The distinct butterscotch and vanilla scent of a ponderosa pine forest is memorable to anyone who has travelled east of the Oregon Cascades in the summer. The ponderosa pine trees of these forests are notable for their tall, straight, red-barked trunks supporting high branches of evergreen needles. Ponderosa pines dominate these forests because of their fire resistance.
The ponderosa pine (Pinus ponderosa) also grows in the Willamette valley. The Willamette valley ponderosa pine subspecies is adapted to our wet winters and dry summers. They don’t grow as tall or boast bark as vibrantly colored as the ponderosa pines east of the cascades, but, importantly, the Willamette valley ponderosa pine is also fire resistant and drought tolerant.
Ponderosa Pine Fire Resistance
The resistance of the ponderosa pine to low intensity fires is due to several factors. Its shade intolerance causes the lower branches to self-prune as they become shaded. This prevents ground fires from spreading easily into the high canopy of mature trees. The puzzle-shaped bark curls and falls off when exposed to fire temperatures, shedding fire from the bark. The relatively sparse foliage of the canopy minimizes the danger of embers catching the canopy on fire. The thick bark of a mature ponderosa pine tree acts as a heat shield, protecting the living cambium inside from the heat of low intensity fires.
Ponderosa Pine Drought Tolerance
The ponderosa pine also has adaptations that make it drought tolerant. Its deep tap root allows it to reach deep moisture when the surface soil has dried out. The stomata, or leaf pores, on the needles can close to prevent moisture loss during drought conditions.
Ponderosa Pine Growth habit
Willamette valley ponderosa pine can grow to over 100 feet tall. The oldest ponderosa pine of any subspecies known is over 900 years old, but 500 years is more common. When young, the ponderosa pine has a uniform, conical canopy. As it matures, it develops an irregular cylindrical silhouette with a straight trunk and high canopy. A mature tree has an airy, open canopy with needles bunched at the tips of the branches. The ponderosa pine is stable and resistant to strong winds. They are also not very susceptible to the tops breaking out.
Ponderosa Pine Features
The needles of the ponderosa pine are sharp, 4-10 inches long, and grow in bundles of 3. The evergreen needles persist on the tree for a few years before the old, innermost needles drop in the fall.
The bark of the ponderosa pine is dark brown when young (seen at left), changing to the characteristic orange-red when mature (seen at right). The distinctive, puzzle-shaped flaking bark of the ponderosa pine has deep grooves in thick bark on mature trees.
The cones of the ponderosa pine mature on a two year cycle, are pineapple-shaped, 3-6 inches long, and have sharp, prickly tips on each scale.
Importance of Ponderosa Pine to Willamette Valley Ecosystem
Ponderosa pine’s tolerance of poor and rocky soils allows it to fill an ecological niche not tolerated by other trees in the Willamette valley. The vigorous root systems of ponderosa pines provide erosion control on slopes, preventing soil from being washed into rivers. In the Willamette valley, the ponderosa pine’s nutritious, oily seeds are an important food source for many birds, including chickadees, evening grosbeaks, finches, and nuthatches.
Ponderosa Pine Planting and Care
The Willamette Valley ponderosa pine’s drought tolerance and fire resistance make it a climate resilient choice for planting in the Portland area. The ponderosa pine should be planted in full sun 15 feet from any other plants or structures. As they grow very tall, they should not be planted under power lines. They are tolerant of many soil types, but grow best on well-draining soil. Although drought tolerant once established, young trees should be watered regularly during dry spells during the first few years. As the ponderosa pines self-prune lower branches, our arborists recommend pruning these away if they present a hazard to structures, plants, or people below.
Notable Local Ponderosa Pine Specimens
Not everyone has room in their yard to grow a large ponderosa pine tree, but there are many to admire in neighborhoods all over the Portland area. Portland has seven ponderosa pine trees on its Heritage Tree list. The stunning Portland Heritage Tree #349 seen above towers over 120 feet near Gabriel Park in southwest Portland. The city of Lake Oswego recognizes the stately ponderosa pine heritage tree that grows along the walking path at Luscher Farm on Rosemont Road.
With their drought tolerance, fire resistance, wind resistance, and ecosystem benefits, the ponderosa pine would make a wonderful addition to a sunny, large Portland area yard.
