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，预计将导致物种分布向两极和更高的海拔转移。在加拿大，这些变化最有可能在北方森林的北方边缘检测到，预计那里的气候变化最大。颤白杨是南部和中部北方森林的主要组成部分。它是北方森林和草原草原之间过渡地带的优势树种。白杨在其南端的极限可能是水分可用性的结果。它的北方界限似乎是由温度和生长季节的长度来确定的，这些因素将受到气候变化的影响。颤抖的白杨表现出入侵物种的典型特征（例如，小而多的广泛分散的种子），这使得它适合占领新的地区，只要有有利的苗床。目前，许多北方土壤主要是厚的有机层，不提供良好的网站为白杨建立。矿物质土壤或分解良好的有机物质被认为是良好的苗床，因为它们可以提供充足和稳定的水分条件。这些类型的苗床在北方地区很少见，可能只有在火灾等干扰后才会形成，减少了表面有机层，并通过创造更温暖的土壤条件来促进有机物的分解。我建议的工作将调查是否白杨运动显着加速的干扰的发生。 本研究计划的重点是在北方和南方分布区建立白杨幼苗。具体来说，这项研究将集中在三个关键过程相关的白杨幼苗建立：（1）的生理限制白杨发芽过程中建立早期的叶面积和根系;（2）的特征的microsites成功白杨建立在其目前的分布的边缘;（3）的因素，影响白杨幼苗死亡率在这些新的建立网站。

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.