Pine Dining
By Megan Wilde
Long before pines became Christmas trees, people around the world venerated and used these fragrant evergreens, from ancient Aztecs to ancient Greeks. Today, pines are some of the world’s most commercially important trees. Their wood is valued as timber and paper pulp, their nuts eaten as food, and their resin used in turpentine and other products. But pines are perhaps even more important as a food source for wildlife. Who dines on pines in the Chihuahuan Desert region?
Creatures great and small feast on fat- and protein-rich pine nuts, from rock squirrels and piñon mice, to black bears and desert bighorn sheep. Emerald pine needles sustain a variety of moths and butterflies, which depend on pines to host their larvae.
Pine phloem is a favored fare of many rodents, particularly porcupines. This soft tissue beneath bark circulates nutrients through a tree. Porcupines sometimes gnaw away bark from a pine’s entire circumference to get at this nutritious tissue. When they do, porcupines weaken or kill the tree.
More pernicious are mountain pine beetles. They nibble through a pine’s bark to create a nursery inside the phloem, where they mate and lay eggs. The beetle’s larvae in turn devour phloem, cutting off the tree’s nutrient flow. The beetles can also infect pines with blue-stain fungus, which plugs the tree’s sapwood. Healthy pines can ward off such attacks, but drought-stressed trees are more vulnerable to a beetle onslaught. Recently these beetles have been blamed for killing millions of acres of pine forest around the West.
Not all pine diners harm the trees that feed them. In fact, some birds help pines.
Piñons are a particularly drought-hardy pine common in the desert southwest, and their nuts are a favorite food of certain jays and nutcrackers. These birds stash piñon seeds in the soil, so they can eat them in the future. But many seeds are forgotten and later grow into trees.
But the most exceptional piñon stewards are piñon jays. From late summer through fall, these jays busily harvest piñon seeds, which they whisk away to their nesting area and cache underground by the thousands. Because piñon cones ripen over several months, the jays enjoy long access to this rich source of fat and protein.
As jays sort through cones, they don’t reap every seed. Tan-colored seeds usually house a dried-up, aborted tree embryo, while dark brown seeds are filled with nutritious endosperm and a vigorous embryo. Piñon jays know this and don’t fool with tan seeds. Only the darker seeds pass their initial visual evaluation. The jays then weigh and clap each dark seed in their bill, to see if it sounds sufficiently full to be worth storing. For the tree, this means only its healthiest seeds are likely to be planted by jays.
When courtship season begins, male jays excavate seeds from their nesting grounds and feed them to mates. Unearthed piñon nuts continue to sustain female jays as they incubate their eggs, as well as their nestlings once they’ve hatched.
This relationship between bird and tree is so intimate, the jays’ reproductive cycle is linked to that of the piñons. Testes development in males is actually triggered by the appearance of green piñon cones in summer. And when piñon crops fail, jays skip a breeding season.
Piñons, unlike many pines, have heavy, wingless seeds. Without the jays’ help, these clunky seeds would likely drop to the ground beneath their parents and rarely grow into trees. Piñon jays not only carry the seeds far away, but plant them in favorable conditions, perpetuating the forest that feeds them.
Have a question or comment about this episode? Contact Nature Notes Coordinator Megan Wilde at mwilde [at] cdri [dot] org. Or discuss this episode on Nature Notes’ Facebook page. This episode originally aired on December 23, 2010.
References & Resources for Educators
- The Piñon Pine: A Natural and Cultural History by Ronald Lanner (University of Nevada Press, 1981)
- “A Pine Beyond Time” by Dale Weisman, in Texas Parks and Wildlife Magazine (May 2007)
- The Story of Pines by Nicholas T. Mirov and Jean Hasbrouck (Indiana University Press, 1976)
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Nature Notes is sponsored by the Meadows Foundation and the Dixon Water Foundation and is produced in cooperation with Marfa Public Radio.
