Background and rationale 

A well site (Fig 1.) is typically a 100 x 100 m (1 hectare) disturbance caused by the oil and gas industry in order to install a well and pump jack to drill for natural resources. This disturbance is characterized by clearing vegetation and leveling the soil because the drilling machinery requires a flat surface. As a consequence, the organic horizon and native seed bank are removed. Further disturbance can be caused through soil compaction by heavy machinery use and contamination via hydrocarbon spills. 

When a company ceases operations on a well site, they are required by the Alberta Energy Regulator to remediate and reclaim the land to an "equivalent land capacity" and apply for a reclamation certificate. The intention of reclamation in this case is to return the land to its pre-disturbance state; however, research assessing ecosystem recovery on reclaimed well sites has shown that these techniques are not achieving this goal - with sites experiencing arrested or slowed succession (Lupardus et al., 2019; Azeria et al., 2020). This may be due to low reclamation standards in the past that accepted any revegetation ("Green is good") even if it was non-native or agronomic (Powter et al., 2012). 

This contrast between the well site and surrounding ecosystem results in a fragmented landscape (Fig 2.) where reclaimed well pads in forested ecosystems are essentially grasslands rather than progressing towards the reference condition. Such fragmentation leads to decreased connectivity, biodiversity loss, increased edge effects, higher vulnerability to invasive species, and changes to ecosystem processes (Saunders et al., 1991; Fahrig, 2003). In addition, reclamation is a very costly and lengthy process, so if it's not achieving the goal of promoting recovery towards the reference condition, it's a waste of time, resources, and money. 

We know that plant communities on many reclaimed well pads aren't recovering as expected; however, it is unclear which attributes are driving this arrested succession. Further reclamation activities can reboot the successional timeline of a well pad in arrest or slowed succession, but it is impractical to reclaim all well pads, especially if some appear to be on successful (or nearly so) trajectories towards adjacent forest conditions. Therefore, relationships between biological, physical, and chemical characteristics of reclaimed well pads must be explored and sites need to be ranked to prioritize where funding and resources are best allocated. 

Once it is clear which attributes are most important for ecosystem recovery and sites are prioritized for reclamation activities, specific recommendations can be given based on the soil attributes and plant cover data to efficiently establish conditions that can encourage natural succession.

The main objectives of this research are: (i) to inform management of reclaimed well pads by identifying which reclaimed well pads require further intervention and what attributes are most important to address, and (ii) to recommend reclamation actions to start high priority sites on a path towards recovery to pre-disturbance conditions. To achieve this, we will explore what biophysical data are contributing to the differences between reclaimed well pads and their vegetation cover by:

1) Visualizing the relationships between soil physical, chemical, and biological properties on reclaimed well pads of different natural regions and ages and clustering the sites into groups to rank which should be reclaimed first;

2) Visualizing and quantifying the relationships between plant cover of life-form groups (i.e., graminoid, herb, shrub) on reclaimed well pads of different natural regions and ages and comparing these relationships with established groups (1) to inform revegetation of high priority sites. 

Predictions:

Previous research has found many reclaimed well pads in arrested succession, so highest priority will likely be given to sites with higher grass cover (graminoid/herb species cover) and lower shrub cover. Removal of soil layers and subsequent soil compaction may have caused more severe decreases in soil quality of some sites  These are also conditions where non-native herbs tend to outcompete shrubs.

If the forest edge around the well pad is able to propagate inward, then we expect older sites (reclaimed >25 years ago) may be low priority because they are in a further state of recovery. If reclamation practices (specifically consulting companies) have moved towards using more native plants for revegetation, then we also expect some younger sites to have greater cover diversity and similarity to reference forest conditions.