Consequences of Global change on the composition of boreal forest.

经典的植被理论预测，在恒定的气候和场地条件下，决定性的过程导致一个独特的稳定状态。然而，许多生态系统已经报告了几种稳定状态。北方森林仍然是一个较大的相对完整的生物群落，受到诸如火灾和昆虫爆发等大干扰的控制。收敛到一个单一的稳定状态和多个轨迹的选择稳定的稳定状态已被报道。全球变化，无论是通过气候变暖还是通过人为干扰，都可能促使目前稳定的状态转变为另一种状态，因此，未来的森林可能在一次干扰之后发生巨大变化。尽管两种树种（白杨和黑云杉）对生态系统过程和动态的影响非常不同，但它们可以在北美北方森林的大部分地区共享相同的生态位。控制一个物种对另一个物种的历史优势的因素仍然部分未知，更好地了解过去和现在的动态可以帮助预测在全球变化影响下未来的森林组成。我的长期目标是了解是什么因素控制了这两个物种的分布和优势地位，并了解全球变化对北方森林组成和动态的影响。在接下来的5年里，我建议通过检查以下补充问题来解决这一研究目标：I)在全新世期间，混交木和黑云杉占主导地位的历史比例是多少？它与气候和火灾制度的变化有何关系？ii)什么机制有利于白杨和黑云杉的火后优势？iii)在气候变化的背景下，用白杨取代黑云杉对未来演替轨迹的影响是什么？***这些问题将通过一系列的研究项目来解决，从而培养3名博士，2名硕士，几名本科生和1名博士后。这些项目将包括古生态学、野外生态学、实验设计和建模方面的培训。这项工作将增加我们对森林组成如何受历史干扰控制以及森林组成如何影响生态系统过程和动态的基本知识。它还可以预测全球变化对未来森林的影响，从而有助于制定更可持续的管理战略

Classical vegetation theory predicts that under a constant climate and site conditions determinist processes lead towards a unique steady state. However, several stable states have been reported for many ecosystems. The boreal forest is still a large relatively intact biome controlled by large disturbances such as fires and insect outbreaks. Both convergence towards a single steady state and multiple trajectories towards alternative stable steady states have been reported. Global change, either via climate warming or via human disturbance, may contribute to move a currently stable state into an alternative state, and consequently future forests may change dramatically following a single disturbance. Two species (aspen and black spruce), despite their very different impacts on ecosystem processes and dynamics, can share the same niche in a large part of the North American boreal forest. Factors controlling the historical dominance of one species over the other remains partially unknown, and a better understanding of past and current dynamics could help forecast future forest composition under the impact of global changes. My long term objective is to understand what factors control the distribution and dominance of these two species and understand the consequences of global change on the composition and dynamics of the boreal forest. During the next 5 years I propose to address this research objective by examining the following complementary questions: i) What was the historical proportion of mixedwood and black spruce dominance during the Holocene and how does it relate to changes in climate and fire regime? ii)What are the mechanisms favoring aspen and black spruce post-fire dominance? And iii)In the context of climate change what are the consequences on future successional trajectory of replacing black spruce by aspen?***These questions will be addressed by a series of research projects resulting in the training of 3 Ph.D, 2 M Sc., several undergraduated students and 1 post-doctoral fellow. These projects will imply training in paleoecology, field ecology, experimental design and modeling. This work will add to our basic knowledge on how forest composition is controlled by historical disturbances and how forest composition influences ecosystem processes and dynamics. It will also allow forecasting the impacts of global change on future forests and therefore could contribute to a more sustainable management strategy.**