Lodgepole Pine - Ecology

Ecology

P. contorta subsp. latifolia forest 23 years before (above) and 10 years after (below) the Yellowstone fires of 1988

The Pinus contorta as a species is a very dependent on fire as a mode of replacing itself. The bark of the lodgepole pine is fairly thin, minimizing the defense the tree has to fire. The stands are so densely populated that the trees self thin, or out compete, each other leaving dead trees in the stand. These dead trees become a dry ladder fuel to accelerate the fire to the crown of the tree. When the fire reaches the crowns of the trees, it can jump from tree to tree and becomes relatively unstoppable. These stand-replacing fires open the cones, releasing the seeds, and are what most species of lodgepole pine rely on to be able to regenerate.

The fire regime for this species is primarily driven by climate. The fires occur most often after years of drought. Lodgepole Pine occurs from the upper montane to the subalpine region. These types of forests experience a lot of moisture in the form of snow in the winter due to their altitude. The density of the tree stand also prohibits the establishment of an understory. With all of that being said, the likelihood of a surface fire occurring are rare. Thus, infrequent, high severity fires dominate this species.

An example of the climate that plays a huge role in the fire regime of the lodgepole pine is quite complex. There are three different oscillations that play a major role in droughts. These are the Pacific Decadal Oscillation (PDO), Atlantic Multi-decadal Oscillation (AMO) and El Nino (ENSO). A combination of these oscillation being in effect (+) or not in effect (-) have a global effect on the water available to these forests. So when the AMO +, ENSO – and PDO -, there is going to be a drought and likely a severe subalpine fire.

Suillus tomentosus, a fungus, produces specialized structures called tuberculate ectomycorrhizae with the roots of lodgepole pine (Pinus contorta var. latifolia). These structures have been shown to be the location of concentrations of nitrogen fixing bacteria which contribute a significant amount of nitrogen to tree growth and allow the pines to colonize nutrient-poor sites.