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Spatial partitioning of competitive effects from neighbouring herbaceous vegetation on establishing hybrid poplars in plantations

Spatial effects of vegetation control on early tree growth were investigated in central Alberta, Canada for four years after the establishment of hybrid poplar plantations including two clones: Walker (Populus deltoides x (P. laurifolia x P. nigra)) and its progeny Okanese (Walker x (P. laurifolia x P. nigra)). Tree survival and growth, herbaceous vegetation cover, soil nutrient availability, moisture and temperature, and light availability were assessed. Tree growth in the first two years post-establishment was improved through selective in-row vegetation control close (within 50 cm) to trees for both aboveground (mechanical) and above- and belowground (chemical) control. This was associated with increased light availability for trees. In contrast, growth in the third and fourth years benefited from control of aboveground vegetation within 140 cm of the stem and this was associated with increased nutrient availability. These findings suggest effects of neighbouring vegetation on trees shifts from abovegr...