Acorns are scattered on grass.

Acorns aplenty: GVSU botanist explains why the familiar fall underfoot crunch is more pronounced

Acorns abound right now, indicating the oak trees are in overdrive, producing potential offspring, as part of a cycle that has environmental and ecological implications, a Grand Valley botanist said.

And while this process, known as masting, produces a veritable feast for squirrels, the oak tree cycle of peaks and valleys of acorn production actually is a process for controlling acorn predators, said Tim Evans, professor of biology. 

Masting typically happens every few years, though its mechanisms are still somewhat of a mystery to scientists, Evans said. And this year seems to be a particularly robust masting season, he added.

First, a reminder of what an acorn is and its function: It is a fruit, specifically a nut, sprouted from a small flower on the tree, Evans said.

"Its primary role from the plant's perspective is that it's the next generation. The tree wants as many of those acorns to sprout into new trees as possible," Evans said. "Very few acorns actually survive to grow into a tree, because their other function is as food. Most of them get eaten."

That's where the squirrels — and to be fair, other animals — come in. Squirrels, though, are undeniably the most visible predator of the oak tree's reproductive intentions.

The overabundance of acorns in a masting season means there are more acorns than predators can eat, something known as predator saturation, Evans said.

"Oaks are well known for doing this," Evans said. "The squirrels, deer, just have a feast year, but then there’s still plenty of acorns out there to sprout into the next generation of trees."

But the oak trees giveth and taketh away from the predators. A valley in the acorn production cycle also has implications for the critters, Evans said.

Without as much to eat for the animals, "That puts a check onto the population growth," he said.

Acorns are scattered on grass.
A canopy of oak trees seen from below, leaves set against a blue sky.
Evans said scientists believe another condition that can lead to robust acorn production is a freeze the previous year that affects fruit production, causing the tree to conserve energy that season and produce even more acorns the next.

Those scenarios are some of the ecological factors. There are also some environmental factors when considering masting.

The previous year's weather conditions tend to play a significant role in the event, Evans said. A hot, dry summer appears to put the trees into a stress response where they shift resource allocation to reproduction, rather than maintaining themselves.

Another condition that can affect masting is a dry, windy spring that encourages vigorous pollination, Evans said, noting last year's summer conditions and this year's spring conditions seemed to combine appropriately for masting.

Oak trees, which can last hundreds or even thousands of years, still need to make the necessary evolutionary adaptations to ensure species survival, Evans said. Pathogens are a threat, as are windstorms or fires.

But even the masting adaptation appears to be undergoing some change, Evans said.

"There’s some long-term evidence that masting cycles are getting shorter for some species, probably due to climate change, especially temperature increases," Evans said. "When they do mast, you get years like this, where the number produced is more extreme masting."