Background

Nowadays, natural disturbances and human interventions are crucial components of the boreal forest landscape, with their impacts spanning from as small as square meters (e.g., individual tree falls, selective logging) to several million hectares (e.g., insect outbreaks, widespread wildfires) (Kuuluvainen and Aakala 2011). When natural and anthropogenic disturbances combine, they lead to both spatial and temporal changes in the northern forest range beyond its historical range of variability (Pasher et al. 2013). With the development of oil and gas extraction, the canopy height of the active forest decreases, edge density increases, and patch sizes vary by region (Pickell et al. 2015).

There are 170,558 idle or abandoned oil wells in Alberta as of  2023 (Alberta Energy Regulator 2023).  An abandoned well is a well that has been securely closed and is no longer in active use and an idle well is defined as one not engaged in oil or gas production, fluid injection, or waste disposal for 6 or 12 months (Alberta Energy Regulator 2023). The preparation of oil and gas well sites in Canada's boreal forests necessitates a comprehensive process involving the clearance of trees and vegetation, the leveling of subsurface soils, and the complete removal of surface soil to establish a stable foundation (Lupardus et al. 2019). The cumulative impact of such a large number of abandoned oil wells on the boreal forest ecosystem cannot be underestimated. Compared to the surrounding forests, the reclaimed oil well sites exhibit lower seed counts and predominantly feature understory plants, with a noticeable absence of tall trees (Lupardus et al. 2019). Additionally, the soil is more compact than the surrounding forest, demonstrating lower quality and fertility (Allred et al. 2015; Van Dyke et al. 2022). Moreover, the plant composition in abandoned well sites undergoes heightened instability, potentially facilitating the introduction of invasive species (Bergquist et al. 2007). According to the Reclamation Process and Criteria for Oil and Gas Sites, once the oil well production is completed, the site will be reclaimed, which means the land can sustain different purposes following conservation and restoration efforts, possessing a comparable capacity to its original state before any human activities took place (ARSD 2013). Therefore, under ideal circumstances, abandoned oil well sites can gradually recover through an extended process of secondary succession, eventually resembling the surrounding forest ecosystem (Azeria et al. 2020). And it's important to continue monitoring the trajectory of this succession.