopter action when falling through the air being the central component of most of that play.
This spring, kids will find no shortage of maple samaras lying about our yards, sidewalks, and patios. It was certainly a bumper crop this year! So, why are some years better than others for maple seed production?
The simple explanation is that many of our native, wind-pollinated trees perform a cyclical feat referred to as “masting” or “mast seeding”. Seed production among our native trees varies considerably from year to year, but tends to increase across the board during certain years. One recent example in our area was the high production of white oak acorns in 2017, which was truly a bumper crop. However, last year’s production paled in comparison.
Masting is a widespread occurrence in nature which has led to a large body of research on the topic. There is some debate as to how this phenomenon happens and what drives the cycles of production. Researchers have measured seed production across large populations and among individual trees to attempt to establish patterns.
One recent study of tree populations in Michigan suggests that seed production varies greatly among individuals within a species in any given year, regardless of whether or not mast seeding occurs. The study identified “super-producers” that consistently produced more seed per year than other individuals. These super-producers were also more synchronized in their annual production rates, kicking up seed output together in masting years.
The concept of super-producing individuals within a population really makes sense to me, confirmed by some of my personal observation. I can think of a number of trees I’ve observed over the years, a few silver maples in particular, that consistently produce a lot of seed every year.
In masting years, they may produce more, but often it is not that observable (without quantitative measures such as those from research) since they always produce so much. I would guess many gardeners can think of examples of trees that consistently produce heavy seed crops in their own landscapes. Perhaps these individuals are the super-producers in your neighborhood?
In the past, some common hypotheses suggest that trees store up energy over several seasons to expend it in seed production during a masting year. However, there is little actual data to support this theory, despite regular mention in a variety of studies.
A newer line of thinking has emerged which suggests that trees may simply change their energy use in mast seeding years. During spring leaf out, trees can shift more energy into seed production at the expense of leaf production. This energy shift is believed to be independent of past year’s production, meaning that a good growing season last year does not necessarily translate into a masting event this year.
The concept of shifting energy during leaf out was pretty evident on silver maples this spring. Earlier this month, a lot of silver maples looked barren or not healthy. Many folks worried their trees may not be leafing out as usual or not leafing out at all. Upon closer inspection, the trees were in fact leafing out, but the green in their canopy was primarily from developing samaras. They had shifted energy into this year’s bumper crop at the expense of leaf growth over the short-term. We saw a ton of green samaras and tiny, slowly developing leaves.
As those samaras began to mature and turn brown, tree canopies appeared to be unhealthy since what used to be the primarily green color was now brown. With seeds fully mature and dropping at this point in the season, leaf growth has caught up and silver maple canopies are starting to look more normal.
Whether or not you have a regular super-producer on your hands, expect a little extra seed cleanup this spring. We can also expect a greater number of seedlings sprouting up in our landscape beds. However, the good news is that any concerns for poor leaf production this year can be set aside now that maple canopies are again shading our landscape.