Ecosystem recovery : pine forests vegetation response to a reduction in nitrogen deposition

Abstract

Vegetation of pine (Pinus sylvetris L.) forests subjected to intense air pollution stress in the impact zone of one of the largest air pollution sources in Lithuania – the mineral fertilizer plant Achema data were analysed to determine potential ecosystem recovery between 1988 and 2004. The study sites were established at 3-22 km distances in the prevailing wind direction where vegetation data from pine stands which had first been surveyed by prof. S.Karazija in 1987-1988 were available. Stands with an age of 55 years with vegetation assigned to the Vaccinio-myrtillosa site type and with similar dendrometrical characteristics were preferred and were investigated in July, 2004. The species that had increased were typical for Vaccinio-myrtillosa site type. Frequency of such species as Rubus idaeus, Rubus caesius, Impatiens noli-tangere and Chamerion angustifolium decreased significantly (p<0.05), others species also decreased but was not so significantly (p>0.05) – Galeopsis tetrahit, Stellaria media, while the other nitrophilic species were relatively extinct – Aegopodium podagraria, Epilobium montanum. The mean nitrophilic species frequency per sample quadrate was significantly higher in 1988 than in 2004 (p<0.01). The cover of nitrophilous plants comprised the significantly larger part of the sample quadrates in 1988 (58%) comparing with 2004 (21%) (p<0.001).