Changes in ground vegetation of arable lands under afforestation in Latvia

Dynamics of herb and bryophyte layer following afforestation of arable land were analyzed on two research sites - Vestiena and Malta, Latvia. Vegetation data on a twelve year period were processed, and data were collected in 1996, 1999, 2003 and 2008. Environment and vegetation of both areas were quite similar at the beginning of the research -fallow land vegetation dominated by ruderal grasses and annual herbs. Changes in vegetation were negligible during the first years because young planted trees grew slowly and light conditions did not change substantially. At the end of the observation period, the herb layer became very scarce, ruderal species declined, and typical species of forests and forests edges appeared. Most of plant species had wide ecological amplitude of climatic and edaphic factors, which indicates that the ground vegetation composition on research sites remained very different from the vegetation of forests ecosystem. There were no differences among birch plantations with different density of planted trees, and only small differences among plantations with different tree species (spruce, pine, birch), which appeared only in the last observation year.