Effects of fire radiative energy density dose on Pinus contorta and Larix occidentalis seedling physiology and mortality

Abstract

Climate change is projected to exacerbate the intensity of heat waves and drought, leading to a greater incidence of large and high-intensity wildfires in forested ecosystems. Predicting responses of seedlings to such fires requires a process-based understanding of how the energy released during fires affects plant physiology and mortality. Understanding what fire ‘doses’ cause seedling mortality is important for maintaining grasslands or promoting establishment of desirable plant species. We conducted controlled laboratory combustion experiments on replicates of well-watered nursery-grown seedlings. We evaluated the growth, mortality and physiological response of Larix occidentalis and Pinus contorta seedlings to increasing fire radiative energy density (FRED) doses created using natural fuels with known combustion properties. We observed a general decline in the size and physiological performance of both species that scaled with increasing FRED dose, including decreases in leaf-level photosynthesis, seedling leaf area and diameter at root collar. Greater FRED dose increased the recovery time of chlorophyll fluorescence in the remaining needles. This study provides preliminary data on what level of FRED causes mortality in these two species, which can aid land managers in identifying strategies to maintain (or eliminate) woody seedlings of interest.

Litter moisture adsorption is tied to tissue structure, chemistry, and energy concentration

“…Symbols and lines as in Fig. Reported values of DH c in wildland fire science range from 17.10 kJ/g for oak litter, 18.03 kJ/g in grasses, and 22.60 kJ/g in western white pine needles (Smith et al 2017). et al 2017.…”

Spectral Indices Accurately Quantify Changes in Seedling Physiology Following Fire: Towards Mechanistic Assessments of Post-Fire Carbon Cycling

“…To elucidate the potential physiological properties that cause the observed changes in the spectral indices, we draw on data from a related study [20]. That study collected additional seedling physiological metrics and sought to understand the underlying mechanisms associated with mortality and post-fire recovery.…”

“…That study collected additional seedling physiological metrics and sought to understand the underlying mechanisms associated with mortality and post-fire recovery. More detail of the methods can be found in [20] but the subset of metrics that are used in this study are briefly described here. Light-saturated (1100 mmol¨m´2¨s´1 PPFD) gas exchange (photosynthesis) and chlorophyll fluorescence measurements were performed following standard protocols [40,41] using a LI-6400XT and 6400-05 LED light source and conifer chamber (LI-COR, Inc., Lincoln, NE, USA) one day prior to the burns and then at 1, 4, 7, 14, and 28 days following the burns on five randomly-selected plants in each dose group.…”

Pyro-Ecophysiology: Shifting the Paradigm of Live Wildland Fuel Research

“…A new, ecophysiology-based approach to live fuel research that considers how plant water and carbon cycles independently and collectively interact at the leaf and whole plant level to regulate flammability and subsequent fire behavior could vastly improve our ability to predict intraand inter-species fire potential across both space and time. This discipline of pyro-ecophysiology is in its infancy, but the mechanisms of fire-induced changes in plant physiology, flammability, and the resulting mortality are already being explored [32][33][34]. This new approach can also help us expand our understanding of plants' potential responses to environmental change as well as how those physiological changes may impact plant flammability; moreover, it may ultimately help us better manage for fire under an uncertain future.…”