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.