Grigaliūnas,V. and Ruseckas, J. 2005. The Effect of Soil Properties on Natural Forest Regeneration on Drained Fens. Baltic Forestry, 11 (2): 75-83

The objective of this study was to assess the success of natural regeneration in cutovers on drained fens (eutrophic peatland) depending on the soil properties and the depth to the water table in the forests of Birzai and Panevezys state forest enterprises in Lithuania. The assessments were carried out in 100-300 m long transects allocated perpendicularly to the drainage ditches. 131 water wells were drilled to measure the depth to the water table and 131 sample plots of 10 × 10 m were established. The soil properties were assessed in the soil chemistry laboratory. The results showed that natural forest regeneration on drained cutblocks in fens was affected by the following factors: the depth to the water table (HV.01) (measured at the beginning of the growth period), the pH level, the potential hydrolytic soil acidity (HA), the base saturation and the thickness of the peat layer. Multiple regression analysis was used to assess the dependence of the number of regenerating trees (N) on the main factors (HV.01 and HA): N = 168059.7 – 3446.5 HV.01 – 35.180 HA; (R2 = 0.8, F = 7.51, p < 0.0007). The maximum critical depth to the water table (allowing sufficient number of regenerating trees) was mainly affected by the subsoil texture of the shallow peat soils (HSs– ph) and was 18.0 ± 3.7 cm, 26.5 ± 6.6 cm, 26.6 ± 3.9 cm, 29.6 ± 6.6 cm and 42.2 ± 9.6 cm in the soils with subsoil of gravel, sand, sandy loam, light loam and medium loam, respectively. The mean hydrolytic acidity of the soil in the cutblocks with sufficient regeneration was 820.99 ± 56.05 mekv/kg, which was significantly lower than in the cutblocks with insufficient forest regeneration (ΔHA = 212.29 ± 94.99 mekv/kg, t = 2.23, p = 0.038). In conclusion, to improve the natural regeneration of forests in the clear-cuttings on low peatland soils, the soil water regime should be improved by the technical means to maintain the optimum soil moisture (mainly by damming the ditches) and, in soils of very high acidity (HA <1100 mekv/kg), alkaline enrichment may be needed.

Key words: cutovers, drainage, natural regeneration, peat soils, water table.