KATIE BURNS

Staff Writer

Q: Why do pine cones open when warm and dry and close when coldand wet?

A: “There are actually male and female pine cones,” said BetsyRead, a biology professor at Cal State San Marcos. “The female pinecone is the one we are most familiar with that opens and closes.The opening and closing of the cone is part of the life cycle ofthe pine.”


The male pine cone, which is small and bumpy, produces pollen.Wind-blown pollen falls on a female pine cone on either the sametree or another tree. Over the course of a few years, seeds developunder the scales of the female cone. The female pine cone openswhen the seeds are mature and the conditions are right.

“The reason why the pine cones open when it’s warm and dry isbecause that’s a more favorable condition for the seed dispersaland germination,” Read said.

Wet and cold weather would prevent the seeds, which are oftenwinged, from spreading far enough from the tree to find a place togrow. Seedlings also wouldn’t last long in winter rain or snow.

After a pine cone falls from the tree, it can still open andclose. The scales open when dry because their outer halves shrinkmore than their inner halves, and they pull away from the cone.When wet, the scales swell shut.


People who make crafts from pine cones often heat the cones inan oven to make the scales open. Trying to wash off the cones willmake the scales close again.

The cones of some species of pines only open in extremecircumstances such as forest fires. Other cones open after rottingor being pulled apart by an animal looking for a meal. In eachcase, though, the cone usually opens when the seeds are ready andthe conditions are right for the species of pine to flourish.

The cones of the Torrey pine, which grows only along the coastof San Diego County and Santa Rosa Island, open slowly over time torelease seeds -- with cones staying on a tree for as long as 14years -- but will open completely after a fire.

“You get a much higher rate of establishment of seedlings aftera fire,” said Mike Wells, a senior resource ecologist with theTorrey Pines State Reserve.


Fire changes chemicals in the soil in a way conducive to thegermination of the Torrey pine’s seeds. The fire also clears awayother plants that would compete with seedlings for water andlight.

Please direct your science and technology questions, along withyour name and hometown, to Katie Burns at (760) 740-5442,kburns@nctimes.com or 207 E. Pennsylvania Ave., Escondido, CA92025.

2/11/01