A GROWTH RATE FOR THE LICHEN XANTHOPARMELIA SOMLOENSIS FROM CENTRAL VERMONT – A TOOL FOR DATING ROCK SURFACE EXPOSURE
Lichen dating has not been used in Vermont due to a lack of information on lichen growth rate and variables affecting growth. Lichen growth rate is affected by: physiology of the particular species; elevation; moisture availability; amount of direct solar radiation; annual mean temperature; and nutrient availability of the substrate. This study provides the first determination of a lichen growth rate in Vermont.
We used a statistically robust measurement of diameter for lichens on granite surfaces (pylons on the Norwich University campus) of known age in order to calculate the growth rate of the lichen Xanthoparmelia somloensis. In addition, by measuring the lichen abundance on various rock faces, and at different heights above ground, we find that a major variable in growth rate is the facing direction of the rock surface, presumably related to solar radiation. Therefore, we can now address the two critical variables necessary for using lichen growth as a dating tool in central Vermont. First, we provide a maximum rate of growth of 0.31 cm/yr and, second we have established that the maximum growth occurs on the northwest face of rock.