NURSE LOGS/TREES
NEGATIVE INTERACTION
When you visit Ravenna Park, facilitation is a very common sight. Unfortunately I did not get a very clear picture of various typed of facilitation. In this picture (taken from the King County's website, we see what looks to be English Ivy (Hedera helix) taking over a Western Hemlock (Tsuga heterophylla). This is not a common type of facilitation or what we would call "commensalism" or "mutualisms". In is not the best example of a positive ecological interaction, but it more of an example of a NEGATIVE ecological interaction, in which one species (the English Ivy) is benefiting from the Western Hemlock, but the Hemlock is actually suffering because the Ivy is invasive.
POSITIVE INTERACTION
Although this tree had already fallen, this is a great example of commensalism relationship between trees and lichen. This lichen I believe is Oakmoss Lichen (Evernia prunastri). This tree (probably some sort of broadleaf tree) facilitated this Oakmoss Lichen. Lichen are actually very good for environments. They help direct pollution, regulate gases in the environment, and some even return nitrogen to the soil which helps the trees that are facilitating their growth, flourish.
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