Cut-block Seedling/Sucker Trial


To evaluate the impact of sludge application without incorporation on tree growth and landscape quality.


The cut-block seedling/sucker trial southwest of the SLP mill operations was initiated in 1996 in an area dominated by aspen and white spruce that had recently been harvested.  The experiment included: 

  • 15 m x 25 m plots
  • ~85 t/ha of sludge applied November 1996
  • 112 bare root white spruce seedlings were planted in May, 1997
  • Soil samples were obtained from 1997 to 2006 in 15 to 25 cm intervals to 200 cm
  • Soil temperature and moisture sensors were installed in one control and one sludge treatment
  • Total number of aspen and balsam suckers were determined for each area
  • Randomly selected suckers were selected for height measurements
  • Impact of sludge application on the composition or diversity of the understory cover in the nine seasons after sludge application was evaluated

Results and Conclusions

  • The benefit of sludge was not as obvious in the early years of growth for all species.
  • Measurements several years after application indicated that the white spruce in the sludge amended plots demonstrated greater diameters and volumes than the spruce in the control plots.
  • The control plots had higher survival rates (average = 91%) than the sludge amended plots (average = 52%).
    • The higher mortality in the sludge amended plots was likely caused by competing herbaceous species which thrived with the addition of sludge. 
  • Aspen and balsam poplar suckers were less frequent in the sludge amended plots than in the controls with an average of 0.9 suckers per 1 m x 1 m quadrat in the sludge amended plots and 3 suckers per quadrat in the control plots. 
    • This could have resulted from the impact sludge had on soil temperature and moisture conditions for suckering. 
    • Growth of the aspen suckers was greater in the control plots than the sludge amended plots until six years after the study began, likely due to the slower emergence of the suckers in the sludge treatments and subsequently was greater in the sludge amended plots. 
    • Growth of the balsam poplar suckers was greater in the sludge amended treatments than the controls for all years of measurement. 
  • An application rate of 50 t/ha (BDT) is recommended as opposed to the 85 t/ha which was applied in this experiment to reduce the effect of competition from competing species, increase seeding survival rates and growth and minimize the risk of nutrient losses due to leaching.
Area Application Rate (t/ha) Species Age Shift Growth Multiplier
 Height Diam Height  Diam 
SLP Cut-Block Seedling/Sucker Trial 85 Spruce 0.0 2.2 0.98 1.29
85 Poplar -0.1 27.4 1.15 1.74
85 Aspen 3.4 22.9 1.14 1.63

Poplar tree stem volume and projection

Aspen tree stem volume and projection

Spruce tree stem volume and projection