Thompson Rivers University

Graduate Thesis Defence: Matthew Coghill

Matthew Coghill, Master of Science in Environmental Science, will defend his thesis: Examining the soil legacy effects of spotted knapweed (Centaurea stoebe).

This is an open defence and will take place via BlueJeans.

Meeting Link

Abstract: Spotted knapweed (Centaurea stoebe) is the most aggressive invasive forb in North American grasslands. Since its arrival in the late 1800’s, it has spread from the west coast of North America and reached far east. It has been able to accomplish this via the production of many small seeds per plant, and the alteration of soil conditions making it difficult for native plants to grow in. Control efforts have been extensive. Broadcast chemical controls have been applied, as well as biological and physical controls; however, despite these interventions, spotted knapweed continues to have negative effects on ecosystems and their functions. It may be that spotted knapweed has a negative legacy effect in the soils they inhabit, which perpetuates even after removal of this plant. To test this, a greenhouse experiment was devised in which spotted knapweed and rough fescue (Festuca campestris) were grown in different soil types to detect potential soil legacy effects. Activated carbon and ash were used as soil amendments in each soil type, and after a 90-day growing period it was found that rough fescue grew best in unamended invaded soil types. Pre-growing conditions of this soil displayed lower levels of both carbon and nitrogen compared to other soil types, indicating that the token native plant grew best in less hospitable conditions. As this was an unexpected result, a field experiment was designed in which different concentrations of ash was applied to transplanted rough fescue plugs; however, plug viability tapered off quickly after transplanting. Conclusions drawn from this study indicate ash as a potential soil amendment for knapweed-affected soils. Further investigation into the use of ash as a broadscale solution to negative soil legacy effects is warranted. The highlight is that ash, an industrial waste product, can be potentially useful in areas heavily invaded by spotted knapweed in order to deter the spread of these noxious weeds.