Manipulating aspen (Populus tremuloides) seedling size characteristics to improve initial establishment and growth on competitive sites

ABSTRACT

Trembling aspen is an important component of the boreal mixedwood forest region and is a key component of numerous ecological functions. As a result, aspen has become a target species for forest restoration after industrial disturbance; however, aspen seedling afforestation research is still in its infancy as seedling and site characteristics and their interactions which drive establishment success in the field are poorly understood. This study examined the growth response of three aspen size classes across six sites differing in competition and soil moisture availability. With competing vegetation present, tall seedlings with lower root-to-shoot ratios had less height growth aboveground and reduced root egress (relative to total root mass) belowground, indicating that light was not the most limiting factor aboveground and that higher root-to-shoot ratios may aid in competition for rooting space. Differences between size classes were less pronounced on sites with no competition or sites with extreme conditions (high competition or low soil moisture availability) during outplanting. Reducing competing vegetation before outplanting improved height growth, particularly in seedlings with high root-to-shoot ratios. For aspen, planting short to medium-sized seedlings with higher root-to-shoot ratios offers a reasonable balance between cost and production of a stress-tolerant seedling.

KEYWORDS:

• Root-to-shoot ratio
• grass competition
• seedling quality
• soil moisture availability
• forest restoration

Acknowledgements

We thank Daishowa-Marubeni International Ltd., PennWest Exploration, and Bonavista Energy Corporation for providing research sites. We would also like to extend our gratitude to Frances Leishman, Pak Chow, Trevor Floreani, Jeremy Dostie, and other past and present members of the Landhäusser Research Group and NAIT Center for Boreal Research for their support during various stages of the experiment, and to both anonymous reviewers for their helpful comments on this manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Stefan G. Schreiber http://orcid.org/0000-0001-5033-8884

Simon M. Landhäusser http://orcid.org/0000-0002-4466-1607

Additional information

Funding

We thank the Natural Sciences and Engineering Research Council of Canada (NSERC), TransAlta Corporation, and Canadas Oil Sands Innovation Alliance (COSIA) through Syncrude Canada, Suncor, Canadian Natural Resources, and Imperial Oil for providing funding.