Patterns of restoration of soil physicochemical properties and microbial biomass in different landslide sites in the sal forest ecosystem of Nepal Himalaya

The pattern of natural restoration in soil components and processes was doc umented in five landslide-damaged (1-58-year-old) sites in the moist tropic al sal (Shorea robusta) forest ecosystem of Nepal Himalaya. Comparisons wer e made with an undisturbed forest site in the same region. Concentrations o f soil organic C, total N, total P and extractable nutrients (Ca, Mg and K) increased with the age of sites. The 58-year-old site showed concentration s of soil organic C, total N and total P that were 75-89% of concentrations in the undisturbed sal forest. The soil microbial biomass, the active frac tion of soil organic matter, showed similar seasonal variations at all site s. The amount of mean microbial biomass (expressed as C, N and P contents) increased 4-5 times at the 58-year-old site relative to the I-year-old site , and the bulk increase occurred within the initial 15 year. The increase i n the C/N ratio of soil microbial biomass with age (9.4-11.6 years) reflect ed change in its composition. Although the net N-mineralization rate increa sed consistently until 58 years of age, the proportion of nitrification rat e relative to ammonification rate distinctly decreased beyond 40 years. On the other hand, the soil available-N (both NO3- and NH4+) concentrations in creased from 1 to 40 year and then declined; with age the proportion of NH4 + increased, however. Rates of restoration in soil properties were faster i n the early successional stages (1-15 year) than late stages. Among differe nt soil properties the restoration of soil microbial biomass (C and N) was faster than soil organic C and total N. Best fit power function models show ed that the estimated times for the 58-year-old site to reach the level of the undisturbed, mature sal forest would be about 30-35 year for microbial biomass (C and N)and about 100-150 year for organic C and total N. Higher a ccumulation of soil microbial biomass and high N-mineralization rate at lat e successional stages indicated the re-establishment of enriched soil and r estitution of nutrient cycling during the course of ecosystem restoration. (C) 2001 Elsevier Science B.V. All rights reserved.