Learning From Fire: Studying Ecosystem Recovery Following Parry Sound 33

The Parry Sound 33 (PS33) wildfire burned over 11,000 hectares of the eastern Georgian Bay landscape between mid July and the end of October 2018.

In the years since the fire, researchers from the McMaster University Ecohydrology Lab have been measuring burn severity and tracking ecosystem recovery at several sites in the Georgian Bay Biosphere, including near Key Harbour and in French River Provincial Park. They focus mostly on peatlands (wetlands with over 40 cm of organic soil), temporary wetlands in rock depressions, and upland rock barrens and forests.

In spring 2019, seven months after the PS33 fire was extinguished, researchers from the Ecohydrology Lab measured burn severity in several peatlands and surrounding uplands. They estimated the severity of burning at 1,350 different locations by assessing the depth of organic soil that had burned away. The researchers found that much more soil had burned off in shallow upland forests, while less soil combustion was measured in peatlands. Soil along the shallow edges of peatlands was also more severely burned than middle peatland areas.

The McMaster group found that areas with organic soil deeper than 70 cm before the fire were less likely to be severely burned. This is an important observation for peatland conservation and restoration, because deeper and older peat deposits may be more resilient to future wildfires.

These results also mean that upland ecosystems, including rock barrens and forests, bear the brunt of wildfire impacts. Turtles nest in these upland areas, and can require a soil depth of at least 8 to 20 cm for their nests. Because of the PS33 fire and soil erosion, severe soil loss on the uplands led to a 71–73% reduction in suitable turtle nesting habitat. The loss of soil remains a big issue, and the Ecohydrology Group is developing strategies and technologies to restore turtle nesting habitat. They look forward to updating the Georgian Bay Biosphere community with their results in the next few years.

In deeper peatland ecosystems, wildfire can also affect the overwintering habitat of Massasauga rattlesnakes. These snakes hibernate in “resilience zones,” which are areas in the peat between the frost line and the water table. When fire passes through, it burns off insulating top layers of peat. At the same time, the water level in the peatland can rise after a fire, because burning causes upland areas to lose soil and vegetation that would have previously slowed the flow of runoff. As a result, peatland resilience zones can shrink and reduce the amount of suitable overwintering habitat for Massasauga rattlesnakes.

Deep peat might be less likely to burn severely because it is able to store large amounts of water during drought. This ability to avoid drying out means deeper peatlands likely continue to act as carbon sinks, taking carbon out of the atmosphere during summer drought periods. On the other hand, shallower peatlands are more likely to become carbon sources that emit carbon to the atmosphere, because they are more susceptible to drying out. As they dry, peatland plants become stressed and less productive, and decompose faster.

After the PS33 fire, the researchers observed strong recovery of mosses and vascular plants in peatlands that were less-severely burned. Perennial plants like leatherleaf and Labrador tea were the first to return, likely because they re-grew from underground rhizomes that survived the fire. Mosses re-established from spores or expanded out from surviving patches. In particular, Sphagnum moss cover has rebounded by up to 75% in some peatlands, three years after the fire. This new growth means the recovering peatlands are once again able to take carbon out of the atmosphere. However, the researchers estimate it will still take over 30 years for these peatlands to recapture the roughly 500 kilotonnes of carbon dioxide released by the 2018 fire.

Unburned patches within the fire footprint can help to accelerate this recovery, because they act as refuges for fire-sensitive plants and displaced animals, from which these species can disperse and re-establish after fire. These patches, called “fire refugia,” improve the overall resilience of the landscape to fire. The McMaster group estimates that fire refugia make up about 9% of the PS33 fire footprint, and they are currently developing a model to help conservationists and fire managers target and protect potential fire refugia.

You can help the McMaster Ecohydrology Group as they continue to study peatlands and rock barrens in the Georgian Bay Biosphere! As they continue to monitor post-fire vegetation recovery, they encourage the public to post observations of any plant, moss, or reptile species in this area (both inside and outside the Parry Sound 33 fire footprint) on the iNaturalist website (www.iNaturalist.org). You can also help them track water levels in wetlands across the Georgian Bay Biosphere to better understand fire risk and drought conditions through their iWetland program! Visit their website (http://ecohydrology.mcmaster.ca/iwetland.html) or the iWetland Facebook page (www.facebook.com/iWetland) for more information.

Content courtesy of the McMaster Ecohydrology Lab

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