Friday, 7 December 2012

A Moss Mystery

If you observe nature closely enough and long enough, you begin to notice changes and anomalies. I am probably more interested in mosses than any other organisms, and as a result observed something I had never seen previously. Whether any other naturalists noticed it, I do not know, but for a bryologist it stood out loud and clear.

In the spring of 2011, while walking along the Cleveland Trail in Pacific Spirit Park I saw that one of the mosses, Ulota obtusiuscula, had died. This is a common moss that grows on alder trunks, where it forms compact dark green clumps. When dry its leaves are very shriveled, much more so than other mosses. It often has spore cases, and the cap which covers these cases has many little projecting hairs. If you are interested in finding Ulota, these are the three features to look for. 

On this particular day not only were the Ulota shriveled but every clump on every alder trunk along the trail edge was brown and dead! There are several other mosses on these trees, and none of them showed the least sign of being unhealthy. First conclusion was that something had occurred along this trail, and poisoned the Ulota, but that no other species was as sensitive as this one. 

Ulota obtusiuscula
Photo by Terry Taylor

It has been claimed that there is a psychological principle which states something to the effect that if you notice something unusual or it is pointed out to you, you will have difficulty not seeing it on future occasions. I could not help but be aware of Ulota everywhere I went, and it soon became apparent that this dieback was not a local thing. It was all across the Lower Mainland. As of autumn 2012 the little dead moss clumps are still clinging to the trees, and I also saw some on alders on the lower slopes of Mt. Fromme

How does Ulota differ from other mosses? For one thing it is adapted to grow on the driest, most exposed parts of the tree. Mosses with this growth form are those of extreme environments. Mosses which creep across the substrate require humid conditions. That is why they are the dominant growth form in shady forests. Look at a big leaf maple trunk. you will see that creeping mosses occupy the lower levels, but the branches are covered by mosses in clumps.

The other mosses on these tree trunks are clustered on the lower, humid zones of trunks, or in cracks, and other sites where conditions are less extreme. The Ulota is found on the smooth bark where the other species do not grow. Maybe Ulota occupies a niche too dry for its competitors, close to the edge of survival. If conditions remain stable there is no problem. Something like running out of food in the refrigerator. No problem as long as the grocery store is open. I do not know if there was an extreme weather event at that time, but have never experienced a Ulota catastrophe in previous years. 

There may be many processes taking place in nature that few notice, or that nobody notices. Others that I have seen over the years involve slugs and ants. The common slug in the forest is the banana slug (Ariolimax columbianus). The common one in urban areas is the black European one (Arion sp.). The black slug did not live in the forest, but now it is fairly common in the surrounding second growth conifer stands. Does it compete with the banana slug or do they eat different things? Probably nobody knows, but there may be a problem here. 

During the 1950’s and 1960’s an ant that belongs to the Formica fusca group was extremely common in Vancouver. When I was a child I used to call them sidewalk ants, because they could be seen running rapidly across sidewalks all over town. Now these ants are very rare within the city limits, although they are still common on mountain tops, and are found in surrounding areas. 

If you look closely for long enough you will notice changes taking place in our local ecology. Some of these are rapid like the moss dieback. Others are slower like the ant and slug ones. They all, however, indicate some sort of environmental change, although the nature of this change may be hidden from us.

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