The Biogeography of the Ponderosa Pine (Pinus ponderosa)
 

by Iris Meisenbach, student in Geography 316  Fall 2003

Thank you for visiting our site. This web page was written by a student in Geography 316: Biogeography and edited by the instructor, Barbara Holzman, PhD.  All photos and maps are posted with specific copyright permission for the express use of education on these web pages. The students have tried to be as accurate as possible with the information provided and sources and references are cited at the end of each page.

Species Name:

Kingdom:                 Plantae Subkingdom:            Tracheobionta Superdivision:           Spermatophyta Division:                   Coniferophyta Class:                       Pinopsida Order:                      Pinales Family:                     Pinaceae Genus:                     Pinus Species                    Pinus ponderosa. subspecies           P. ponderosa  ponderosa                          P. ponderosa  benthiama                          P. ponderosa  brachyptera                         P. ponderosa  scopulorum

Figure 1 P. ponderosa trunk. (Frankis 1998)

Description of Species:   

          Ponderosa pine (Pinus ponderosa) is a North American pine discovered in 1826 by David Douglas near Spokane, Washington.  A few common names for the species include yellow pine, western pine, and Sierra redbark among many others.  Pinus ponderosa belongs to the Plantae kingdom, Pinophyta division, Pinopsida class, Pinales order, and Pinaceae family.  The subspecies P. ponderosa benthiama is distributed in California, mainly in the Sierra Nevada and west of the Cascade crest (Frankis 1998). 

The Latin name ponderosa (trans. ponderous, heavy) is a descriptive reference to the wood, denoting its significant weight (USDA Forest Service 2005). The subspecies P. ponderosa benthamiana, found in the Sierra Nevada and west of the Cascade crest in California, is the largest of all subspecies.  Trees can grow to 72 m in height and 2.5 m in diameter (Frankis 1998). The bark is scaled and yellow-brown with irregularities and grooves. Twigs are red-brown, with resinous buds and about 3 needles per fascicle and red pollen cones (Frankis 1998).  Pinus ponderosa is a yellow pine, rather than white, although each pine is similar in properties.  The heartwood is yellow or light brown with straight grains and uniform texture with little tendency to warp or twist (USDA 2005).   Trees are straight with a pyramidal crown.  Twigs and bark are an orange gray color and rough, twigs are not glaucous.  Needles occur in bundles of three and are 12 to 28 cm in length with pointed and toothed edges, spread ascending, and live 4-6 years (Frankis 1998). Pollen cones are cylindrical and mostly red with seeds maturing in 2 years (Frankis 1998).        

Figure 3 P. ponderosa seed and cone. (Frankis 1998)

Figure 4 Pinus ponderosa cone. Drawing by the author.

Natural History:

          There are five additional unique subspecies; P. ponderosa ponderosa, P. ponderosa scopulorum, P. ponderosa brachyptera, P. ponderosa arizonica and P. ponderosa stormiae, which are distributed in other regions outside of California, evolving in response to a variety of distinct geographic climates (Wikipedia 2004).  In general, the species flourishes mainly in mountain ranges or conifer forests. The “Pacific” group of subspecies P. ponderosa subsp. benthiama, endemic to the Sierra Nevada and west of the Cascade crest of California, is the largest of all the pines (Frankis 1998).

         Pinus ponderosa can thrive in a variety of soil types such as limestone, basalt, and sandy clay-loan (Oliver and Russell 2005).  Due to complex root systems and competition for water with other trees, trees that grow in dryer climates or where less soil is available tend to be spaced further apart as root structure spreads far and deep into the topsoil.  Conversely, trees that grow along the west coast of California or the U-shaped valleys of the Sierra Nevada where either precipitation from the westerlies provide adequate rainfall or snow capped mountains provide year long water run-off, trees are known to grow in dense groves and are generally greater in overall size and dimensions than their inland dry climate cousins (Oliver and Russell 2005).  John Muir, for example found the largest Pinus ponderosa (common name: Western Yellow Pine) in the Sierra Nevada that measured 220 feet high and had a diameter of 8 feet (Peattie 1953) much larger than the largest size pine of 125 feet high in the Rocky Mountain regions (Oliver and Russell 2005).   

        Pinus ponderosa is monoecious and regenerates by seed which requires sunlight to germinate and grow.  Seed maturation occurs in two-year cycles.  Seeds are small and trees bear cones as early as seven years old and continue for 350 years, with cones bearing up to 70 seeds each. Seeds are damaged or eaten by insects, birds, and small mammals such as mice, chipmunks, and tree squirrels but can withstand high temperatures although frost can easily damage them.  Pine seedlings are threatened by moisture stress as well as competition from shrubs that hinder growth (Kocher 1990; Thomas 1979).  

Evolution:
          Pinus ponderosa has distinct geographic differences over a widespread range. Among varieties of P. ponderosa scopulorum for example, studies show genetic variation in growth, stem and germination ability under moisture stress (Oliver and Russell 2005).  Studies suggest that var. P. ponderosa ponderosa consists of three major geographic subspecies and var. P ponderosa scopulorum of two major geographic subspecies.  Variety P. ponderosa ponderosa which is also known as the Pacific "race" in California has large needles, cones, seeds and are the most rapid growing (Oliver and Russell 2005).  The North Plateau "race", east of the Sierra Nevada, has needles with thick layers of hypoderm and sunken stomata and is almost indistinguishable from the Rocky Mountain race which has compact foliage while the least understood Southern California race has open foliage (Oliver and Russell 2005).  Seeds from California races suffer injury from cold, whereas seeds from Arizona and Oregon are only slightly damaged (Oliver and Russell 2005).

            The oldest remains of Pinus ponderosa in the Western United States are 600,000-year-old fossils found in west central Nevada (Bettancourt 1990).  The exact origins of Pinus ponderosa are unknown.  However, the genetic diversity of the species suggest evidence that Pinus ponderosa survived the northern glaciation of the Pleistocene epoch, including areas of the Sierra Nevada (Alt 2000, Frankis 1998).  Pinus ponderosa evolution was greatly influenced by the glacial period known as the Wisconsin Ice Age (50,000-14,000 B.P.).  While this majestic tree grows on lower mountain slopes today, during glacial periods cold temperatures pushed Pinus ponderosa out of the Rockies and to the south to Arizona, Mexico and beyond (Brittingham 2005). Although the species was absent from most of North America during this Ice Age epoch,  Pinus ponderosa distribution later emerged and continued to appear along central Arizona, as well as California (Frankis 1998).

During this time, the Sierra Nevada mountains were filled with glaciers which forced forests to shift down as much as 2000 feet to avoid the cold altitudes.  As a result, Pinus ponderosa survived in diverse forests along with other species of trees such as juniper, cedar, fir, oak and hickory (Brittingham 2005).  Shortly after the Wisconsin glacier retreat, the various diverse forests began to shift and sort into unique forests as trees migrated northward about 18,000 years ago (Brittingham 2005).  Interglacial periods ranging from 10,000 to 16,000 years separate the Nebraskan, Kansan, Illinoisan, and Wisconsin ice ages during which time range expansion of Pinus ponderosa was most favorable (Brittingham 2005).

          Fossil evidence from fossilized rat middens in New Mexico suggests Pinus ponderosa was absent during the Wisconsin glacier period (Betancourt 1987).  With the beginning of warming in the early Holocene, Pinus ponderosa began colonization of the Colorado Plateau. However, fire is a critical factor in the ecology of  Pinus ponderosa, thus climate changes, seasonal rains and lightning brought on by the Holocene age has a larger impact on  Pinus ponderosa than other western conifers (Biota 2005). The present distribution of Pinus ponderosa forests in the interior West and Southwest was apparently the result of the Holocene climate change, although the exact cause and manner of this expansion is unknown (Anderson 1989; Betancourt 1987).

Figure 5.  P ponderosa bark, cone, tree, stature, needles and male strobi.  (Aust et. al. 2005) 

Distribution::

Pinus ponderosa lives throughout much of the western states as well as parts of Canada and Mexico in arid regions as high as 10,000 feet in elevation. Virtually all western states with mountain ranges contain Pinus ponderosa at low altitudes (Peattie 1953).  Pinus ponderosa is geographically distributed in British Columbia, Washington, Oregon and also circling the west mountain ranges of Colorado and Western North Dakota as well as varieties in the mountains of Mexico where climate is arid and temperate (see figure 6).  In the Western United States the trees live as far north as latitude 52˚n to as far south as 32˚ n near San Diego (Oliver and Russell 2005). Pinus ponderosa grows in an average annual temperature range between 5° and 10° C, with an extreme annual range between -40°  to 43° C (Oliver and Russell 2005)

Figure 6 P. ponderosa distribution (USGS)

Pinus ponderosa can grow over burnt forest floors, along cliff sides, valleys carved by glaciers such as the Sierra Nevada, high plateaus or mesas and can be located well inland where summers are very dry such as northern Arizona and along the rim of the Grand Canyon (Oliver and Russell 2005). Additionally, trees can grow on flat or rolling landscapes as well as on mountainsides where soil is less available (Peattie 1953). In California  Pinus ponderosa is distributed throughout the Coast Range, Klamath, Cascades, and the Sierra Nevada, as far south as San Diego. Its elevation ranges from 500 to 3,500 feet in Northern California and 5,300 to 7,300 feet in Southern California (Kocher 1990).

Figure 7 P. Ponderosa Bark texture and color (Frankis 1998)        

Other interesting issues:

The species Pinus ponderosa is currently the most abundant pine today and adapts well to small forest fires, as do many taxa under the genus Pinus.  In the past, frequent low intensity forest burns allowed seedlings to survive while doing minimal damage to the fire resistant bark of adult trees. New growth seems to be suppressed because of lack of of fire in many areas.  Current fire prevention techniques minimize small fires and encourage forest floor growth creating fuel for large forest fires that destroy adult trees and seedlings (Frankis 1998).