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Rethinking the conservation value of old-growth forests


By Kelly Foss

New research from two Canadian biologists, including one from Memorial University, is recommending a paradigm shift in how old growth forests in North America are assessed and managed.

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

Dr. Troy McMullin and Dr. Yolanda Wiersma
From left are Dr. Troy McMullin and Dr. Yolanda Wiersma.
Photo: Donna Crossland

Sensitive bioindicators

Lichens are found on every continent and grow in all climates – from polar regions to harsh deserts.

A symbiotic association between different organisms, lichen can be part fungus and part green alga or a cyanobacterium, or both, and are sensitive bioindicators of environmental change.

Dr. Yolanda Wiersma
Dr. Yolanda Wiersma
Photo: Rich Blenkinsopp

“As a group they are fascinating, because they’re so diverse and in the boreal forests there isn’t a lot of taxonomic diversity in other organisms,” said Dr. Wiersma.

“Here in Newfoundland and Labrador we have only about five species of trees and about 12 shrubs, but we have over 300 documented species of lichen, and likely many more we just haven’t found yet.”

Old-growth forests, especially those in North America, are usually defined by the age of the trees, with conservation and management practices developed accordingly.

“We can use a lichen inventory to determine which [forest area] is more special.” — Dr. Yolanda Wiersma

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

“In Newfoundland and Labrador, we have some amazing protected areas, but there are parts of the province that are underrepresented,” said Dr. Wiersma. “When government is prioritizing which new protected area to put in place and are looking at two forest areas we think are old and special, we can use a lichen inventory to determine which is more special.”

By looking at the presence of forests in the context of the broader landscape, they can determine which areas of the landscape have been forests for the longest period of time, which may not always be the one with the oldest trees.

There are an estimated 2,500 species of lichens in Canada. The provide food for animals, habitats for insects and can serve as monitors for air pollution.
Photo: Rich Blenkinsopp

Dr. Wiersma says that also in this province, there are some places where there are old forests, but there was a time when the hills around some communities that were completely denuded, due to heavy shipbuilding in the 1800s, meaning that some of these forests may be old, but haven’t been continuous forests since then.

“There are certain lichen that will only show up in areas which have always been forests, regardless of whether the trees in them are old. That doesn’t mean old trees aren’t important, it’s just a different way of assessing the relative conservation value of different patches of forest.”

Ecological continuity

One advantage of lichens as indicators for this biodiversity is that they don’t go anywhere and can be studied at any time of the year. Because they “eat the air,” they are also some of the most sensitive organisms in the forest.

In their paper, Drs. Wiersma and McMullin propose developing “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 lichen it contains that are associated with old-growth areas, the higher the forest’s conservation value. This process is already being used in some areas of Europe.

Their recommendation would see the development of lists of appropriate lichen suites for forest types such as Carolinian, boreal or Great Lakes-St. Lawrence. Further steps would 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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