Weed vegetation (wild flora) of long established organic versus conventional cereal fields in Denmark

Abstract

SummaryThe vegetation of weeds was sampled in matched pairs of long established organic and contemporary conventional cereal fields in summer 1987, and in spring and summer 1988, with an extended Raunkiaer circle at distances up to 50 m from the field boundary. In spring 1988, the number of plants were also counted. Species density, plant density, a proxy measure of plant density (accumulated Frequency Sum), crop and weed biomass, and occurrence of plants assigned to functional groups, are compared between farming systems. The plants were assigned to functional groups according to: (i) herbivore associations to broad‐leaved taxa and (ii) flower location in the canopy, i.e. visibility and availability to flying insects. Furthermore, crop margin and mid‐field were compared concerning species density and accumulated Frequency Sum.All variables that differed among the two farming systems had highest values ‐ often several times higher ‐ in the organic system with four exceptions: total biomass, biomass of crop, proportion of a single broad‐leaved taxon and of grasses. The differences between the two systems were largest mid‐field due to a pronounced pre‐herbicide spraying gradient in species and plant density from crop margin to mid‐field in conventional fields. A similar gradient was not found in the organic fields.

Effects of agri-environment schemes in a long-term ecological time series

“…This is not, however, unique to this sort of study and has perhaps been best studied in the context of climate change (Rosenzweig et al, 2007). It is necessary both to demonstrate that results are consistent with the effects which would be expected on the basis of theory and that there is no An increase in plant species richness has been shown in a number of other studies on organic farms (Hald, 1999;van Elsen, 2000;Bengtsson et al, 2005;Boutin et al, 2008), with the increases in species richness probably the result of the cessation of fertiliser and herbicide applications (Hyvönen & Salonen, 2002). In permanent grasslands this increase was primarily due to higher numbers of broad-leaved perennial plants, as has also been found in arable field studies (Hald, 1999;Boutin et al, 2008).…”

Organic fields sustain weed metacommunity dynamics in farmland landscapes

“…OF fields in general harbour more insect-pollinated plants [54], forbs [55], and rare or threatened weeds [56,57], and fewer nitrophilous species [31,56], while conventional fields have fewer broad-leaved species due to the use of auxin herbicides to control them [58], and more herbicide resistant weeds, in particular grasses [59]. Though in some cases OF may not increase weed species richness [60,61], our results agree with most previous studies [11,12,33], indicating a positive effect on weed species richness (roughly þ30% in the latter studies compared with þ48.9% in the field core and þ30% in the field margin in this study).…”

Uncertainties in the application of the species area relationship for characterisation factors of land occupation in life cycle assessment

“…Fourth, our assumption of field edges, representing the amount of species present on low intensive or organic fields, is debatable. Hald (1999) compared the species density of field margins with field centers for both organic and conventional farming. This research indicates that the species density of field margins of organic farming is representative for the whole field while the species density of the field center of conventional fields is 30-40% lower than of the field margins (Hald 1999).…”

“…Hald (1999) compared the species density of field margins with field centers for both organic and conventional farming. This research indicates that the species density of field margins of organic farming is representative for the whole field while the species density of the field center of conventional fields is 30-40% lower than of the field margins (Hald 1999). While it is generally recognized that organic farming has positive effects on the species richness compared with conventional farming, in some cases, field studies indicate negative or mixed effects (Hole et al 2005).…”