Lichen diversity in city parks

June 7, 2018

Lichens on tree by Jocelyn Kelly

Lichens are among some of the most fascinating and often overlooked and undervalued organisms of our natural communities.  They emerge from a mutualistic relationship between a fungus and a photosynthetic organism, either a cyanobacterium or alga. 


Most of us are familiar with the sight of lichens growing on the surface of rocks, trees and wood, however there are likely few among us that know their ecological role.  Lichens provide food and habitat for invertebrates (e.g., spiders, insects, and snails), nesting materials for birds and squirrels, are involved in nutrient cycling, and have been used as bioindicators of air quality.


A team at the university of Guelph under the direction of professor Karl Cottenie, set out to study lichens growing on trees in urban parks in an effort to better understand how management of parks can maximize lichen biodiversity (McDonald et al., 2017).  They examined 124 trees located in seven parks in the City of Guelph, Ontario.  At the time of the study, park management plans with the city included only limited consideration for biodiversity and ecosystem conservation. 


For the study, the researchers collected samples of bark to measure pH, evaluated the degree of bark fissuring, and measured tree diameter as a proxy for age.  They also recorded the species of lichen on each tree with the exception of 25 trees that had no lichens. 


Overall, they found a positive association between lichen diversity and tree species and diameter.  These results indicate that lichen communities in urban parks such as Guelph's, may benefit from management plans that include planting a variety of tree species of different ages.  For this to work, cities may well need to adopt naturalist Henry David Thoreau's advice when he said:  "There is a low mist in the woods - It is a good day to study lichens."


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McDonald, L., Van Woudenberg, M., Dorin, B., Adcock, A.M., McMullin, R.T., and Cottenie, K. (2017) The effects of bark quality on corticolous lichen community composition in urban parks of southern Ontario. Botany. 95:1141-1149.