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Competition Impacts on Hybrid Poplar and Implications for Alternative Establishment Systems

Goehing, J.. 2015. University of Alberta, M.Sc

Abstract

The effects of different vegetation control practices on tree-weed interactions and associated establishment and early tree growth were investigated in 1-3 year old hybrid poplar plantations containing Walker poplar (Populus deltoides x (P. laurifolia x P. nigra)) and its progeny Okanese poplar (Walker x (P. laurifolia x P. nigra). Two field experiments were established on research sites in northeastern Alberta during two years (2012- 2013). Tree survival and growth, herbaceous vegetation cover and composition, soil nutrient availability, soil water content, soil temperature and light availability were measured over two growing seasons. Results showed that an extended full year of chemical and mechanical site preparation prior to tree planting reduced weed impacts on resource availability and improved tree performance. Improved biotic and abiotic growing conditions included the sustained control of understory vegetation, in particular competitive perennial forbs and graminoids, as well as increased availability of light and nutrients. Results also highlighted the need to effectively control perennial rather than annual herbaceous competitors. The findings further demonstrated a spatial and temporal shift in the competitive effects of neighboring vegetation. Trees competed primarily aboveground with weeds (i.e. for light) near the stem (< 50 cm) during the first year, which then shifted increasingly to belowground competition for nutrients later in the establishment period, both near- and far from the tree stem. Okanese also outperformed Walker poplar across all treatments and sites tested, and was more responsive to vegetation control, reflecting its superior performance, higher plasticity, and greater potential for short-rotation-intensive-culture plantations.

Key Words

Hybrid poplar; Walker poplar; Okanese poplar; Competition; Vegetation control; Integrated weed management; Alternative establishment systems; Light; Soil moisture; Soil temperature; Soil nutrient supply rates