Effects of alternative establishment systems on resource availability, understorey composition and tree performance in juvenile hybrid poplar plantations

Abstract

The effects of different understorey management practices on tree-weed dynamics and associated tree establishment were investigated in newly planted hybrid poplar plantations containing Walker poplar (Populus deltoides × (P. laurifolia × P. nigra)) and its progeny Okanese poplar (Walker × (P. laurifolia × P. nigra)). Trees were established in 2012 on a research site in northeastern Alberta using one of four treatments: Businessas- usual (BAU; herbicide, tillage, then planting), extended fallow (BAU + additional tillage and herbicide before planting), a cover crop interseeded on BAU areas, and a no-till treatment where trees were planted directly into sod receiving prior chemical weed control but no tillage. Tree survival and growth, herbaceous vegetation cover and composition, soil conditions (N availability, water content and temperature), together with light availability, were measured over three consecutive growing seasons (2012-2014). Okanese outperformed Walker in all treatments and was more responsive to vegetation control, indicating greater plasticity and potential for short-rotation-intensive-culture plantations. Further, tree performance was improved by extended chemical and mechanical (fallow) site preparation prior to tree planting. This treatment resulted in sustained control of understorey vegetation, in particular competitive perennial forbs and graminoids, and increased light and nutrient availability to trees. These results also highlighted the importance of controlling perennial rather than annual herbaceous competitors prior to and during plantation establishment.