Impact of wildfire on soil carbon and nitrogen storage and vegetation succession in the Nanweng'he National Natural Wetlands Reserve, Northeast China

Abstract

In boreal regions, wildfires have a major impact on vegetation and permafrost. The ecosystem-protected Xing’an permafrost is sensitive to warming climate and wildfires, particularly on the southern margin of boreal coniferous forest and patchy permafrost zone. However, it remains unclear how fire disturbances are linked with changes in ecosystem composition and soil nutrients in the permafrost zones of Northeast China. Here, 13 years after the fire in the Yile’huli mountain knots, we investigated the parameters like vegetation cover, ground temperatures, active layer thickness, and soil carbon and nitrogen storage at burned and unburned sites of shrub wetlands. The fire resulted in ground warming of 0.1–5.0 °C at depths of 1.0–20.0 m and active layer deepening of 0.5 m, and gravimetric soil moisture content increasing of 26%-266%. Fire also increased the number of herbs and tall shrubs. After the fire, graminoids and tall shrubs increased significantly, and the species of herbs increased by five species. However, dwarf shrubs like Ledum palustre and Vaccinium uliginosum were missing from the burned site. A massive loss of total organic carbon (TOC) (248.40 t C/hm2) and nitrogen (TN) (11.87 t N/hm2) was observed by comparing their storage at burned and unburned sites. These results highlighted that the post-fire responses of vegetation cover and TOC and TN storage were dependent on the thermal regimes of near-surface permafrost and active layer, recovery of vegetation and organic layer, and soil moisture content. This study can provide an important reference for carbon storage and emission in boreal shrub wetlands under a warming climate and increasing fire disturbances.