Processes in boreal forest stand dynamics and succession

预计的气候变化可能会影响全球动植物物种的分布，并预计将导致物种分布向两极和更高海拔地区转移。在加拿大，这些变化很可能在北方森林的北部边缘被发现，那里的气候变化预计是最大的。颤杨是南部和中部北方森林的主要组成部分。是寒带森林和草原草原过渡带的优势树种。白杨在其最南端的限制可能是水分供应的结果。它的北界似乎是由温度和生长季节的长度决定的，这些因素将受到预计气候变化的影响。颤杨表现出入侵物种的典型特征（例如，种子小而数量多且分布广泛），这使得它适合占据新的区域，只要有有利的苗床即可。目前，许多北方土壤以厚有机层为主，无法为白杨的生长提供良好的场所。矿质土或分解良好的有机质被认为是良好的苗床，因为它们可以提供充足且稳定的水分条件。这些类型的苗床在北方地区很少见，很可能只有在火灾等干扰后才会形成，减少表面有机层，并通过创造温暖的土壤条件来促进有机质分解。我提议的工作将调查白杨运动是否因干扰的发生而显着加速。   该拟议研究计划的重点是白杨幼苗在其北部和南部分布范围内的建立。具体来说，该研究将重点关注与白杨幼苗建立相关的三个关键过程：（1）白杨发芽在叶面积和根系早期建立过程中的生理限制； (2) 在目前分布的边缘成功建立白杨所需的微型地点的特征； (3) 影响这些新建立地点的白杨幼苗死亡率的因素。

Projected changes in climate are likely to influence the distribution of plant and animal species globally and are expected to result in a shift in species distributions toward the poles and into higher altitudes. In Canada, these shifts will most likely be detectable at the northern edge of the boreal forest, where changes to climate are predicted to be greatest. Trembling aspen is a major component of the southern and central boreal forest. It is the dominant tree species of the transition zone between the boreal forest and the prairie grasslands. The limit of aspen at its southern extreme is likely a result of moisture availability. Its northern limit seems to be defined by temperature and length of the growing season, factors that will be affected by projected changes in climate. Trembling aspen exhibits characteristics typical of an invasive species (e.g., small and numerous widely dispersed seeds), which make it suitable to occupy new areas, provided that favourable seedbeds are available. Currently, many northern soils are dominated by thick organic layers that do not provide good sites for aspen establishment. Mineral soil or well-decomposed organic matter are considered good seedbeds since they can provide sufficient and stable moisture conditions. These types of seedbeds are rare in northern regions and likely only develop after disturbances, such as fire, reduce surface organic layers and enhance organic matter decomposition by creating warmer soil conditions. My proposed work will investigate whether aspen movement is significantly accelerated by the occurrence of disturbances.   This proposed research program focuses on aspen seedling establishment at its northern and southern distribution limits. Specifically, the study will focus on three critical processes related to aspen seedling establishment: (1) the physiological limitations of aspen germination during the early establishment of leaf area and root systems; (2) the characterisation of microsites required for successful aspen establishment at the fringe of its current distribution; and (3) the factors that impact aspen seedling mortality at these new establishment sites.