The conifer forests that make up most of the nature park have a long and interesting relationship with fire. Variations in climate, weather and the age and density of trees have produced a number of historic fires.
These range from gentle ground fires that rejuvenated shrubs and maintained open patches of mature trees to stand-replacing fires that burned everything that could burn and started the forest anew.
The low-intensity fires have left some interesting evidence of their passage in fire scars on the trunks of some of the veteran trees. When a low-intensity fire burns along the ground, it rarely sets larger trees on fire. Douglas fir, western larch and ponderosa pine, which are encased in fire-resistant bark, are particularly impervious to such fires. Occasionally however, a tongue of flame fueled by an accumulation of twigs and needles at the tree’s base will run up the side of a trunk.
A tongue of flame runs up a western larch along Duck Pond Trail during a fuel treatment burn.
If the fire is hot enough, the bark may be scorched or consumed, and a black scar will be left revealing the inner wood of the tree. If the tree is not damaged too badly, it will survive this event. Over time, it will attempt to seal the scar to prevent insects and diseases from gaining a foothold. Healthy bark adjacent to the scar will grow over it, and in time may cover it completely.
Since the process of growing new bark over the wound takes many years, it is not uncommon for another fire to occur before the original scar heals. With protective bark absent, it is now easy for the fire to climb the trunk and damage the tree again. Again the tree will attempt to cover the scar with new bark. This process can be repeated many times over the tree’s lifetime.
This western larch on Romantic Ridge has an obvious burn scar on the uphill side of the trunk.
In study plots on Bootleg Mountain, just outside the nature park, scars have revealed that fires can return to a site every 15 to 25 years. On some trees, the fire history is recorded in visible layers of regrowth inside the scar. One western larch on Romantic Ridge between Hillside Trail and Cabin Trail has four visible attempts at regrowth, which means the tree was scorched by fire at least four times.
You can clearly see four attempts to seal the wound in this scar.
These fire-scarred trees can be found here and there throughout the park, and winter is a good time to look for them as the black scars show up well against a snowy background. Many scars will show only one attempt at regrowth, but fire ecologists have seen old stumps in the area with as many as a dozen attempts.
Next time you are out for a snowshoe, look at some of the older trees and see what you can discover about the park’s fascinating fire history.