arable land, climate, crop, gradient analysis, seasonal dynamics, soil type

Factors determining changes in species composition of arable field weed vegetation in the northeastern part of the Czech Republic were studied. Gradsect sampling, i.e. a priori stratified selection of sampling sites, was used for the field research. Using this method, a data set of 174 vegetation plots covering a whole range of basic environmental characteristics in the study area, was compiled in 2001-2003. A set of environmental variables (altitude, annual precipitation, mean annual temperature, soil type, soil pH and crop type) together with date of sampling was obtained for each plot. Ordination methods were used to determine the effects of variables on arable weed composition. For each variable the gross and net effect on weed species composition were calculated.