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Boom or bust

Photo by Dave Cooney White-tailed Deer are one of almost 100 animals that eat acorns.

When I pull into the parking lot of a state forest to walk the dog, I’m reminded of Christmas. The abundant red and green color scheme of the hawthorn trees evokes the holiday season. The hawthorn trees were just loaded with ripe red fruit. It seemed like there were more of these grape-sized, apple-like fruits this October than I’m used to seeing. In contrast to the dark green leaves, there was just a holiday flair.

There was more than average Black Cherry fruit on the trees in August too. While the Black Cherry trees produce clusters of small cherries every summer, this August there was just more. On the edges of fields and open areas, the branches of this sun-loving tree were low enough to grab. The small, dark purple cherries could be gathered by the bunch by day campers.

While sunny summer has passed and it’s a bit too early to decorate for the winter holiday season, there is plenty to celebrate in the fall. For fall is the season of harvest. It is when we reap what was sown. It is the season of abundance. And when it comes to the crops from plants, some years are just more abundant than others. This is most noticeable in nut trees such as hickories and walnuts. But no other tree has a boom and bust cycle more noticeable than oaks.

Oak trees produce acorns every year, but in some years they produce a lot. In other years they produce fewer acorns. A year where the majority of oaks in a region have more acorns than normal is called a mast year. Mast, in the botany world, is the fruit of trees and shrubs. Oaks have mast years every 2-7 years, depending on the species of oak trees.

Observers in the Midwest noticed that this year is a mast year. While I haven’t seen this yet in forests here, I have noticed it in some parks. Parks often have large trees surrounded by neatly mowed grass, which makes it easy to spot acorns. In one Rochester park, there were so many acorns under the large Bur Oaks I was worried I’d twist my ankle walking among them.

Photo by Katie Finch Every few years, oaks have bumper crops of acorns. This year appears to be one of those years, as witnessed under a Bur Oak tree in a city park.

The occurrence of this natural cycle of boom and bust is well known. But why it happens is still a bit of a mystery. It could be that the oaks had a good year. They had more than enough sun, water, nutrients, and the right weather to create an abundance of seeds. And the seeds are how plants pass on their genetics into the future. So why not put extra energy into ensuring your future?

Producing an overabundance of acorns takes a lot of energy. If they have a large mast year, it takes time to recover. You can’t throw a blow-out dinner party too often. It just takes too much work. So, the reason for the cycle could be that the trees just need to rest and recover.

Weather certainly has an effect on acorn development. Extreme temperatures, both high and low, can negatively affect acorn growth. If it is a cold and rainy spring, fewer oak flowers may be pollinated. A late spring frost or drought can also play a role. While the exact combination of ideal weather isn’t known, the idea that a big acorn year leads to a cold, harsh winter is just a myth. Acorn production is not a predictor of the future but more likely tells the story of the past.

There are still connections between plants, animals and the environment they live in. Mast years don’t just happen to one tree in a forest alone. Trees in a region synchronize their production of acorns year to year. One reason the oaks synchronize has to do with the animals that eat acorns.

Acorns are an important food source for myriad of animals — over 100 species, in fact. Birds such as Blue Jays, turkeys, crows, and some ducks eat acorns. Mammals like chipmunks, squirrels, opossums, racoons, voles, and rabbits are also acorn predators. In the fall, acorns can make up almost 75% of a White-tailed Deer’s diet. They are an easy to find, high-calorie, high-fat food in a tidy package made available right before a season of scarcity.

If the oaks produced the same amount of acorns each year, the population of acorn-eaters would eventually grow to match the amount of food available. They would eat all the acorns. Animals would know what to expect. They would know how much food is available so they would have as many young as the forest could support.

To ensure that large oak trees can also reproduce, the oaks become unpredictable. In years with a lot of acorns, the animals eat well and their population rises. In years with fewer acorns, there is not enough food and animal populations drop. If a lean acorn year is followed by an acorn boom, there are fewer acorn predators to eat all the acorns. And what the animals don’t eat can germinate and grow in to a new tree. Population waves of boom and bust end up coordinating, just not at the same time.

Cycles and patterns happen all around us. The individual parts of the natural world, such as one acorn, are connected to another part, like a web. Go outside and check them out.

Audubon Community Nature Center builds and nurtures connections between people and nature. ACNC is located just east of Route 62 between Warren and Jamestown. The trails are open from dawn to dusk and birds of prey can be viewed anytime the trails are open. The Nature Center is open from 10 a.m. until 4:30 p.m. daily except Sunday when it opens at 1 p.m. More information can be found online at auduboncnc.org or by calling (716) 569-2345.

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