News Release

REF NO.: 44

SUBJECT: Rethinking old-growth forests using lichens as indicators of conservation value

DATE: March 5, 2019

Two Canadian biologists are proposing a better way to assess the conservation value of old-growth forests in North America by using lichens — sensitive bioindicators of environmental change.

Dr. Yolanda Wiersma, a landscape ecologist in the Department of Biology, Faculty of Science, at Memorial, and Dr. Troy McMullin, a lichenologist at the Canadian Museum of Nature, propose their lichen-focused system in a paper published today in the Ecological Society of America journal, Frontiers in Ecology and the Environment.

“We are presenting a paradigm shift for the way we assess forests and manage them,” said Dr. McMullin. “How do we select the forests with highest conservation value? How do we decide what to protect and what to cut? Lichens are part of the answer.”

Importance of diversity

Old-growth forests, especially those in North America, are perceived to be rich in biodiversity, in addition to capturing aesthetic and spiritual values. These forests are usually defined by the age of the trees, with conservation and management practices developed accordingly.

Drs. McMullin and Wiersma say this is an over-simplification, as it overlooks the importance of biodiversity in those habitats.

“Forests with old trees in them are certainly awesome and important,” said Dr. Wiersma. “However, forests change through time and something that is an older forest now may not always be a forest.”

Their approach looks at the presence of forests in the context of the broader landscape.

“If we think of the landscape as a patchwork quilt of different types of forests of different ages, some of those patches of forest will stick around for a long time, while others might wink in and out over different time frames,” Dr. Wiersma added. “Using lichens can help us discriminate different areas and identify which patch has been a forest for the longest period of time, even if it’s not the one with the oldest trees.”

Ideal candidates

The researchers' argue that old trees are only a proxy for biodiversity in old-forest ecosystems and that biodiversity should be measured directly – with lichens as the ideal candidates.

“The advantage of lichens as indicators for this biodiversity is that they don’t go anywhere, you can study them anytime of the year and they “eat the air,” which makes them one of the most sensitive organisms in the forest,” said Dr. McMullin.

“Many old-growth forests have high sustained moisture and a high number of microhabitats suitable for certain species, which can’t disperse easily. Having these forests in the landscape provides a refuge for the seeds and spores that helps with the continued preservation of this biodiversity.”

In the paper, Drs. McMullin and Wiersma propose that suites of lichens associated with known old-growth areas can be used to develop “an index of ecological continuity” for forests of interest.

This scorecard of lichen species could then be used as a tool by conservation biologists and forest mangers — the more species that are old-growth dependent, the higher the forest’s conservation value.

European approach

The scientists note that lichens are already being used to assess old-growth value and forest continuity in parts of Europe, but less so in North America.

As examples, they cite the studies of British botanist Dr. Francis Rose, who developed an index of about 30 lichens associated with Britain’s Royal Forests, which have been relatively untouched going back hundreds or even thousands of years.

Drs. McMullin and Wiersma believe they can build on this knowledge to develop lists of appropriate lichen suites for forest types such as Carolinian, boreal or Great Lakes-St. Lawrence.

Next steps could include training those responsible for assessing the forests, offering access to the expertise of trained lichenologists and taking advantage of new technologies such as DNA barcoding.

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