Wed August 14, 2013
Earth Notes: The Ponderosa Crop
The life of ponderosa pine seed is a high-stakes lottery. Only a few get to spread their branches in the sun.
An individual ponderosa pine tree is both male and female. In the spring, tiny male cones release yellow pollen to the winds that carry it to female cones. Female cones are the ones most of us would recognize as a pinecone. They produce the seeds.
It takes about 27 months for the seeds to mature. They are nutritious to animals, so the tree tries to protect them with sharp spines on the cones. But a tassel-eared squirrel can chew right through them, and specialist birds like the red crossbill can twist seeds out of cones.
To ensure that some seeds survive, ponderosa pines evolved a strategy called masting. That means trees produce massive amounts of seeds in some years, and hardly any in other years. During mast years, the quantity of seeds overwhelms the seed-eaters.
It turns out that warm spring temperatures stimulate the trees to mast. Two years later, the cones hang thick from the branches, and the seeds are fat and primed for germination.
But sprouting isn't the end of the story. Here, too, the odds are steep. Pine seedlings need just the right combination of rain and snow to get established during their first year.
Observers have reported a bumper crop of tiny seedlings in some parts of northern Arizona this year. Only time will tell if winter and spring moisture will allow them to survive.