Dynamics of soil organic carbon reservoir and microbial biomass carbon under controlled fire in the northwestern Himalaya

Fluctuations in soil organic carbon (SOC) and microbial biomass carbon (MBC) following controlled fire were examined for one year under four land-use systems, viz. chir pine forest (Pinus roxburghii), grassland, scrubland and non-fire site in chir pine (control) in Solan district, Himachal Pradesh, India. The experiment consisted of five replications in a factorial randomized block design. A controlled fire was set in March 2018, and soil samples were taken before and after burning at three soil depths, viz. 0–5, 5–10 and 10– 15 cm. Fire impact was rated in terms of SOC and MBC, which were found to be the lowest in the month immediately following the fire (April 2018) but started increasing in subsequent months and reached the highest at the end of the experiment, i.e. 12 months after fire; however, the remained slightly below pre-fire levels. Post-fire, SOC content was found to be the highest under unburnt chir pine site (11.9 g kg^–1 ) and the lowest (11.0 g kg^–1 ) under burnt chir pine forest. The highest per cent reduction in SOC content (1.63) post-fire was found in the surface layer (0–5 cm depth) compared to the other two depths. The unburnt chir pine forest recorded the highest MBC (181.04 µg g^–1 soil), while the lowest (138.83 µg g^–1 soil) was recorded in the scrubland. The highest MBC (167.77 µg g^–1 soil) was recorded at 5–10 cm and the lowest (162.18 µg g^–1 soil) at 10–15 cm soil depth. Unlike wildfires, post-fire negative effects of controlled burning on SOC and MBC were for a shorter period and thus, the soil recovered rapidly. Despite corresponding to a short monitoring time, these findings may add to a better understanding of the potential of controlled fire as a management tool for preventing wildfires.