Arcy, most oak species do indeed alternate heavy mast years with scant ones. That's a bit of oversimplification, but generally holds true.

+oM

True we have noticed this cycle but never have we had a year with none and never before have the acorns sprouted. I suppose a few always do but they are in such small numbers they are not noticed. This year I have dense runs of them where they fell and sprouted. This winter is going to be bad. The squirrels and pocket gophers will have little to eat, when they die off what ever eats them will also suffer.... I am assuming the previous mild winter caused the massive sprouting.

Bur oaks are white oaks so the roots sprouted the same fall that they fell off the trees. Perhaps your fall had primo sprouting conditions.

we had 80F in march -- so some acorns came early

For the last several years, including last year, our northern red oak nearly covered the ground with acorns in the fall. Squirrels loved it! Last summer had 53 days over 100 degrees and provided lots of stress. This year there were NO acorns at all - this season wasn't as bad as last with only 30-some days over 100 degrees.

Red oak acorns take two years to develop (unlike bur oak). The first year after flowering they put on a small "pre-acorn" (not sure of the correct term) on a short stem. The following year it develops into the large acorn red oaks are known for. This year upon thorough inspection there are no pre-acorns so likely there will be nothing again next year.

I was guessing that heat stress was preventing them from forming. The tree has gone from dependable, prolific production to nil. Perhaps your trees are just responding to some type of stress, too.

Oh, and strangely enough the bur oak produced an acorn crop this year! Truly odd happenings.

hortster