Fire Severity and Post-fire Hydrology Drive Nutrient Cycling and Plant Community Recovery in Intermittent Wetlands

Fire is a critical driver of plant and soil nutrient cycling in nutrient-limited ecosystems. Phosphorus (P)-limited and fire-adapted ecosystems can uptake fire-released P, but it is uncertain how post-fire hydrology interacts with fire severity to affect carbon (C) and P cycling in plants and soils. We examined the interactive effects of fire severity and post-fire hydroperiod (defined as the number of days of surface soil inundation in a year for which maximum water depth is a proxy) on soil and plant C and P cycling in intermittent wetlands in south-central Florida. We burned eight wetlands (maximum water depth 0-60 cm), maintaining replicates of four unburned wetlands (maximum water depth 0-48 cm) for reference. We collected surface water, plant and soil chemistries, plant species composition, and % cover during pre- and post-fire periods and measured hydroperiod in all wetlands post-fire. Fire severity-measured as the relative amount of vegetation consumed-was higher in shallower, shorter-hydroperiod wetlands than in deeper, longer-hydroperiod wetlands. Surface water total and dissolved C and nutrient concentrations declined following experimental burns and likely interacted with post-burn flooding. Pre-fire, we detected higher soil C concentrations in longer- than shorter-hydroperiod wetlands; however, soil P was similar among wetlands despite differences in soil C concentrations. Post-fire, soil C and P concentrations were higher in longer-hydroperiod, burned wetlands compared to unburned and shorter-hydroperiod, burned wetlands. Pre- and post-fire plant C and P concentrations were higher than soil C and P concentrations, and post-fire plant C and P were similar among all wetlands regardless of experimental burn treatment. Post-fire plant cover varied with hydroperiod and was largely unaffected by fire, and cover of mineral soil (that is, sand) increased by 6-14 times and bare organic soil increased by 5-30 times post-fire in longer-hydroperiod wetlands. Our results demonstrate that fire severity and post-fire hydrology drive the amount of nutrient release and the extent of post-fire plant succession in nutrient-poor, intermittent wetlands. The impacts of fire on ecosystem recovery are linked to nutrient and water availability.

Automated summary

Fire severity and post-fire hydrology are crucial factors influencing carbon and phosphorus cycling in plants and soils, particularly in nutrient-limited ecosystems. Fire can impact plant cover and vegetation succession in wetlands.