Lichen Biomonitoring

Riparian forests along the Fraser and Nechako rivers have long been recognized as a critical wildlife habitat and key biodiversity resource in British Columbia. However, at their junction in Prince George, these habitats are subjected to major air pollution discharges, including pulp mill and refinery emissions. 

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Air pollution emissions within the Prince George air shed are often trapped near the ground during late winter inversions.


Monitoring programs for air pollution in the Prince George area are limited to a few locations, primarily in the downtown core, where they provide a basis for issuing health advisories during periods of poor air quality. Outside the city core, however, air pollution impacts are poorly understood. 

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Study plots were located in riparian forests along the Fraser River, seen here near Prince George.


We have now used biomonitoring with lichens, a group of organisms with well-documented sensitivity to air pollution, to assess patterns of regional air pollution. Our findings show major impacts from air pollution within the Prince George area, where trunks of cottonwood trees support an acidiphilic lichen flora that is characteristic of low-pH environments, this in contrast to the acidiphobic lichens characteristic of cottonwood trunks under unpolluted conditions. 

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Study plots were placed within mature riparian forest galleries in B.C.’s central-interior, respectively from west to east at: 1) Miworth (Nechako R.), 2) Prince George – Cottonwood (Fraser R.), 3) Prince George – Canfor (Fraser R.), 4) Salmon River, 5) Hubble Homestead (Fraser R.), 6) Willow River, 7) Upper Fraser (Fraser R.).

Select Publications

Coxson, D.S., C. Björk, and M.D. Bourassa. 2014. The influence of regional gradients in climate and air pollution on epiphytes in riparian forest galleries of the upper Fraser River watershed. Botany: 92:23–45. http://dx.doi.org/10.1139/cjb-2013-0151

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Exceptional Black Cottonwood (Populus balsamifera ssp. trichocarpa) riparian gallery forests develop along the Fraser River near Prince George.  Note the researcher standing in dense ostrich ferns (Matteuccia struthiopteris) in the foreground.
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Poplar trunks within Prince George are often dominated by acidophilic species such as Usnea (abundant yellow-green fruticose lichen in image). 
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One method for assessing lichen response to air pollution is through transplant studies, here show with Lobaria species.
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Lichenologist Curtis Bjork conducts surveys for lichen biodiversity in high air pollution zone.
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Dense growth of the sensitive lichen species Lobaria pulmonaria on conifers indicates pristine air quality in the upper Fraser River watershed.