Processes in boreal forest stand dynamics and succession

预估的气候变化可能影响全球动植物物种的分布，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，这些变化最有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。它是北方森林与草原草原过渡地带的优势树种。白杨在其最南端的极限可能是水分可用性的结果。它的北部边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的气候变化的影响。颤杨表现出入侵物种的典型特征（例如，小而多的种子广泛传播），这使得它适合占领新的地区，只要有有利的苗床。目前，许多北方土壤由厚厚的有机层主导，不为白杨的建立提供良好的场所。矿质土壤或分解良好的有机物被认为是良好的苗床，因为它们能提供充足和稳定的水分条件。这种类型的苗床在北方地区很少见，可能只有在受到干扰（如火灾）后才会发展，通过创造更温暖的土壤条件，减少表层有机层并促进有机质分解。我提议的工作将调查白杨的运动是否因干扰的发生而显著加速。本研究的重点是杨树在其北部和南部分布边界的苗木建立。具体而言，研究将集中在与杨树幼苗建立相关的三个关键过程中：(1)杨树萌发在叶面积和根系建立早期的生理限制；(2)在其当前分布的边缘成功建立白杨所需的微型站点的特征；(3)影响新立地杨树幼苗死亡率的因素。

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.