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It's Raining Acorns!

     It seems like this year is a good one for the oaks. The past few days I have literally heard acorns raining down in the forest around my yard, and they are littering walkways and sidewalks everywhere. I am sure many in my neck of the woods remember the exceptionally big "mast" year for acorns- 2010. That year it was a painful proposition to take a walk under an oak tree, they rained down for days. Mast is the word used for the reproductive part of woody plants, in other words, the seeds of trees and shrubs. There are soft masts and hard masts. Soft masts include tree buds, catkins and berries, whereas hard masts-you guessed it- are harder "fruits" such as acorns, hickory nuts and beech nuts. In some seasons there are more hard masts, like acorns, produced than others. It is a phenomena that scientists have difficulty predicting with great certainty, although there can be some predictable factors such as weather. Like all things in nature there are so many causes and interconnections that predicting a good mast crop year is a little tricky. These abundant years could happen two years in a row, or may have two to five years in-between. Weather may be a factor, however, since most acorns or nuts are on a two-year growth cycle, the weather that is advantageous for producing a larger quantity of seeds may occur in the year before we notice the seed production.
     As you can imagine, more acorns means good eating for herbivores such as chipmunks, squirrels, turkey and deer. Squirrels not only have a lot to eat, but they also help the tree to disperse its seeds. Gray squirrels bury their acorns in a variety of different places and then only recover some. These forgotten seeds often grow into saplings. In essence they are planting the seeds for the oaks.
Gray squirrels are smarter than you might think when it comes to acorns. Scientists have found that the squirrels can differentiate the acorns from white oaks and the acorns from red oaks. The white oak seeds germinate very quickly, and therefore lose their nutritional value hastily. The squirrels eat these first, rather than store them for later. They prefer to store the red oak acorns to eat over the winter and spring. Even more incredibly, sometimes the squirrels will bite through the embryo of the white oak acorns, prohibiting them from sprouting. This makes the white oak acorns just as valuable to store as the red. The wonders of nature never cease to amaze- if only they could evolve the behavior to look both ways before crossing the road!
     Obviously, there are pros and cons for many natural phenomena, depending on your species and perspective. Scientists have linked larger Lyme disease carrying tick populations to years with small acorn crops. A good mast year in the northeast can lead to a boom in the population of white-footed mice, whereas a meager crop causes a big drop in the mouse population. White-footed mice are the preferred host for the black-footed tick which is very good at carrying and transmitting Lyme disease. When the population drops, the ticks are forced to find other hosts- including us. This was very clear after the huge mast crop in 2010. The mouse population sky-rocketed, then the following year the acorn crop was practically non-existent. The subsequent mouse population crash caused the potential for an influx of Lyme disease that year. Many believe that the tick population has only to do with the weather, but again, there are many factors at work in the complex natural world.
     Regardless of the larger food web implications of raining acorns, it's probably best to duck and cover this fall if you venture out under the oak trees- they come down pretty fast!

Read more:

Tree Activities and Resources

Mast Tree Network

Arbor Day Tree ID online field guide

Arbor Day Tree ID lesson plan (grades 4-12)

Project BudBurst- Citizen Science Project

Acorn Craft Ideas

Acorn Science Story for kids- Highlights magazine


  1. I am really enjoying your blog, Sarah! Chock full of info and great resources-

    1. I'm glad you're enjoying it, I'm having fun writing it. Thanks for reading!