Changes in life history trait composition during undisturbed old-field succession

This paper describes the patterns of vegetation change by spontaneous succession on former agricultural land. In 1968, initiated by Heinz Ellenberg, an experimental study site was set up on an arable field in the new botanical garden of Göttingen University (Germany). The undisturbed successions on four plots of a long sere (since 1968/69) and on four additional plots of a shorter sere (since 1982) were evaluated. The seres were classified into stages by cluster analysis, which yield to four subsequent stages for the long sere and to three subsequent stages for the short sere. The early succession is characterized by a high proportion of species invasion, whereas with developing time species extinction increased. On all study plots undisturbed succession directed to the development of pioneer forests. Altogether 247 vascular plant species were recorded. The total species richness shows a fluctuating course during the successional seres, with significantly increased numbers shortly after succession has started and a decline in the pioneer-forest stage, when stands age and close down. The primary aim was to compare the characteristics (particular traits) of species occurring at different stages of succession. The majority of the traits concerned exhibited some clear trends in the course of succession. Exclusive reproduction by seeds decreased and the ability for additional vegetative reproduction increased. Anemochorous dispersal significantly decreased, whereas the importance of dispersal by animals, especially endochorous, dominates in the pioneer-forest stage. The mean seed weight significantly increased. During early succession, plant species staying green over winter dominated, but are of none relevance in the pioneer-forest stage, where summergreen plant species dominate. The change in strategy type features a significant increase of competitive species. The mean indicator value for light in the herb layer decreased significantly in the pioneer-forest stage.