Vegetation recovery and edge effects of low impact seismic lines over eight-year period in boreal uplands of northern Alberta

As of the mid-1990 s, low impact seismic (LIS) line construction (<3 m wide) became common practice in western Canada and replaced construction of wider (5-10 m) conventional seismic lines, with the intention of mitigating the known negative environmental impacts (e.g., severe soil damage and minimal vegetation re-covery) of these long, narrow corridors used by the Oil and Gas (O&G) industry for exploration. Though the apparent disturbance severity on LIS lines is lower compared to conventional lines and it is expected that suc-cession would proceed more readily towards the conditions resembling pre-disturbance forested state in the upland boreal, there is little scientific evidence that supports this. Here, we assess environmental conditions, successional trajectories and potential edge effects extending into the adjacent forest from the LIS line edges three (2014) and eight (2019) years after their construction in 2011, in the southern upland boreal forest of Swan Hills region in northwestern Alberta, to determine if active restoration measures should be recommended. Soil moisture and light were higher on the lines compared to the adjacent forest. Bryophytes (particularly feath-ermosses associated with late-succession forests) recovered well within eight years of disturbance (attaining nearly 90 % cover in 2019, from a relatively low cover (-25 %) on the lines in 2014, compared to -80-90 % in the adjacent forest in both years), while the shrub and herbaceous layers recovered minimally, and tree species were still mostly absent on these lines. Herbaceous species also had a lower cover in the -2 m zone away from the line edges compared to the interior 75 m away, indicating edge effects in both years. Our results indicate that LIS lines appear to possess a unique combination of similarities and differences to other common boreal dis-turbances (fire, harvest), resulting in the equally unique successional trajectories that do not generally follow patterns known to occur in upland boreal forests. Long-term monitoring is imperative to determine whether LIS lines will eventually return to the pre-disturbance conditions or whether human intervention will be required to promote the growth of the canopy cover, especially as they constitute part of the habitat for Woodland caribou, an important threatened wildlife species.

Automated summary

Low impact seismic lines (<3 m wide) have replaced wider conventional seismic lines (5-10 m) in western Canada to mitigate the negative environmental impacts caused by Oil and Gas exploration. However, there is limited scientific evidence on whether these low impact seismic lines can restore to pre-disturbance forested state. Long-term monitoring is necessary to determine their successional trajectories, especially as they provide habitat for the threatened Woodland caribou species.