Lichens: a Bellwether of Biodiversity in City Parks

Parmelia sulcata, a type of lichen found in Guelph city parks (photo by J. Opiola)

Planting a variety of tree types in city parks can increase the diversity of lichens and other species found there, according to researchers in the Department of Integrative Biology.

Lichens are a type of hybrid organism composed of a fungus, algae and/or bacteria all growing together. According to Prof. Karl Cottenie, lead author Leanne McDonald, graduate student collaborator Aimée Adcock and their colleagues, lichens can be a useful way to measure of biodiversity in a particular habitat. The group was interested in finding the best way to increase biodiversity in city parks, and – using lichens as an indicator – they discovered that planting trees of different ages and types is the best approach.

“City forests are becoming fragmented,” says Adcock. “We are losing biodiversity.  But parks can play an important role in providing habitat for different species in urban environments.”

The research team looked at lichen communities growing on trees in several parks in Guelph and found that older trees have a greater diversity of lichens. Many of the youngest trees, in fact, were excluded from the study because there were simply no lichens on them at all. As trees get older, their bark becomes more cracked or fissured, creating the ideal dark, moist environment for lichens to grow. However, the researchers did not find a direct link between the amount of fissuring and the abundance of lichen species.

Xanthomendoza fallax,
a lichen found
in the
University of Guelph
arboretum
(photo by T. McMullin)

Different types of lichens grow on different types of trees, and the team also found that having more species of trees was a natural way to increase lichen diversity as well.

The team also looked at whether the acidity, or pH, of the bark had an effect on how many lichens grew there, but again lichen diversity had more to do with tree variety than acidity. This was somewhat of a surprise because pollution is known to reduce biodiversity by increasing acidity. One explanation may be that having a variety of trees can counteract, to some extent, the negative effects of a more polluted environment.

The results of the study can help conservation workers plan tree planting in parks to better support diversity.  Says Adcock, “It doesn’t suffice to just plant young trees of the same species. A variety of species and ages are needed to improve biodiversity.”  Diversity in lichens and trees creates a chain effect, where more animal species can be supported. Squirrels, birds and insects are just some of the animals that use different types of lichens as part of their habitat, and increasing tree diversity can thus have a positive effective on the wider animal community. One approach suggested by Adcock is to leave old trees and plant new trees around them, rather than planting stands of trees that are all the same age.

With spring now upon us, no doubt the city parks of Guelph will see an increase in both animals and visitors. Adcock suggests that human visitors should take a closer look at particularly colourful-looking trees when strolling in a city park. “A lot of people don’t notice lichens,” she says. “But once you notice them, they’re beautiful.”

Mya VanWoudenberg and Briann Dorin (University of Guelph) and Richard Troy McMullin (Canadian Museum of Nature) also contributed to the study.

Read the full article the journal Botany.

Read about other CBS Research Highlights.