Long-term effects of site preparation and postplanting vegetation control on Picea glauca survival, growth and predicted yield in boreal British Columbia

Abstract

The 19–20-year effects of mechanical site preparation, windrow burning, chemical site preparation, and postplanting vegetation control on survival and growth of planted white spruce are reported from two boreal sites in British Columbia, Canada. Survival differed between treatments at both sites, but was relatively good (≥77%) even in untreated plots. Current data regarding the proportion of spruce that were physically overtopped by vegetation and previous results from related soils and vegetation studies suggest that lasting reductions in tall shrub and aspen abundance were more important to spruce growth than early microenvironmental effects associated with manipulating the rooting environment. At Inga Lake, postplanting vegetation control produced a 13-fold increase in spruce volume over the control after 19 years, which was statistically equivalent to increases resulting from fine mixing, plow-inverting and windrow burning site preparation treatments. At Iron Creek, chemical site preparation and plow-inverting quadrupled spruce volume, whereas mounding, patch scarification and disc trenching were ineffective. Growth and yield simulations using treatment-specific site index curves for Inga Lake suggested that rotation length could be shortened by 12–16 years through the use of site preparation or postplanting vegetation control. However, untreated areas, due to the relatively good survival of white spruce at age 19, were predicted to produce equivalent volume if left to grow to mean annual increment culmination age.

Keywords:

• Boreal
• burning
• chemical site preparation
• mechanical site preparation
• postplanting vegetation control
• TASS
• white spruce

Acknowledgements

We thank Dr Robert McMinn, Marvin Grismer, BC Ministry of Forests and Range staff and contractors who were involved in the installation, measurement and maintenance of the study sites, and Linda Stordeur for work on early data compilation and statistical analysis. We are grateful to Dr Phil Comeau, Dr Chris Hawkins, Richard Kabzems, Pat Martin, John McClarnon and Allan Powelson for guidance during preparation of the manuscript and review comments. We thank Dr Sybille Haeussler for input regarding vegetation community attributes, and Ken Polsson and Dr Gordon Nigh for assisting with TASS simulations. Funding for the study was provided by the BC Ministry of Forests and Range (MFR), Canada–British Columbia Economic and Regional Development Agreements (FRDA), Forest Renewal British Columbia (FRBC) and BC Forest Investment Account: Forest Science Program (FIA-FSB). Funding assistance does not imply endorsement of any statement or information in this paper.