Decomposition of Main Litter Types and Nitrogen Release in Post-fire Larch Forests of the Russian Far East

Decomposition processes in larch forests, which occupy a significant part of the boreal zone and are most frequently affected by devastating ground fires, are poorly researched. In the course of a long-term (850 days) field experiment, the decomposition of litter types typical for boreal larch forests of the Russian Far East (needles, leaves, branches, and grass) was monitored in larch stands, both natural ones and those disturbed by fire. The following litter parameters were measured: mass loss, carbon (C) and nitrogen (N) dynamics, respiration, and environmental conditions (temperature and humidity). It is established that, 15 years after a long-lasting ground fire, the inflow of C and N with ground litter has decreased 2.2 times in comparison with the prefire level. At this stage of post-fire succession, the share of tree litter is lower, while the share of low-lignin grass litter is higher in comparison with the control. No differences in mass loss rates were identified between the studied stands for leaves, grass, and branches. However, at the end of the experiment (day 850, p = 0.0035), needles were decomposing more slowly in the burned larch forest than in the control. A lower CO₂ emission intensity featured by the needle litter in the postfire forest (p = 0.0207) in comparison with the control and a lower nitrogen content in decomposing needles at later stages of the experiment (p = 0.0234) indicate that the post-fire factor inhibits microbiological activities. A decrease in the total N inflow with litter in the post-fire stand, combined with a lower needle decomposition rate, results in a slower release of nitrogen and its availability to plants and microorganisms, which may affect the restoration of boreal larch forest ecosystems damaged by fires.