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.

中文翻译：

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操纵白杨（Populus tremuloides）幼苗大小特征以改善竞争地点的初始建立和生长

摘要 颤杨是寒带混交林区的重要组成部分，是众多生态功能的重要组成部分。因此，白杨成为工业干扰后森林恢复的目标树种；然而，白杨幼苗造林研究仍处于起步阶段，因为人们对幼苗和场地特征以及它们之间推动该领域成功建立的相互作用知之甚少。本研究考察了竞争和土壤水分可用性不同的六个地点的三个白杨大小等级的生长响应。由于存在竞争植被，根茎比较低的高大幼苗地上高度生长较少，地下根部出口减少（相对于总根质量），表明光不是地上最大的限制因素，较高的根茎比可能有助于争夺生根空间。在外植期间，在没有竞争的地点或具有极端条件（竞争激烈或土壤水分利用率低）的地点，大小等级之间的差异不太明显。在外植前减少竞争植被可改善高度生长，特别是在根茎比高的幼苗中。对于白杨，种植具有较高根茎比的短到中型幼苗可在抗逆幼苗的成本和生产之间实现合理的平衡。在外植期间，在没有竞争的地点或具有极端条件（竞争激烈或土壤水分利用率低）的地点，大小等级之间的差异不太明显。在外植前减少竞争植被可改善高度生长，特别是在根茎比高的幼苗中。对于白杨，种植具有较高根茎比的短到中型幼苗可在抗逆幼苗的成本和生产之间实现合理的平衡。在外植期间，在没有竞争的地点或具有极端条件（竞争激烈或土壤水分利用率低）的地点，大小等级之间的差异不太明显。在外植前减少竞争植被可改善高度生长，特别是在根茎比高的幼苗中。对于白杨，种植具有较高根茎比的短到中型幼苗可在抗逆幼苗的成本和生产之间实现合理的平衡。