Consequences of Global change on the composition of boreal forest.

经典植被理论预测，在恒定的气候和场地条件下，决定论过程会导致一个唯一的稳定状态。然而，据报道，许多生态系统处于几种稳定状态。北方森林仍然是一个大型的、相对完整的生物群，受到火灾和虫害等大干扰的控制。已经报道了向单一稳定状态收敛和向另一种稳定稳定状态的多轨迹收敛。全球变化，无论是通过气候变暖还是通过人类干扰，都可能有助于将目前稳定的状态转变为另一种状态，因此，未来的森林可能在单一干扰后发生巨大变化。两个物种(白杨和黑云杉)，尽管它们对生态系统过程和动态的影响非常不同，但在北美北部森林的大部分地区可以共享相同的生态位。控制一种物种对另一种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能有助于预测在全球变化影响下的未来森林构成。我的长期目标是了解是什么因素控制着这两个物种的分布和优势，并了解全球变化对北方针叶林的组成和动态的影响。在接下来的5年里，我建议通过研究以下补充问题来解决这一研究目标：i)在全新世期间，混交木和黑云杉的历史比例是多少，它与气候和火灾制度的变化有什么关系？Ii)火灾后有利于白杨和黑云杉占优势的机制是什么？3)在气候变化的背景下，白杨取代黑云杉的未来演替轨迹会产生什么后果？

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?