Oak Mast

We currently seem to be experiencing a bumper crop of acorns – enough so that it’s noticeable even though oaks aren’t all that common here. The technical term for this is mast. We are having a mast year.

Oaks don’t produce large amounts of acorns every year (same goes for other nut trees). Instead, the trees in area will synchronize themselves so that, at irregular intervals, they all go acorn-crazy at the same time. The most popular theory as to why is that when all of the trees go all out at the same time, there are just so many nuts around that the squirrels and other nut-eating critters can’t eat them all even if they gorge themselves, so at least a few will get to germinate and grow. If one oak tree were to be a rebel and produce a lot of acorns in a year when the other trees were holding back, all the squirrels in the forest would descend on that one tree and it wouldn’t get to reproduce. (Squirrels aren’t the only animals that eat acorns, of course – earlier this summer one of the people I work with spotted a black bear way up in the highest branches of an oak tree, feasting on them.)

Of course, the real question here is how the heck are a bunch of trees spread across a forest communicating with each other and reaching a consensus on when to produce mast? And how are they balancing this cooperation with competition, natural selection favoring the trees that manage to reproduce more than their neighbors?

The simple answer seems to be that no one is really sure, but that doesn’t mean there aren’t a couple ideas. Plants can communicate with each other through chemical signals, messages like “look out everybody, there are lots of herbivores around.” A new study that’s gotten some media coverage even suggests that some communicate by producing clicking sounds in their roots that other plants can sense – plants don’t have ears, but maybe they can sense vibrations? So maybe our oaks are doing something like this, but they’re not in dense stands here like the maples and hemlocks are, they’re scattered in among the other more common trees. It’s questionable whether chemicals and clicks would really be effective at transmitting information across an entire forest.

There are other ideas too, like maybe trees are responding to some environmental cue and we just don’t know what it is, or maybe they need a certain number of years to store up energy before they flower and, since they need each other’s pollen to produce acorns, eventually they all either get on the same cycle or fail to pass on their genes.

In any case, tree mast is a really cool phenomenon, and if you know more about it than this feel free to jump in via the comments. Is it a mast year where you are?