Estimating Forage Lichen Biomass

The availability of forage lichens is a key component of habitat quality for boreal woodland caribou, a species designated as a Threatened in Canada. Under a changing climate, fire regimes are expected to change as weather becomes warmer and drier. It will inevitably alter forest successional dynamics and thus, caribou habitat. One possible mechanism by which this could occur is the shortening of fire return intervals of Canadian forests. Fire regimes vary across regions, depending on climate, landform and stand composition. Lichen growth rates have also been demonstrated to vary depending on geographic location. Many lichen species take decades to recover substantial cover and depth after severe disturbance such as wildfire. Lichen ecology has been well-studied in areas with generally high abundance and infrequent fire. Hence, estimates of lichen biomass determined in some regions of the boreal forest may not apply to regions with shorter fire return intervals. Accurately predicting lichen abundance in forest stands is important for understanding requirements and the effect of disturbances on lichen recovery.

The Taiga Plains and Taiga Shield of the Northwest Territories rank among the ecozones with the shortest fire return intervals in Canada. Both ecozones are dominated by coniferous tree species such as black spruce, found primarily on poor drained soils, and jack pine, commonly found in well-drained soils. Multiple environmental conditions can influence lichen growth including light availability, stand age and soil moisture. Open canopies and dry soils are favourable conditions for lichen establishment and growth, in which they tend to compete efficiently with vascular species. For these reasons, the lichen recovery in jack pine dominated stands occurs at a faster rate than in black spruce. Due to the slow growth of lichen, old stands contain high lichen abundance. Estimating lichen abundance at a large scale as well as in different stand types with a consistent method is rarely performed. To our knowledge, the current study is the first to address these issues.

Due to the difference in regional climatic gradient and landform, we hypothesize that the lichen abundance will vary between ecozones as well as time since fire. Our first objective is to present a method for estimating lichen biomass. Our second objective is to quantify the variability in lichen recovery in different stand types across ecozones.

During the summer of 2018, our team established a network of permanent sampling plots in historic fire scars (recent burn, 70s and area without a record fire history) near Behchoko, Ingraham trail, Discovery mine and Norman Wells. We measured stand age and structure, soil conditions, and vegetation. We also collected destructive samples of forage lichen, which are used to relate biomass to volume by developing allometric equations. Then we can estimate stand-scale lichen biomass from cover and depth measured for each site, evaluate how it varies among stand types, ecozones, and stand age.

Unusually short fire return intervals may disrupt the resilience of boreal forests in northwestern Canada, and have important consequence on caribou habitat. Changes in lichen abundance would increase the risk of predation and disease, as habitat becomes more suitable for other ungulates and their predators. Therefore, using an accurate and efficient method for estimating lichen biomass as well as considering difference in recovery time between ecozones is critical for assessing habitat quality and improving boreal caribou habitat management. This project will contribute to forecast of caribou habitat quality with the expected increases in fire activity following on climate warming.

Author: Geneviève Degré-Timmons, Research Technician, Wilfrid Laurier University 

Authors Note

Field crew: Geneviève Degré-Timmons ( Research Technician, Wilfrid Laurier University; Kristen Bill, Graduate student (University of Guelph); Julie Trus, Research assistant (University of Guelph); Emily Ogden, Research assistant (University of Guelph); Rosie Savage, Research assistant (Western University).

Project led by: Dr. Jennifer Baltzer (Laurier), Dr. Steven Cumming (Université Laval), Dr. Jill Johnstone (University of Saskatchewan) and Dr. Merritt Turestsky (University of Guelph).

Collaborators: NWT Dept. of Environment & Natural Resources, Tłı̨chǫ Government and Norman Wells Ɂehdzo Got’ı̨nę.

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