Boreal Mixedwood Project - 130-301

Description: Demand for mixed stand conditions on upland boreal sites has increased due to the significant economic, ecological, and social values these sites typically support. Despite the fact that boreal mixed species compositions represent a transition successional phase, foresters are increasingly being asked to regenerate boreal sites to a mixedwood stand condition immediately following harvest. With current silvicultural practices and knowledge focusing on the regeneration of a single species, maintaining a mixedwood stand condition subsequent to clearcutting presents a particular challenge.

This study is designed to identify optimum silvicultural strategies for regenerating trembling aspen and white spruce on boreal mixedwood sites, where long-term objectives include an aspen fibre crop by age 35-45 and a high quality spruce sawlog crop by age 80 plus. The hypothesis being tested is that white spruce may be planted at a target sawlog density of 400 stems per hectare and “nursed” by naturally regenerating aspen. The degree of radial relief from competition around planted spruce and aspen stem density are factors being optimized through a response-surface design. Key silvicultural questions to be addressed by this study include:

  1. How important is the control of Calamagrostis and other herbaceous vegetation to the establishment and development of white spruce and aspen? How long should herbaceous vegetation control be maintained for optimum effects?
  2. How does aspen stem density influence the growth and development of the mixedwood?
  3. Does the presence or absence of understory herbaceous vegetation interact with the effects of aspen density in the above question?
  4. How do the growth and yield responses of the mixedwood approach compare to those of a single-species approach focusing on pure white spruce or pure aspen?

In short term, the study will provide a better understanding of the degree to which competition from grass, herbaceous vegetation, and shrubs must be controlled in the establishment of white spruce and aspen mixtures. Over the long term, results from this research will help forest managers understand the dynamics of mixedwood stands and develop better silvicultural strategies for their management. This research will explore individual-tree rather than broadcast vegetation management tactics. The outcomes of this research could help “pest-proof” white spruce plantations by providing a more favorable growing environment that is less prone to damage by frost, drying, and insects. In addition, research outcomes could significantly increase plantation efficiency through reduced planting and tending costs, revenue generated by an aspen fibre crop mid spruce rotation, potentially increased overall yields, and the ecological, social, and wildlife values associated with mixed species stands.


The Project Team:  Doug Pitt, CFS



Pitt, D.G. et al. 2010. Early vegetation control for the regeneration of a single-cohort, intimate mixture of white spruce and trembling aspen on upland boreal sites. Can.J.For.Res. 40: 549-564.

Effects of herbaceous and woody vegetation control on early boreal mixedwood stand development (Abstract)


Tree Tips:

Tree Tip for Project 130-302, April 2004



Boreal Seminar 2008

Keeping mixedwood forests mixed: An experiment addressing the feasibility of regenerating aspen and white spruce (Abstract- Oral & Poster)

Keeping mixedwoods mixed: a study of the feasibilty of regenerating aspen and white spruce (Poster)


Status Reports:

Partner's Field Report 2003

Partner's Field Report 2004

Partner's Field Report 2005

Partner's Field Report 2006

Partner's Field Report 2007

Partner's Field Report 2008

Project Work Report (2007-2008)

Status Report (2008-2009)

Financial Summary (2008-2009)

Status Report (2009-2010)

Status Report (2010-2011)

Partner's Field Report 2010

Partner's Field Report 2012


For Additional Information Contact:

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