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

Abstract

ABSTRACTTrembling 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.