Lichens as Environmental Indicators

August 27, 2006

By Clare Nunamaker

For some time now, lichens have been used in the monitoring of air quality. So when I recently had the pleasure of meeting Dr. Joe Hope, a consultant involved in lichen studies, I asked if that was his line of work.

He explained that no, air quality -- at least where he works in the UK -- is generally improving, and that lichens are much more helpful as indicators when air quality is declining. This is because the recolonization of lichens is much less predictable than their demise.

Instead, he is involved in using lichens to help judge the age of various forests. This is done primarily through looking at species presence and also measuring the size of colonies and their rates of growth.

The basic idea of species presence is that the more types of lichen there are, the older the forest is. Young forests may have a few dozen types of lichen, whereas old forests can have well over one hundred.

The size of colonies is another clue to forest age. Dr Hope estimates growth rates at 0.5 mm/year to 9 cm/year depending on the kind of lichen, with slower growth rates much more common.

"The oldest lichens," says Hope, "tend to be in extreme environments like mountaintops and Polar Regions. Maximum ages have been estimated at 1000 to (possibly) 4500 years. These are on rocks. Obviously epiphytic (tree-dwelling) lichens are limited by the longevity of their hosts and the rate of turnover of the bark."

Lichens have qualities that make them very well suited to serving as environmental indictors. "Many other biological groups," he explains, "have complicated life cycles, they move about, or they only manifest occasionally (like some fungi)."

So if you're interested in getting to know your favorite woods in a new way, you might want get to know your lichens.

You can now view Tree Tips on the web. Go to www.nwwg.org, click on Resources and click on Tree Tips.

You can contact Clare Nunamaker at forestry@nunamaker.com. Clare is a California Registered Professional Forester currently living near Edinburgh, Scotland.