Hardwood trees are dropping more nuts than usual this fall

SCOTT SIMON, HOST:

Ah, autumn.

(SOUNDBITE OF LEAVES CRUNCHING)

SIMON: Good times for a walk in the woods to watch the trees turn colors. But you might also notice something beneath your feet.

(SOUNDBITE OF ACORNS CRUNCHING)

SIMON: Hundreds of acorns cracking and crunching under every step. And if you thought there seemed to be more nuts than in past years - and this is not any kind of sly political comment - you'd be right.

MURPHY WESTWOOD: There are nuts everywhere.

SIMON: I'll say. That's Murphy Westwood, vice president of science and conservation at the Morton Arboretum outside Chicago, where she says a mast year is underway. That means trees are dropping more nuts than usual.

WESTWOOD: Both our white oaks and our red oaks. We have walnuts. We have hickories. Lots of different types of nut trees are all having a mast year. So the squirrels are loving it. You can see them running around with big cheeks.

SIMON: Aw. Mast years are hard to quantify. Naturalists say they know one when they see one. One authority is the USA National Phenology Network. They keep track of tens of thousands of observations on phenology, natural patterns like when flowers bloom or deer have offspring, BJ Leiderman writing our theme music. And many of those observations indicate a mast year, at least for oak trees, and especially in the Northeast and California. Murphy Westwood says these events tend to happen every two to five years and are caused by a number of factors, like pollen.

WESTWOOD: In the springtime, having a lot of pollen availability and pollen that can move around in the wind is one of the ways that we have a really good mast year. And if it's really cold, if there's a late frost, if it's really rainy, that sort of minimizes the ability of pollen to move around. So not having a very cold or a wet spring can have a big impact on a mast year. Similarly, very dry, hot summers can cause trees to abort their acorns or their nuts because they can't get enough nutrients; they can't get enough water.

SIMON: She says this year, there was enough water to go around to make up for the early dry months of summer. Alonso Abugattas says people have sent photos to his Facebook page, Capital Naturalist.

ALONSO ABUGATTAS: A couple people have posted just wheelbarrowfuls (ph) of walnuts and hickory nuts and things like that. Other people just have taken a couple of shots of the ground and are like, wow, you can't walk through here. You got to be careful you don't slip and fall because you're walking on nuts here, left and right.

SIMON: Yeah. I know the feeling. It takes a lot of energy for trees to produce so many nuts. Why do they go to all the extra effort?

ABUGATTAS: So on a normal year, you produce a regular amount of fruit and you know that a lot of it is going to get eaten. But if you produce so much fruit, then some of them are going to germinate. Deer can still eat, you know, the sprouting saplings, whatever, but you're out of danger for a lot of things.

SIMON: Murphy Westwood says there is a purpose to this reproductive timeline. If trees overproduced every year, the population of squirrels and deer would explode. There called seed predators, after all, and no nuts would germinate and turn into new trees.

WESTWOOD: It benefits the trees that it is unpredictable.

SIMON: For humans, it's another story.

WESTWOOD: I was giving a presentation in our oak collection, and we were standing underneath an outdoor classroom that we have that has a metal roof, and it was deafening hearing the, like, thunk, thunk, thunk of acorns falling on the roof. They were falling in our coffee cups.

SIMON: Well, something's got to follow pumpkin spice.

(SOUNDBITE OF MUSIC) Transcript provided by NPR, Copyright NPR.