Jessica Hudson | ALES Graduate Seminar

A graduate exam seminar is a presentation of the student’s final research project for their degree.
This is an ALES MSc Final Exam Seminar by Jessica Hudson. This seminar is open to the general public to attend.

Thesis Topic: An evaluation of hitchhiker seedlings with native boreal species as a revegetation tool of industrially disturbed sites in Alberta, Canada

MSc with Drs. Derek MacKenzie and Amanda Schoonmaker

Seminar Abstract:

Herbaceous forbs hitchhiked, or co-grown, with a woody species, is a solution to establish both native woody and herbaceous species at recently disturbed sites. The broad study objectives were to (1) assess the growth of fireweed hitchhiked with three deciduous woody species and one conifer over two growing seasons as a reclamation tool, and (2) evaluate the growth responses of singly grown native species to a range of existing soil conditions.

To test the hitchhiker seedling concept, fireweed was sown with woody species at different time intervals to produce seedling stock with two species in each container with a range of root and shoot characteristics. Fireweed (Chamerion angustifolium) was sown with green alder (Alnus viridis), paper birch (Betula papyrifera), and Bebb’s willow (Salix bebbiana) at the same time, 2 weeks later and 4 weeks later as well as grown alone. Fireweed was sown with white spruce (Picea glauca) 8 weeks and 10 weeks later.

Hitchhiker seedlings were planted at a soil stockpile and recently reclaimed borrow pit near Fort McMurray, Alberta, Canada. The growth and survival of woody and fireweed plants differed among sow dates with later sow dates consisting of a larger woody plant and a smaller fireweed plant as the woody plants had a longer period of growth prior to adding fireweed into the container. Initial seedling characteristics were especially evident after one growing season and faded after the second growing season. Fireweed spread was not determined by sow date, but rather site conditions. Sow dates recommended for revegetation of industrially disturbed sites were based on balanced growth of woody and fireweed plants relative to singly grown plants: 2-week alder, 0-week willow, and 10-week white spruce. The sow dates used in this study did not lead to a birch and fireweed hitchhiker seedlings with balanced growth and survivorship.

Although species responded differently to soil conditions due to their life history characteristics and autecology, most species growth was better in soil with lower bulk density and moderate total nitrogen and labile organic matter, while greater survival occurred in soils with greater bulk density.

The production of hitchhiker seedlings is encouraged as a revegetation tool at reclamation sites where the natural ingress of native herbaceous and woody species may be limited, and non-native species are controlled. Other herbaceous species should be tested with the hitchhiker concept with the consideration that deciduous woody species grow more quickly than conifers, each species may differ in autecology traits, and species selected should be site specific.