Friday, October 29, 2010

This year's acorn crop cont.

More on this year's magnificent crop of acorns.  I did hear back from the forester on the question of why so many acorns this year.  He says that oaks are generally sporadic fruit producers, with really good crops every 4 to 7 years.  There are several reasons for this, one being the weather and the other an ecological adaptation.

A late spring frost is hard on oak flowers, and will lead to a low yield, he says.  And, insects play a role.  There are on the order of 30 different species of acorn weevils "that can destroy up to 90% of any given year's production either while it is on the tree developing or after they fall in the autumn."  The cyclic nature of fruit production helps keep the insect population down.

And, he says that there are advantages to sporadic fruit production.  It keeps predator populations down, which increases the chances that some acorns from a given tree will survive and grow.  If not, my informant says, the tree would always be having to produce more and more fruit to stay ahead of the rodents.  Similarly, the fluctuation keeps weevil populations down, and thus acorn destruction down.  Good for the tree, not so good for the predators. 

Both explanations sound plausible.  However, regular MT readers won't be surprised if we are a bit reluctant to accept the adaptive explanation right off the shelf. First, an oak tree is lucky if even a few of the acorns it produces in any given year makes its perilous way to treehood.  Even in a bad year, oaks way overproduce acorns relative to what will take root, or replacement needs and so on.

However, sporadic fruit production in response to the vagaries of climate or other means of destruction of flowers or developing acorns is completely in keeping with the adaptability or facultativeness that is a core evolutionary principle.  Oak trees need to be able to adapt to change, and good and bad fruit production years is one way they do so.  It's easier to suggest but a lot more difficult to conceive how a tree 'knows' (genetically evolves) to adjust for variable predator loads in the hypothesized way, when climate itself is unpredictable.


Anne Buchanan said...

We've just gotten an email from an MT reader who has been trying to post a comment, but to no avail (several people have told us they can't post comments, to our frustration, and we are planning to try to move the blog to a different host at the end of the semester). He sent several citations about masting in oak trees, which I am happy to have, and closed with the following:

"And remember leaves are called leaves for a reason: leave them, otherwise they would be called takes, as a wag here once wrote in a funny and wonderful poem. I think about it, never convincing anyone, as I help rake."

Arturo Saez said...

I think that in this autumm in Barcelona there is a greater ammount of acorns. Till a couple of week ago, many many squirels were seen in my backyard. Very nice. Now it is time to clean it, not so nice!!


PD: I like a lot the blog. sorry about my bad english!!

Ken Weiss said...

That is very interesting, because why would the same thing be happening in Spain and our part of the US?

Anne Buchanan said...

Gràcies, Arturo! Interesting that you've had a large number of acorns in Barcelona this year, too. I feel your pain now that it's time to clean up the acorns!