Post-fire habitat conditions as drivers of progressive and retrogressive succession: seedbed filter, species traits and feedback of dominant plants

发现干扰后群落聚集和演替的驱动因素一直是生态学家长期关注的问题。可靠的演替轨迹预测对于发展自然资源管理的生态学理论和战略是至关重要的。人们普遍认为，北方森林中的野火重置演替，最终达到火灾前的林分结构。在这种渐进式的演替中，竞争性排斥被认为是主要驱动力。但重要的例外发生在火灾后的北部和温带针叶林中，下层为红壤，在这些森林中，低强度的火灾往往会导致退化演替。在这里，基于竞争的组装规则被以厚重的残留有机物(ROM)为特征的栖息地条件先发制人。我之前在以黑云杉(Picea Mariaia)和卡尔米亚(Kalia Angustifolia)为主的这样一个系统上所做的工作表明，厚厚的ROM为云杉形成了糟糕的苗床，但保护了卡尔米亚的地下芽，这些芽迅速出现，主导着火灾后的群落，并抵抗树木的殖民。关于这种石南花的持续时间和动态还不够清楚：一些人认为它持续几年到几十年，而另一些人则建议交替稳定状态，几乎没有关于群落动态和植物土壤反馈的数据。这一知识对于了解大西洋两岸许多营养贫乏的针叶林和灌木林群落的退化演替机制和可持续森林管理至关重要。我的研究计划的长期目标是了解干扰介导的群落动态，特别是优势林下物种和冠层物种之间的相互作用。以黑云杉-卡尔米亚群落为研究体系，围绕当代几个广泛的生态概念和土地管理挑战，框定我的研究问题，在接下来的五年里，我将重点关注四个短期目标，即1.研究火灾后残留有机质(ROM)的生物物理性质和如何过滤物种再生特征，2.测试群落水平的特征分析如何描述演替方向和生态系统功能，3.评估喀尔米亚灌丛的寿命和生长阶段，4.探索在白垩纪石楠中恢复针叶树的创新方法。这一研究将促进我们对生境驱动群落组装和次生演替的基础知识，检验优势植物种群动态、群落特征过滤和植物土壤反馈调节的停滞演替或交替稳定状态的稳定性，以及iii)评估与恢复生态学有关的生物抗性。本研究聚焦于几个与荒漠形成的前因后果有关的当代生态学概念，将发现与火的严重程度相关的苗床过滤和优先效应对次生演替方向的重要性。这项研究的创新之处在于确定功能性状多样性沿演替轨迹，而不是传统的分类物种多样性和组成自干扰以来随时间变化的计算。我还将通过现场测量硬性状来使用优势植物的种内性状变异性。通过将群落水平的功能特征与优势植物的反应和效果特征相结合，这种方法将使我能够提供对卡尔米亚健康和森林动态的功能解释。这项研究将培养1名博士、3名硕士和5名HBSC学生。这一新知识可以用于设计卡尔米亚森林恢复的创新方法，这对加拿大东部具有重要的土地管理意义。

Discovering the drivers of post-disturbance community assembly and succession has been a long-term preoccupation amongst ecologists. A reliable prediction of successional trajectory is essential for developing ecological theory and strategy for natural resource management. It is generally believed that wildfires in the boreal forest reset succession culminating to pre-fire stand structure. In this progressive succession competitive exclusion is thought to be the main driver. But important exceptions occur in post-fire boreal and temperate conifer forests with ericaceous understory where low-severity fires often lead to retrogressive succession. Here the competition based assembly rule is pre-empted by habitat conditions characterized by thick residual organic matter (ROM). My previous work on such a system dominated by black spruce (Picea mariaia) and Kalmia (Kalmia angustifolia) showed that thick ROM forms poor seedbeds for spruce but protects the belowground buds of Kalmia that emerge quickly and dominate the post-fire community and resist tree colonization. Not enough is known about the duration and dynamics of this ericaceous heath: some suggest it lasts for several years to several decades while others suggest alternate stable states with little data on community dynamics and plant soil-feedbacks. This knowledge is essential to understand the mechanism of retrogressive succession and for sustainable forest management in many nutrient-poor conifer-ericaceous communities on both sides of the Atlantic. The long-term goal of my research program is to understand disturbance mediated community dynamics particularly the interactions between the dominant understory and canopy species. Using black spruce-Kalmia community as a study system and framing my research questions around several contemporary broad ecological concepts and land management challenges, in the next five years I shall focus on four short-term objectives, to 1. examine the biophysical properties of post-fire residual organic matter (ROM) and how that filter species regeneration traits, 2. test how successional direction and ecosystem function can be described by community level trait analysis, 3. assess the longevity and growth phases of Kalmia heaths, and 4. discover innovative methods of conifer restoration in ericaceous heaths. This research will i) advance our fundamental knowledge on habitat driven community assembly and secondary succession, ii) test the stability of arrested succession or alternate stable states mediated by population dynamics of dominant plants, community trait filtering and plant soil feedbacks, and iii) evaluate biotic resistance in relation to restoration ecology. Focusing on several contemporary ecological concepts pertaining to causes and consequences of heath formation this research will discover the significance of fire severity related seedbed filter and priority effect on the direction of secondary succession. The novelty of the proposed approach of this study is to determine functional trait diversity along successional trajectories as opposed to the traditional calculation of taxonomic species diversity and composition change along time since disturbance. I shall also use intra-species trait variability of dominant plants by onsite measurement of hard traits. By combining community level functional traits with dominant plants' response and effect traits this approach will enable me to offer functional interpretation of Kalmia heath and forest dynamics. This new knowledge on dynamics and longevity of Kalmia heath can be used in devising innovative methods of forest restoration in Kalmia heath, which has significant land management implications for eastern Canada.This research will train 1 PhD, 3 MSc and 5 HBSc students.