Hybrid poplar roots actively avoid competing with roots from other plant species

Background/Question/Methods Hybrid poplar plantations are increasingly used worldwide for our needed wood products. To be successful, however, such plantations require good soil conditions and virtually no belowground competition from other plants. With the increasing ban on herbicide use in many parts of the world, it is becoming increasingly important to better understand the underlying mechanisms favouring the development of such fast-growing plantations, in order to devise efficient vegetation management practices. Various vegetation management treatments were tested on previously forested sites in central Quebec, Canada to determine the best growing conditions for hybrid poplar. A mixture of soil treatments, including mounding, manual vegetation removal and soil scarification, were applied to create a range of growing conditions with and without competing vegetation. Forty-five hybrid poplars were excavated after four years to evaluate the root systems of these trees in different soil conditions.

Results/Conclusions The best root growth was found in soils where root competition from other plant species was the lowest, but not on the nutrient-richest soils. Hybrid poplar roots avoided soil layers with root competition even if these layers were often nutrient-richer. It appears that hybrid poplar roots are actively avoiding soil areas with already present roots from competing plants. We concluded that competition for space is an important mechanism explaining the failure of hybrid poplar plantation, even in nutrient- and water-rich conditions.