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

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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.