Spatial pattern analysis of weed seeds in the cultivated soil seed bank.
The spatial pattern of weed seeds in soil was analysed after harvesting winter barley at a site near Dijon, France, in July 1987. Three hundred samples were collected from a 7.5 × 10 m area. Three indices of dispersion (variance-to-mean ratio, Lloyd's mean crowding and Lloyd's patchiness) and the Moran's I statistic of spatial autocorrelation were calculated. It was found that the seed bank was composed almost exclusively of annual species, dominated by Thlaspi arvense (43.8%) and a subset of 6 species (Galium aparine, Sinapis arvensis, Anagallis arvensis, Fallopia convolvulus, Euphorbia exigua and Kickxia spuria) which, together, comprised 41.7% of the seeds. For most species with a mean >0.2 seeds/core (20.25 cm in length and 4.6 cm diam.), seed pattern was patchy. Only 2 species, Avena fatua and Chenopodium polyspermum, exhibited random patterns. For the other species, aggregation was due to biological and agricultural factors.