Have you ever walked through an autumn forest and wondered why some years the ground is covered in a crunchy carpet of acorns, while other years it’s almost bare? If so, you’re not alone. For centuries, both scientists and curious observers have puzzled over this phenomenon.

Why do trees, especially mighty oaks, sometimes drop so many seeds one year, only to produce hardly any the next?

Seeds and the Cycle of Nature

Imagine a grand oak tree, its branches heavy with acorns. As the seeds fall, squirrels scramble to gather them, feasting and storing these treasures for the cold months ahead. This scene is familiar to many living in the temperate Northern Hemisphere, where oaks and squirrels thrive. But there’s more to this story than meets the eye.

This pattern, known as **seed masting**, is where trees produce an overwhelming number of seeds in some years and very few in others. It’s not just oaks; thousands of tree species and other long-lived plants employ this strategy.

For years, scientists believed this was primarily about predator satiation. The idea is simple: drop so many seeds at once that predators, like squirrels and birds, can’t eat them all, ensuring that some seeds survive to grow into new trees.

However, this isn’t the only explanation.

Unseen Forces: Seeds and Pollinators

Another theory suggests that masting might benefit the trees’ pollination process. If all trees of the same species flower and produce seeds simultaneously, pollinators such as bees can move efficiently from tree to tree, enhancing the chances of successful pollination.

But what if there’s another, less obvious reason? What if the secret lies in something much smaller than a squirrel or a bee?

Seeds and Disease: A New Hypothesis

Recently, researchers in Canada proposed an intriguing new theory. Published in *Current Biology*, their paper suggests that disease might play a critical role in seed masting. While seeds like acorns are gobbled up from above by animals, they are also under attack from below by fungi, bacteria, and other pathogens.

These tiny invaders can destroy large numbers of seeds, and the timing of seed release might help trees manage these threats.

Jonathan Davies, a botanist at the University of British Columbia, draws a parallel with farming practices. “Farmers often let fields lie fallow to clear pests and pathogens.

Removing the crop for a few years can purge the field, allowing for healthier future harvests,” he explains. Could trees be doing something similar?

This idea came about in a casual conversation between Davies and Janneke Hille Ris Lambers, a plant ecologist. They were discussing the variability of seed production in Washington state when the concept of pathogens came up. To their surprise, no one had explored this angle before.

Building the Seed Hypothesis

Testing this theory in the field would take decades due to the long reproductive cycles of trees. So, Ailene MacPherson, a math professor at Simon Fraser University, built a mathematical model to explore the idea. These models, though simplified, provided a foundation for understanding how seed masting could disrupt disease cycles.

The models suggested that in years with few seeds, the population of pathogens dwindles due to a lack of hosts. When a mast year follows, the sudden abundance of seeds overwhelms the reduced pathogen population, ensuring more seeds survive and grow.

The Path Ahead: Seeds of Discovery

The initial steps of this theory are in place, and Davies and MacPherson hope other researchers will build upon their work. Long-term data from places like Mount Rainier National Park, where Hille Ris Lambers has been studying trees since 2007, could provide valuable insights.

The idea of pathogen-driven masting doesn’t replace older theories but adds another layer to our understanding. As Davies notes, “There’s probably no one explanation. This is likely part of the puzzle.”

So, next time you marvel at the abundance or scarcity of seeds in the forest, remember: these cycles are part of a complex dance involving predators, pollinators, and even microscopic pathogens. Nature, in its wisdom, continues to surprise and teach us about the intricate balance of life.