Impact of chipping residues and its leachate on the initiation and growth of aspen root suckers

Field chipping operations often disperse chipping residues of bark and branches in layers or piles in cut-overs. We tested the effects of these residues on the root sucker regeneration of aspen (Populus tremuloides Michx.), using root systems established in large pots. After decapitation of the stems, the root systems were covered with a 4 cm thick layer of chipping residues. Other root systems were treated with an extract of the water-soluble compounds leached from a similar amount of residues while others were left untreated as controls; all three treatments were left to sucker for 7 wk. There were no differences in the number of root suckers that were initiated on the aspen root system among the three treatments. There were, however, significantly lower numbers of suckers that emerged through the chipping residue and their emergence was delayed relative to the other treatments. The delay in emergence and the reduction in sucker numbers were likely a result of the residues acting as a physical barrier. After 7 wk, concentrations of water-soluble phenolic compounds, sugars, and carbon from the chipping residues were elevated in the soil; however, they appeared to be below a level that affects sucker emergence and development. Key words: Allelochemistry, leachate, physical barrier, Populus tremuloides, regeneration