Biodiversions: Ponderosa Pine

By Elizabeth Enslin | Posted on May 12, 2009

Crossposted from Yips and Howls

Ponderosa pine needles and cone

Growing up in Seattle on the west side of the Cascade Mountains, I always thought of ponderosa pines (Pinus ponderosa, also sometimes called western yellow pine) as exotic trees.  They belonged to what we called “the other side of the mountains.”  Whenever we drove over Stevens Pass or Snoqualmie Pass, the first glimpse of ponderosa pines thrilled me.  I knew we had left behind the rain and dense undergrowth of douglas fir forests (which I also loved) to more open stands where I could wander miles without a trail.

A hardy Ponderosa pine on canyon walls of West Bear Creek winding towards the Grande Ronde.  Photo: Jerry Gaffke

Now, my partner and I are gradually moving our lives to “the other side” in Oregon, to a piece of land dominated on its higher slopes by ponderosa pines.  We’ll watch the sun rise over them, smell the sweet vanilla scent of their bark, nurture saplings moving into old pastures, and thin out some of the denser stands and use the beams for the house we hope to build.  These trees I once thought exotic will now frame my daily life.

In my travels in the West - California, Arizona, Montana, Mexico - I’ve been surprised at how often I find myself among ponderosa pines.  It’s one of the most wide-ranging trees in the western North America.  There are at least two subspecies Pinus ponderosa var. ponderosa and Pinus ponderosa var. scopulorum. The wide genetic diversity of the species helps it adapt to very different regions, but it also challenges scientists trying to reach agreement on neat classifications.

Besides diversity, one of the keys to ponderosa pine’s success is a deep taproot, which allows it to take advantage of diverse soils and rainfall patterns in relatively arid environments.  The seeds germinate when the soil is warm and wet (in eastern Oregon that could be May or June; on the Colorado plateau it could be July).  Then they sink their taproots 10- 20 inches, even through dense grasses.  In subsequent years, that taproot reaches further, and lateral roots take hold closer to the surface.  The trees eventually top out anywhere from 60 to 100 feet high, depending on a combination of geography and genetics.

The other key to success has been the ability of the thick, red bark of adult trees to withstand the kind of light forest fires that summer lightning strikes bring to the West.  The fires thin out young trees and brush but leave the older trees to a larger share of water and nutrients.  These mature trees put out vigorous seeds for the next generation and tower over an open understory.  On our property, the forest floor nurtures an exuberant display of wildflowers in the spring (check my blog over the next few weeks for pictures).

Young Ponderosa pine colonizing an old pasture. Photo: Jerry Gaffke.

With fire suppression in the West, ponderosa pines have become too dense in places and susceptible to ravages by diseases and insects.  And now when fires burn, they burn hotter and create more destruction.  Restoration of these forests requires either controlled burning or selective thinning.  On our land, we’ll have to make some decisions soon about how to thin the dense forest on the north slope, where to let young stands grow and where to take them out to grow grains or try to restore grassland habitats.

Although ponderosa pine still defines for me the landscapes of the Inland Northwest, the largest contiguous stand of ponderosa Pine is in Northern Arizona.  A recent agreement between representatives of the Grand Canyon Trust, Arizona Forest Restoration Products, and Center for Biological Diversity will allow thinning and controlled burns to restore the health of the forest while also providing employment in the region.  It’s an intriguing model that could be used throughout the range of this beautiful and hardy tree.