Changes in Understorey Vegetation of Scots Pine Stands under the Decreased Impact of Acidifying and Eutrophying Pollutants

摘要

Understorey vegetation of Scots pine (Pinus sylvetris L.) forests subjected to intense air pollution stress in the impact /one of one of the largest air pollution sources in central Lithuania - nitrogen fertilizer plant Achema - were studied in 31 sample plots first in 1988 and again in 2004. A recovery of the vegetation was observed since the first sample time and interpreted as due to a distinct reduction of emission of nitrogen and sulphur oxides. Study stands were 85-100 years old with vegetationassigned to the Vaccinw-myrtillosa site type. Species which occurence changed little (Vaccinium myrtillus, Pteridium aquilinum) and increased in occurence (Trientalis europaea, Luzula pilosa, Vaccinium vitis-idaea, Melampyrum pratense) were typical of site type species. During the study period nitrophilous species with indicator values for nitrogen 26 decreased in occurence. In 1988 nitrophilous plants comprised 58% of all herbaceous cover, while in 2004 only 21%. According to the unweighted Ellenbergindicator values the stands had become darker and less acidic. A significant decrease in nitrogen indicators was observed in 2004. The process of ground vegetation recovery was documented in terms of an increase in keystone species (Vaccinium myrtillus,V.vitis-idaea) and a reduction of nitrophilous species (e.g. Rubus idaeus).