Early weed succession on an abandoned field: vegetation composition and production of biomass

We investigated the early stage (second to fourth year) of weed succession on an experimental fallow field in central Bohemia (western Czech Republic). The experimental ground was ploughed in the autumn, harrowed and rolled in the spring, and divided into 5 x 5 m plots. In the control the weed stands were left intact, the other variants were mowed with or without cultivation of the superficial soil layer in June and July. The position of the plots and the treatments were the same each year. The production of aboveground biomass and proportion of monocotyledonous and dicotyledonous annuals and perennials in different years (1993 to 1995) were recorded. The production of biomass (the aboveground crop of weeds in September) was highest in the controls with no treatment. In mowed or cultivated plots the total biomass production (the sum of biomass at the time of the treatment plus biomass re-grown after the treatment) was greater when the treatment was made in July than in June. In the second year of succession, the biomass of annuals was greater than that of perennials. From the third year on, perennial dicotyledonous species became the dominant weed community, in controls as well as on mowed or superficially cultivated plots. The rate of increase of the proportion of dicotyledonous perennial weeds was greatest in mowed plus superficially cultivated plots, intermediate in the controls, and lowest in plots where the weeds were only mowed.