Perhaps there are lots of potential acorns every year but a wet or harsh year knocks them off the trees as buds. Just guessing.
I did read that in the biosphere the trees all grew very tall and skinny and then fell over. Without the stress caused by wind the trunks never bothered to get thick and strong and they couldn't hold their own weight. So the biospherians had to go shaking trees to simulate wind and stimulate growth. All of which has nothing to do with acorns but it amused me.