Weekly Journal 3: Old Growth Forests in the Olympic National Forest

In the old growth forest ecosystem, competition can be seen everywhere between species. Trees in the forest must compete for adequate sunlight to thrive based on their tolerance for different light conditions. Western Hemlocks are shade tolerant and so require less sunlight to survive whereas Douglas Fir trees require more sun. Therefore, trees and plants have mechanisms to compete for light in many ways. Some like the Douglas Fir grow tall to achieve exposure to more sun while smaller species that need sun can grow on fallen snags to gain more sun exposure. These plants are called epiphytes. For example, the Red Huckleberry often grows on other trees.

Disturbance is when an event impacts a forest and changes the forest structure. An example of disturbance that can be seen in the old growth forest is wind gusts which wipe out certain trees in the landscape that are more susceptible to the winds force from many factors, wood rot, lack of maturity, or lack of root support. The resulting forest environment will be spatially complex. Not all trees are affected by the disturbance so there will be patches of fallen snags and patches of unharmed vegetation. The old growth forest we visited on the Olympic National Forest demonstrated this spatial complexity that occurs because of prior disturbances.

There was also evidence of predation in the old growth forests of the Olympic National Forest.

Insects, especially bark beetles, can produce wood rot and damage trees. This is a form of predation because the beetles consume the tree while harming the tree system. However, some species like Douglas Fir have mechanisms to protect them from the destructive effects of insect predators. These trees can produce resin, a thick liquid which rushes to the wounded tree area and heals the afflicted region of the tree, preventing further harm and the death of the tree.

Disturbance events of a forest can also have a ripple effect through the ecosystem when they occur. One example is when branches or mosses fall from taller trees, crushing smaller trees or spatially close trees and restricting their access to growth and light. The destroyed smaller trees will then serve as a habitat for new species to colonize and thrive upon for will decay and return organic nutrients to the soil for use by the whole ecosystem.

Slope aspect has a significant effect of the structure and species seen in old growth forests, as seen by the different vegetation along the Mt. Stormking and Marymere Falls trails. The Marymere trail, the east facing slope receives a lot more moisture than the west-facing Mt. Stormking. As a result moisture-indicating species like Sword Ferns, Maidenhair Ferns, and Devil’s Club are abundant in this region of the forest. Additionally, the area is contains a number of the tree species

like Western Hemlock and Douglas Fir which thrive in these moist forest conditions are prevalent in the area. On Mt. Stormking, the rocky, dryer soil is more suited for wildflowers and trees that thrive in drier conditions. On our walk up we observed small scrubs like Salal and Cascade Oregon Grape as well as a number of wildflowers like Chocolate Lilies and Western Trillium. The trees in this region are also well suited for drier conditions and higher elevations like the Madrones and Subalpine Fir.

This sketch shows an area of the old growth forest where past disturbance events have had a tremendous effect on the landscape. The fallen snags in the foreground are evidence of past disturbance events, like wind gusts or wood rot, which have caused the vegetation to fall to the forest floor. Since these species have fallen, new species like mosses and small shrubs have since colonized the fallen snags. In the center of the sketch there is a tree which has been disturbed by a wildfire, has survived the damage, and is now recovering. The tree has been hollowed at the bottom portion and charcoal coats the interior. By observing this tree I would hypothesize that this is a legacy tree which has survived a wildfire. Wildfires do not hit every tree in the forest, but can damage the vegetation unevenly. Sparse areas around this tree may be evidence that trees were burned during the prior forest fire while many trees like this legacy tree still survive and have managed to recover from the inflicted damage.