The Mighty Acorn

HOW DOES YOUR GARDEN GROW

By Kit Flynn

Some years I have a vast accumulation of acorns and yet other years I have a dearth of them. While I appreciate the lack of acorns on my sidewalk during these shortages, I was surprised to learn that the acorn is an interesting fruit, one that is more than a mere crunch under my feet.

In some autumns, oaks can produce a glut of acorns – as much as 250 pounds per oak – in years described as “mast” years whereas in other years the squirrels are lucky to get ½ pound from that same tree. Why is there such an annual variation in acorn production? No one really knows although for once global warming doesn’t appear to be the culprit.

One theory is termed the “predator satiation hypothesis” by Ritchie S. King in an article appearing in The New York Times. According to this supposition, during mast years, the oaks produce so many acorns that the squirrels, jays, deer, and bears cannot eat them all. Obviously, this benefits the oaks as some of their fruits will manage to germinate. The lean years of acorn production help to limit the population growth of those species who feast on acorns.

We know that a scarcity of acorns can affect animal populations. In the West, the acorn woodpecker (Melanerpes formicivorus) is highly dependent upon acorn production; for this reason, they reproduce in the fall when acorn production is at its peak rather than in the spring.

In the East, acorn shortages can decrease the size of rodent and deer populations, forcing the mice to prey on the nests of ground-nesting birds. With the demise of mice populations, ticks will look to other individuals – including us – for their next bloody feast, which you will agree is not welcome news. Scientists believe that 2012 was an exceptionally bad year for Lyme disease, all because the oaks failed to produce an adequate quota of acorns in 2011.

Oaks vary considerably in their ability to produce acorns. Some require 18 months to produce their share of acorns, with pollination occurring in the spring. Others, such as the white oak, will have a mast year for one or two years out of a period of five years. Some individual oaks simply are heavier producers than others. Oaks depend upon the wind for a successful pollination so animals play almost no role in this process. Warm, dry conditions in the spring seem to correlate with a larger acorn production cycle.

Filled with tannin, acorns are quite bitter. In order to digest the tannin, animals who feast on acorns require a digestive system that can break it down, something we lack. Therefore, Native Americans subjected acorns to a long soak, thereby ridding them of the tannin.

Fortunately for those animals who are dependent on acorn production, different oak species have different mast years. Typically, not all oaks will experience a low acorn production at the same time. However, what made 2011 unusual in the Northeast was that all the dominant oaks, from the scarlet oaks to the black oaks to the red oaks, demonstrated low acorn production.

Acorns fall at a different rate, depending upon the oak species. White oak acorns fall earlier than red oak acorns. Germination rates also differ with white acorns germinating almost immediately after they have hit the ground whereas red oak acorns need to overwinter before germination occurs. For some reason, there are five times the number of white oak seedlings, compared to red oak seedlings.

Oaks are long-lived trees: A white oak can live for 300 years whereas a red oak has life span of a mere 200 years. The years of low acorn production have little effect on the oaks themselves, although, of course animal populations may be greatly affected.

The next time your foot goes crunch on a scattering of acorns, realize that this small fruit really does matter to us.

After being an active member of the Durham County Extension Master Gardeners for 13 years, Kit Flynn now holds emeritus status. For five years she was the gardening correspondent for “Senior Correspondent” and shared “The Absentee Gardener” column with fellow Master Gardener Lise Jenkins. She has given numerous presentations on various gardening topics to Triangle organizations and can be reached at howdoesyourgardengrow@icloud.com.