Decreased Functional Diversity and Biological Pest Control in Conventional Compared to Organic Crop Fields

Organic farming is one of the most successful agri-environmental schemes, as humans benefit from high quality food, farmers from higher prices for their products and it often successfully protects biodiversity. However there is little knowledge if organic farming also increases ecosystem services like pest control. We assessed 30 triticale fields (15 organic vs. 15 conventional) and recorded vascular plants, pollinators, aphids and their predators. Further, five conventional fields which were treated with insecticides were compared with 10 non-treated conventional fields. Organic fields had five times higher plant species richness and about twenty times higher pollinator species richness compared to conventional fields. Abundance of pollinators was even more than one-hundred times higher on organic fields. In contrast, the abundance of cereal aphids was five times lower in organic fields, while predator abundances were three times higher and predator-prey ratios twenty times higher in organic fields, indicating a significantly higher potential for biological pest control in organic fields. Insecticide treatment in conventional fields had only a short-term effect on aphid densities while later in the season aphid abundances were even higher and predator abundances lower in treated compared to untreated conventional fields. Our data indicate that insecticide treatment kept aphid predators at low abundances throughout the season, thereby significantly reducing top-down control of aphid populations. Plant and pollinator species richness as well as predator abundances and predator-prey ratios were higher at field edges compared to field centres, highlighting the importance of field edges for ecosystem services. In conclusion organic farming increases biodiversity, including important functional groups like plants, pollinators and predators which enhance natural pest control. Preventative insecticide application in conventional fields has only short-term effects on aphid densities but long-term negative effects on biological pest control. Therefore conventional farmers should restrict insecticide applications to situations where thresholds for pest densities are reached

Inflow of seeds through the forest edge: evidence from seed bank and vegetation patterns

To determine the influence of the proximity of a forest edge on seed bank composition and diversity, we per-formed a seed bank sampling at ancient deciduous forests bordering intensive arable fields. Also vegetation pat-terns were taken into account. We hypothised that forest edges may facilitate the entrance of diaspores of invasive species into the forest and the successive incorporation of these species in the forest seed bank. We noticed a substantial influence of the proximity of an edge on seed bank composition at as well the forested side of the edge as the field side. The forest edge zone was limited to 3 m into the forest and the field edge zone extended 3 m into the field. The seed bank samples of field and forest edge are characterised by a higher species diversity and seed density and a higher similarity between seed bank and vegetation, compared to field or forest samples. The forest edges contains fewer pioneer species in comparison with the forest interior and more competitive species and species of edges and clearings compared with field and forest samples. The seed longevity index increases towards the forest interior. We can conclude from our data that the forest and edge seed bank are com-posed by both seeds from recent dispersal processes and local seed set and by seeds originating from past veg-etation on the site. Near the edge, actual seed input seems of primal importance. Further towards the forest interior seed input decreases and long-living seeds of past vegetation become more important. Ancient forest edges thus act as a barrier for seeds of species of the surrounding arable field

Hoe belangrijk is indringing van niet-bossoorten doorheen de bosrand?

A

Soil seedbank: Old methods for new challenges in agroecology?

National audienceThe weed soil seedbank is of interest in agroecosystems as a major source of weedinfestation in fields and as a reservoir of plant and seed-feeder diversity. A seedbankis a characteristic of annual plants and has been the focus of numerous studies, as itreflects the past aboveground vegetation and is the reservoir of the future vegetation.Therefore, it potentially can be used to evaluate the past, present and futureannual weed communities. The goal of this paper was to provide guidelines to helpresearchers to do a weed seedbank survey. Through a qualitative review of 60 weedseedbank articles, we investigate why and how the seedbank has been studied inagronomy. It shows that seedbank studies have been performed to address the followingfour major objectives: (a) the assessment of weed management practices onweed communities; (b) the relationship between seedbank and aboveground vegetation;(c) the study of composition and diversity of seedbank in a given area; and,(d) the quantification of seedbank as a food resource for wildlife. Because the analysishighlighted a wide range of methodologies to estimate the seedbank, we criticallyreviewed them. We show that the selected methodology strongly affects theseedbank estimate. Nevertheless, in our sample of research articles, the analysis revealedthat the choice of the methodology was not always justified in terms of achievinga particular scientific goal, but was often determined by the resources availablefor the experiment (e.g., workload). While studying the soil seedbank remains ofinterest for scientists (proved by the amount of recent publications), it is time consumingand requires considerable botanical skill. Innovative methods of estimationare scarce and novel methodological developments are needed to increase the qualityand reliability of the data obtained