Changes in Undergrowth on Drained Forested Fens in Lithuania

Abstract

Draining of birch and blac alder stands had essentially changed species composition of their undergrowth. For instance, the proportion of spruce i undergrowth decreased from 10.6 to 35.6% (p < 0.05) while that of ash increased from 10.6 to 41.5% (p < 0.05; Moreover, a tendency of a decrease in the proportion of black alder was observed in the undergrowth of drained fen-Lowering the ground water level due to drainage had led to an increased number of ash seedlings (up to 3000-4400 tree ha1) and weakened natural regeneration of black alder. Overall area of fens occupies 143.6 thousand hectares in Lithuania, including 79.3 thousand ha or 55.2% of drain fens. The influence of drainage on undergrowth formation regularities was studied in meso-eutrophic and eutrophic fe of the Panevezys and Birzai forests using transects, from 100 to 300 m long, perpendicular to the ditch axes or to t longest edge of the fen. Sixty-one water wells were dug along each transect for ground water level measurements. T same number of sampling plots (10*10 m) was delineated for investigating the forest vegetation. Furthermore, da from alt forest enterprises of Lithuania (34,855 plots) on the species composition of the undergrowth in drained ai undrained forest fens were analysed. Results from this analysis indicated that intensive drainage of fens (i.e. lowering the level of ground water table (HV|) up to 40 cm and more) increased the number of european ash seedlings and decreasi the number of black aider, downy birch and partially Norway spruce seedlings. The highest number of spruce seedlini was found in extensively drained fens (H = 11-30 cm) characterized by forest stands with average (0.7) and low stocking level. Results from our sampling design indicated that drainage in mature birch stands on meso-eutrophic fens and i black alder stands on meso-eutrophic and eutrophic fens increased undergrowth densities as well as the areas of stanc with second tree layers. Moreover, stands with dense undergrowth (3,000 trees ha"1 and more) expanded from 3.2 i 4.0%. However, the undergrowth density under mature spruce stands on drained meso-eutrophic fens decreased by 255±3 trees ha1 (p < 0.05). It was attributed to the fact that the stocking level of drained spruce stands was higher and th; the undergrowth was shaded more considerably in comparison to undrained spruce stands.