Decline in Net Ecosystem Productivity Following Canopy Transition to Late-Succession Forests Anthony R. Taylor, 1,2 * Meelis Seedre, 1,3 Brian W. Brassard, 1 and Han Y. H. Chen 1 1 Faculty of Natural Resources Management, Lakehead University, 955 Oliver Road, Thunder Bay, Ontario P7B 5E1, Canada 2 Present address: Natural Resources Canada, Canadian Forest Service - Atlantic Forestry Centre, 1350 Regent Street, PO Box 4000, Fredericton, New Brunswick E3B 5P7, Canada; 3 Faculty of Forestry and Wood Sciences, Czech University of Life Sciences, Kamycka 129, 165 21 Prague, Czech Republic ABSTRACT Boreal forests are critical to the global carbon (C) cycle. Despite recent advances in our understanding of boreal C budgets, C dynamics during compositional transition to late-succession forests remain unclear. Using a care- fully replicated 203-year chronosequence, we exam- ined long-term patterns of forest C stocks and net eco- system productivity (NEP) following stand-replacing fire in the boreal forest of central Canada. We measured all C pools, including understorey vegetation, below- ground biomass, and soil C, which are often missing from C budgets. We found a slight decrease in total eco- system C stocks during early stand initiation, between 1 and 8 years after fire, at -0.90 Mg C ha -1 y -1 . As stands regenerated, live vegetation biomass increased rapidly, with total ecosystem C stocks reaching a max- imum of 287.72 Mg C ha -1 92 years after fire. Total ecosystem C mass then decreased in the 140- and 203- year-old stands, losing between -0.50 and -0.74 Mg C ha -1 y -1 , contrasting with views that old-growth forests continue to maintain a positive C balance. The C decline corresponded with canopy transition from dominance of Populus tremuloides, Pinus banksiana, and Picea mariana in the 92-year-old stands to Betula papy- rifera, Picea glauca, and Abies balsamea in the 203-year- old stands. Results from this study highlight the role of succession in long-term forest C dynamics and its importance when modeling terrestrial C flux. Key words: boreal forest; carbon; climate change; productivity; succession; disturbance; fire. INTRODUCTION The world’s boreal forests are increasingly recog- nized for their importance in regulating atmospheric carbon dioxide and mitigating anthropogenic cli- mate change (Bonan 2008; Pan and others 2011). Wildfire is considered the most prevalent form of stand-replacing disturbance across the circumpolar boreal forest and a major driver of forest dynamics, significantly affecting the capacity of the forest to sequester carbon (C) (Bond-Lamberty and others 2007; Stocks 1991). Global warming is anticipated to affect the frequency and intensity of fire disturbance (Flannigan and others 2009), highlighting the importance of understanding its effects on forest C dynamics. Yet, until recently, long-term patterns (>100 years since disturbance) of forest C dynamics Received 16 October 2013; accepted 30 January 2014 Electronic supplementary material: The online version of this article (doi:10.1007/s10021-014-9759-3) contains supplementary material, which is available to authorized users. Author Contributions: Conceived of or designed study (ART, MS, HYH, BWB), performed research (ART, MS, BWB), analyzed data (ART, MS, HYH), wrote paper (ART, MS, BWB, HYH). *Corresponding author; e-mail: anthony.taylor@nrcan.gc.ca Ecosystems DOI: 10.1007/s10021-014-9759-3 Ó 2014 Her Majesty the Queen in Right of Canada