Ponderosa Pine: a Fire Evolved Species
Incident: San Miguel Wildfire
Released: 7/15/2009
The life history characteristics of ponderosa pine (Pinus ponderosa) show that this species, which is thought to have been present in the southwest for approximately 8000 to 12,000 years, is a fire evolved species. "Fire evolved" means that present-day ponderosa pine trees have characteristics that have been influenced and shaped by fire, and these characteristics have allowed them to persist through time in the presence of frequent, low intensity, surface fires. Low to moderate intensity fires create favorable conditions, such as exposed mineral soil and a surplus of nutrients, for the establishment of ponderosa pine. Ponderosa pines have a thick, insulating bark that is relatively inflammable.
Ponderosa pines have thick, protective bud scales. They also have tight needle bunches that enclose and protect meristems (plant tissue from which new cells are formed), but then later open into a loose arrangement that does not easily propagate flames.
Ponderosa pines go through a process of self pruning, or natural limbing, of the lower branches. Without these lower branches to carry fire up into the crowns, fire tends to stay on the forest floor. If fire were to get into the crowns, which did occasionally happen historically, the open structure of the canopy doesn't promote flames, or extensive crown fires.
Ponderosa pines have a deep rooting habit, which protects the roots from the extreme heat on the forest floor during a fire. Once established, ponderosa pine forests perpetuate and promote frequent surface fires because the forest litter layer consists of long needles that loose moisture quickly and contain highly flammable compounds.
