DRAINAGE IMPACT ON PLANT COVER AND HYDROLOGY OF AUKŠTUMALA RAISED BOG (WESTERN LITHUANIA)

One-third of the former Aukštumala raised bog (western Lithuania) has been preserved as Telmological Reserve since 1995, while the remaining territory is still under active industrial peat mining or are abandoned peat harvesting fields. The present study was carried out in 2013 and aimed to assess long-term human impact on the structure of plant cover and hydrology of Aukštumala raised bog. On the basis of vegetation assessment (Twinspan analysis), four habitat types were identified: i) active raised bog, ii) degraded raised bog drained by ditches, iii) contact zone of the bog and the peat mining fields and iv) recently burnt areas. The largest anthropogenic impact on vegetation co ver was found in the degraded raised bog drained by the ditches and in the burnt area, where the proportion of plant species atypical to ombrotrophic raised bogs was the highest. Water electrical conductivity negatively correlated (r = -0.57) with bog water level, whereas correlation between pH and bog water level was weaker (r = -0.38). Water level in the active raised bog was significantly higher than in the rest three habitat types. Electrical conductivity values in the active raised bog were significantly lower compared to the degraded raised bog and burned area habitats. In order to recreate favourable conditions for peat accumulation and natural functioning of bog ecosystem, mean bog water level should be raised at least up to -32 cm (the optimum water level assigned for most of the typical ombrotrophic species fell into the range of -20 – -32 cm).