Tom's Blog

This is the time of year when acorns are dropping and you can hear them crunch under your feet as you walk through the woods. However, only a few oak trees are dropping acorns. This year at Pleasant Valley Conservancy only one oak species seems to be producing acorns: northern red oak.

Acorns from an oak in Unit 11B at the edge of the gravel road. Listen for the crunch as you walk by!

Mast is a term used to describe the hard fruit of various trees such as beech or oak. Oaks as a group produce lots of acorns only every three or four years, and a high production year is called a good mast year. I discussed the masting phenomenon in 2011 when bur and white oak were heavy acorn producers. 

This year, so far, the only trees I have found dropping acorns are red oaks (Quercus rubra). Other oak species in the red-oak group such as Hill's and black oaks do not (so far) seem to be dropping acorns. The last good mast year for the whole red-oak group was in 2010.

It is not unusual for masting to occur only in a single species, such as we seem to be having this year, although the mechanism by which the trees bring this process about is a mystery. There are lots of papers discussing this mystery, but no concrete data. Look for the work of Walter D. Koenig, although his research has focussed on California oaks.

I was surprised to find that other oaks of the red-oak group were not producing acorns. At the east end of Toby's Prairie there is a large grove of Hill's oak (also in the red-oak group), none of which were dropping acorns. And right at the edge of that grove was a single red oak dropping acorns. (The ground was covered, just under this tree.)

How do they synchronize acorn production? Not by chemical signalling, apparently.