Ecological impacts of shortening fire return intervals on boreal peatlands and transition zones using integrated in situ field sampling and lidar approaches

Abstract

Aridity associated with rising air temperatures in northern latitudes is expected to contribute to increased frequency of wildland fires. Here, we examined regenerating vegetation following short return interval (SRI) fire (56 years post‐fire) compared to long return interval (LRI) fire (>80 years post‐fire) in boreal peatlands and their adjacent transitional areas. The objectives of this study were to quantify if differences exist between (1) peatland and transitional soil characteristics in LRI versus SRI areas and (2) regenerating vegetation species, structural characteristics and diversity. We also determined if patterns of vegetation structural characteristics observed using field data also occur across the broader landscape using airborne lidar data. The Utikuma Region Study Area (URSA) is located in central Alberta, Canada. Here, 19 peatlands were sampled, coincident with an airborne lidar survey of the broader region, where 120 peatlands in short and long fire return intervals were identified. We found that SRI transitional areas had significantly deeper organic soil deposits than those found in LRI (p < 0.0001). Proportions of regenerating species differed significantly between peatlands and transitional areas in SRI versus LRI, where greater proportion of coniferous species were observed in LRI. Deciduous transitional–upland species and taller post‐fire vegetation heights were more commonly found SRI peatlands compared with LRI. This suggest that fires with SRIs in this region may result in enhanced deciduous succession, which may transition boreal peatlands into ecosystems that have some characteristics of transitional and upland forests.

Shortening fire return interval predisposes west‐central Canadian boreal peatlands to more rapid vegetation growth and transition to forest cover

“…(2016), Jones et al. (2022), and Guêné‐Nanchen et al. (2022) observed post‐fire proliferation of short‐statured shrubs, such as Labrador tea ( R. groenlandicum ) in a sample of measured peatlands.…”

“…), paper birch ( Betula paperifera ), and willow species ( Salix spp.) (Figure 1, Jones et al., 2022).…”

“…Sherwood et al (2013) and Kettridge Turetsky et al (2015) observed greater evapotranspiration rates from fens following fire, resulting in enhanced shrub/vascular vegetation productivity. Bourgeau-Chavez et al ( 2020) also observed lower burn severity in fens, which, when combined with greater evaporative potential, produces conditions favorable for the encroachment of deciduous species (Grzesik et al, 2022;Jones et al, 2022;Langdon et al, 2020;Lukenbach et al, 2017;Moore et al, 2022). However, trait plasticity and adaptability of shrubs to varied environmental conditions, including hydrology, require further assessment (Dabros et al, 2022;Moore et al, 2022;Turetsky et al, 2008).…”

“…The boundary between peatlands and uplands, referred to here as the peatland ecotone (Figure 1), may be especially sensitive to wildland fire, including the potential to enhance fire spread into peatlands associated with changing moisture (Lieffers & Macdonald, 1990; Nelson et al., 2021; Wilkinson et al., 2018), afforestation (Waddington, Morris, Kettridge, Granath, Thompson, & Moore, 2015, Waddington, Morris, Kettridge, Granath, Thompson, Moore, & Sveriges, 2015; Weltzin et al., 2003), and post‐fire hydro‐ecological impacts (Jones et al., 2022). These include but are not limited to variable evaporative losses and water repellency feedbacks (Kettridge et al., 2014; Thompson et al., 2014), changes in hummock‐hollow elevational variability (Benscoter & Vitt, 2008), and post‐fire species recovery (Jones et al., 2022). Peatland ecotones can be characterized by a range of both terrestrial/hydrophobic and aquatic/hydrophilic vegetation species, including feather mosses (e.g., Pleurozium schreberi ), Rhododendron groenlandicum , willows (e.g., Salix borealis ), and low‐density Picea mariana as these transition from uplands into peatlands along with reduced depth of organic soils and increasing depth to water table from peatland to upland forests (Dimitrov et al., 2014; Elmes et al., 2018; Mayner et al., 2018).…”

“…), paper birch (Betula paperifera), and willow species (Salix spp.) (Figure1,Jones et al, 2022).F I G U R E 2 (a)The Utikuma Region Study Area (URSA) is located within the Boreal Plains Ecozone approximately 100 km north of Slave Lake, Alberta, Canada (inset). (b) Polygons indicate peatland class and form found within the areas burned by fire in 1956 only, 2011 only (LRI), and in the overlap of both fires (SRI).…”