Some years have lots of acorns and some don't

Several articles in the press and out on the web today have sensationalist titles like "Where are the acorns?", "Acorns disappear across the country" and "Acorn Watchers Wonder What Happened to Crop". Even Topix has a a forum topic devoted to it. Then the various articles ring the climate alarm quite vigorously. Others use the false analogy of disappearing acorns to disappearing bees. Once again eye catching headlines win out over even reasonably thoughtful study.

The acorns and other edible parts of woody plants like tress are call mast. These acorns are a food source for many animals in a forest from squirrels, to mice to deer. Pig farmers sometimes let their pigs loose in forests to fatten up on acorns. The important thing to realize is that these trees don't produce acorns every year in the same quantity like a fruit tree or like a farmer farms wheat. There are good years and bad years. Good years (here is an example in California last year) are called mast years, in fact. The cycle is reported to be 3 to 4 years and tied to a wet or a dry spring (this abstract reports other factors as well). The article sometimes points this out but then go on to say no one knows to heighten the mystery. The lack of acorns discussed in the Washington Post is centered around northern Virginia. Not all areas report the same thing.

I wonder if this boom and bust cycle has ever happened anywhere before. A precursory search using google (which I imagine any reporter could do) reveals several free articles on the topic, one with a very good chart. Other articles would cost money, but I am sure that a newspaper might even be able to purchase an article if they needed it.

One the article has an interesting chart (click the chart for larger) with some data that I have adapted by stretching and lining up the years, that shows boom (1994) and bust (1995, 1998) cycles for oak trees in California, Missouri, and Massachusetts and over several years. Some years have no acorns at all, some have plenty. Even different species seem to produce or not to produce in synchrony. I guess an article reporting that some years there just aren't any acorns doesn't get the hits of one with a dire end of the acorn death knell.

From the figure caption from the article: Fig. 1 Example time series of mast production. (a) Hastings Reservation (California) site, Q. agrifolia, (b) Hastings Reservation, Q. douglasii, (c) Missouri, Q. coccinea, (d) Missouri, Q. alba, (e) Massachusetts, Q. rubra. In (a–b) each line represents values for individual trees; in (c–e), lines represent yearly means for each plot. Heavy lines represent yearly grand means.

Another article has an appendix with line after line of articles with historical levels of acorns and other mast over many years, some as long as 31 years. I would love to have the data from that article because I think it would put this issue to rest even better than the small amount shown above. Here is a chart (click for larger) of acorn production for different oak species in Florida (source abstract, source .pdf). Some years show almost no production, and even some synchrony between species.

It is interesting that people at least notice their environment somewhat, but noticing only the negative events and lacking the scientific curiosity to determine if the phenomena is fleeting or cyclic or permanent almost defeats the benefit of being observant in the first place.

The acorns will return.