Thompson Rivers University

Graduate Thesis Defence: Steven Kega

Steven Kega, Master of Science in Environmental Science, will defend his thesis: Evaluating the Potential for Increased Forage Productivity and Soil Carbon Sequestration in Strip-Thinned Silvopastures.

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

Meeting Link


Abstract: In British Columbia, conventional forest and range management has historically considered multiple-use landscape resources independently. Often, with little consideration towards the potential value of forage for livestock and wildlife, or the potential benefits of grasslands for soil carbon sequestration. We explored an opportunity to integrate the forest and ranching industries, in order to enhance both forestry and grazing practices, so that forest production and understory forage productivity can be fully realized. Silvopasture, which is the complementary use of land for forestry and range productivity for livestock, is a practice that integrates these two sectors. Previous research has shown that a successful integration of forage, cattle and timber management can provide significant economic, social and environmental benefits such as increasing forage yield and quality, enhancing soil carbon storage, and increasing soil water availability. Our objective was to test the integration of forage and timber management to improve forage quantity and quality and to enhance soil carbon sequestration. In British Columbia, Canada, a mid-rotation forest of planted 45-year old Pinus contorta (lodgepole pine) was harvested July 2018 at 10 m, 15 m and 20 m width strips in three adjacent forest sites at an elevation range between 1340 – 1400 m. We tested two hypotheses: (H1) 20 m width strip–thinning will maximize forage yield and quality and (H2) 20 m width thinning will sequester more soil carbon than uncut control or 10 m and 15 m thinning. Baseline data including tree stand density, understory plant species composition, and soil carbon and nitrogen were collected pre-harvest, June 2018. An agronomic seed mix was broadcast at 12 kg/ha: 30% Dactylis glomerata, 30% Bromus riparius, 30% Thinopyrum intermedium, and 10% Trifolium repens was seeded in October 2018. Field experiments, laboratory analysis and remote sensing were used in the second and third phase to monitor forage quality and quantity, soil total carbon, nitrogen and organic matter as well as soil carbon sequestration. We found that all strip widths enhanced forage quality, but the 20 m strips produced more yield than other treatment units. We found higher soil compaction and increased pH level in 20 m strips than other treatment units. However, a higher soil carbon and nitrogen was found in 15 m and 10 m strips than in 20 m. Our results provide evidence for optimizing land use in silvopasture.