Development of alder carr after the abandonment of wet grasslands during the last 70 years

The secondary succession of wet grasslands to communities of alder carr dominated by Alnus glutinosa was recorded in different parts of Europe during the 20th century. However, knowledge of such development of alder carr remains insufficient. The development of alder carr was reconstructed at five sites in the Czech Republic, using historical aerial photographs and methods of dendrochronology. The aims were to investigate the succession from wet grasslands to alder carr at sites previously intensively managed for agriculture and to find out the role of fluctuations in the groundwater table, caused by artificial drainage channels, in the observed stand dynamics and tree growth. The spread of forest (i.e.,an increase in forest cover) predominated until the 1970s at all sites. This trend was disrupted by a large-scale dieback of forest stands in four of the five sites after the 1970s, followed by an increase in patch heterogeneity, as indicated by landscape metrics. The radial growth increment in Alnus glutinosa has been affected predominately by local environmental factors, probably including the changing degree of waterlogging. Forest dieback was presumably connected with a lesser extent of drainage channels. Our results indicate that observed successional pathways at sites of alder carr were probably caused by local changes in the groundwater table.