Carbon consequences of drought differ in forests that resprout

• Published in: Global change biology 2019-05, Vol.25 (5), p.1653-1664
• Main Authors: Walden, Lewis L., Fontaine, Joseph B., Ruthrof, Katinka X., Matusick, George, Harper, Richard J., Hardy, Giles E. St. J.
• Format: Article
• Language: English
• Subjects: Branches; Carbon; carbon sequestration; Carbon sinks; Carbon sources; Climate change; climate change impacts; climate mitigation; Decay rate; Drought; Duration; Dynamics; Eucalyptus marginata; Fires; Foliage; forest dynamics; Forests; Heat sinks; Mediterranean; Mitigation; Mortality; Pools; Regrowth; Replenishment; Storage; Tissue; tree mortality
• ISSN: 1354-1013; 1365-2486
• DOI: 10.1111/gcb.14589

Prolonged drought and intense heat‐related events trigger sudden forest die‐off events and have now been reported from all forested continents. Such die‐offs are concerning given that drought and heatwave events are forecast to increase in severity and duration as climate change progresses. Quantifying consequences to carbon dynamics and storage from die‐off events are critical for determining the current and future mitigation potential of forests. We took stand measurements five times over 2+ years from affected and unaffected plots across the Northern Jarrah Forest, southwestern Australia, following an acute drought/heatwave in 2011. We found a significant loss of live standing carbon (49.3 t ha−1), and subsequently a significant increase in the dead standing carbon pool by 6 months post‐die‐off. Of the persisting live trees, 38% experienced partial mortality contributing to the rapid regrowth and replenishment (82%–88%) of labile carbon pools (foliage, twigs, and branches) within 26 months. Such regrowth was not substantial in terms of net carbon changes within the timeframe of the study but does reflect the resprouting resilience of this forest type. Dead carbon generated by the die‐off may persist for centuries given low fragmentation and decay rates resulting in low biogenic emission rates relative to other forest types. However, future fire may threaten persistence of both dead and live pools via combustion and mortality of live tissue and impaired regrowth capacity. Resprouting forests are commonly regarded as resilient systems, however, a changing climate could see vulnerable portions of forests become carbon sources rather than carbon sinks. We quantified carbon storage dynamics following a drought‐induced die‐off in a resprouting forest. We found a significant loss (49.3 t ha−1) of live carbon and accumulation of dead material in affected stands following die‐off. Of the persisting live trees, 38% experienced partial mortality contributing to rapid regrowth and replenishment (82%–88%) of labile carbon pools (foliage, twigs, and branch) within 26 months. However, future fire may threaten persistence of both dead and live pools via combustion and mortality of live tissue and impaired regrowth capacity. Our work questions the previously assumed stability of these carbon stores.