Disturbing to restore? Effects of mounding on understory communities on seismic lines in treed peatlands

Abstract

In peatlands, micro-topography strongly affects understory plant communities. Disturbance can result in a loss of micro-topographic variation, primarily through the loss of hummocks. To address this, mounding treatments can be used to restore micro-topography. We examined the effects of mounding on the understory vegetation on seismic lines in wooded fens. Seismic lines are deforested linear corridors (~3-8 m wide), created for oil and gas exploration. Our objectives were to compare the recovery of understory communities on unmounded and mounded seismic lines and determine how recovery varies with micro-topographic position. Recovery was evident in the unmounded seismic lines, with higher shrub and total understory cover at the ‘tops’ of the small, natural hummocks than at lower micro-topographic positions —much like the trends in adjacent treed fens. In contrast, mounding treatments that artificially created hummocks on seismic lines significantly changed understory communities. Mounded seismic lines had higher forb cover, much lower bryophyte cover, less variation along the micro-topographic gradient, and community composition less similar to the reference sites than were unmounded seismic lines, due to higher abundance of marsh-associated species. Our results suggest mounding narrow seismic lines can be detrimental to the recovery of the understory communities in treed peatlands.

Linear Disturbances Shift Boreal Peatland Plant Communities Toward Earlier Peak Greenness

“…These linear clearings can be between 1.5 and 10 m wide, creating a dense grid across the landscape. These lines are cleared using a combination of tree removal and soil disturbance/compaction, altering hydrological conditions (Braverman & Quinton, 2015), vegetation communities (Echiverri et al., 2020) and ecosystem functions such as carbon exchange (Dabros et al., 2018; Davidson et al., 2020). Furthermore, these lines have a persisting legacy on the landscape, with many lines still lacking tree cover decades after the initial disturbance (van Rensen et al., 2015).…”

“…Restoration of seismic lines often involves a technique called mounding, used to bring back localized microtopography necessary for tree regeneration (Pyper et al., 2014). Yet, this method may be detrimental to the post‐disturbance vegetation communities in peatlands, especially given that the species present are still peat forming and therefore important to the overall carbon balance (Echiverri et al., 2020). Furthermore, the disturbance caused by these mounding techniques has been shown to increase decomposition and carbon loss from soils (Davidson et al., 2020).…”

How mounds are made matters: seismic line restoration techniques affect peat physical and chemical properties throughout the peat profile

“…While often successful for promoting tree growth, mechanical mounding (hereafter referred to as inverted mounding) methods have drawbacks, especially in peatlands. Mounding has been observed 4 to shift vegetation succession trajectories away from the surrounding natural areas (Echiverri, Macdonald, & Nielsen, 2020). Unlike mounded lines, untreated seismic lines often have recovering vegetation on the trajectory of restoring natural peatland plant communities (Echiverri, Macdonald, & Nielsen, 2020).…”

“…Mounding has been observed 4 to shift vegetation succession trajectories away from the surrounding natural areas (Echiverri, Macdonald, & Nielsen, 2020). Unlike mounded lines, untreated seismic lines often have recovering vegetation on the trajectory of restoring natural peatland plant communities (Echiverri, Macdonald, & Nielsen, 2020). Keeping the peat profile intact during mounding instead of inverting the soil and burying recovering vegetation could provide benefits to both understory vegetation and tree recovery.…”

“…Additionally, while tree recovery may benefit from inverted mounding, general vegetation communities are shifted from surrounding natural conditions (Echiverri et al, 2020). Changing inverted mounding methods to keep the peat profile intact and preserve recovering vegetation may maintain peat properties more similar to undisturbed conditions and improve restoration success, but this has not yet been quantified.…”