Which mosses are commonly found on rooftops?

The Pacific Northwest is known for its moist temperate environment in which mosses flourish, even in the most urban areas.  Urban mosses are of concern to homeowners because many people believe mosses damage rooftops. For example, some people think that a thick mat of moss may retain moisture that could potentially damage shingles and shakes.  On the other hand, some authors suggest that mosses may be beneficial to roofs because they moderate the damaging effects of the summer sun.  (See Need for Control: Rooftops).

Knowing which mosses are growing on rooftops is basic information that may ultimately prove useful in evaluating their effects.  We (a group of students) identified the ten most common rooftop mosses in the Corvallis and Eugene areas of western Oregon. Our climate is moist and temperate, with wet winters and dry summers.

Rooftops were chosen for their generous moss growth and accessibility.  A total of nine rooftops were sampled in Eugene and Corvallis, OR. The three most abundant mosses on each roof were collected and evaluated for percent cover.  All roofs sampled had a mild slope and were predominately north and west facing.

Mosses were identified in the lab using Lawton (1971), Schofield (1992), and McCune (2000).  Voucher specimens were deposited at the Oregon State University Herbarium.

For results of this study, click here.


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