Recently I went and visited my family in Washington and noted that there was a lot of moss around all the trees there. I don’t have a lot of moss in the forest where I live. I figured it had to do with the amount of rain, as we generally have a warmer, drier climate.
But then I went out to my forest between the rain this week, and was struck by the sight of an enormous tree completely coated in moss. The entire trunk was green.
But none of the trees around it had any moss. Poking around a bit more, I realized that all the trees with moss were Douglas firs, and the trees without (but often with a lichen?), were redwoods. This remained true wherever I went, suggesting it wasn’t some something to do with that particular tree’s environment. Being very much not a plant scientist (or a moss scientist), I didn’t know much about what was going on, and wondered if the species-specific moss growth had to do with something structural (is redwood bark too smooth for moss to grab on to? do douglas firs move water/nutrients in a way that moss can better appreciate?), or chemical (do redwoods deter moss growth?). I decided the chemical deterrent hypothesis made more sense, because I found moss on old redwood stumps that had lost most of their outer bark.
Having wasted a great deal of time eating lunch and staring at trees, I went back to the lab and did some reading:
- Other people have observed this phenomenon (link to paper on JSTOR) through studies of epiphytes in redwood forest. The authors of this paper suggest moss are deterred by anti-fungals produced by redwoods. Also fascinating, they describe their tree-climbing equipment/process in their methods section! Also more complex tree structure/surface area = more species growing on it.
- FYI: authors of the above paper were familiar from a book I read recently, The Wild Trees: A Story of Passion and Daring
- Redwoods are insect and fungus resistant; fungi-resistance may come from tannins
- Concerns about tree disease
- Basic moss biology
In non-moss related news: