Hitchhiker Field Trial at Kearl Operations

Hitchhiker planting can provide later successional species with shade and protection while also promoting early herbaceous cover. Separate plugs for the two plants may be planted at the same planting site (companion planting) to achieve the same effect. A trial was established at Imperial’s Kearl Oil Sands Mine in July 2018 using shrub species (green alder [Alnus viridis] and willow [Salix spp.]), partner forb species (common fireweed [Chamerion angustifolium] and bunchberry [Cornus canadensis]) and two planting methods (hitchhiker and companion) as well as controls. Main objectives were to determine: (1) is survival and growth of woody shrubs facilitated by co-planting with locally common forb species? (2) can similar survival and growth rates be achieved by both methods? and (3) do co-planting methods provide additional vegetative cover compared to sites with woody shrub seedlings only, thereby providing extra erosion control in newly reclaimed areas?

5 year trial findings: (1) co-planting encouraged herbaceous cover, but decreased shrub survival when partner forb was common fireweed; (2) hitchhiker planting resulted in taller seedlings with higher survival rates than companion planting, but performance of seedlings co-planted was similar to control plots in many cases; (3) co-planting, and particularly hitchhiker planting, is a costly method of revegetating reclaimed areas; similarity between control and co-planted plots at the end of the 5th year suggest neither method is worth the extra cost. Suggestions for follow up trials: (1) seed newly reclaimed areas with nurse crop of partner forb – less costly, more operationally feasible and more likely to provide protection for young shrub seedlings; (2) explore different pairings including difficult to establish species, such as common blueberry (Vaccinium myrtilloides); and (3) use remote imagery to quantify changes in vegetation health and cover over the full trial area.