Spatial distribution of weed diversity within a cereal fieldJ. Izquierdo1, J.M. Blanco-Moreno2, L. Chamorro2, J.L. González-Andújar3 and F.X. Sans2
1 Departament Enginyeria Agroalimentària i Biotecnología, Universitat Politècnica de Catalunya. Campus del Baix Llobregat, Av. Canal Olímpic s/n, 08860, Castelldefels, Catalunya, Spain
2 Departament Biologia Vegetal, Universitat de Barcelona, Av. Diagonal 645, 08028 Barcelona, Catalunya, Spain
3 Departamento Protección de Cultivos, Instituto de Agricultura Sostenible, P.O. Box 4084, 14080 Córdoba, Spain
Accepted 14 April 2009; published online 1 July 2009
Abstract - Weeds are key components of agroecosystems because they support biological diversity within crop fields. Ecological indicators of weed diversity are usually assessed on a field scale, but weeds are distributed unevenly within fields. Here, we explore spatial distribution of diversity in weed seed banks, and how a failure of grass weed control may affect biodiversity indicators. We studied spatial distribution and stability of species richness, Shannon's diversity index, and Pielou's evenness index of a weed seed bank, site-specifically and for the entire field, over three years in a commercial winter wheat field regularly treated with narrow- and broad-leaved herbicides. 254 soil samples were taken on 10 m 10 m grids at the beginning of each season. Seeds were identified by germination in a greenhouse and indices were assessed for each point. The spatial structure of the indices was described by spherical isotropic semivariograms. Our findings show that diversity and evenness computed for the entire field both decreased by 63% after lack of grass weed control, and increased 32% and 31%, respectively, the following year. However, richness, diversity and evenness were not homogeneous across the field. Diversity and evenness became increasingly patchy over time, as shown by a spatial dependence increasing by 21% and 40%, respectively, after two years. This finding is related to the reduction in the patch extension of broad-leaved species due to broad-leaved herbicide application each year and the expansion of grass patches due to the lack of grass control in the first year. Spatial location of patches was not stable over time. Nevertheless, weedy areas remained on the field and represent plant diversity caches that may contribute to maintaining global biodiversity. This information is missed if a single biodiversity index is computed for the entire field. Knowledge of spatial distribution of weed diversity within a field will be useful for identifying wildlife conservation areas and understanding changes in biodiversity in cropland ecosystems better.
Key words: seedbank / species richness / Shannon diversity index / Pielou evenness index / mapping / herbicides / kriging / nonparametric test / patches.
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© INRA, EDP Sciences 2009