Factorial Thinning and Fertilization Research Trial - Fourth-year Re-measurement
Weldwood of Canada Ltd.
Lead Researcher: 
Dick Dempster, PhD, RPF, Dick Dempster Consulting Ltd.
The general objective of this trial was to determine the effect of thinning and fertilization, alone and in combination, on the growth and yield of dense lodgepole pine stands.

The factorial trial, which included combinations of two thinning levels (control and 50% basal area removal) and six fertilization treatments (control and five nitrogen fertilizers with additional elements), was established in a 68 year-old, fire origin lodgepole pine stand located in the McLeod Working Circle in Weldwood’s Forest Management Agreement area. Measurements were taken in April 2000 and re-measurements followed in February and March 2004.

Fourth-year results demonstrated relative increases in merchantable basal area and volume increment. Increases of over 30% could be attributed to fertilization regimes alone, whereas increases of more than 80% were attributed to the best fertilization and thinning combinations. Gross diameter and net basal area increments showed positive responses to thinning. Although interactions between thinning and fertilization effects are only marginally significant statistically, there is some evidence that thinning improves the stand’s ability to respond to fertilization. Inconclusive results were observed for height and crown growth, and disease incidence. Correlations between various measures of annual increment and foliar weight or N concentrations however, were found to be more apparent in thinned versus non-thinned stands. Moss biomass was also found to be substantially lower in fertilized plots relative to non-fertilized control plots. This effect dominated the higher herbaceous biomass observed in fertilized versus control plots. Inconsistencies between observed increments and those predicted by TIPSY, and difficulties establishing TIPSY runs comparable to experimental conditions, suggest that other models or calibration of existing models are required.