Long-term afforestation effect and help to optimize degraded forest lands and reducing climate changes

Abstract

The present study examined the forest floor, soil properties, and dynamics of greenhouse gas fluxes in 23-years old stands of alder (Alnus subcordata C. A. M.), maple (Acer velutinum Bioss.), cypress (Cupressus sempervirens L. var. horizontalis), and pine (Pinus nigra) sites in northern Iran. A degraded natural forest (DNF) with sparse trees including Parrotia persica C. A. M., Carpinus betulus L., and Diospyros lotus L. located near the afforested stands was selected as the control region. Fifteen forest floor and topsoil (0–15 cm) samples per site were taken and analyzed in the laboratory. In addition, the seasonal changes in the fluxes of CO2, CH4, and N2O were studied over a year. The quality of the forest floor differed among the sites, indicating the highest N, and the lowest C concentrations in the alder stand. The soil bulk density, pH, available nutrients (P, Ca, and Mg), earthworm activities and microbial biomass N were significantly higher in the alder stand with organic C being the least. The microbial biomass C did not differ among the studied sites, whereas the total N was significantly higher in the alder ≈ maple sites having the minimum C/N ratios. High contents of water were found in the DNF site. The highest CO2 (0.31 mg CO2 m−2 d−1) and N2O (0.42 mg N2O m−2 d−1) fluxes were observed in the DNF site. The CH4 flux showed higher amounts in the DNF ≈ cypress ≈ pine (0.12, 0.11 and 0.07 mg CH4 m−2 d−1, respectively) sites than in the maple ≈ alder (−0.05, and − 0.04 mg CH4 m−2 d−1, respectively) plantations. The highest values of all fluxes were measured in August, whereas the lowest were detected in February. This research recommends a plantation with suitable native broad-leaved species along with a forestation management plan to rehabilitate the forests of the DNF area.